chapter 3: transport layer - bilkent...

Transport Layer 3-1

Chapter 3 Transport LayerOur goals

understand principles behind transport layer services

multiplexingdemultiplexing

reliable data transferflow controlcongestion control

learn about transport layer protocols in the Internet

UDP connectionless transportTCP connection-oriented transportTCP congestion control

Transport Layer 3-2

Transport services and protocolsprovide logical communicationbetween app processes running on different hoststransport protocols run in end systems

send side breaks app messages into segments passes to network layerrcv side reassembles segments into messages passes to app layer

more than one transport protocol available to apps

Internet TCP and UDP

applicationtransportnetworkdata linkphysical


networkdata linkphysical



networkdata linkphysicalnetwork

data linkphysical

logical end-end transport

Transport Layer 3-3

Transport vs network layer

network layer logical communication between hoststransport layer logical communication between processes

relies on enhances network layer services

Household analogy12 kids sending letters

to 12 kidsprocesses = kidsapp messages = letters in envelopeshosts = housestransport protocol = Ayşe and Buumllentnetwork-layer protocol = postal service

Transport Layer 3-4

Internet transport-layer protocols

reliable in-order delivery (TCP)

congestion control flow controlconnection setup

unreliable unordered delivery UDP

no-frills extension of ldquobest-effortrdquo IP

services not available delay guaranteesbandwidth guarantees







data linkphysical


Transport Layer 3-5

Multiplexingdemultiplexing

application

transport

network

link

physical

P1 application

transport

network

link

physical

application

transport

network

link

physical

P2P3 P4P1

host 1 host 2 host 3

= process= socket

delivering received segmentsto correct socket

Demultiplexing at rcv hostgathering data from multiplesockets enveloping data with header (later used for demultiplexing)

Multiplexing at send host

Transport Layer 3-6

How demultiplexing workshost receives IP datagrams

each datagram has source IP address destination IP addresseach datagram carries 1 transport-layer segmenteach segment has source destination port number (recall well-known port numbers for specific applications)

host uses IP addresses amp port numbers to direct segment to appropriate socket

source port dest port

32 bits

applicationdata

(message)

other header fields

TCPUDP segment format

Transport Layer 3-7

Connectionless demultiplexing

Create sockets with port numbers

DatagramSocket mySocket1 = new DatagramSocket(9111)


UDP socket identified by two-tuple

(dest IP address dest port number)

When host receives UDP segment

checks destination port number in segmentdirects UDP segment to socket with that port number

IP datagrams with different source IP addresses andor source port numbers directed to same socket

Transport Layer 3-8

Connection-oriented demux

TCP socket identified by 4-tuple

source IP addresssource port numberdest IP addressdest port number

recv host uses all four values to direct segment to appropriate socket

Server host may support many simultaneous TCP sockets

each socket identified by its own 4-tuple

Web servers have different sockets for each connecting client

non-persistent HTTP will have different socket for each request

Transport Layer 3-9

Connection-oriented demux(cont)

ClientIPB

P1

clientIP A

P1P2P4

serverIP C

SP 9157DP 80

SP 9157DP 80

P5 P6 P3

D-IPCS-IP AD-IPC

S-IP B

SP 5775DP 80

D-IPCS-IP B

Transport Layer 3-10

Connection-oriented demuxThreaded Web Server

ClientIPB

P1

clientIP A

P1P2P4

serverIP C

SP 9157DP 80

SP 9157DP 80

P5 P6 P3

D-IPCS-IP AD-IPC

S-IP B

SP 5775DP 80

D-IPCS-IP B

P4


UDP User Datagram Protocol [RFC 768]

ldquono frillsrdquo ldquobare bonesrdquoInternet transport protocolldquobest effortrdquo service UDP segments may be

lostdelivered out of order to app

connectionlessno handshaking between UDP sender receivereach UDP segment handled independently of others

Why is there a UDPno connection establishment (which can add delay)simple no connection state at sender receiversmall segment headerno congestion control UDP can blast away as fast as desired


UDP moreoften used for streaming multimedia apps

loss tolerantrate sensitive

other UDP usesDNSSNMP

reliable transfer over UDP add reliability at application layer

application-specific error recovery


32 bits

Applicationdata

(message)

UDP segment format

length checksumLength in

bytes of UDPsegmentincluding

header


UDP checksum

Sendertreat segment contents as sequence of 16-bit integerschecksum addition (1rsquos complement sum) of segment contents with wraparound of carry out bitsender puts checksum value into UDP checksum field

Receivercompute checksum of received segmentcheck if computed checksum equals checksum field value

NO - error detectedYES - no error detected

Goal detect ldquoerrorsrdquo (eg flipped bits) in transmitted segment


Principles of Reliable data transferimportant in app transport link layerstop-10 list of important networking topics

characteristics of unreliable channel will determine complexity of reliable data transfer protocol (rdt)

netw

ork

laye

r


Reliable data transfer getting started

sendside

receiveside

rdt_send() called from above (eg by app) Passed data to

deliver to receiver upper layer

udt_send() called by rdtto transfer packet over

unreliable channel to receiver

rdt_rcv() called when packet arrives on rcv-side of channel

deliver_data() called by rdt to deliver data to upper


Reliable data transfer getting startedWersquoll

incrementally develop sender receiver sides of reliable data transfer protocol (rdt)consider only unidirectional data transfer

but control info will flow on both directionsuse finite state machines (FSM) to specify sender receiver

state1

state2

event causing state transitionactions taken on state transition

state when in this ldquostaterdquo next state

uniquely determined by next event

eventactions


Rdt10 reliable transfer over a reliable channel

underlying channel perfectly reliableno bit errorsno loss of packets

separate FSMs for sender receiversender sends data into underlying channelreceiver read data from underlying channel

Wait for call from above packet = make_pkt(data)

udt_send(packet)

rdt_send(data)extract (packetdata)deliver_data(data)

Wait for call from

below

rdt_rcv(packet)

sender receiver


Rdt20 channel with bit errors

underlying channel may flip bits in packetrecall checksum to detect bit errors

the question how to recover from errorsacknowledgements (ACKs) receiver explicitly tells sender that pkt received OKnegative acknowledgements (NAKs) receiver explicitly tells sender that pkt had errorssender retransmits pkt on receipt of NAK

new mechanisms in rdt20 (beyond rdt10)error detectionreceiver feedback control msgs (ACKNAK) rcvr-gtsender


rdt20 FSM specification

Wait for call from above

snkpkt = make_pkt(data checksum)udt_send(sndpkt)

extract(rcvpktdata)deliver_data(data)udt_send(ACK)

rdt_rcv(rcvpkt) ampamp notcorrupt(rcvpkt)

rdt_rcv(rcvpkt) ampamp isACK(rcvpkt)

udt_send(sndpkt)

rdt_rcv(rcvpkt) ampampisNAK(rcvpkt)

udt_send(NAK)

rdt_rcv(rcvpkt) ampamp corrupt(rcvpkt)

Wait for ACK or

NAK

Wait for call from

belowsender

receiverrdt_send(data)

Λ


rdt20 operation with no errors






udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)

Λ


rdt20 error scenario






udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)

Λ


rdt20 has a fatal flaw

What happens if ACKNAK corruptedsender doesnrsquot know what happened at receivercanrsquot just retransmit possible duplicate

What to dosender ACKsNAKs receiverrsquos ACKNAK What if sender ACKNAK lostretransmit but this might cause retransmission of correctly received pkt

Handling duplicates sender adds sequence number to each pktsender retransmits current pkt if ACKNAK garbledreceiver discards (doesnrsquot deliver up) duplicate pkt

Sender sends one packet then waits for receiver response

stop and wait


rdt21 sender handles garbled ACKNAKs

Wait for call 0 from

above

sndpkt = make_pkt(0 data checksum)udt_send(sndpkt)

rdt_send(data)

Wait for ACK or NAK 0 udt_send(sndpkt)

rdt_rcv(rcvpkt) ampamp ( corrupt(rcvpkt) ||isNAK(rcvpkt) )


rdt_send(data)

rdt_rcv(rcvpkt) ampamp notcorrupt(rcvpkt) ampamp isACK(rcvpkt)

udt_send(sndpkt)



Wait forcall 1 from

above

Wait for ACK or NAK 1

ΛΛ


rdt21 receiver handles garbled ACKNAKs

Wait for 0 from below

sndpkt = make_pkt(NAK chksum)udt_send(sndpkt)

rdt_rcv(rcvpkt) ampamp not corrupt(rcvpkt) ampamphas_seq0(rcvpkt)

rdt_rcv(rcvpkt) ampamp notcorrupt(rcvpkt) ampamp has_seq1(rcvpkt)

extract(rcvpktdata)deliver_data(data)sndpkt = make_pkt(ACK chksum)udt_send(sndpkt)




rdt_rcv(rcvpkt) ampamp (corrupt(rcvpkt)

sndpkt = make_pkt(ACK chksum)udt_send(sndpkt)






rdt21 discussion

Senderseq added to pkttwo seq rsquos (01) will suffice Whymust check if received ACKNAK corrupted twice as many states

state must ldquorememberrdquowhether ldquocurrentrdquo pkt has 0 or 1 seq

Receivermust check if received packet is duplicate

state indicates whether 0 or 1 is expected pkt seq

note receiver can notknow if its last ACKNAK received OK at sender


rdt22 a NAK-free protocol

same functionality as rdt21 using ACKs onlyinstead of NAK receiver sends ACK for last pkt received OK

receiver must explicitly include seq of pkt being ACKed duplicate ACK at sender results in same action as NAK retransmit current pkt


rdt22 sender receiver fragments


above


rdt_send(data)

udt_send(sndpkt)

rdt_rcv(rcvpkt) ampamp ( corrupt(rcvpkt) ||

isACK(rcvpkt1) )

rdt_rcv(rcvpkt) ampamp notcorrupt(rcvpkt) ampamp isACK(rcvpkt0)

Wait for ACK

0sender FSM

fragment



extract(rcvpktdata)deliver_data(data)sndpkt = make_pkt(ACK1 chksum)udt_send(sndpkt)

rdt_rcv(rcvpkt) ampamp (corrupt(rcvpkt) ||

has_seq1(rcvpkt))

udt_send(sndpkt)receiver FSM

fragment

Λ


rdt30 channels with errors and loss

New assumptionunderlying channel can also lose packets (data or ACKs)

checksum seq ACKs retransmissions will be of help but not enough

Q how to deal with losssender waits until certain data or ACK lost then retransmitsdrawbacks

Approach sender waits ldquoreasonablerdquo amount of time for ACK retransmits if no ACK received in this timeif pkt (or ACK) just delayed (not lost)

retransmission will be duplicate but use of seq rsquos already handles thisreceiver must specify seq of pkt being ACKed

requires countdown timer


rdt30 sendersndpkt = make_pkt(0 data checksum)udt_send(sndpkt)start_timer

rdt_send(data)

Wait for

ACK0

rdt_rcv(rcvpkt) ampamp ( corrupt(rcvpkt) ||isACK(rcvpkt1) )


above

sndpkt = make_pkt(1 data checksum)udt_send(sndpkt)start_timer

rdt_send(data)




stop_timerstop_timer

udt_send(sndpkt)start_timer

timeout


timeout

rdt_rcv(rcvpkt)

Wait for call 0from

above

Wait for

ACK1

Λrdt_rcv(rcvpkt)

ΛΛ

Λ


rdt30 in action


rdt30 in action


Performance of rdt30

rdt30 works but performance stinksexample 1 Gbps link 15 ms e-e prop delay 1KB packet

Ttransmit = 8kbpkt109 bsec = 8 microsec

U sender utilization ndash fraction of time sender busy sending1KB pkt every 30 msec -gt 33kBsec thruput over 1 Gbps linknetwork protocol limits use of physical resources

U sender=

008 30008

= 000027 L RRTT + L R

=

L (packet length in bits)R (transmission rate bps) =


rdt30 stop-and-wait operation

first packet bit transmitted t = 0

sender receiver

RTT

last packet bit transmitted t = L R

first packet bit arriveslast packet bit arrives send ACK

ACK arrives send next packet t = RTT + L R

U sender=

00830008

= 000027 L RRTT + L R

=


Pipelined protocolsPipelining sender allows multiple ldquoin-flightrdquo yet-to-

be-acknowledged pktsrange of sequence numbers must be increasedbuffering at sender andor receiver

Two generic forms of pipelined protocols go-Back-N selective repeat


Pipelining increased utilization


sender receiver

RTT

last bit transmitted t = L R



last bit of 2nd packet arrives send ACKlast bit of 3rd packet arrives send ACK

U sender=

024 30008

= 000083 L RRTT + L R

=

Increase utilizationby a factor of 3


Utilization=N(LR)(RTT+LR) if NLRltRTT+LR Utilization=1 if and the sender pauses after it transmits a window NLRgtRTT+LR and the of packets until it receives first ACK sender does not pause


Go-Back-NSender

k-bit seq in pkt headerldquowindowrdquo of up to N consecutive unackrsquoed pkts allowed

ACK(n) ACKs all pkts up to including seq n - ldquocumulative ACKrdquomay receive duplicate ACKs (see receiver)

timer for the entire windowtimeout(n) retransmit pkt n and all higher seq pkts in window


GBN sender extended FSM

Wait start_timerudt_send(sndpkt[base])udt_send(sndpkt[base+1])hellipudt_send(sndpkt[nextseqnum-1])

timeout

rdt_send(data)

if (nextseqnum lt base+N) sndpkt[nextseqnum] = make_pkt(nextseqnumdatachksum)udt_send(sndpkt[nextseqnum])if (base == nextseqnum)

start_timernextseqnum++

elserefuse_data(data)

base = getacknum(rcvpkt)+1If (base == nextseqnum)

stop_timerelse

start_timer


base=1nextseqnum=1


Λ

Λ


GBN receiver extended FSM

ACK-only always send ACK for correctly-received pktwith highest in-order seq

may generate duplicate ACKsneed only remember expectedseqnum

out-of-order pkt discard (donrsquot buffer) -gt no receiver bufferingRe-ACK pkt with highest in-order seq

Wait

udt_send(sndpkt)default

rdt_rcv(rcvpkt)ampamp notcurrupt(rcvpkt)ampamp hasseqnum(rcvpktexpectedseqnum)

extract(rcvpktdata)deliver_data(data)sndpkt = make_pkt(expectedseqnumACKchksum)udt_send(sndpkt)expectedseqnum++

expectedseqnum=1sndpkt =

make_pkt(0ACKchksum)

Λ


GBN inaction


Selective Repeat

receiver individually acknowledges all correctly received pkts

buffers pkts as needed for eventual in-order delivery to upper layer

sender only resends pkts for which ACK not received

sender timer for each unACKed pktsender window

N consecutive seq rsquosagain limits seq s of sent unACKed pkts


Selective repeat sender receiver windows


Selective repeat

data from above if next available seq in window send pkt

timeout(n)resend pkt n restart timer

ACK(n) in [sendbasesendbase+N-1]

mark pkt n as receivedif n smallest unACKed pkt advance window base to next unACKed seq

senderpkt n in [rcvbase rcvbase+N-1]

send ACK(n)out-of-order bufferin-order deliver (also deliver buffered in-order pkts) advance window to next not-yet-received pkt

pkt n in [rcvbase-Nrcvbase-1]

ACK(n)otherwise

ignore

receiver


Selective repeat in action


Selective repeatdilemma

Example seq rsquos 0 1 2 3window size=3

receiver sees no difference in two scenariosincorrectly passes duplicate data as new in (a)

Q what relationship between seq size and window size


Sequence Number vs Window SizeSuppose we use k bits to represent SNQuestion Whatrsquos the minimum number of bits k necessary for a window size of N

sender

receiver

Go-Back-N

expectedSN

snd_base=expectedSN

Q For a given expectedSN whatrsquos the largest possible value for snd_baseA If all the last N ACKs sent by the receiver are received

snd_base = expectedSNexpectedSN+N-1

senderrsquos window



sender

receiver

Go-Back-N

expectedSN

snd_base=expectedSN-N

Q For a given expectedSN whatrsquos the smallest possible value for snd_baseA If all the last N ACKs sent by the receiver are not received

snd_base = expectedSN-NexpectedSN-1

senderrsquos window


Sequence Number vs Window Size

sender

receiver

Go-Back-N

expectedSN


All SNs in the interval [expectedSN-NexpectedSN+N-1] (an interval of size 2N) can be received by the receiver Since the receiver accepts on the packet with SN=expectedSN there should be no other packet within this interval with SN=expectedSN Therefore

2k ge N+1expectedSN+N-1



sender

receiver

Selective Repeat

rcv_base

snd_base=rcv_base

Q For a given rcv_base whatrsquos the largest possible value for snd_baseA If all the last N ACKs sent by the receiver are received

snd_base = rcv_base (same as go_back-N)rcv_base+N-1

senderrsquos window

receiverrsquos window

rcv_base+N-1



sender

receiver

Selective Repeat

rcv_base

snd_base=rcv_base-N

Q For a given rcv_base whatrsquos the smallest possible value for snd_baseA If all the last N ACKs sent by the receiver are not received

snd_base = rcv_base-N (same as Go-Back-N)rcv_base-1

senderrsquos window

rcv_base


rcv_base+N-1



sender

receiver

Selective Repeat

snd_base=rcv_base-N

All SNs in the interval [rcv_base-Nrcv_base+N-1] (an interval of size 2N) can be received by the receiver Since the receiver should be able to distinguish between all packets in this interval and take corresponding action there should be no two packets within thisinterval having the same SN Therefore

2k ge 2Nrcv_base+N-1

rcv_basercv_base


rcv_base+N-1


TCP Overview RFCs 793 1122 1323 2018 2581

full duplex databi-directional data flow in same connectionMSS maximum segment size

connection-orientedhandshaking (exchange of control msgs) initrsquossender receiver state before data exchange

flow controlledsender will not overwhelm receiver

point-to-pointone sender one receiver

reliable in-order byte stream

no ldquomessage boundariesrdquopipelined

TCP congestion and flow control set window size

send amp receive buffers

socketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment

applicationwrites data

applicationreads data


TCP segment structure


32 bits

applicationdata

(variable length)

sequence numberacknowledgement number

Receive windowUrg data pnterchecksum

FSRPAUheadlen

notused

Options (variable length)

URG urgent data (generally not used)

ACK ACK valid

PSH push data now(generally not used)

RST SYN FINconnection estab(setup teardown

commands)

bytes rcvr willingto accept

Internetchecksum

(as in UDP)

countingby bytes of data(not segments)


TCP seq rsquos and ACKsSeq rsquos

byte stream ldquonumberrdquo of first byte in segmentrsquos dataACKs

seq of next byte expected from other sidecumulative ACK

Q how receiver handles out-of-order segmentsA TCP spec doesnrsquot say - up to implementationWidely used implementations of TCP buffer out-of-order segments


TCP Round Trip Time and Timeout

Q how to set TCP timeout valuelonger than RTT

but RTT variestoo short premature timeout

unnecessary retransmissions

too long slow reaction to segment loss

Q how to estimate RTTSampleRTT measured time from segment transmission until ACK receipt

ignore retransmissionsSampleRTT will vary want estimated RTT ldquosmootherrdquo

average several recent measurements not just current SampleRTT



EstimatedRTT = (1- α)EstimatedRTT + αSampleRTT

Exponential weighted moving averageinfluence of past sample decreases exponentially fasttypical value α = 0125


Example RTT estimationRTT gaiacsumassedu to fantasiaeurecomfr

100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

iseco

nds)

SampleRTT Estimated RTT


TCP Round Trip Time and TimeoutSetting the timeout

EstimatedRTT plus ldquosafety marginrdquolarge variation in EstimatedRTT -gt larger safety margin

first estimate of how much SampleRTT deviates from EstimatedRTT

TimeoutInterval = EstimatedRTT + 4DevRTT

DevRTT = (1-β)DevRTT +β|SampleRTT-EstimatedRTT|

(typically β = 025)

Then set timeout interval


TCP reliable data transfer

TCP creates rdtservice on top of IPrsquos unreliable servicePipelined segmentsCumulative acksTCP uses single retransmission timer however it just retransmits the first segment in the window

Retransmissions are triggered by

timeout eventsduplicate acks

Initially consider simplified TCP sender

ignore duplicate acksignore flow control congestion control


TCP sender eventsdata rcvd from app

Create segment with seq seq is byte-stream number of first data byte in segmentstart timer if not already running (think of timer as for oldest unacked segment)expiration interval TimeOutInterval

timeoutretransmit segment that caused timeout (first segment in the window)restart timer

Ack rcvdIf acknowledges previously unacked segments

update what is known to be ackedstart timer if there are outstanding segments


TCP sender(simplified)

NextSeqNum = InitialSeqNumSendBase = InitialSeqNum

loop (forever) switch(event)

event data received from application above create TCP segment with sequence number NextSeqNumif (timer currently not running)

start timerpass segment to IP NextSeqNum = NextSeqNum + length(data)

event timer timeoutretransmit not-yet-acknowledged segment with

smallest sequence numberstart timer

event ACK received with ACK field value of y if (y gt SendBase)

SendBase = yif (there are currently not-yet-acknowledged segments)

start timer

end of loop forever

Commentbull SendBase-1 last cumulatively ackrsquoed byteExamplebull SendBase-1 = 71y= 73 so the rcvrwants 73+ y gt SendBase sothat new data is acked


TCP retransmission scenariosHost A

Seq=100 20 bytes data

ACK=100

timepremature timeout

Host B

Seq=92 8 bytes data

ACK=120

Seq=92 8 bytes data

Seq=

92 t

imeo

ut

ACK=120

Host A

Seq=92 8 bytes data

ACK=100

loss

tim

eout

lost ACK scenario

Host B

X

Seq=92 8 bytes data

ACK=100

time

Seq=

92 t

imeo

utSendBase

= 100

SendBase= 120

SendBase= 120

Sendbase= 100


TCP retransmission scenarios (more)Host A

Seq=92 8 bytes data

ACK=100

loss

tim

eout

Cumulative ACK scenario

Host B

X


ACK=120

time

SendBase= 120


TCP ACK generation [RFC 1122 RFC 2581]

Event at Receiver

Arrival of in-order segment withexpected seq All data up toexpected seq already ACKed

Arrival of in-order segment withexpected seq One other segment has ACK pending

Arrival of out-of-order segmenthigher-than-expect seq Gap detected

Arrival of segment that partially or completely fills gap

TCP Receiver action

Delayed ACK Wait up to 500msfor next segment If no next segmentsend ACK

Immediately send single cumulative ACK ACKing both in-order segments

Immediately send duplicate ACK indicating seq of next expected byte

Immediate send ACK provided thatsegment startsat lower end of gap


Fast Retransmit

Time-out period often relatively long

long delay before resending lost packet

Detect lost segments via duplicate ACKs

Sender often sends many segments back-to-backIf segment is lost there will likely be many duplicate ACKs

If sender receives 3 ACKs for the same data it supposes that segment after ACKeddata was lost

fast retransmit resend segment before timer expires


Fast RetransmitResend a segment after 3 duplicate ACKs since a duplicate ACK means that an out-of sequence segment was receivedduplicate ACKs due to packet reorderingif window is small donrsquot get duplicate ACKs

Host A

tim

eout

Host B

time

X

resend seq X2

seq x1seq x2seq x3seq x4seq x5

ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer

else increment count of dup ACKs received for yif (count of dup ACKs received for y = 3)

resend segment with sequence number y

Fast retransmit algorithm

a duplicate ACK for already ACKed segment

fast retransmit


TCP Flow Control

receive side of TCP connection has a receive buffer

speed-matching service matching the send rate to the receiving apprsquos drain rate

app process may be slow at reading from buffer

sender wonrsquot overflowreceiverrsquos buffer by

transmitting too muchtoo fast

flow control


TCP Flow control how it works

(Suppose TCP receiver discards out-of-order segments)spare room in buffer

= RcvWin

= RcvBuffer-[LastByteRcvd -LastByteRead]

Rcvr advertises spare room by including value of RcvWin in segmentsSender limits unACKeddata to RcvWin

guarantees receive buffer doesnrsquot overflow


Sliding Window Flow Control Example

3K

2K SeqNo=0

ReceiverBuffer

0 4KSendersends 2Kof data

2K

AckNo=2048 RcvWin=2048Sendersends 2Kof data 2K SeqNo=2048

4K

AckNo=4096 RcvWin=0

AckNo=4096 RcvWin=1024

Sender blocked


Principles of Congestion Control

Congestioninformally ldquotoo many sources sending too much data too fast for network to handlerdquodifferent from flow controlmanifestations

lost packets (buffer overflow at routers)long delays (queueing in router buffers)

a top-10 problem


Causescosts of congestion scenario 1

two senders two receiversone router infinite buffers no retransmission

large delays when congestedmaximum achievable throughput

unlimited shared output link buffers

Host Aλin original data

Host B

λout



one router finite buffers sender retransmission of lost packet

finite shared output link buffers

Host A λin original data

Host B

λout

λin original data plus retransmitted data


Causescosts of congestion scenario 2always (goodput)ldquoperfectrdquo retransmission only when loss

retransmission of delayed (not lost) packet makes larger(than perfect case) for same

λin

λout=

λin

λoutgtλ

inλout

ldquocostsrdquo of congestionmore work (retrans) for given ldquogoodputrdquounneeded retransmissions link carries multiple copies of pkt

R2

R2λin

λ out

b

R2

R2λin

λ out

a

R2

R2λin

λ out

c

R4

R3


Causescosts of congestion scenario 3four sendersmultihop pathstimeoutretransmit

λin

Q what happens as and increase λ

in



Host B

λout




another ldquocostrdquo of congestionwhen packet dropped any ldquoupstream transmission capacity used for that packet was wasted

Host A

Host B

λou

t


Approaches towards congestion control

End-end congestion controlno explicit feedback from networkcongestion inferred from end-system observed loss delayapproach taken by TCP

Network-assisted congestion controlrouters provide feedback to end systems

single bit indicating congestion (SNA DECbit TCPIP ECN ATM)explicit rate sender should send at

Two broad approaches towards congestion control


TCP Congestion Control

end-end control (no network assistance)sender limits transmissionLastByteSent-LastByteAcked

le CongWin

CongWin is dynamic function of perceived network congestion

How does sender perceive congestionloss event = timeout or3 duplicate acksTCP sender reduces rate (CongWin) after loss event

two modes of operationSlow Start (SS)Congestion avoidance (CA) or Additive Increase Multiplicative Decrease (AIMD)


TCP congestion control bandwidth probing

ldquoprobing for bandwidthrdquo increase transmission rate on receipt of ACK until eventually loss occurs then decrease transmission rate

continue to increase on ACK decrease on loss (since available bandwidth is changing depending on other connections in network)

ACKs being received so increase rate

X

X

XX

X loss so decrease rate

send

ing

rate

time

Q how fast to increasedecreasedetails to follow

TCPrsquosldquosawtoothrdquobehavior


TCP Congestion Control details

sender limits rate by limiting number of unACKed bytes ldquoin pipelinerdquo

cwnd differs from rwnd (how why)sender limited by min(cwndrwnd)

roughly

cwnd is dynamic function of perceived network congestion

rate = cwndRTT bytessec

LastByteSent-LastByteAcked le cwnd

cwndbytes

RTT

ACK(s)


TCP Congestion Control more details

segment loss event reducing cwndtimeout no response from receiver

cut cwnd to 13 duplicate ACKs at least some segments getting through (recall fast retransmit)

cut cwnd in half less aggressively than on timeout

ACK received increase cwndTwo modes of operation

slowstart phase bull increase exponentially

fast (despite name) at connection start or following timeout

congestion avoidance bull increase linearly


TCP Slow Start Phasewhen connection begins cwnd = 1 MSS

example MSS = 500 bytes amp RTT = 200 msecinitial rate = 20 kbps

available bandwidth may be gtgt MSSRTT

desirable to quickly ramp up to respectable rate

increase rate exponentially until first loss event or when threshold reached

double cwnd every RTTdone by incrementing cwnd by 1 for every ACK received

Host A

one segment

RTT

Host B

time

two segments

four segments


Slow Start ExampleThe congestion window size grows very rapidly

For every ACK we increase CongWin by 1 irrespective of the number of segments ACKrsquoeddouble CongWinevery RTTinitial rate is slow but ramps up exponentially fast

TCP slows down the increase of CongWinwhen CongWin gt ssthresh

segment 1

ACK for segment 1

cwnd = 1

cwnd = 2 segment 2segment 3

ACK for segments 2

cwnd = 4 segment 4segment 5segment 6

ACK for segments 4

cwnd = 7

ACK for segments 3

ACK for segments 5

ACK for segments 6

cwnd = 3

cwnd = 5

cwnd = 6ACK for segments 7

cwnd = 8

segment 7


TCP Congestion Avoidance Phase

when cwnd gt ssthreshgrow cwnd linearly

increase cwnd by 1 MSS per RTT approach possible congestion slower than in slowstartimplementation cwnd= cwnd + MSScwndfor each ACK received

ACKs increase cwndby 1 MSS per RTT additive increaseloss cut cwnd in half (non-timeout-detected loss ) multiplicative decrease

AIMD

AIMD Additive IncreaseMultiplicative Decrease


Congestion AvoidanceCongestion avoidance phase is started if CongWin has reached the slow-start threshold value

If CongWin gt= ssthresh then each time an ACK is received increment CongWin as follows

bull CongWin = CongWin + 1CongWin (CongWin in segments)

bull In actual TCP implementation CongWin is in BytesCongWin = CongWin + MSS (MSSCongWin)

So CongWin is increased by one only if all CongWinsegments have been acknowledged


Example Slow StartCongestion AvoidanceAssume that

ssthresh = 8

cwnd = 1

cwnd = 2

cwnd = 4

cwnd = 8

cwnd = 9

cwnd = 10

02468

101214

t=0

t=2

t=4

t=6

Roundtrip times

Cw

nd(in

seg

men

ts)

ssthresh

cwnd = 3

cwnd = 5cwnd = 6cwnd = 7


Slow Start Congestion AvoidanceA typical plot of CongWin for a TCP connection

(MSS = 1500 bytes) with TCP Tahoe

SS

CA

ssthresh


Responses to CongestionTCP assumes there is congestion if it detects a packet lossA TCP sender can detect lost packets via loss events

bull Timeout of a retransmission timerbull Receipt of 3 duplicate ACKs (fast retransmit)

TCP interprets a Timeout as a binary congestion signal When a timeout occurs the sender performs

ssthresh is set to half the current size of the congestion window

ssthresh = CongWin 2CongWin is reset to one

CongWin = 1and slow-start is entered


Fast Recovery (differentiation btwn two loss events) After 3 dup ACKs (fast Retransmit)

ssthresh = CongWin2CongWin = CongWin2window then grows linearly

But after timeout eventCongWin = 1 MSS window then grows exponentiallyto the threshold then grows linearly

bull 3 dup ACKs indicates network capable of delivering some segmentsbull timeout before 3 dup ACKs is ldquomore alarmingrdquo

Philosophy

3-90

TCP Congestion ControlInitially

CongWin = 1ssthresh = advertised window size

New Ack receivedif (CongWin lt ssthresh) Slow Start

CongWin = CongWin + 1else Congestion Avoidance

CongWin = CongWin + 1CongWinTimeout

ssthresh = CongWin2CongWin = 1

Fast Retransmissionssthresh = CongWin2CongWin = CongWin2

Slow Start (exponential increase phase) is continued until CongWin reaches half of the level where the loss event occurred last time CongWin is increased slowly after (linear increase in Congestion Avoidance phase)


Popular ldquoflavorsrdquo of TCP

ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)


Summary TCP Congestion ControlWhen CongWin is below Threshold sender in slow-start phase window grows exponentiallyWhen CongWin is above Threshold sender is in congestion-avoidance phase window grows linearlyWhen a triple duplicate ACK occurs Threshold set to CongWin2 and CongWin set to ThresholdWhen timeout occurs Threshold set to CongWin2 and CongWin is set to 1 MSS The actual sender window size is determined based on the congestion and flow control algorithms

SenderWin=min(RcvWinCongWin)


TCP Congestion Control SummaryEvent State TCP Sender Action Commentary

ACK receipt for previously unackeddata

Slow Start (SS)

CongWin = CongWin + MSS If (CongWin gt Threshold)

set state to ldquoCongestion Avoidancerdquo

Resulting in a doubling of CongWin every RTT


CongestionAvoidance (CA)

CongWin = CongWin+MSS (MSSCongWin)

Additive increase resulting in increase of CongWin by 1 MSS every RTT

Loss event detected by triple duplicate ACK

SS or CA Threshold = CongWin2 CongWin = ThresholdSet state to ldquoCongestion Avoidancerdquo

Fast recovery implementing multiplicative decrease CongWin will not drop below 1 MSS

Timeout SS or CA Threshold = CongWin2 CongWin = 1 MSSSet state to ldquoSlow Startrdquo

Enter slow start

Duplicate ACK

SS or CA Increment duplicate ACK count for segment being acked

CongWin and Threshold not changed


TCP throughput

Q whatrsquos average throughout of TCP as function of window size RTT

ignoring slow startlet W be window size when loss occurs

when window is W throughput is WRTTjust after loss window drops to W2 throughput to W2RTT average throughout 75 WRTT


TCP Futures TCP over ldquolong fat pipesrdquo

example 1500 byte segments 100ms RTT want 10 Gbps throughputrequires window size W = 83333 in-flight segmentsthroughput in terms of loss rate

L = 210-10 Wownew versions of TCP for high-speed

LRTTMSSsdot221


Fairness goal if K TCP sessions share same bottleneck link of bandwidth R each should have average rate of RK

TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness


Why is TCP fairTwo competing sessions

Additive increase gives slope of 1 as throughout increasesmultiplicative decrease decreases throughput proportionally

R

R

equal bandwidth share

Connection 1 throughput

Conn

ecti

on 2

thr

ough

p ut

congestion avoidance additive increaseloss decrease window by factor of 2



Fairness (more)Fairness and UDP

Multimedia apps often do not use TCP

do not want rate throttled by congestion control

Instead use UDPpump audiovideo at constant rate tolerate packet loss

Research area TCP friendly

Fairness and parallel TCP connectionsnothing prevents app from opening parallel cnctionsbetween 2 hostsWeb browsers do this Example link of rate R supporting 9 cnctions

new app asks for 1 TCP gets rate R10new app asks for 11 TCPs gets R2


TCP Connection ManagementRecall TCP sender receiver

establish ldquoconnectionrdquobefore exchanging data segmentsinitialize TCP variables

seq sbuffers flow control info (eg RcvWindow)

client connection initiatorSocket clientSocket = new Socket(hostnameport

number)

server contacted by clientSocket connectionSocket = welcomeSocketaccept()

Three way handshakeStep 1 client host sends TCP

SYN segment to serverspecifies initial seq no data

Step 2 server host receives SYN replies with SYNACK segment

server allocates buffersspecifies server initial seq

Step 3 client receives SYNACK replies with ACK segment which may contain data


TCP Connection Management (cont)

Closing a connection

client closes socketclientSocketclose()

Step 1 client end system sends TCP FIN control segment to server

Step 2 server receives FIN replies with ACK Closes connection sends FIN

client

FIN

server

ACK

ACK

FIN

close

close

closed

tim

ed w

ait



Step 3 client receives FIN replies with ACK

Enters ldquotimed waitrdquo -will respond with ACK to received FINs

Step 4 server receives ACK Connection closed

client

FIN

server

ACK

ACK

FIN

closing

closing

closed

tim

ed w

ait

closed



TCP clientlifecycle

TCP serverlifecycle


Tuning TCPIP Parameters TCPIP parameters

A set of default values may not be optimal for all applicationsThe network administrator may wish to turn on or off some TCPIP functions for performance or security considerations

Many Unix and Linux systems provide some flexibility in tuning the TCPIP kernelsbinsysctl is used to configure the Linux kernel parameters at runtime

Default kernel configuration file is sbinsysctlconfFrequently used sysctl options

bull sysctl ndasha or sysctl ndashA list all current valuesbull sysctl ndashp file_name load the sysctl setting from a configuration

filebull sysctl ndashw variable=value change the value of the parameter


SomeTCP Parameters in Linux Kerneltcp_syn_retries

Number of SYN packets the kernel will send before giving up on the new connection

tcp_synack_retriesnumber of SYN+ACK packets sent before the kernel gives up on the connection

tcp_window_scalingMaximum window size of 65535 bytes not enough for for really fast networks The window scaling options allows for almost gigabyte windows which is good for connections with large delay-bandwidth product

tcp_max_syn_backlogMaximal number of remembered connection requests which still did not receive an acknowledgment from connecting client

tcp_fin_timeoutHow many seconds to wait for a final FIN packet before the socket is closed required to prevent denial-of-service (DoS) attacks Default value is 60 seconds


SomeTCP Parameters in Linux Kerneltcp_rmem

This is a vector of 3 integers [min default max] These parameters are used by TCP to dynamically adjust receive buffer sizesmin - minimum size of the receive buffer used by each TCP socket The default value is 4K default - the default size of the receive buffer for a TCP socket The default value is 87380 bytes and is lowered to 43689 in low memory systems If larger receive buffer sizes are desired this value should be increased max - the maximum size of the receive buffer used by each TCP socket The default value of 873802 bytes is lowered to 87380 in low memory systems

tcp_smemSend buffer parameters [min default max] similar to tcp_rmem

Chapter 3 Transport Layer

Transport services and protocols




How demultiplexing works



Connection-oriented demux (cont)

Connection-oriented demux Threaded Web Server


UDP more

UDP checksum

Principles of Reliable data transfer











rdt21 discussion




rdt30 sender

rdt30 in action

rdt30 in action



Pipelined protocols


Go-Back-N



GBN inaction

Selective Repeat


Selective repeat


Selective repeat dilemma









TCP seq rsquos and ACKs



Example RTT estimation



TCP sender events


TCP retransmission scenarios

TCP retransmission scenarios (more)


Fast Retransmit

Fast Retransmit


TCP Flow Control














TCP Slow Start Phase

Slow Start Example


Congestion Avoidance

Example Slow StartCongestion Avoidance

Slow Start Congestion Avoidance

Responses to Congestion

Fast Recovery (differentiation btwn two loss events)



Summary TCP Congestion Control

TCP Congestion Control Summary

TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)

TCP Connection Management




Tuning TCPIP Parameters

SomeTCP Parameters in Linux Kernel


Transport Layer 3-2

Transport services and protocolsprovide logical communicationbetween app processes running on different hoststransport protocols run in end systems

send side breaks app messages into segments passes to network layerrcv side reassembles segments into messages passes to app layer

more than one transport protocol available to apps

Internet TCP and UDP







data linkphysical


Transport Layer 3-3






Transport Layer 3-4













data linkphysical


Transport Layer 3-5


application

transport

network

link

physical

P1 application

transport

network

link

physical

application

transport

network

link

physical

P2P3 P4P1


= process= socket




Transport Layer 3-6





32 bits

applicationdata

(message)

other header fields


Transport Layer 3-7










Transport Layer 3-8









Transport Layer 3-9


ClientIPB

P1

clientIP A

P1P2P4

serverIP C

SP 9157DP 80

SP 9157DP 80

P5 P6 P3

D-IPCS-IP AD-IPC

S-IP B

SP 5775DP 80

D-IPCS-IP B



ClientIPB

P1

clientIP A

P1P2P4

serverIP C

SP 9157DP 80

SP 9157DP 80

P5 P6 P3

D-IPCS-IP AD-IPC

S-IP B

SP 5775DP 80

D-IPCS-IP B

P4














32 bits

Applicationdata

(message)

UDP segment format



header


UDP checksum








netw

ork

laye

r



sendside

receiveside











state1

state2




eventactions






udt_send(packet)


Wait for call from

below

rdt_rcv(packet)

sender receiver













udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

belowsender


Λ








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)

Λ








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)

Λ







stop and wait




above


rdt_send(data)




rdt_send(data)


udt_send(sndpkt)



Wait forcall 1 from

above


ΛΛ


















rdt21 discussion













above


rdt_send(data)

udt_send(sndpkt)


isACK(rcvpkt1) )


Wait for ACK

0sender FSM

fragment





has_seq1(rcvpkt))


fragment

Λ











rdt_send(data)

Wait for

ACK0



above


rdt_send(data)






timeout


timeout

rdt_rcv(rcvpkt)

Wait for call 0from

above

Wait for

ACK1

Λrdt_rcv(rcvpkt)

ΛΛ

Λ


rdt30 in action


rdt30 in action






U sender=

008 30008

= 000027 L RRTT + L R

=





sender receiver

RTT




U sender=

00830008

= 000027 L RRTT + L R

=








sender receiver

RTT





U sender=

024 30008

= 000083 L RRTT + L R

=





Go-Back-NSender







timeout

rdt_send(data)





stop_timerelse

start_timer


base=1nextseqnum=1


Λ

Λ






Wait






Λ


GBN inaction


Selective Repeat









Selective repeat








ACK(n)otherwise

ignore

receiver










sender

receiver

Go-Back-N

expectedSN

snd_base=expectedSN



senderrsquos window



sender

receiver

Go-Back-N

expectedSN




senderrsquos window



sender

receiver

Go-Back-N

expectedSN






sender

receiver

Selective Repeat

rcv_base

snd_base=rcv_base



senderrsquos window


rcv_base+N-1



sender

receiver

Selective Repeat

rcv_base

snd_base=rcv_base-N



senderrsquos window

rcv_base


rcv_base+N-1



sender

receiver

Selective Repeat

snd_base=rcv_base-N



rcv_basercv_base


rcv_base+N-1











socketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment






32 bits

applicationdata

(variable length)



FSRPAUheadlen

notused



ACK ACK valid



commands)


Internetchecksum

(as in UDP)






















100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

iseco

nds)

































start timer

end of loop forever





ACK=100


Host B

Seq=92 8 bytes data

ACK=120

Seq=92 8 bytes data

Seq=

92 t

imeo

ut

ACK=120

Host A

Seq=92 8 bytes data

ACK=100

loss

tim

eout

lost ACK scenario

Host B

X

Seq=92 8 bytes data

ACK=100

time

Seq=

92 t

imeo

utSendBase

= 100

SendBase= 120

SendBase= 120

Sendbase= 100



Seq=92 8 bytes data

ACK=100

loss

tim

eout


Host B

X


ACK=120

time

SendBase= 120



Event at Receiver





TCP Receiver action






Fast Retransmit









Host A

tim

eout

Host B

time

X

resend seq X2


ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer





fast retransmit


TCP Flow Control






flow control




= RcvWin






3K

2K SeqNo=0

ReceiverBuffer


2K


4K

AckNo=4096 RcvWin=0


Sender blocked





a top-10 problem







Host B

λout






Host B

λout





λin

λout=

λin

λoutgtλ

inλout


R2

R2λin

λ out

b

R2

R2λin

λ out

a

R2

R2λin

λ out

c

R4

R3



λin


in



Host B

λout





Host A

Host B

λou

t










le CongWin









X

X

XX


send

ing

rate

time







roughly




cwndbytes

RTT

ACK(s)

















Host A

one segment

RTT

Host B

time

two segments

four segments





segment 1

ACK for segment 1

cwnd = 1


ACK for segments 2


ACK for segments 4

cwnd = 7

ACK for segments 3

ACK for segments 5

ACK for segments 6

cwnd = 3

cwnd = 5


cwnd = 8

segment 7






AIMD










ssthresh = 8

cwnd = 1

cwnd = 2

cwnd = 4

cwnd = 8

cwnd = 9

cwnd = 10

02468

101214

t=0

t=2

t=4

t=6

Roundtrip times

Cw

nd(in

seg

men

ts)

ssthresh

cwnd = 3





SS

CA

ssthresh













Philosophy

3-90











ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







Slow Start (SS)












Enter slow start

Duplicate ACK




TCP throughput








LRTTMSSsdot221



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness




R

R



Conn

ecti

on 2

thr

ough

p ut
















number)













client

FIN

server

ACK

ACK

FIN

close

close

closed

tim

ed w

ait






client

FIN

server

ACK

ACK

FIN

closing

closing

closed

tim

ed w

ait

closed



TCP clientlifecycle

TCP serverlifecycle






























UDP more

UDP checksum












rdt21 discussion




rdt30 sender

rdt30 in action

rdt30 in action



Pipelined protocols


Go-Back-N



GBN inaction

Selective Repeat


Selective repeat

















TCP sender events





Fast Retransmit

Fast Retransmit


TCP Flow Control















Slow Start Example











TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)








Transport Layer 3-3






Transport Layer 3-4













data linkphysical


Transport Layer 3-5


application

transport

network

link

physical

P1 application

transport

network

link

physical

application

transport

network

link

physical

P2P3 P4P1


= process= socket




Transport Layer 3-6





32 bits

applicationdata

(message)

other header fields


Transport Layer 3-7










Transport Layer 3-8









Transport Layer 3-9


ClientIPB

P1

clientIP A

P1P2P4

serverIP C

SP 9157DP 80

SP 9157DP 80

P5 P6 P3

D-IPCS-IP AD-IPC

S-IP B

SP 5775DP 80

D-IPCS-IP B



ClientIPB

P1

clientIP A

P1P2P4

serverIP C

SP 9157DP 80

SP 9157DP 80

P5 P6 P3

D-IPCS-IP AD-IPC

S-IP B

SP 5775DP 80

D-IPCS-IP B

P4














32 bits

Applicationdata

(message)

UDP segment format



header


UDP checksum








netw

ork

laye

r



sendside

receiveside











state1

state2




eventactions






udt_send(packet)


Wait for call from

below

rdt_rcv(packet)

sender receiver













udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

belowsender


Λ








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)

Λ








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)

Λ







stop and wait




above


rdt_send(data)




rdt_send(data)


udt_send(sndpkt)



Wait forcall 1 from

above


ΛΛ


















rdt21 discussion













above


rdt_send(data)

udt_send(sndpkt)


isACK(rcvpkt1) )


Wait for ACK

0sender FSM

fragment





has_seq1(rcvpkt))


fragment

Λ











rdt_send(data)

Wait for

ACK0



above


rdt_send(data)






timeout


timeout

rdt_rcv(rcvpkt)

Wait for call 0from

above

Wait for

ACK1

Λrdt_rcv(rcvpkt)

ΛΛ

Λ


rdt30 in action


rdt30 in action






U sender=

008 30008

= 000027 L RRTT + L R

=





sender receiver

RTT




U sender=

00830008

= 000027 L RRTT + L R

=








sender receiver

RTT





U sender=

024 30008

= 000083 L RRTT + L R

=





Go-Back-NSender







timeout

rdt_send(data)





stop_timerelse

start_timer


base=1nextseqnum=1


Λ

Λ






Wait






Λ


GBN inaction


Selective Repeat









Selective repeat








ACK(n)otherwise

ignore

receiver










sender

receiver

Go-Back-N

expectedSN

snd_base=expectedSN



senderrsquos window



sender

receiver

Go-Back-N

expectedSN




senderrsquos window



sender

receiver

Go-Back-N

expectedSN






sender

receiver

Selective Repeat

rcv_base

snd_base=rcv_base



senderrsquos window


rcv_base+N-1



sender

receiver

Selective Repeat

rcv_base

snd_base=rcv_base-N



senderrsquos window

rcv_base


rcv_base+N-1



sender

receiver

Selective Repeat

snd_base=rcv_base-N



rcv_basercv_base


rcv_base+N-1











socketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment






32 bits

applicationdata

(variable length)



FSRPAUheadlen

notused



ACK ACK valid



commands)


Internetchecksum

(as in UDP)






















100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

iseco

nds)

































start timer

end of loop forever





ACK=100


Host B

Seq=92 8 bytes data

ACK=120

Seq=92 8 bytes data

Seq=

92 t

imeo

ut

ACK=120

Host A

Seq=92 8 bytes data

ACK=100

loss

tim

eout

lost ACK scenario

Host B

X

Seq=92 8 bytes data

ACK=100

time

Seq=

92 t

imeo

utSendBase

= 100

SendBase= 120

SendBase= 120

Sendbase= 100



Seq=92 8 bytes data

ACK=100

loss

tim

eout


Host B

X


ACK=120

time

SendBase= 120



Event at Receiver





TCP Receiver action






Fast Retransmit









Host A

tim

eout

Host B

time

X

resend seq X2


ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer





fast retransmit


TCP Flow Control






flow control




= RcvWin






3K

2K SeqNo=0

ReceiverBuffer


2K


4K

AckNo=4096 RcvWin=0


Sender blocked





a top-10 problem







Host B

λout






Host B

λout





λin

λout=

λin

λoutgtλ

inλout


R2

R2λin

λ out

b

R2

R2λin

λ out

a

R2

R2λin

λ out

c

R4

R3



λin


in



Host B

λout





Host A

Host B

λou

t










le CongWin









X

X

XX


send

ing

rate

time







roughly




cwndbytes

RTT

ACK(s)

















Host A

one segment

RTT

Host B

time

two segments

four segments





segment 1

ACK for segment 1

cwnd = 1


ACK for segments 2


ACK for segments 4

cwnd = 7

ACK for segments 3

ACK for segments 5

ACK for segments 6

cwnd = 3

cwnd = 5


cwnd = 8

segment 7






AIMD










ssthresh = 8

cwnd = 1

cwnd = 2

cwnd = 4

cwnd = 8

cwnd = 9

cwnd = 10

02468

101214

t=0

t=2

t=4

t=6

Roundtrip times

Cw

nd(in

seg

men

ts)

ssthresh

cwnd = 3





SS

CA

ssthresh













Philosophy

3-90











ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







Slow Start (SS)












Enter slow start

Duplicate ACK




TCP throughput








LRTTMSSsdot221



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness




R

R



Conn

ecti

on 2

thr

ough

p ut
















number)













client

FIN

server

ACK

ACK

FIN

close

close

closed

tim

ed w

ait






client

FIN

server

ACK

ACK

FIN

closing

closing

closed

tim

ed w

ait

closed



TCP clientlifecycle

TCP serverlifecycle






























UDP more

UDP checksum












rdt21 discussion




rdt30 sender

rdt30 in action

rdt30 in action



Pipelined protocols


Go-Back-N



GBN inaction

Selective Repeat


Selective repeat

















TCP sender events





Fast Retransmit

Fast Retransmit


TCP Flow Control















Slow Start Example











TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)








Transport Layer 3-4













data linkphysical


Transport Layer 3-5


application

transport

network

link

physical

P1 application

transport

network

link

physical

application

transport

network

link

physical

P2P3 P4P1


= process= socket




Transport Layer 3-6





32 bits

applicationdata

(message)

other header fields


Transport Layer 3-7










Transport Layer 3-8









Transport Layer 3-9


ClientIPB

P1

clientIP A

P1P2P4

serverIP C

SP 9157DP 80

SP 9157DP 80

P5 P6 P3

D-IPCS-IP AD-IPC

S-IP B

SP 5775DP 80

D-IPCS-IP B



ClientIPB

P1

clientIP A

P1P2P4

serverIP C

SP 9157DP 80

SP 9157DP 80

P5 P6 P3

D-IPCS-IP AD-IPC

S-IP B

SP 5775DP 80

D-IPCS-IP B

P4














32 bits

Applicationdata

(message)

UDP segment format



header


UDP checksum








netw

ork

laye

r



sendside

receiveside











state1

state2




eventactions






udt_send(packet)


Wait for call from

below

rdt_rcv(packet)

sender receiver













udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

belowsender


Λ








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)

Λ








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)

Λ







stop and wait




above


rdt_send(data)




rdt_send(data)


udt_send(sndpkt)



Wait forcall 1 from

above


ΛΛ


















rdt21 discussion













above


rdt_send(data)

udt_send(sndpkt)


isACK(rcvpkt1) )


Wait for ACK

0sender FSM

fragment





has_seq1(rcvpkt))


fragment

Λ











rdt_send(data)

Wait for

ACK0



above


rdt_send(data)






timeout


timeout

rdt_rcv(rcvpkt)

Wait for call 0from

above

Wait for

ACK1

Λrdt_rcv(rcvpkt)

ΛΛ

Λ


rdt30 in action


rdt30 in action






U sender=

008 30008

= 000027 L RRTT + L R

=





sender receiver

RTT




U sender=

00830008

= 000027 L RRTT + L R

=








sender receiver

RTT





U sender=

024 30008

= 000083 L RRTT + L R

=





Go-Back-NSender







timeout

rdt_send(data)





stop_timerelse

start_timer


base=1nextseqnum=1


Λ

Λ






Wait






Λ


GBN inaction


Selective Repeat









Selective repeat








ACK(n)otherwise

ignore

receiver










sender

receiver

Go-Back-N

expectedSN

snd_base=expectedSN



senderrsquos window



sender

receiver

Go-Back-N

expectedSN




senderrsquos window



sender

receiver

Go-Back-N

expectedSN






sender

receiver

Selective Repeat

rcv_base

snd_base=rcv_base



senderrsquos window


rcv_base+N-1



sender

receiver

Selective Repeat

rcv_base

snd_base=rcv_base-N



senderrsquos window

rcv_base


rcv_base+N-1



sender

receiver

Selective Repeat

snd_base=rcv_base-N



rcv_basercv_base


rcv_base+N-1











socketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment






32 bits

applicationdata

(variable length)



FSRPAUheadlen

notused



ACK ACK valid



commands)


Internetchecksum

(as in UDP)






















100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

iseco

nds)

































start timer

end of loop forever





ACK=100


Host B

Seq=92 8 bytes data

ACK=120

Seq=92 8 bytes data

Seq=

92 t

imeo

ut

ACK=120

Host A

Seq=92 8 bytes data

ACK=100

loss

tim

eout

lost ACK scenario

Host B

X

Seq=92 8 bytes data

ACK=100

time

Seq=

92 t

imeo

utSendBase

= 100

SendBase= 120

SendBase= 120

Sendbase= 100



Seq=92 8 bytes data

ACK=100

loss

tim

eout


Host B

X


ACK=120

time

SendBase= 120



Event at Receiver





TCP Receiver action






Fast Retransmit









Host A

tim

eout

Host B

time

X

resend seq X2


ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer





fast retransmit


TCP Flow Control






flow control




= RcvWin






3K

2K SeqNo=0

ReceiverBuffer


2K


4K

AckNo=4096 RcvWin=0


Sender blocked





a top-10 problem







Host B

λout






Host B

λout





λin

λout=

λin

λoutgtλ

inλout


R2

R2λin

λ out

b

R2

R2λin

λ out

a

R2

R2λin

λ out

c

R4

R3



λin


in



Host B

λout





Host A

Host B

λou

t










le CongWin









X

X

XX


send

ing

rate

time







roughly




cwndbytes

RTT

ACK(s)

















Host A

one segment

RTT

Host B

time

two segments

four segments





segment 1

ACK for segment 1

cwnd = 1


ACK for segments 2


ACK for segments 4

cwnd = 7

ACK for segments 3

ACK for segments 5

ACK for segments 6

cwnd = 3

cwnd = 5


cwnd = 8

segment 7






AIMD










ssthresh = 8

cwnd = 1

cwnd = 2

cwnd = 4

cwnd = 8

cwnd = 9

cwnd = 10

02468

101214

t=0

t=2

t=4

t=6

Roundtrip times

Cw

nd(in

seg

men

ts)

ssthresh

cwnd = 3





SS

CA

ssthresh













Philosophy

3-90











ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







Slow Start (SS)












Enter slow start

Duplicate ACK




TCP throughput








LRTTMSSsdot221



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness




R

R



Conn

ecti

on 2

thr

ough

p ut
















number)













client

FIN

server

ACK

ACK

FIN

close

close

closed

tim

ed w

ait






client

FIN

server

ACK

ACK

FIN

closing

closing

closed

tim

ed w

ait

closed



TCP clientlifecycle

TCP serverlifecycle






























UDP more

UDP checksum












rdt21 discussion




rdt30 sender

rdt30 in action

rdt30 in action



Pipelined protocols


Go-Back-N



GBN inaction

Selective Repeat


Selective repeat

















TCP sender events





Fast Retransmit

Fast Retransmit


TCP Flow Control















Slow Start Example











TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)








Transport Layer 3-5


application

transport

network

link

physical

P1 application

transport

network

link

physical

application

transport

network

link

physical

P2P3 P4P1


= process= socket




Transport Layer 3-6





32 bits

applicationdata

(message)

other header fields


Transport Layer 3-7










Transport Layer 3-8









Transport Layer 3-9


ClientIPB

P1

clientIP A

P1P2P4

serverIP C

SP 9157DP 80

SP 9157DP 80

P5 P6 P3

D-IPCS-IP AD-IPC

S-IP B

SP 5775DP 80

D-IPCS-IP B



ClientIPB

P1

clientIP A

P1P2P4

serverIP C

SP 9157DP 80

SP 9157DP 80

P5 P6 P3

D-IPCS-IP AD-IPC

S-IP B

SP 5775DP 80

D-IPCS-IP B

P4














32 bits

Applicationdata

(message)

UDP segment format



header


UDP checksum








netw

ork

laye

r



sendside

receiveside











state1

state2




eventactions






udt_send(packet)


Wait for call from

below

rdt_rcv(packet)

sender receiver













udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

belowsender


Λ








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)

Λ








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)

Λ







stop and wait




above


rdt_send(data)




rdt_send(data)


udt_send(sndpkt)



Wait forcall 1 from

above


ΛΛ


















rdt21 discussion













above


rdt_send(data)

udt_send(sndpkt)


isACK(rcvpkt1) )


Wait for ACK

0sender FSM

fragment





has_seq1(rcvpkt))


fragment

Λ











rdt_send(data)

Wait for

ACK0



above


rdt_send(data)






timeout


timeout

rdt_rcv(rcvpkt)

Wait for call 0from

above

Wait for

ACK1

Λrdt_rcv(rcvpkt)

ΛΛ

Λ


rdt30 in action


rdt30 in action






U sender=

008 30008

= 000027 L RRTT + L R

=





sender receiver

RTT




U sender=

00830008

= 000027 L RRTT + L R

=








sender receiver

RTT





U sender=

024 30008

= 000083 L RRTT + L R

=





Go-Back-NSender







timeout

rdt_send(data)





stop_timerelse

start_timer


base=1nextseqnum=1


Λ

Λ






Wait






Λ


GBN inaction


Selective Repeat









Selective repeat








ACK(n)otherwise

ignore

receiver










sender

receiver

Go-Back-N

expectedSN

snd_base=expectedSN



senderrsquos window



sender

receiver

Go-Back-N

expectedSN




senderrsquos window



sender

receiver

Go-Back-N

expectedSN






sender

receiver

Selective Repeat

rcv_base

snd_base=rcv_base



senderrsquos window


rcv_base+N-1



sender

receiver

Selective Repeat

rcv_base

snd_base=rcv_base-N



senderrsquos window

rcv_base


rcv_base+N-1



sender

receiver

Selective Repeat

snd_base=rcv_base-N



rcv_basercv_base


rcv_base+N-1











socketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment






32 bits

applicationdata

(variable length)



FSRPAUheadlen

notused



ACK ACK valid



commands)


Internetchecksum

(as in UDP)






















100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

iseco

nds)

































start timer

end of loop forever





ACK=100


Host B

Seq=92 8 bytes data

ACK=120

Seq=92 8 bytes data

Seq=

92 t

imeo

ut

ACK=120

Host A

Seq=92 8 bytes data

ACK=100

loss

tim

eout

lost ACK scenario

Host B

X

Seq=92 8 bytes data

ACK=100

time

Seq=

92 t

imeo

utSendBase

= 100

SendBase= 120

SendBase= 120

Sendbase= 100



Seq=92 8 bytes data

ACK=100

loss

tim

eout


Host B

X


ACK=120

time

SendBase= 120



Event at Receiver





TCP Receiver action






Fast Retransmit









Host A

tim

eout

Host B

time

X

resend seq X2


ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer





fast retransmit


TCP Flow Control






flow control




= RcvWin






3K

2K SeqNo=0

ReceiverBuffer


2K


4K

AckNo=4096 RcvWin=0


Sender blocked





a top-10 problem







Host B

λout






Host B

λout





λin

λout=

λin

λoutgtλ

inλout


R2

R2λin

λ out

b

R2

R2λin

λ out

a

R2

R2λin

λ out

c

R4

R3



λin


in



Host B

λout





Host A

Host B

λou

t










le CongWin









X

X

XX


send

ing

rate

time







roughly




cwndbytes

RTT

ACK(s)

















Host A

one segment

RTT

Host B

time

two segments

four segments





segment 1

ACK for segment 1

cwnd = 1


ACK for segments 2


ACK for segments 4

cwnd = 7

ACK for segments 3

ACK for segments 5

ACK for segments 6

cwnd = 3

cwnd = 5


cwnd = 8

segment 7






AIMD










ssthresh = 8

cwnd = 1

cwnd = 2

cwnd = 4

cwnd = 8

cwnd = 9

cwnd = 10

02468

101214

t=0

t=2

t=4

t=6

Roundtrip times

Cw

nd(in

seg

men

ts)

ssthresh

cwnd = 3





SS

CA

ssthresh













Philosophy

3-90











ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







Slow Start (SS)












Enter slow start

Duplicate ACK




TCP throughput








LRTTMSSsdot221



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness




R

R



Conn

ecti

on 2

thr

ough

p ut
















number)













client

FIN

server

ACK

ACK

FIN

close

close

closed

tim

ed w

ait






client

FIN

server

ACK

ACK

FIN

closing

closing

closed

tim

ed w

ait

closed



TCP clientlifecycle

TCP serverlifecycle






























UDP more

UDP checksum












rdt21 discussion




rdt30 sender

rdt30 in action

rdt30 in action



Pipelined protocols


Go-Back-N



GBN inaction

Selective Repeat


Selective repeat

















TCP sender events





Fast Retransmit

Fast Retransmit


TCP Flow Control















Slow Start Example











TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)








Transport Layer 3-6





32 bits

applicationdata

(message)

other header fields


Transport Layer 3-7










Transport Layer 3-8









Transport Layer 3-9


ClientIPB

P1

clientIP A

P1P2P4

serverIP C

SP 9157DP 80

SP 9157DP 80

P5 P6 P3

D-IPCS-IP AD-IPC

S-IP B

SP 5775DP 80

D-IPCS-IP B



ClientIPB

P1

clientIP A

P1P2P4

serverIP C

SP 9157DP 80

SP 9157DP 80

P5 P6 P3

D-IPCS-IP AD-IPC

S-IP B

SP 5775DP 80

D-IPCS-IP B

P4














32 bits

Applicationdata

(message)

UDP segment format



header


UDP checksum








netw

ork

laye

r



sendside

receiveside











state1

state2




eventactions






udt_send(packet)


Wait for call from

below

rdt_rcv(packet)

sender receiver













udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

belowsender


Λ








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)

Λ








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)

Λ







stop and wait




above


rdt_send(data)




rdt_send(data)


udt_send(sndpkt)



Wait forcall 1 from

above


ΛΛ


















rdt21 discussion













above


rdt_send(data)

udt_send(sndpkt)


isACK(rcvpkt1) )


Wait for ACK

0sender FSM

fragment





has_seq1(rcvpkt))


fragment

Λ











rdt_send(data)

Wait for

ACK0



above


rdt_send(data)






timeout


timeout

rdt_rcv(rcvpkt)

Wait for call 0from

above

Wait for

ACK1

Λrdt_rcv(rcvpkt)

ΛΛ

Λ


rdt30 in action


rdt30 in action






U sender=

008 30008

= 000027 L RRTT + L R

=





sender receiver

RTT




U sender=

00830008

= 000027 L RRTT + L R

=








sender receiver

RTT





U sender=

024 30008

= 000083 L RRTT + L R

=





Go-Back-NSender







timeout

rdt_send(data)





stop_timerelse

start_timer


base=1nextseqnum=1


Λ

Λ






Wait






Λ


GBN inaction


Selective Repeat









Selective repeat








ACK(n)otherwise

ignore

receiver










sender

receiver

Go-Back-N

expectedSN

snd_base=expectedSN



senderrsquos window



sender

receiver

Go-Back-N

expectedSN




senderrsquos window



sender

receiver

Go-Back-N

expectedSN






sender

receiver

Selective Repeat

rcv_base

snd_base=rcv_base



senderrsquos window


rcv_base+N-1



sender

receiver

Selective Repeat

rcv_base

snd_base=rcv_base-N



senderrsquos window

rcv_base


rcv_base+N-1



sender

receiver

Selective Repeat

snd_base=rcv_base-N



rcv_basercv_base


rcv_base+N-1











socketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment






32 bits

applicationdata

(variable length)



FSRPAUheadlen

notused



ACK ACK valid



commands)


Internetchecksum

(as in UDP)






















100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

iseco

nds)

































start timer

end of loop forever





ACK=100


Host B

Seq=92 8 bytes data

ACK=120

Seq=92 8 bytes data

Seq=

92 t

imeo

ut

ACK=120

Host A

Seq=92 8 bytes data

ACK=100

loss

tim

eout

lost ACK scenario

Host B

X

Seq=92 8 bytes data

ACK=100

time

Seq=

92 t

imeo

utSendBase

= 100

SendBase= 120

SendBase= 120

Sendbase= 100



Seq=92 8 bytes data

ACK=100

loss

tim

eout


Host B

X


ACK=120

time

SendBase= 120



Event at Receiver





TCP Receiver action






Fast Retransmit









Host A

tim

eout

Host B

time

X

resend seq X2


ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer





fast retransmit


TCP Flow Control






flow control




= RcvWin






3K

2K SeqNo=0

ReceiverBuffer


2K


4K

AckNo=4096 RcvWin=0


Sender blocked





a top-10 problem







Host B

λout






Host B

λout





λin

λout=

λin

λoutgtλ

inλout


R2

R2λin

λ out

b

R2

R2λin

λ out

a

R2

R2λin

λ out

c

R4

R3



λin


in



Host B

λout





Host A

Host B

λou

t










le CongWin









X

X

XX


send

ing

rate

time







roughly




cwndbytes

RTT

ACK(s)

















Host A

one segment

RTT

Host B

time

two segments

four segments





segment 1

ACK for segment 1

cwnd = 1


ACK for segments 2


ACK for segments 4

cwnd = 7

ACK for segments 3

ACK for segments 5

ACK for segments 6

cwnd = 3

cwnd = 5


cwnd = 8

segment 7






AIMD










ssthresh = 8

cwnd = 1

cwnd = 2

cwnd = 4

cwnd = 8

cwnd = 9

cwnd = 10

02468

101214

t=0

t=2

t=4

t=6

Roundtrip times

Cw

nd(in

seg

men

ts)

ssthresh

cwnd = 3





SS

CA

ssthresh













Philosophy

3-90











ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







Slow Start (SS)












Enter slow start

Duplicate ACK




TCP throughput








LRTTMSSsdot221



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness




R

R



Conn

ecti

on 2

thr

ough

p ut
















number)













client

FIN

server

ACK

ACK

FIN

close

close

closed

tim

ed w

ait






client

FIN

server

ACK

ACK

FIN

closing

closing

closed

tim

ed w

ait

closed



TCP clientlifecycle

TCP serverlifecycle






























UDP more

UDP checksum












rdt21 discussion




rdt30 sender

rdt30 in action

rdt30 in action



Pipelined protocols


Go-Back-N



GBN inaction

Selective Repeat


Selective repeat

















TCP sender events





Fast Retransmit

Fast Retransmit


TCP Flow Control















Slow Start Example











TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)








Transport Layer 3-7










Transport Layer 3-8









Transport Layer 3-9


ClientIPB

P1

clientIP A

P1P2P4

serverIP C

SP 9157DP 80

SP 9157DP 80

P5 P6 P3

D-IPCS-IP AD-IPC

S-IP B

SP 5775DP 80

D-IPCS-IP B



ClientIPB

P1

clientIP A

P1P2P4

serverIP C

SP 9157DP 80

SP 9157DP 80

P5 P6 P3

D-IPCS-IP AD-IPC

S-IP B

SP 5775DP 80

D-IPCS-IP B

P4














32 bits

Applicationdata

(message)

UDP segment format



header


UDP checksum








netw

ork

laye

r



sendside

receiveside











state1

state2




eventactions






udt_send(packet)


Wait for call from

below

rdt_rcv(packet)

sender receiver













udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

belowsender


Λ








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)

Λ








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)

Λ







stop and wait




above


rdt_send(data)




rdt_send(data)


udt_send(sndpkt)



Wait forcall 1 from

above


ΛΛ


















rdt21 discussion













above


rdt_send(data)

udt_send(sndpkt)


isACK(rcvpkt1) )


Wait for ACK

0sender FSM

fragment





has_seq1(rcvpkt))


fragment

Λ











rdt_send(data)

Wait for

ACK0



above


rdt_send(data)






timeout


timeout

rdt_rcv(rcvpkt)

Wait for call 0from

above

Wait for

ACK1

Λrdt_rcv(rcvpkt)

ΛΛ

Λ


rdt30 in action


rdt30 in action






U sender=

008 30008

= 000027 L RRTT + L R

=





sender receiver

RTT




U sender=

00830008

= 000027 L RRTT + L R

=








sender receiver

RTT





U sender=

024 30008

= 000083 L RRTT + L R

=





Go-Back-NSender







timeout

rdt_send(data)





stop_timerelse

start_timer


base=1nextseqnum=1


Λ

Λ






Wait






Λ


GBN inaction


Selective Repeat









Selective repeat








ACK(n)otherwise

ignore

receiver










sender

receiver

Go-Back-N

expectedSN

snd_base=expectedSN



senderrsquos window



sender

receiver

Go-Back-N

expectedSN




senderrsquos window



sender

receiver

Go-Back-N

expectedSN






sender

receiver

Selective Repeat

rcv_base

snd_base=rcv_base



senderrsquos window


rcv_base+N-1



sender

receiver

Selective Repeat

rcv_base

snd_base=rcv_base-N



senderrsquos window

rcv_base


rcv_base+N-1



sender

receiver

Selective Repeat

snd_base=rcv_base-N



rcv_basercv_base


rcv_base+N-1











socketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment






32 bits

applicationdata

(variable length)



FSRPAUheadlen

notused



ACK ACK valid



commands)


Internetchecksum

(as in UDP)






















100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

iseco

nds)

































start timer

end of loop forever





ACK=100


Host B

Seq=92 8 bytes data

ACK=120

Seq=92 8 bytes data

Seq=

92 t

imeo

ut

ACK=120

Host A

Seq=92 8 bytes data

ACK=100

loss

tim

eout

lost ACK scenario

Host B

X

Seq=92 8 bytes data

ACK=100

time

Seq=

92 t

imeo

utSendBase

= 100

SendBase= 120

SendBase= 120

Sendbase= 100



Seq=92 8 bytes data

ACK=100

loss

tim

eout


Host B

X


ACK=120

time

SendBase= 120



Event at Receiver





TCP Receiver action






Fast Retransmit









Host A

tim

eout

Host B

time

X

resend seq X2


ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer





fast retransmit


TCP Flow Control






flow control




= RcvWin






3K

2K SeqNo=0

ReceiverBuffer


2K


4K

AckNo=4096 RcvWin=0


Sender blocked





a top-10 problem







Host B

λout






Host B

λout





λin

λout=

λin

λoutgtλ

inλout


R2

R2λin

λ out

b

R2

R2λin

λ out

a

R2

R2λin

λ out

c

R4

R3



λin


in



Host B

λout





Host A

Host B

λou

t










le CongWin









X

X

XX


send

ing

rate

time







roughly




cwndbytes

RTT

ACK(s)

















Host A

one segment

RTT

Host B

time

two segments

four segments





segment 1

ACK for segment 1

cwnd = 1


ACK for segments 2


ACK for segments 4

cwnd = 7

ACK for segments 3

ACK for segments 5

ACK for segments 6

cwnd = 3

cwnd = 5


cwnd = 8

segment 7






AIMD










ssthresh = 8

cwnd = 1

cwnd = 2

cwnd = 4

cwnd = 8

cwnd = 9

cwnd = 10

02468

101214

t=0

t=2

t=4

t=6

Roundtrip times

Cw

nd(in

seg

men

ts)

ssthresh

cwnd = 3





SS

CA

ssthresh













Philosophy

3-90











ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







Slow Start (SS)












Enter slow start

Duplicate ACK




TCP throughput








LRTTMSSsdot221



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness




R

R



Conn

ecti

on 2

thr

ough

p ut
















number)













client

FIN

server

ACK

ACK

FIN

close

close

closed

tim

ed w

ait






client

FIN

server

ACK

ACK

FIN

closing

closing

closed

tim

ed w

ait

closed



TCP clientlifecycle

TCP serverlifecycle






























UDP more

UDP checksum












rdt21 discussion




rdt30 sender

rdt30 in action

rdt30 in action



Pipelined protocols


Go-Back-N



GBN inaction

Selective Repeat


Selective repeat

















TCP sender events





Fast Retransmit

Fast Retransmit


TCP Flow Control















Slow Start Example











TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)








Transport Layer 3-8









Transport Layer 3-9


ClientIPB

P1

clientIP A

P1P2P4

serverIP C

SP 9157DP 80

SP 9157DP 80

P5 P6 P3

D-IPCS-IP AD-IPC

S-IP B

SP 5775DP 80

D-IPCS-IP B



ClientIPB

P1

clientIP A

P1P2P4

serverIP C

SP 9157DP 80

SP 9157DP 80

P5 P6 P3

D-IPCS-IP AD-IPC

S-IP B

SP 5775DP 80

D-IPCS-IP B

P4














32 bits

Applicationdata

(message)

UDP segment format



header


UDP checksum








netw

ork

laye

r



sendside

receiveside











state1

state2




eventactions






udt_send(packet)


Wait for call from

below

rdt_rcv(packet)

sender receiver













udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

belowsender


Λ








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)

Λ








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)

Λ







stop and wait




above


rdt_send(data)




rdt_send(data)


udt_send(sndpkt)



Wait forcall 1 from

above


ΛΛ


















rdt21 discussion













above


rdt_send(data)

udt_send(sndpkt)


isACK(rcvpkt1) )


Wait for ACK

0sender FSM

fragment





has_seq1(rcvpkt))


fragment

Λ











rdt_send(data)

Wait for

ACK0



above


rdt_send(data)






timeout


timeout

rdt_rcv(rcvpkt)

Wait for call 0from

above

Wait for

ACK1

Λrdt_rcv(rcvpkt)

ΛΛ

Λ


rdt30 in action


rdt30 in action






U sender=

008 30008

= 000027 L RRTT + L R

=





sender receiver

RTT




U sender=

00830008

= 000027 L RRTT + L R

=








sender receiver

RTT





U sender=

024 30008

= 000083 L RRTT + L R

=





Go-Back-NSender







timeout

rdt_send(data)





stop_timerelse

start_timer


base=1nextseqnum=1


Λ

Λ






Wait






Λ


GBN inaction


Selective Repeat









Selective repeat








ACK(n)otherwise

ignore

receiver










sender

receiver

Go-Back-N

expectedSN

snd_base=expectedSN



senderrsquos window



sender

receiver

Go-Back-N

expectedSN




senderrsquos window



sender

receiver

Go-Back-N

expectedSN






sender

receiver

Selective Repeat

rcv_base

snd_base=rcv_base



senderrsquos window


rcv_base+N-1



sender

receiver

Selective Repeat

rcv_base

snd_base=rcv_base-N



senderrsquos window

rcv_base


rcv_base+N-1



sender

receiver

Selective Repeat

snd_base=rcv_base-N



rcv_basercv_base


rcv_base+N-1











socketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment






32 bits

applicationdata

(variable length)



FSRPAUheadlen

notused



ACK ACK valid



commands)


Internetchecksum

(as in UDP)






















100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

iseco

nds)

































start timer

end of loop forever





ACK=100


Host B

Seq=92 8 bytes data

ACK=120

Seq=92 8 bytes data

Seq=

92 t

imeo

ut

ACK=120

Host A

Seq=92 8 bytes data

ACK=100

loss

tim

eout

lost ACK scenario

Host B

X

Seq=92 8 bytes data

ACK=100

time

Seq=

92 t

imeo

utSendBase

= 100

SendBase= 120

SendBase= 120

Sendbase= 100



Seq=92 8 bytes data

ACK=100

loss

tim

eout


Host B

X


ACK=120

time

SendBase= 120



Event at Receiver





TCP Receiver action






Fast Retransmit









Host A

tim

eout

Host B

time

X

resend seq X2


ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer





fast retransmit


TCP Flow Control






flow control




= RcvWin






3K

2K SeqNo=0

ReceiverBuffer


2K


4K

AckNo=4096 RcvWin=0


Sender blocked





a top-10 problem







Host B

λout






Host B

λout





λin

λout=

λin

λoutgtλ

inλout


R2

R2λin

λ out

b

R2

R2λin

λ out

a

R2

R2λin

λ out

c

R4

R3



λin


in



Host B

λout





Host A

Host B

λou

t










le CongWin









X

X

XX


send

ing

rate

time







roughly




cwndbytes

RTT

ACK(s)

















Host A

one segment

RTT

Host B

time

two segments

four segments





segment 1

ACK for segment 1

cwnd = 1


ACK for segments 2


ACK for segments 4

cwnd = 7

ACK for segments 3

ACK for segments 5

ACK for segments 6

cwnd = 3

cwnd = 5


cwnd = 8

segment 7






AIMD










ssthresh = 8

cwnd = 1

cwnd = 2

cwnd = 4

cwnd = 8

cwnd = 9

cwnd = 10

02468

101214

t=0

t=2

t=4

t=6

Roundtrip times

Cw

nd(in

seg

men

ts)

ssthresh

cwnd = 3





SS

CA

ssthresh













Philosophy

3-90











ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







Slow Start (SS)












Enter slow start

Duplicate ACK




TCP throughput








LRTTMSSsdot221



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness




R

R



Conn

ecti

on 2

thr

ough

p ut
















number)













client

FIN

server

ACK

ACK

FIN

close

close

closed

tim

ed w

ait






client

FIN

server

ACK

ACK

FIN

closing

closing

closed

tim

ed w

ait

closed



TCP clientlifecycle

TCP serverlifecycle






























UDP more

UDP checksum












rdt21 discussion




rdt30 sender

rdt30 in action

rdt30 in action



Pipelined protocols


Go-Back-N



GBN inaction

Selective Repeat


Selective repeat

















TCP sender events





Fast Retransmit

Fast Retransmit


TCP Flow Control















Slow Start Example











TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)








Transport Layer 3-9


ClientIPB

P1

clientIP A

P1P2P4

serverIP C

SP 9157DP 80

SP 9157DP 80

P5 P6 P3

D-IPCS-IP AD-IPC

S-IP B

SP 5775DP 80

D-IPCS-IP B



ClientIPB

P1

clientIP A

P1P2P4

serverIP C

SP 9157DP 80

SP 9157DP 80

P5 P6 P3

D-IPCS-IP AD-IPC

S-IP B

SP 5775DP 80

D-IPCS-IP B

P4














32 bits

Applicationdata

(message)

UDP segment format



header


UDP checksum








netw

ork

laye

r



sendside

receiveside











state1

state2




eventactions






udt_send(packet)


Wait for call from

below

rdt_rcv(packet)

sender receiver













udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

belowsender


Λ








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)

Λ








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)

Λ







stop and wait




above


rdt_send(data)




rdt_send(data)


udt_send(sndpkt)



Wait forcall 1 from

above


ΛΛ


















rdt21 discussion













above


rdt_send(data)

udt_send(sndpkt)


isACK(rcvpkt1) )


Wait for ACK

0sender FSM

fragment





has_seq1(rcvpkt))


fragment

Λ











rdt_send(data)

Wait for

ACK0



above


rdt_send(data)






timeout


timeout

rdt_rcv(rcvpkt)

Wait for call 0from

above

Wait for

ACK1

Λrdt_rcv(rcvpkt)

ΛΛ

Λ


rdt30 in action


rdt30 in action






U sender=

008 30008

= 000027 L RRTT + L R

=





sender receiver

RTT




U sender=

00830008

= 000027 L RRTT + L R

=








sender receiver

RTT





U sender=

024 30008

= 000083 L RRTT + L R

=





Go-Back-NSender







timeout

rdt_send(data)





stop_timerelse

start_timer


base=1nextseqnum=1


Λ

Λ






Wait






Λ


GBN inaction


Selective Repeat









Selective repeat








ACK(n)otherwise

ignore

receiver










sender

receiver

Go-Back-N

expectedSN

snd_base=expectedSN



senderrsquos window



sender

receiver

Go-Back-N

expectedSN




senderrsquos window



sender

receiver

Go-Back-N

expectedSN






sender

receiver

Selective Repeat

rcv_base

snd_base=rcv_base



senderrsquos window


rcv_base+N-1



sender

receiver

Selective Repeat

rcv_base

snd_base=rcv_base-N



senderrsquos window

rcv_base


rcv_base+N-1



sender

receiver

Selective Repeat

snd_base=rcv_base-N



rcv_basercv_base


rcv_base+N-1











socketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment






32 bits

applicationdata

(variable length)



FSRPAUheadlen

notused



ACK ACK valid



commands)


Internetchecksum

(as in UDP)






















100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

iseco

nds)

































start timer

end of loop forever





ACK=100


Host B

Seq=92 8 bytes data

ACK=120

Seq=92 8 bytes data

Seq=

92 t

imeo

ut

ACK=120

Host A

Seq=92 8 bytes data

ACK=100

loss

tim

eout

lost ACK scenario

Host B

X

Seq=92 8 bytes data

ACK=100

time

Seq=

92 t

imeo

utSendBase

= 100

SendBase= 120

SendBase= 120

Sendbase= 100



Seq=92 8 bytes data

ACK=100

loss

tim

eout


Host B

X


ACK=120

time

SendBase= 120



Event at Receiver





TCP Receiver action






Fast Retransmit









Host A

tim

eout

Host B

time

X

resend seq X2


ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer





fast retransmit


TCP Flow Control






flow control




= RcvWin






3K

2K SeqNo=0

ReceiverBuffer


2K


4K

AckNo=4096 RcvWin=0


Sender blocked





a top-10 problem







Host B

λout






Host B

λout





λin

λout=

λin

λoutgtλ

inλout


R2

R2λin

λ out

b

R2

R2λin

λ out

a

R2

R2λin

λ out

c

R4

R3



λin


in



Host B

λout





Host A

Host B

λou

t










le CongWin









X

X

XX


send

ing

rate

time







roughly




cwndbytes

RTT

ACK(s)

















Host A

one segment

RTT

Host B

time

two segments

four segments





segment 1

ACK for segment 1

cwnd = 1


ACK for segments 2


ACK for segments 4

cwnd = 7

ACK for segments 3

ACK for segments 5

ACK for segments 6

cwnd = 3

cwnd = 5


cwnd = 8

segment 7






AIMD










ssthresh = 8

cwnd = 1

cwnd = 2

cwnd = 4

cwnd = 8

cwnd = 9

cwnd = 10

02468

101214

t=0

t=2

t=4

t=6

Roundtrip times

Cw

nd(in

seg

men

ts)

ssthresh

cwnd = 3





SS

CA

ssthresh













Philosophy

3-90











ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







Slow Start (SS)












Enter slow start

Duplicate ACK




TCP throughput








LRTTMSSsdot221



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness




R

R



Conn

ecti

on 2

thr

ough

p ut
















number)













client

FIN

server

ACK

ACK

FIN

close

close

closed

tim

ed w

ait






client

FIN

server

ACK

ACK

FIN

closing

closing

closed

tim

ed w

ait

closed



TCP clientlifecycle

TCP serverlifecycle






























UDP more

UDP checksum












rdt21 discussion




rdt30 sender

rdt30 in action

rdt30 in action



Pipelined protocols


Go-Back-N



GBN inaction

Selective Repeat


Selective repeat

















TCP sender events





Fast Retransmit

Fast Retransmit


TCP Flow Control















Slow Start Example











TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)










ClientIPB

P1

clientIP A

P1P2P4

serverIP C

SP 9157DP 80

SP 9157DP 80

P5 P6 P3

D-IPCS-IP AD-IPC

S-IP B

SP 5775DP 80

D-IPCS-IP B

P4














32 bits

Applicationdata

(message)

UDP segment format



header


UDP checksum








netw

ork

laye

r



sendside

receiveside











state1

state2




eventactions






udt_send(packet)


Wait for call from

below

rdt_rcv(packet)

sender receiver













udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

belowsender


Λ








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)

Λ








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)

Λ







stop and wait




above


rdt_send(data)




rdt_send(data)


udt_send(sndpkt)



Wait forcall 1 from

above


ΛΛ


















rdt21 discussion













above


rdt_send(data)

udt_send(sndpkt)


isACK(rcvpkt1) )


Wait for ACK

0sender FSM

fragment





has_seq1(rcvpkt))


fragment

Λ











rdt_send(data)

Wait for

ACK0



above


rdt_send(data)






timeout


timeout

rdt_rcv(rcvpkt)

Wait for call 0from

above

Wait for

ACK1

Λrdt_rcv(rcvpkt)

ΛΛ

Λ


rdt30 in action


rdt30 in action






U sender=

008 30008

= 000027 L RRTT + L R

=





sender receiver

RTT




U sender=

00830008

= 000027 L RRTT + L R

=








sender receiver

RTT





U sender=

024 30008

= 000083 L RRTT + L R

=





Go-Back-NSender







timeout

rdt_send(data)





stop_timerelse

start_timer


base=1nextseqnum=1


Λ

Λ






Wait






Λ


GBN inaction


Selective Repeat









Selective repeat








ACK(n)otherwise

ignore

receiver










sender

receiver

Go-Back-N

expectedSN

snd_base=expectedSN



senderrsquos window



sender

receiver

Go-Back-N

expectedSN




senderrsquos window



sender

receiver

Go-Back-N

expectedSN






sender

receiver

Selective Repeat

rcv_base

snd_base=rcv_base



senderrsquos window


rcv_base+N-1



sender

receiver

Selective Repeat

rcv_base

snd_base=rcv_base-N



senderrsquos window

rcv_base


rcv_base+N-1



sender

receiver

Selective Repeat

snd_base=rcv_base-N



rcv_basercv_base


rcv_base+N-1











socketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment






32 bits

applicationdata

(variable length)



FSRPAUheadlen

notused



ACK ACK valid



commands)


Internetchecksum

(as in UDP)






















100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

iseco

nds)

































start timer

end of loop forever





ACK=100


Host B

Seq=92 8 bytes data

ACK=120

Seq=92 8 bytes data

Seq=

92 t

imeo

ut

ACK=120

Host A

Seq=92 8 bytes data

ACK=100

loss

tim

eout

lost ACK scenario

Host B

X

Seq=92 8 bytes data

ACK=100

time

Seq=

92 t

imeo

utSendBase

= 100

SendBase= 120

SendBase= 120

Sendbase= 100



Seq=92 8 bytes data

ACK=100

loss

tim

eout


Host B

X


ACK=120

time

SendBase= 120



Event at Receiver





TCP Receiver action






Fast Retransmit









Host A

tim

eout

Host B

time

X

resend seq X2


ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer





fast retransmit


TCP Flow Control






flow control




= RcvWin






3K

2K SeqNo=0

ReceiverBuffer


2K


4K

AckNo=4096 RcvWin=0


Sender blocked





a top-10 problem







Host B

λout






Host B

λout





λin

λout=

λin

λoutgtλ

inλout


R2

R2λin

λ out

b

R2

R2λin

λ out

a

R2

R2λin

λ out

c

R4

R3



λin


in



Host B

λout





Host A

Host B

λou

t










le CongWin









X

X

XX


send

ing

rate

time







roughly




cwndbytes

RTT

ACK(s)

















Host A

one segment

RTT

Host B

time

two segments

four segments





segment 1

ACK for segment 1

cwnd = 1


ACK for segments 2


ACK for segments 4

cwnd = 7

ACK for segments 3

ACK for segments 5

ACK for segments 6

cwnd = 3

cwnd = 5


cwnd = 8

segment 7






AIMD










ssthresh = 8

cwnd = 1

cwnd = 2

cwnd = 4

cwnd = 8

cwnd = 9

cwnd = 10

02468

101214

t=0

t=2

t=4

t=6

Roundtrip times

Cw

nd(in

seg

men

ts)

ssthresh

cwnd = 3





SS

CA

ssthresh













Philosophy

3-90











ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







Slow Start (SS)












Enter slow start

Duplicate ACK




TCP throughput








LRTTMSSsdot221



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness




R

R



Conn

ecti

on 2

thr

ough

p ut
















number)













client

FIN

server

ACK

ACK

FIN

close

close

closed

tim

ed w

ait






client

FIN

server

ACK

ACK

FIN

closing

closing

closed

tim

ed w

ait

closed



TCP clientlifecycle

TCP serverlifecycle






























UDP more

UDP checksum












rdt21 discussion




rdt30 sender

rdt30 in action

rdt30 in action



Pipelined protocols


Go-Back-N



GBN inaction

Selective Repeat


Selective repeat

















TCP sender events





Fast Retransmit

Fast Retransmit


TCP Flow Control















Slow Start Example











TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)





















32 bits

Applicationdata

(message)

UDP segment format



header


UDP checksum








netw

ork

laye

r



sendside

receiveside











state1

state2




eventactions






udt_send(packet)


Wait for call from

below

rdt_rcv(packet)

sender receiver













udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

belowsender


Λ








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)

Λ








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)

Λ







stop and wait




above


rdt_send(data)




rdt_send(data)


udt_send(sndpkt)



Wait forcall 1 from

above


ΛΛ


















rdt21 discussion













above


rdt_send(data)

udt_send(sndpkt)


isACK(rcvpkt1) )


Wait for ACK

0sender FSM

fragment





has_seq1(rcvpkt))


fragment

Λ











rdt_send(data)

Wait for

ACK0



above


rdt_send(data)






timeout


timeout

rdt_rcv(rcvpkt)

Wait for call 0from

above

Wait for

ACK1

Λrdt_rcv(rcvpkt)

ΛΛ

Λ


rdt30 in action


rdt30 in action






U sender=

008 30008

= 000027 L RRTT + L R

=





sender receiver

RTT




U sender=

00830008

= 000027 L RRTT + L R

=








sender receiver

RTT





U sender=

024 30008

= 000083 L RRTT + L R

=





Go-Back-NSender







timeout

rdt_send(data)





stop_timerelse

start_timer


base=1nextseqnum=1


Λ

Λ






Wait






Λ


GBN inaction


Selective Repeat









Selective repeat








ACK(n)otherwise

ignore

receiver










sender

receiver

Go-Back-N

expectedSN

snd_base=expectedSN



senderrsquos window



sender

receiver

Go-Back-N

expectedSN




senderrsquos window



sender

receiver

Go-Back-N

expectedSN






sender

receiver

Selective Repeat

rcv_base

snd_base=rcv_base



senderrsquos window


rcv_base+N-1



sender

receiver

Selective Repeat

rcv_base

snd_base=rcv_base-N



senderrsquos window

rcv_base


rcv_base+N-1



sender

receiver

Selective Repeat

snd_base=rcv_base-N



rcv_basercv_base


rcv_base+N-1











socketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment






32 bits

applicationdata

(variable length)



FSRPAUheadlen

notused



ACK ACK valid



commands)


Internetchecksum

(as in UDP)






















100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

iseco

nds)

































start timer

end of loop forever





ACK=100


Host B

Seq=92 8 bytes data

ACK=120

Seq=92 8 bytes data

Seq=

92 t

imeo

ut

ACK=120

Host A

Seq=92 8 bytes data

ACK=100

loss

tim

eout

lost ACK scenario

Host B

X

Seq=92 8 bytes data

ACK=100

time

Seq=

92 t

imeo

utSendBase

= 100

SendBase= 120

SendBase= 120

Sendbase= 100



Seq=92 8 bytes data

ACK=100

loss

tim

eout


Host B

X


ACK=120

time

SendBase= 120



Event at Receiver





TCP Receiver action






Fast Retransmit









Host A

tim

eout

Host B

time

X

resend seq X2


ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer





fast retransmit


TCP Flow Control






flow control




= RcvWin






3K

2K SeqNo=0

ReceiverBuffer


2K


4K

AckNo=4096 RcvWin=0


Sender blocked





a top-10 problem







Host B

λout






Host B

λout





λin

λout=

λin

λoutgtλ

inλout


R2

R2λin

λ out

b

R2

R2λin

λ out

a

R2

R2λin

λ out

c

R4

R3



λin


in



Host B

λout





Host A

Host B

λou

t










le CongWin









X

X

XX


send

ing

rate

time







roughly




cwndbytes

RTT

ACK(s)

















Host A

one segment

RTT

Host B

time

two segments

four segments





segment 1

ACK for segment 1

cwnd = 1


ACK for segments 2


ACK for segments 4

cwnd = 7

ACK for segments 3

ACK for segments 5

ACK for segments 6

cwnd = 3

cwnd = 5


cwnd = 8

segment 7






AIMD










ssthresh = 8

cwnd = 1

cwnd = 2

cwnd = 4

cwnd = 8

cwnd = 9

cwnd = 10

02468

101214

t=0

t=2

t=4

t=6

Roundtrip times

Cw

nd(in

seg

men

ts)

ssthresh

cwnd = 3





SS

CA

ssthresh













Philosophy

3-90











ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







Slow Start (SS)












Enter slow start

Duplicate ACK




TCP throughput








LRTTMSSsdot221



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness




R

R



Conn

ecti

on 2

thr

ough

p ut
















number)













client

FIN

server

ACK

ACK

FIN

close

close

closed

tim

ed w

ait






client

FIN

server

ACK

ACK

FIN

closing

closing

closed

tim

ed w

ait

closed



TCP clientlifecycle

TCP serverlifecycle






























UDP more

UDP checksum












rdt21 discussion




rdt30 sender

rdt30 in action

rdt30 in action



Pipelined protocols


Go-Back-N



GBN inaction

Selective Repeat


Selective repeat

















TCP sender events





Fast Retransmit

Fast Retransmit


TCP Flow Control















Slow Start Example











TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)









UDP checksum








netw

ork

laye

r



sendside

receiveside











state1

state2




eventactions






udt_send(packet)


Wait for call from

below

rdt_rcv(packet)

sender receiver













udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

belowsender


Λ








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)

Λ








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)

Λ







stop and wait




above


rdt_send(data)




rdt_send(data)


udt_send(sndpkt)



Wait forcall 1 from

above


ΛΛ


















rdt21 discussion













above


rdt_send(data)

udt_send(sndpkt)


isACK(rcvpkt1) )


Wait for ACK

0sender FSM

fragment





has_seq1(rcvpkt))


fragment

Λ











rdt_send(data)

Wait for

ACK0



above


rdt_send(data)






timeout


timeout

rdt_rcv(rcvpkt)

Wait for call 0from

above

Wait for

ACK1

Λrdt_rcv(rcvpkt)

ΛΛ

Λ


rdt30 in action


rdt30 in action






U sender=

008 30008

= 000027 L RRTT + L R

=





sender receiver

RTT




U sender=

00830008

= 000027 L RRTT + L R

=








sender receiver

RTT





U sender=

024 30008

= 000083 L RRTT + L R

=





Go-Back-NSender







timeout

rdt_send(data)





stop_timerelse

start_timer


base=1nextseqnum=1


Λ

Λ






Wait






Λ


GBN inaction


Selective Repeat









Selective repeat








ACK(n)otherwise

ignore

receiver










sender

receiver

Go-Back-N

expectedSN

snd_base=expectedSN



senderrsquos window



sender

receiver

Go-Back-N

expectedSN




senderrsquos window



sender

receiver

Go-Back-N

expectedSN






sender

receiver

Selective Repeat

rcv_base

snd_base=rcv_base



senderrsquos window


rcv_base+N-1



sender

receiver

Selective Repeat

rcv_base

snd_base=rcv_base-N



senderrsquos window

rcv_base


rcv_base+N-1



sender

receiver

Selective Repeat

snd_base=rcv_base-N



rcv_basercv_base


rcv_base+N-1











socketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment






32 bits

applicationdata

(variable length)



FSRPAUheadlen

notused



ACK ACK valid



commands)


Internetchecksum

(as in UDP)






















100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

iseco

nds)

































start timer

end of loop forever





ACK=100


Host B

Seq=92 8 bytes data

ACK=120

Seq=92 8 bytes data

Seq=

92 t

imeo

ut

ACK=120

Host A

Seq=92 8 bytes data

ACK=100

loss

tim

eout

lost ACK scenario

Host B

X

Seq=92 8 bytes data

ACK=100

time

Seq=

92 t

imeo

utSendBase

= 100

SendBase= 120

SendBase= 120

Sendbase= 100



Seq=92 8 bytes data

ACK=100

loss

tim

eout


Host B

X


ACK=120

time

SendBase= 120



Event at Receiver





TCP Receiver action






Fast Retransmit









Host A

tim

eout

Host B

time

X

resend seq X2


ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer





fast retransmit


TCP Flow Control






flow control




= RcvWin






3K

2K SeqNo=0

ReceiverBuffer


2K


4K

AckNo=4096 RcvWin=0


Sender blocked





a top-10 problem







Host B

λout






Host B

λout





λin

λout=

λin

λoutgtλ

inλout


R2

R2λin

λ out

b

R2

R2λin

λ out

a

R2

R2λin

λ out

c

R4

R3



λin


in



Host B

λout





Host A

Host B

λou

t










le CongWin









X

X

XX


send

ing

rate

time







roughly




cwndbytes

RTT

ACK(s)

















Host A

one segment

RTT

Host B

time

two segments

four segments





segment 1

ACK for segment 1

cwnd = 1


ACK for segments 2


ACK for segments 4

cwnd = 7

ACK for segments 3

ACK for segments 5

ACK for segments 6

cwnd = 3

cwnd = 5


cwnd = 8

segment 7






AIMD










ssthresh = 8

cwnd = 1

cwnd = 2

cwnd = 4

cwnd = 8

cwnd = 9

cwnd = 10

02468

101214

t=0

t=2

t=4

t=6

Roundtrip times

Cw

nd(in

seg

men

ts)

ssthresh

cwnd = 3





SS

CA

ssthresh













Philosophy

3-90











ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







Slow Start (SS)












Enter slow start

Duplicate ACK




TCP throughput








LRTTMSSsdot221



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness




R

R



Conn

ecti

on 2

thr

ough

p ut
















number)













client

FIN

server

ACK

ACK

FIN

close

close

closed

tim

ed w

ait






client

FIN

server

ACK

ACK

FIN

closing

closing

closed

tim

ed w

ait

closed



TCP clientlifecycle

TCP serverlifecycle






























UDP more

UDP checksum












rdt21 discussion




rdt30 sender

rdt30 in action

rdt30 in action



Pipelined protocols


Go-Back-N



GBN inaction

Selective Repeat


Selective repeat

















TCP sender events





Fast Retransmit

Fast Retransmit


TCP Flow Control















Slow Start Example











TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)











netw

ork

laye

r



sendside

receiveside











state1

state2




eventactions






udt_send(packet)


Wait for call from

below

rdt_rcv(packet)

sender receiver













udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

belowsender


Λ








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)

Λ








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)

Λ







stop and wait




above


rdt_send(data)




rdt_send(data)


udt_send(sndpkt)



Wait forcall 1 from

above


ΛΛ


















rdt21 discussion













above


rdt_send(data)

udt_send(sndpkt)


isACK(rcvpkt1) )


Wait for ACK

0sender FSM

fragment





has_seq1(rcvpkt))


fragment

Λ











rdt_send(data)

Wait for

ACK0



above


rdt_send(data)






timeout


timeout

rdt_rcv(rcvpkt)

Wait for call 0from

above

Wait for

ACK1

Λrdt_rcv(rcvpkt)

ΛΛ

Λ


rdt30 in action


rdt30 in action






U sender=

008 30008

= 000027 L RRTT + L R

=





sender receiver

RTT




U sender=

00830008

= 000027 L RRTT + L R

=








sender receiver

RTT





U sender=

024 30008

= 000083 L RRTT + L R

=





Go-Back-NSender







timeout

rdt_send(data)





stop_timerelse

start_timer


base=1nextseqnum=1


Λ

Λ






Wait






Λ


GBN inaction


Selective Repeat









Selective repeat








ACK(n)otherwise

ignore

receiver










sender

receiver

Go-Back-N

expectedSN

snd_base=expectedSN



senderrsquos window



sender

receiver

Go-Back-N

expectedSN




senderrsquos window



sender

receiver

Go-Back-N

expectedSN






sender

receiver

Selective Repeat

rcv_base

snd_base=rcv_base



senderrsquos window


rcv_base+N-1



sender

receiver

Selective Repeat

rcv_base

snd_base=rcv_base-N



senderrsquos window

rcv_base


rcv_base+N-1



sender

receiver

Selective Repeat

snd_base=rcv_base-N



rcv_basercv_base


rcv_base+N-1











socketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment






32 bits

applicationdata

(variable length)



FSRPAUheadlen

notused



ACK ACK valid



commands)


Internetchecksum

(as in UDP)






















100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

iseco

nds)

































start timer

end of loop forever





ACK=100


Host B

Seq=92 8 bytes data

ACK=120

Seq=92 8 bytes data

Seq=

92 t

imeo

ut

ACK=120

Host A

Seq=92 8 bytes data

ACK=100

loss

tim

eout

lost ACK scenario

Host B

X

Seq=92 8 bytes data

ACK=100

time

Seq=

92 t

imeo

utSendBase

= 100

SendBase= 120

SendBase= 120

Sendbase= 100



Seq=92 8 bytes data

ACK=100

loss

tim

eout


Host B

X


ACK=120

time

SendBase= 120



Event at Receiver





TCP Receiver action






Fast Retransmit









Host A

tim

eout

Host B

time

X

resend seq X2


ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer





fast retransmit


TCP Flow Control






flow control




= RcvWin






3K

2K SeqNo=0

ReceiverBuffer


2K


4K

AckNo=4096 RcvWin=0


Sender blocked





a top-10 problem







Host B

λout






Host B

λout





λin

λout=

λin

λoutgtλ

inλout


R2

R2λin

λ out

b

R2

R2λin

λ out

a

R2

R2λin

λ out

c

R4

R3



λin


in



Host B

λout





Host A

Host B

λou

t










le CongWin









X

X

XX


send

ing

rate

time







roughly




cwndbytes

RTT

ACK(s)

















Host A

one segment

RTT

Host B

time

two segments

four segments





segment 1

ACK for segment 1

cwnd = 1


ACK for segments 2


ACK for segments 4

cwnd = 7

ACK for segments 3

ACK for segments 5

ACK for segments 6

cwnd = 3

cwnd = 5


cwnd = 8

segment 7






AIMD










ssthresh = 8

cwnd = 1

cwnd = 2

cwnd = 4

cwnd = 8

cwnd = 9

cwnd = 10

02468

101214

t=0

t=2

t=4

t=6

Roundtrip times

Cw

nd(in

seg

men

ts)

ssthresh

cwnd = 3





SS

CA

ssthresh













Philosophy

3-90











ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







Slow Start (SS)












Enter slow start

Duplicate ACK




TCP throughput








LRTTMSSsdot221



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness




R

R



Conn

ecti

on 2

thr

ough

p ut
















number)













client

FIN

server

ACK

ACK

FIN

close

close

closed

tim

ed w

ait






client

FIN

server

ACK

ACK

FIN

closing

closing

closed

tim

ed w

ait

closed



TCP clientlifecycle

TCP serverlifecycle






























UDP more

UDP checksum












rdt21 discussion




rdt30 sender

rdt30 in action

rdt30 in action



Pipelined protocols


Go-Back-N



GBN inaction

Selective Repeat


Selective repeat

















TCP sender events





Fast Retransmit

Fast Retransmit


TCP Flow Control















Slow Start Example











TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)










sendside

receiveside











state1

state2




eventactions






udt_send(packet)


Wait for call from

below

rdt_rcv(packet)

sender receiver













udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

belowsender


Λ








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)

Λ








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)

Λ







stop and wait




above


rdt_send(data)




rdt_send(data)


udt_send(sndpkt)



Wait forcall 1 from

above


ΛΛ


















rdt21 discussion













above


rdt_send(data)

udt_send(sndpkt)


isACK(rcvpkt1) )


Wait for ACK

0sender FSM

fragment





has_seq1(rcvpkt))


fragment

Λ











rdt_send(data)

Wait for

ACK0



above


rdt_send(data)






timeout


timeout

rdt_rcv(rcvpkt)

Wait for call 0from

above

Wait for

ACK1

Λrdt_rcv(rcvpkt)

ΛΛ

Λ


rdt30 in action


rdt30 in action






U sender=

008 30008

= 000027 L RRTT + L R

=





sender receiver

RTT




U sender=

00830008

= 000027 L RRTT + L R

=








sender receiver

RTT





U sender=

024 30008

= 000083 L RRTT + L R

=





Go-Back-NSender







timeout

rdt_send(data)





stop_timerelse

start_timer


base=1nextseqnum=1


Λ

Λ






Wait






Λ


GBN inaction


Selective Repeat









Selective repeat








ACK(n)otherwise

ignore

receiver










sender

receiver

Go-Back-N

expectedSN

snd_base=expectedSN



senderrsquos window



sender

receiver

Go-Back-N

expectedSN




senderrsquos window



sender

receiver

Go-Back-N

expectedSN






sender

receiver

Selective Repeat

rcv_base

snd_base=rcv_base



senderrsquos window


rcv_base+N-1



sender

receiver

Selective Repeat

rcv_base

snd_base=rcv_base-N



senderrsquos window

rcv_base


rcv_base+N-1



sender

receiver

Selective Repeat

snd_base=rcv_base-N



rcv_basercv_base


rcv_base+N-1











socketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment






32 bits

applicationdata

(variable length)



FSRPAUheadlen

notused



ACK ACK valid



commands)


Internetchecksum

(as in UDP)






















100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

iseco

nds)

































start timer

end of loop forever





ACK=100


Host B

Seq=92 8 bytes data

ACK=120

Seq=92 8 bytes data

Seq=

92 t

imeo

ut

ACK=120

Host A

Seq=92 8 bytes data

ACK=100

loss

tim

eout

lost ACK scenario

Host B

X

Seq=92 8 bytes data

ACK=100

time

Seq=

92 t

imeo

utSendBase

= 100

SendBase= 120

SendBase= 120

Sendbase= 100



Seq=92 8 bytes data

ACK=100

loss

tim

eout


Host B

X


ACK=120

time

SendBase= 120



Event at Receiver





TCP Receiver action






Fast Retransmit









Host A

tim

eout

Host B

time

X

resend seq X2


ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer





fast retransmit


TCP Flow Control






flow control




= RcvWin






3K

2K SeqNo=0

ReceiverBuffer


2K


4K

AckNo=4096 RcvWin=0


Sender blocked





a top-10 problem







Host B

λout






Host B

λout





λin

λout=

λin

λoutgtλ

inλout


R2

R2λin

λ out

b

R2

R2λin

λ out

a

R2

R2λin

λ out

c

R4

R3



λin


in



Host B

λout





Host A

Host B

λou

t










le CongWin









X

X

XX


send

ing

rate

time







roughly




cwndbytes

RTT

ACK(s)

















Host A

one segment

RTT

Host B

time

two segments

four segments





segment 1

ACK for segment 1

cwnd = 1


ACK for segments 2


ACK for segments 4

cwnd = 7

ACK for segments 3

ACK for segments 5

ACK for segments 6

cwnd = 3

cwnd = 5


cwnd = 8

segment 7






AIMD










ssthresh = 8

cwnd = 1

cwnd = 2

cwnd = 4

cwnd = 8

cwnd = 9

cwnd = 10

02468

101214

t=0

t=2

t=4

t=6

Roundtrip times

Cw

nd(in

seg

men

ts)

ssthresh

cwnd = 3





SS

CA

ssthresh













Philosophy

3-90











ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







Slow Start (SS)












Enter slow start

Duplicate ACK




TCP throughput








LRTTMSSsdot221



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness




R

R



Conn

ecti

on 2

thr

ough

p ut
















number)













client

FIN

server

ACK

ACK

FIN

close

close

closed

tim

ed w

ait






client

FIN

server

ACK

ACK

FIN

closing

closing

closed

tim

ed w

ait

closed



TCP clientlifecycle

TCP serverlifecycle






























UDP more

UDP checksum












rdt21 discussion




rdt30 sender

rdt30 in action

rdt30 in action



Pipelined protocols


Go-Back-N



GBN inaction

Selective Repeat


Selective repeat

















TCP sender events





Fast Retransmit

Fast Retransmit


TCP Flow Control















Slow Start Example











TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)












state1

state2




eventactions






udt_send(packet)


Wait for call from

below

rdt_rcv(packet)

sender receiver













udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

belowsender


Λ








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)

Λ








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)

Λ







stop and wait




above


rdt_send(data)




rdt_send(data)


udt_send(sndpkt)



Wait forcall 1 from

above


ΛΛ


















rdt21 discussion













above


rdt_send(data)

udt_send(sndpkt)


isACK(rcvpkt1) )


Wait for ACK

0sender FSM

fragment





has_seq1(rcvpkt))


fragment

Λ











rdt_send(data)

Wait for

ACK0



above


rdt_send(data)






timeout


timeout

rdt_rcv(rcvpkt)

Wait for call 0from

above

Wait for

ACK1

Λrdt_rcv(rcvpkt)

ΛΛ

Λ


rdt30 in action


rdt30 in action






U sender=

008 30008

= 000027 L RRTT + L R

=





sender receiver

RTT




U sender=

00830008

= 000027 L RRTT + L R

=








sender receiver

RTT





U sender=

024 30008

= 000083 L RRTT + L R

=





Go-Back-NSender







timeout

rdt_send(data)





stop_timerelse

start_timer


base=1nextseqnum=1


Λ

Λ






Wait






Λ


GBN inaction


Selective Repeat









Selective repeat








ACK(n)otherwise

ignore

receiver










sender

receiver

Go-Back-N

expectedSN

snd_base=expectedSN



senderrsquos window



sender

receiver

Go-Back-N

expectedSN




senderrsquos window



sender

receiver

Go-Back-N

expectedSN






sender

receiver

Selective Repeat

rcv_base

snd_base=rcv_base



senderrsquos window


rcv_base+N-1



sender

receiver

Selective Repeat

rcv_base

snd_base=rcv_base-N



senderrsquos window

rcv_base


rcv_base+N-1



sender

receiver

Selective Repeat

snd_base=rcv_base-N



rcv_basercv_base


rcv_base+N-1











socketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment






32 bits

applicationdata

(variable length)



FSRPAUheadlen

notused



ACK ACK valid



commands)


Internetchecksum

(as in UDP)






















100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

iseco

nds)

































start timer

end of loop forever





ACK=100


Host B

Seq=92 8 bytes data

ACK=120

Seq=92 8 bytes data

Seq=

92 t

imeo

ut

ACK=120

Host A

Seq=92 8 bytes data

ACK=100

loss

tim

eout

lost ACK scenario

Host B

X

Seq=92 8 bytes data

ACK=100

time

Seq=

92 t

imeo

utSendBase

= 100

SendBase= 120

SendBase= 120

Sendbase= 100



Seq=92 8 bytes data

ACK=100

loss

tim

eout


Host B

X


ACK=120

time

SendBase= 120



Event at Receiver





TCP Receiver action






Fast Retransmit









Host A

tim

eout

Host B

time

X

resend seq X2


ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer





fast retransmit


TCP Flow Control






flow control




= RcvWin






3K

2K SeqNo=0

ReceiverBuffer


2K


4K

AckNo=4096 RcvWin=0


Sender blocked





a top-10 problem







Host B

λout






Host B

λout





λin

λout=

λin

λoutgtλ

inλout


R2

R2λin

λ out

b

R2

R2λin

λ out

a

R2

R2λin

λ out

c

R4

R3



λin


in



Host B

λout





Host A

Host B

λou

t










le CongWin









X

X

XX


send

ing

rate

time







roughly




cwndbytes

RTT

ACK(s)

















Host A

one segment

RTT

Host B

time

two segments

four segments





segment 1

ACK for segment 1

cwnd = 1


ACK for segments 2


ACK for segments 4

cwnd = 7

ACK for segments 3

ACK for segments 5

ACK for segments 6

cwnd = 3

cwnd = 5


cwnd = 8

segment 7






AIMD










ssthresh = 8

cwnd = 1

cwnd = 2

cwnd = 4

cwnd = 8

cwnd = 9

cwnd = 10

02468

101214

t=0

t=2

t=4

t=6

Roundtrip times

Cw

nd(in

seg

men

ts)

ssthresh

cwnd = 3





SS

CA

ssthresh













Philosophy

3-90











ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







Slow Start (SS)












Enter slow start

Duplicate ACK




TCP throughput








LRTTMSSsdot221



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness




R

R



Conn

ecti

on 2

thr

ough

p ut
















number)













client

FIN

server

ACK

ACK

FIN

close

close

closed

tim

ed w

ait






client

FIN

server

ACK

ACK

FIN

closing

closing

closed

tim

ed w

ait

closed



TCP clientlifecycle

TCP serverlifecycle






























UDP more

UDP checksum












rdt21 discussion




rdt30 sender

rdt30 in action

rdt30 in action



Pipelined protocols


Go-Back-N



GBN inaction

Selective Repeat


Selective repeat

















TCP sender events





Fast Retransmit

Fast Retransmit


TCP Flow Control















Slow Start Example











TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)













udt_send(packet)


Wait for call from

below

rdt_rcv(packet)

sender receiver













udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

belowsender


Λ








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)

Λ








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)

Λ







stop and wait




above


rdt_send(data)




rdt_send(data)


udt_send(sndpkt)



Wait forcall 1 from

above


ΛΛ


















rdt21 discussion













above


rdt_send(data)

udt_send(sndpkt)


isACK(rcvpkt1) )


Wait for ACK

0sender FSM

fragment





has_seq1(rcvpkt))


fragment

Λ











rdt_send(data)

Wait for

ACK0



above


rdt_send(data)






timeout


timeout

rdt_rcv(rcvpkt)

Wait for call 0from

above

Wait for

ACK1

Λrdt_rcv(rcvpkt)

ΛΛ

Λ


rdt30 in action


rdt30 in action






U sender=

008 30008

= 000027 L RRTT + L R

=





sender receiver

RTT




U sender=

00830008

= 000027 L RRTT + L R

=








sender receiver

RTT





U sender=

024 30008

= 000083 L RRTT + L R

=





Go-Back-NSender







timeout

rdt_send(data)





stop_timerelse

start_timer


base=1nextseqnum=1


Λ

Λ






Wait






Λ


GBN inaction


Selective Repeat









Selective repeat








ACK(n)otherwise

ignore

receiver










sender

receiver

Go-Back-N

expectedSN

snd_base=expectedSN



senderrsquos window



sender

receiver

Go-Back-N

expectedSN




senderrsquos window



sender

receiver

Go-Back-N

expectedSN






sender

receiver

Selective Repeat

rcv_base

snd_base=rcv_base



senderrsquos window


rcv_base+N-1



sender

receiver

Selective Repeat

rcv_base

snd_base=rcv_base-N



senderrsquos window

rcv_base


rcv_base+N-1



sender

receiver

Selective Repeat

snd_base=rcv_base-N



rcv_basercv_base


rcv_base+N-1











socketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment






32 bits

applicationdata

(variable length)



FSRPAUheadlen

notused



ACK ACK valid



commands)


Internetchecksum

(as in UDP)






















100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

iseco

nds)

































start timer

end of loop forever





ACK=100


Host B

Seq=92 8 bytes data

ACK=120

Seq=92 8 bytes data

Seq=

92 t

imeo

ut

ACK=120

Host A

Seq=92 8 bytes data

ACK=100

loss

tim

eout

lost ACK scenario

Host B

X

Seq=92 8 bytes data

ACK=100

time

Seq=

92 t

imeo

utSendBase

= 100

SendBase= 120

SendBase= 120

Sendbase= 100



Seq=92 8 bytes data

ACK=100

loss

tim

eout


Host B

X


ACK=120

time

SendBase= 120



Event at Receiver





TCP Receiver action






Fast Retransmit









Host A

tim

eout

Host B

time

X

resend seq X2


ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer





fast retransmit


TCP Flow Control






flow control




= RcvWin






3K

2K SeqNo=0

ReceiverBuffer


2K


4K

AckNo=4096 RcvWin=0


Sender blocked





a top-10 problem







Host B

λout






Host B

λout





λin

λout=

λin

λoutgtλ

inλout


R2

R2λin

λ out

b

R2

R2λin

λ out

a

R2

R2λin

λ out

c

R4

R3



λin


in



Host B

λout





Host A

Host B

λou

t










le CongWin









X

X

XX


send

ing

rate

time







roughly




cwndbytes

RTT

ACK(s)

















Host A

one segment

RTT

Host B

time

two segments

four segments





segment 1

ACK for segment 1

cwnd = 1


ACK for segments 2


ACK for segments 4

cwnd = 7

ACK for segments 3

ACK for segments 5

ACK for segments 6

cwnd = 3

cwnd = 5


cwnd = 8

segment 7






AIMD










ssthresh = 8

cwnd = 1

cwnd = 2

cwnd = 4

cwnd = 8

cwnd = 9

cwnd = 10

02468

101214

t=0

t=2

t=4

t=6

Roundtrip times

Cw

nd(in

seg

men

ts)

ssthresh

cwnd = 3





SS

CA

ssthresh













Philosophy

3-90











ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







Slow Start (SS)












Enter slow start

Duplicate ACK




TCP throughput








LRTTMSSsdot221



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness




R

R



Conn

ecti

on 2

thr

ough

p ut
















number)













client

FIN

server

ACK

ACK

FIN

close

close

closed

tim

ed w

ait






client

FIN

server

ACK

ACK

FIN

closing

closing

closed

tim

ed w

ait

closed



TCP clientlifecycle

TCP serverlifecycle






























UDP more

UDP checksum












rdt21 discussion




rdt30 sender

rdt30 in action

rdt30 in action



Pipelined protocols


Go-Back-N



GBN inaction

Selective Repeat


Selective repeat

















TCP sender events





Fast Retransmit

Fast Retransmit


TCP Flow Control















Slow Start Example











TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)




















udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

belowsender


Λ








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)

Λ








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)

Λ







stop and wait




above


rdt_send(data)




rdt_send(data)


udt_send(sndpkt)



Wait forcall 1 from

above


ΛΛ


















rdt21 discussion













above


rdt_send(data)

udt_send(sndpkt)


isACK(rcvpkt1) )


Wait for ACK

0sender FSM

fragment





has_seq1(rcvpkt))


fragment

Λ











rdt_send(data)

Wait for

ACK0



above


rdt_send(data)






timeout


timeout

rdt_rcv(rcvpkt)

Wait for call 0from

above

Wait for

ACK1

Λrdt_rcv(rcvpkt)

ΛΛ

Λ


rdt30 in action


rdt30 in action






U sender=

008 30008

= 000027 L RRTT + L R

=





sender receiver

RTT




U sender=

00830008

= 000027 L RRTT + L R

=








sender receiver

RTT





U sender=

024 30008

= 000083 L RRTT + L R

=





Go-Back-NSender







timeout

rdt_send(data)





stop_timerelse

start_timer


base=1nextseqnum=1


Λ

Λ






Wait






Λ


GBN inaction


Selective Repeat









Selective repeat








ACK(n)otherwise

ignore

receiver










sender

receiver

Go-Back-N

expectedSN

snd_base=expectedSN



senderrsquos window



sender

receiver

Go-Back-N

expectedSN




senderrsquos window



sender

receiver

Go-Back-N

expectedSN






sender

receiver

Selective Repeat

rcv_base

snd_base=rcv_base



senderrsquos window


rcv_base+N-1



sender

receiver

Selective Repeat

rcv_base

snd_base=rcv_base-N



senderrsquos window

rcv_base


rcv_base+N-1



sender

receiver

Selective Repeat

snd_base=rcv_base-N



rcv_basercv_base


rcv_base+N-1











socketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment






32 bits

applicationdata

(variable length)



FSRPAUheadlen

notused



ACK ACK valid



commands)


Internetchecksum

(as in UDP)






















100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

iseco

nds)

































start timer

end of loop forever





ACK=100


Host B

Seq=92 8 bytes data

ACK=120

Seq=92 8 bytes data

Seq=

92 t

imeo

ut

ACK=120

Host A

Seq=92 8 bytes data

ACK=100

loss

tim

eout

lost ACK scenario

Host B

X

Seq=92 8 bytes data

ACK=100

time

Seq=

92 t

imeo

utSendBase

= 100

SendBase= 120

SendBase= 120

Sendbase= 100



Seq=92 8 bytes data

ACK=100

loss

tim

eout


Host B

X


ACK=120

time

SendBase= 120



Event at Receiver





TCP Receiver action






Fast Retransmit









Host A

tim

eout

Host B

time

X

resend seq X2


ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer





fast retransmit


TCP Flow Control






flow control




= RcvWin






3K

2K SeqNo=0

ReceiverBuffer


2K


4K

AckNo=4096 RcvWin=0


Sender blocked





a top-10 problem







Host B

λout






Host B

λout





λin

λout=

λin

λoutgtλ

inλout


R2

R2λin

λ out

b

R2

R2λin

λ out

a

R2

R2λin

λ out

c

R4

R3



λin


in



Host B

λout





Host A

Host B

λou

t










le CongWin









X

X

XX


send

ing

rate

time







roughly




cwndbytes

RTT

ACK(s)

















Host A

one segment

RTT

Host B

time

two segments

four segments





segment 1

ACK for segment 1

cwnd = 1


ACK for segments 2


ACK for segments 4

cwnd = 7

ACK for segments 3

ACK for segments 5

ACK for segments 6

cwnd = 3

cwnd = 5


cwnd = 8

segment 7






AIMD










ssthresh = 8

cwnd = 1

cwnd = 2

cwnd = 4

cwnd = 8

cwnd = 9

cwnd = 10

02468

101214

t=0

t=2

t=4

t=6

Roundtrip times

Cw

nd(in

seg

men

ts)

ssthresh

cwnd = 3





SS

CA

ssthresh













Philosophy

3-90











ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







Slow Start (SS)












Enter slow start

Duplicate ACK




TCP throughput








LRTTMSSsdot221



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness




R

R



Conn

ecti

on 2

thr

ough

p ut
















number)













client

FIN

server

ACK

ACK

FIN

close

close

closed

tim

ed w

ait






client

FIN

server

ACK

ACK

FIN

closing

closing

closed

tim

ed w

ait

closed



TCP clientlifecycle

TCP serverlifecycle






























UDP more

UDP checksum












rdt21 discussion




rdt30 sender

rdt30 in action

rdt30 in action



Pipelined protocols


Go-Back-N



GBN inaction

Selective Repeat


Selective repeat

















TCP sender events





Fast Retransmit

Fast Retransmit


TCP Flow Control















Slow Start Example











TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)















udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)

Λ








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)

Λ







stop and wait




above


rdt_send(data)




rdt_send(data)


udt_send(sndpkt)



Wait forcall 1 from

above


ΛΛ


















rdt21 discussion













above


rdt_send(data)

udt_send(sndpkt)


isACK(rcvpkt1) )


Wait for ACK

0sender FSM

fragment





has_seq1(rcvpkt))


fragment

Λ











rdt_send(data)

Wait for

ACK0



above


rdt_send(data)






timeout


timeout

rdt_rcv(rcvpkt)

Wait for call 0from

above

Wait for

ACK1

Λrdt_rcv(rcvpkt)

ΛΛ

Λ


rdt30 in action


rdt30 in action






U sender=

008 30008

= 000027 L RRTT + L R

=





sender receiver

RTT




U sender=

00830008

= 000027 L RRTT + L R

=








sender receiver

RTT





U sender=

024 30008

= 000083 L RRTT + L R

=





Go-Back-NSender







timeout

rdt_send(data)





stop_timerelse

start_timer


base=1nextseqnum=1


Λ

Λ






Wait






Λ


GBN inaction


Selective Repeat









Selective repeat








ACK(n)otherwise

ignore

receiver










sender

receiver

Go-Back-N

expectedSN

snd_base=expectedSN



senderrsquos window



sender

receiver

Go-Back-N

expectedSN




senderrsquos window



sender

receiver

Go-Back-N

expectedSN






sender

receiver

Selective Repeat

rcv_base

snd_base=rcv_base



senderrsquos window


rcv_base+N-1



sender

receiver

Selective Repeat

rcv_base

snd_base=rcv_base-N



senderrsquos window

rcv_base


rcv_base+N-1



sender

receiver

Selective Repeat

snd_base=rcv_base-N



rcv_basercv_base


rcv_base+N-1











socketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment






32 bits

applicationdata

(variable length)



FSRPAUheadlen

notused



ACK ACK valid



commands)


Internetchecksum

(as in UDP)






















100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

iseco

nds)

































start timer

end of loop forever





ACK=100


Host B

Seq=92 8 bytes data

ACK=120

Seq=92 8 bytes data

Seq=

92 t

imeo

ut

ACK=120

Host A

Seq=92 8 bytes data

ACK=100

loss

tim

eout

lost ACK scenario

Host B

X

Seq=92 8 bytes data

ACK=100

time

Seq=

92 t

imeo

utSendBase

= 100

SendBase= 120

SendBase= 120

Sendbase= 100



Seq=92 8 bytes data

ACK=100

loss

tim

eout


Host B

X


ACK=120

time

SendBase= 120



Event at Receiver





TCP Receiver action






Fast Retransmit









Host A

tim

eout

Host B

time

X

resend seq X2


ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer





fast retransmit


TCP Flow Control






flow control




= RcvWin






3K

2K SeqNo=0

ReceiverBuffer


2K


4K

AckNo=4096 RcvWin=0


Sender blocked





a top-10 problem







Host B

λout






Host B

λout





λin

λout=

λin

λoutgtλ

inλout


R2

R2λin

λ out

b

R2

R2λin

λ out

a

R2

R2λin

λ out

c

R4

R3



λin


in



Host B

λout





Host A

Host B

λou

t










le CongWin









X

X

XX


send

ing

rate

time







roughly




cwndbytes

RTT

ACK(s)

















Host A

one segment

RTT

Host B

time

two segments

four segments





segment 1

ACK for segment 1

cwnd = 1


ACK for segments 2


ACK for segments 4

cwnd = 7

ACK for segments 3

ACK for segments 5

ACK for segments 6

cwnd = 3

cwnd = 5


cwnd = 8

segment 7






AIMD










ssthresh = 8

cwnd = 1

cwnd = 2

cwnd = 4

cwnd = 8

cwnd = 9

cwnd = 10

02468

101214

t=0

t=2

t=4

t=6

Roundtrip times

Cw

nd(in

seg

men

ts)

ssthresh

cwnd = 3





SS

CA

ssthresh













Philosophy

3-90











ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







Slow Start (SS)












Enter slow start

Duplicate ACK




TCP throughput








LRTTMSSsdot221



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness




R

R



Conn

ecti

on 2

thr

ough

p ut
















number)













client

FIN

server

ACK

ACK

FIN

close

close

closed

tim

ed w

ait






client

FIN

server

ACK

ACK

FIN

closing

closing

closed

tim

ed w

ait

closed



TCP clientlifecycle

TCP serverlifecycle






























UDP more

UDP checksum












rdt21 discussion




rdt30 sender

rdt30 in action

rdt30 in action



Pipelined protocols


Go-Back-N



GBN inaction

Selective Repeat


Selective repeat

















TCP sender events





Fast Retransmit

Fast Retransmit


TCP Flow Control















Slow Start Example











TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)















udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)

Λ







stop and wait




above


rdt_send(data)




rdt_send(data)


udt_send(sndpkt)



Wait forcall 1 from

above


ΛΛ


















rdt21 discussion













above


rdt_send(data)

udt_send(sndpkt)


isACK(rcvpkt1) )


Wait for ACK

0sender FSM

fragment





has_seq1(rcvpkt))


fragment

Λ











rdt_send(data)

Wait for

ACK0



above


rdt_send(data)






timeout


timeout

rdt_rcv(rcvpkt)

Wait for call 0from

above

Wait for

ACK1

Λrdt_rcv(rcvpkt)

ΛΛ

Λ


rdt30 in action


rdt30 in action






U sender=

008 30008

= 000027 L RRTT + L R

=





sender receiver

RTT




U sender=

00830008

= 000027 L RRTT + L R

=








sender receiver

RTT





U sender=

024 30008

= 000083 L RRTT + L R

=





Go-Back-NSender







timeout

rdt_send(data)





stop_timerelse

start_timer


base=1nextseqnum=1


Λ

Λ






Wait






Λ


GBN inaction


Selective Repeat









Selective repeat








ACK(n)otherwise

ignore

receiver










sender

receiver

Go-Back-N

expectedSN

snd_base=expectedSN



senderrsquos window



sender

receiver

Go-Back-N

expectedSN




senderrsquos window



sender

receiver

Go-Back-N

expectedSN






sender

receiver

Selective Repeat

rcv_base

snd_base=rcv_base



senderrsquos window


rcv_base+N-1



sender

receiver

Selective Repeat

rcv_base

snd_base=rcv_base-N



senderrsquos window

rcv_base


rcv_base+N-1



sender

receiver

Selective Repeat

snd_base=rcv_base-N



rcv_basercv_base


rcv_base+N-1











socketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment






32 bits

applicationdata

(variable length)



FSRPAUheadlen

notused



ACK ACK valid



commands)


Internetchecksum

(as in UDP)






















100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

iseco

nds)

































start timer

end of loop forever





ACK=100


Host B

Seq=92 8 bytes data

ACK=120

Seq=92 8 bytes data

Seq=

92 t

imeo

ut

ACK=120

Host A

Seq=92 8 bytes data

ACK=100

loss

tim

eout

lost ACK scenario

Host B

X

Seq=92 8 bytes data

ACK=100

time

Seq=

92 t

imeo

utSendBase

= 100

SendBase= 120

SendBase= 120

Sendbase= 100



Seq=92 8 bytes data

ACK=100

loss

tim

eout


Host B

X


ACK=120

time

SendBase= 120



Event at Receiver





TCP Receiver action






Fast Retransmit









Host A

tim

eout

Host B

time

X

resend seq X2


ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer





fast retransmit


TCP Flow Control






flow control




= RcvWin






3K

2K SeqNo=0

ReceiverBuffer


2K


4K

AckNo=4096 RcvWin=0


Sender blocked





a top-10 problem







Host B

λout






Host B

λout





λin

λout=

λin

λoutgtλ

inλout


R2

R2λin

λ out

b

R2

R2λin

λ out

a

R2

R2λin

λ out

c

R4

R3



λin


in



Host B

λout





Host A

Host B

λou

t










le CongWin









X

X

XX


send

ing

rate

time







roughly




cwndbytes

RTT

ACK(s)

















Host A

one segment

RTT

Host B

time

two segments

four segments





segment 1

ACK for segment 1

cwnd = 1


ACK for segments 2


ACK for segments 4

cwnd = 7

ACK for segments 3

ACK for segments 5

ACK for segments 6

cwnd = 3

cwnd = 5


cwnd = 8

segment 7






AIMD










ssthresh = 8

cwnd = 1

cwnd = 2

cwnd = 4

cwnd = 8

cwnd = 9

cwnd = 10

02468

101214

t=0

t=2

t=4

t=6

Roundtrip times

Cw

nd(in

seg

men

ts)

ssthresh

cwnd = 3





SS

CA

ssthresh













Philosophy

3-90











ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







Slow Start (SS)












Enter slow start

Duplicate ACK




TCP throughput








LRTTMSSsdot221



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness




R

R



Conn

ecti

on 2

thr

ough

p ut
















number)













client

FIN

server

ACK

ACK

FIN

close

close

closed

tim

ed w

ait






client

FIN

server

ACK

ACK

FIN

closing

closing

closed

tim

ed w

ait

closed



TCP clientlifecycle

TCP serverlifecycle






























UDP more

UDP checksum












rdt21 discussion




rdt30 sender

rdt30 in action

rdt30 in action



Pipelined protocols


Go-Back-N



GBN inaction

Selective Repeat


Selective repeat

















TCP sender events





Fast Retransmit

Fast Retransmit


TCP Flow Control















Slow Start Example











TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)














stop and wait




above


rdt_send(data)




rdt_send(data)


udt_send(sndpkt)



Wait forcall 1 from

above


ΛΛ


















rdt21 discussion













above


rdt_send(data)

udt_send(sndpkt)


isACK(rcvpkt1) )


Wait for ACK

0sender FSM

fragment





has_seq1(rcvpkt))


fragment

Λ











rdt_send(data)

Wait for

ACK0



above


rdt_send(data)






timeout


timeout

rdt_rcv(rcvpkt)

Wait for call 0from

above

Wait for

ACK1

Λrdt_rcv(rcvpkt)

ΛΛ

Λ


rdt30 in action


rdt30 in action






U sender=

008 30008

= 000027 L RRTT + L R

=





sender receiver

RTT




U sender=

00830008

= 000027 L RRTT + L R

=








sender receiver

RTT





U sender=

024 30008

= 000083 L RRTT + L R

=





Go-Back-NSender







timeout

rdt_send(data)





stop_timerelse

start_timer


base=1nextseqnum=1


Λ

Λ






Wait






Λ


GBN inaction


Selective Repeat









Selective repeat








ACK(n)otherwise

ignore

receiver










sender

receiver

Go-Back-N

expectedSN

snd_base=expectedSN



senderrsquos window



sender

receiver

Go-Back-N

expectedSN




senderrsquos window



sender

receiver

Go-Back-N

expectedSN






sender

receiver

Selective Repeat

rcv_base

snd_base=rcv_base



senderrsquos window


rcv_base+N-1



sender

receiver

Selective Repeat

rcv_base

snd_base=rcv_base-N



senderrsquos window

rcv_base


rcv_base+N-1



sender

receiver

Selective Repeat

snd_base=rcv_base-N



rcv_basercv_base


rcv_base+N-1











socketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment






32 bits

applicationdata

(variable length)



FSRPAUheadlen

notused



ACK ACK valid



commands)


Internetchecksum

(as in UDP)






















100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

iseco

nds)

































start timer

end of loop forever





ACK=100


Host B

Seq=92 8 bytes data

ACK=120

Seq=92 8 bytes data

Seq=

92 t

imeo

ut

ACK=120

Host A

Seq=92 8 bytes data

ACK=100

loss

tim

eout

lost ACK scenario

Host B

X

Seq=92 8 bytes data

ACK=100

time

Seq=

92 t

imeo

utSendBase

= 100

SendBase= 120

SendBase= 120

Sendbase= 100



Seq=92 8 bytes data

ACK=100

loss

tim

eout


Host B

X


ACK=120

time

SendBase= 120



Event at Receiver





TCP Receiver action






Fast Retransmit









Host A

tim

eout

Host B

time

X

resend seq X2


ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer





fast retransmit


TCP Flow Control






flow control




= RcvWin






3K

2K SeqNo=0

ReceiverBuffer


2K


4K

AckNo=4096 RcvWin=0


Sender blocked





a top-10 problem







Host B

λout






Host B

λout





λin

λout=

λin

λoutgtλ

inλout


R2

R2λin

λ out

b

R2

R2λin

λ out

a

R2

R2λin

λ out

c

R4

R3



λin


in



Host B

λout





Host A

Host B

λou

t










le CongWin









X

X

XX


send

ing

rate

time







roughly




cwndbytes

RTT

ACK(s)

















Host A

one segment

RTT

Host B

time

two segments

four segments





segment 1

ACK for segment 1

cwnd = 1


ACK for segments 2


ACK for segments 4

cwnd = 7

ACK for segments 3

ACK for segments 5

ACK for segments 6

cwnd = 3

cwnd = 5


cwnd = 8

segment 7






AIMD










ssthresh = 8

cwnd = 1

cwnd = 2

cwnd = 4

cwnd = 8

cwnd = 9

cwnd = 10

02468

101214

t=0

t=2

t=4

t=6

Roundtrip times

Cw

nd(in

seg

men

ts)

ssthresh

cwnd = 3





SS

CA

ssthresh













Philosophy

3-90











ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







Slow Start (SS)












Enter slow start

Duplicate ACK




TCP throughput








LRTTMSSsdot221



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness




R

R



Conn

ecti

on 2

thr

ough

p ut
















number)













client

FIN

server

ACK

ACK

FIN

close

close

closed

tim

ed w

ait






client

FIN

server

ACK

ACK

FIN

closing

closing

closed

tim

ed w

ait

closed



TCP clientlifecycle

TCP serverlifecycle






























UDP more

UDP checksum












rdt21 discussion




rdt30 sender

rdt30 in action

rdt30 in action



Pipelined protocols


Go-Back-N



GBN inaction

Selective Repeat


Selective repeat

















TCP sender events





Fast Retransmit

Fast Retransmit


TCP Flow Control















Slow Start Example











TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)











above


rdt_send(data)




rdt_send(data)


udt_send(sndpkt)



Wait forcall 1 from

above


ΛΛ


















rdt21 discussion













above


rdt_send(data)

udt_send(sndpkt)


isACK(rcvpkt1) )


Wait for ACK

0sender FSM

fragment





has_seq1(rcvpkt))


fragment

Λ











rdt_send(data)

Wait for

ACK0



above


rdt_send(data)






timeout


timeout

rdt_rcv(rcvpkt)

Wait for call 0from

above

Wait for

ACK1

Λrdt_rcv(rcvpkt)

ΛΛ

Λ


rdt30 in action


rdt30 in action






U sender=

008 30008

= 000027 L RRTT + L R

=





sender receiver

RTT




U sender=

00830008

= 000027 L RRTT + L R

=








sender receiver

RTT





U sender=

024 30008

= 000083 L RRTT + L R

=





Go-Back-NSender







timeout

rdt_send(data)





stop_timerelse

start_timer


base=1nextseqnum=1


Λ

Λ






Wait






Λ


GBN inaction


Selective Repeat









Selective repeat








ACK(n)otherwise

ignore

receiver










sender

receiver

Go-Back-N

expectedSN

snd_base=expectedSN



senderrsquos window



sender

receiver

Go-Back-N

expectedSN




senderrsquos window



sender

receiver

Go-Back-N

expectedSN






sender

receiver

Selective Repeat

rcv_base

snd_base=rcv_base



senderrsquos window


rcv_base+N-1



sender

receiver

Selective Repeat

rcv_base

snd_base=rcv_base-N



senderrsquos window

rcv_base


rcv_base+N-1



sender

receiver

Selective Repeat

snd_base=rcv_base-N



rcv_basercv_base


rcv_base+N-1











socketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment






32 bits

applicationdata

(variable length)



FSRPAUheadlen

notused



ACK ACK valid



commands)


Internetchecksum

(as in UDP)






















100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

iseco

nds)

































start timer

end of loop forever





ACK=100


Host B

Seq=92 8 bytes data

ACK=120

Seq=92 8 bytes data

Seq=

92 t

imeo

ut

ACK=120

Host A

Seq=92 8 bytes data

ACK=100

loss

tim

eout

lost ACK scenario

Host B

X

Seq=92 8 bytes data

ACK=100

time

Seq=

92 t

imeo

utSendBase

= 100

SendBase= 120

SendBase= 120

Sendbase= 100



Seq=92 8 bytes data

ACK=100

loss

tim

eout


Host B

X


ACK=120

time

SendBase= 120



Event at Receiver





TCP Receiver action






Fast Retransmit









Host A

tim

eout

Host B

time

X

resend seq X2


ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer





fast retransmit


TCP Flow Control






flow control




= RcvWin






3K

2K SeqNo=0

ReceiverBuffer


2K


4K

AckNo=4096 RcvWin=0


Sender blocked





a top-10 problem







Host B

λout






Host B

λout





λin

λout=

λin

λoutgtλ

inλout


R2

R2λin

λ out

b

R2

R2λin

λ out

a

R2

R2λin

λ out

c

R4

R3



λin


in



Host B

λout





Host A

Host B

λou

t










le CongWin









X

X

XX


send

ing

rate

time







roughly




cwndbytes

RTT

ACK(s)

















Host A

one segment

RTT

Host B

time

two segments

four segments





segment 1

ACK for segment 1

cwnd = 1


ACK for segments 2


ACK for segments 4

cwnd = 7

ACK for segments 3

ACK for segments 5

ACK for segments 6

cwnd = 3

cwnd = 5


cwnd = 8

segment 7






AIMD










ssthresh = 8

cwnd = 1

cwnd = 2

cwnd = 4

cwnd = 8

cwnd = 9

cwnd = 10

02468

101214

t=0

t=2

t=4

t=6

Roundtrip times

Cw

nd(in

seg

men

ts)

ssthresh

cwnd = 3





SS

CA

ssthresh













Philosophy

3-90











ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







Slow Start (SS)












Enter slow start

Duplicate ACK




TCP throughput








LRTTMSSsdot221



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness




R

R



Conn

ecti

on 2

thr

ough

p ut
















number)













client

FIN

server

ACK

ACK

FIN

close

close

closed

tim

ed w

ait






client

FIN

server

ACK

ACK

FIN

closing

closing

closed

tim

ed w

ait

closed



TCP clientlifecycle

TCP serverlifecycle






























UDP more

UDP checksum












rdt21 discussion




rdt30 sender

rdt30 in action

rdt30 in action



Pipelined protocols


Go-Back-N



GBN inaction

Selective Repeat


Selective repeat

















TCP sender events





Fast Retransmit

Fast Retransmit


TCP Flow Control















Slow Start Example











TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)

























rdt21 discussion













above


rdt_send(data)

udt_send(sndpkt)


isACK(rcvpkt1) )


Wait for ACK

0sender FSM

fragment





has_seq1(rcvpkt))


fragment

Λ











rdt_send(data)

Wait for

ACK0



above


rdt_send(data)






timeout


timeout

rdt_rcv(rcvpkt)

Wait for call 0from

above

Wait for

ACK1

Λrdt_rcv(rcvpkt)

ΛΛ

Λ


rdt30 in action


rdt30 in action






U sender=

008 30008

= 000027 L RRTT + L R

=





sender receiver

RTT




U sender=

00830008

= 000027 L RRTT + L R

=








sender receiver

RTT





U sender=

024 30008

= 000083 L RRTT + L R

=





Go-Back-NSender







timeout

rdt_send(data)





stop_timerelse

start_timer


base=1nextseqnum=1


Λ

Λ






Wait






Λ


GBN inaction


Selective Repeat









Selective repeat








ACK(n)otherwise

ignore

receiver










sender

receiver

Go-Back-N

expectedSN

snd_base=expectedSN



senderrsquos window



sender

receiver

Go-Back-N

expectedSN




senderrsquos window



sender

receiver

Go-Back-N

expectedSN






sender

receiver

Selective Repeat

rcv_base

snd_base=rcv_base



senderrsquos window


rcv_base+N-1



sender

receiver

Selective Repeat

rcv_base

snd_base=rcv_base-N



senderrsquos window

rcv_base


rcv_base+N-1



sender

receiver

Selective Repeat

snd_base=rcv_base-N



rcv_basercv_base


rcv_base+N-1











socketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment






32 bits

applicationdata

(variable length)



FSRPAUheadlen

notused



ACK ACK valid



commands)


Internetchecksum

(as in UDP)






















100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

iseco

nds)

































start timer

end of loop forever





ACK=100


Host B

Seq=92 8 bytes data

ACK=120

Seq=92 8 bytes data

Seq=

92 t

imeo

ut

ACK=120

Host A

Seq=92 8 bytes data

ACK=100

loss

tim

eout

lost ACK scenario

Host B

X

Seq=92 8 bytes data

ACK=100

time

Seq=

92 t

imeo

utSendBase

= 100

SendBase= 120

SendBase= 120

Sendbase= 100



Seq=92 8 bytes data

ACK=100

loss

tim

eout


Host B

X


ACK=120

time

SendBase= 120



Event at Receiver





TCP Receiver action






Fast Retransmit









Host A

tim

eout

Host B

time

X

resend seq X2


ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer





fast retransmit


TCP Flow Control






flow control




= RcvWin






3K

2K SeqNo=0

ReceiverBuffer


2K


4K

AckNo=4096 RcvWin=0


Sender blocked





a top-10 problem







Host B

λout






Host B

λout





λin

λout=

λin

λoutgtλ

inλout


R2

R2λin

λ out

b

R2

R2λin

λ out

a

R2

R2λin

λ out

c

R4

R3



λin


in



Host B

λout





Host A

Host B

λou

t










le CongWin









X

X

XX


send

ing

rate

time







roughly




cwndbytes

RTT

ACK(s)

















Host A

one segment

RTT

Host B

time

two segments

four segments





segment 1

ACK for segment 1

cwnd = 1


ACK for segments 2


ACK for segments 4

cwnd = 7

ACK for segments 3

ACK for segments 5

ACK for segments 6

cwnd = 3

cwnd = 5


cwnd = 8

segment 7






AIMD










ssthresh = 8

cwnd = 1

cwnd = 2

cwnd = 4

cwnd = 8

cwnd = 9

cwnd = 10

02468

101214

t=0

t=2

t=4

t=6

Roundtrip times

Cw

nd(in

seg

men

ts)

ssthresh

cwnd = 3





SS

CA

ssthresh













Philosophy

3-90











ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







Slow Start (SS)












Enter slow start

Duplicate ACK




TCP throughput








LRTTMSSsdot221



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness




R

R



Conn

ecti

on 2

thr

ough

p ut
















number)













client

FIN

server

ACK

ACK

FIN

close

close

closed

tim

ed w

ait






client

FIN

server

ACK

ACK

FIN

closing

closing

closed

tim

ed w

ait

closed



TCP clientlifecycle

TCP serverlifecycle






























UDP more

UDP checksum












rdt21 discussion




rdt30 sender

rdt30 in action

rdt30 in action



Pipelined protocols


Go-Back-N



GBN inaction

Selective Repeat


Selective repeat

















TCP sender events





Fast Retransmit

Fast Retransmit


TCP Flow Control















Slow Start Example











TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)















above


rdt_send(data)

udt_send(sndpkt)


isACK(rcvpkt1) )


Wait for ACK

0sender FSM

fragment





has_seq1(rcvpkt))


fragment

Λ











rdt_send(data)

Wait for

ACK0



above


rdt_send(data)






timeout


timeout

rdt_rcv(rcvpkt)

Wait for call 0from

above

Wait for

ACK1

Λrdt_rcv(rcvpkt)

ΛΛ

Λ


rdt30 in action


rdt30 in action






U sender=

008 30008

= 000027 L RRTT + L R

=





sender receiver

RTT




U sender=

00830008

= 000027 L RRTT + L R

=








sender receiver

RTT





U sender=

024 30008

= 000083 L RRTT + L R

=





Go-Back-NSender







timeout

rdt_send(data)





stop_timerelse

start_timer


base=1nextseqnum=1


Λ

Λ






Wait






Λ


GBN inaction


Selective Repeat









Selective repeat








ACK(n)otherwise

ignore

receiver










sender

receiver

Go-Back-N

expectedSN

snd_base=expectedSN



senderrsquos window



sender

receiver

Go-Back-N

expectedSN




senderrsquos window



sender

receiver

Go-Back-N

expectedSN






sender

receiver

Selective Repeat

rcv_base

snd_base=rcv_base



senderrsquos window


rcv_base+N-1



sender

receiver

Selective Repeat

rcv_base

snd_base=rcv_base-N



senderrsquos window

rcv_base


rcv_base+N-1



sender

receiver

Selective Repeat

snd_base=rcv_base-N



rcv_basercv_base


rcv_base+N-1











socketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment






32 bits

applicationdata

(variable length)



FSRPAUheadlen

notused



ACK ACK valid



commands)


Internetchecksum

(as in UDP)






















100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

iseco

nds)

































start timer

end of loop forever





ACK=100


Host B

Seq=92 8 bytes data

ACK=120

Seq=92 8 bytes data

Seq=

92 t

imeo

ut

ACK=120

Host A

Seq=92 8 bytes data

ACK=100

loss

tim

eout

lost ACK scenario

Host B

X

Seq=92 8 bytes data

ACK=100

time

Seq=

92 t

imeo

utSendBase

= 100

SendBase= 120

SendBase= 120

Sendbase= 100



Seq=92 8 bytes data

ACK=100

loss

tim

eout


Host B

X


ACK=120

time

SendBase= 120



Event at Receiver





TCP Receiver action






Fast Retransmit









Host A

tim

eout

Host B

time

X

resend seq X2


ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer





fast retransmit


TCP Flow Control






flow control




= RcvWin






3K

2K SeqNo=0

ReceiverBuffer


2K


4K

AckNo=4096 RcvWin=0


Sender blocked





a top-10 problem







Host B

λout






Host B

λout





λin

λout=

λin

λoutgtλ

inλout


R2

R2λin

λ out

b

R2

R2λin

λ out

a

R2

R2λin

λ out

c

R4

R3



λin


in



Host B

λout





Host A

Host B

λou

t










le CongWin









X

X

XX


send

ing

rate

time







roughly




cwndbytes

RTT

ACK(s)

















Host A

one segment

RTT

Host B

time

two segments

four segments





segment 1

ACK for segment 1

cwnd = 1


ACK for segments 2


ACK for segments 4

cwnd = 7

ACK for segments 3

ACK for segments 5

ACK for segments 6

cwnd = 3

cwnd = 5


cwnd = 8

segment 7






AIMD










ssthresh = 8

cwnd = 1

cwnd = 2

cwnd = 4

cwnd = 8

cwnd = 9

cwnd = 10

02468

101214

t=0

t=2

t=4

t=6

Roundtrip times

Cw

nd(in

seg

men

ts)

ssthresh

cwnd = 3





SS

CA

ssthresh













Philosophy

3-90











ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







Slow Start (SS)












Enter slow start

Duplicate ACK




TCP throughput








LRTTMSSsdot221



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness




R

R



Conn

ecti

on 2

thr

ough

p ut
















number)













client

FIN

server

ACK

ACK

FIN

close

close

closed

tim

ed w

ait






client

FIN

server

ACK

ACK

FIN

closing

closing

closed

tim

ed w

ait

closed



TCP clientlifecycle

TCP serverlifecycle






























UDP more

UDP checksum












rdt21 discussion




rdt30 sender

rdt30 in action

rdt30 in action



Pipelined protocols


Go-Back-N



GBN inaction

Selective Repeat


Selective repeat

















TCP sender events





Fast Retransmit

Fast Retransmit


TCP Flow Control















Slow Start Example











TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)


















rdt_send(data)

Wait for

ACK0



above


rdt_send(data)






timeout


timeout

rdt_rcv(rcvpkt)

Wait for call 0from

above

Wait for

ACK1

Λrdt_rcv(rcvpkt)

ΛΛ

Λ


rdt30 in action


rdt30 in action






U sender=

008 30008

= 000027 L RRTT + L R

=





sender receiver

RTT




U sender=

00830008

= 000027 L RRTT + L R

=








sender receiver

RTT





U sender=

024 30008

= 000083 L RRTT + L R

=





Go-Back-NSender







timeout

rdt_send(data)





stop_timerelse

start_timer


base=1nextseqnum=1


Λ

Λ






Wait






Λ


GBN inaction


Selective Repeat









Selective repeat








ACK(n)otherwise

ignore

receiver










sender

receiver

Go-Back-N

expectedSN

snd_base=expectedSN



senderrsquos window



sender

receiver

Go-Back-N

expectedSN




senderrsquos window



sender

receiver

Go-Back-N

expectedSN






sender

receiver

Selective Repeat

rcv_base

snd_base=rcv_base



senderrsquos window


rcv_base+N-1



sender

receiver

Selective Repeat

rcv_base

snd_base=rcv_base-N



senderrsquos window

rcv_base


rcv_base+N-1



sender

receiver

Selective Repeat

snd_base=rcv_base-N



rcv_basercv_base


rcv_base+N-1











socketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment






32 bits

applicationdata

(variable length)



FSRPAUheadlen

notused



ACK ACK valid



commands)


Internetchecksum

(as in UDP)






















100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

iseco

nds)

































start timer

end of loop forever





ACK=100


Host B

Seq=92 8 bytes data

ACK=120

Seq=92 8 bytes data

Seq=

92 t

imeo

ut

ACK=120

Host A

Seq=92 8 bytes data

ACK=100

loss

tim

eout

lost ACK scenario

Host B

X

Seq=92 8 bytes data

ACK=100

time

Seq=

92 t

imeo

utSendBase

= 100

SendBase= 120

SendBase= 120

Sendbase= 100



Seq=92 8 bytes data

ACK=100

loss

tim

eout


Host B

X


ACK=120

time

SendBase= 120



Event at Receiver





TCP Receiver action






Fast Retransmit









Host A

tim

eout

Host B

time

X

resend seq X2


ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer





fast retransmit


TCP Flow Control






flow control




= RcvWin






3K

2K SeqNo=0

ReceiverBuffer


2K


4K

AckNo=4096 RcvWin=0


Sender blocked





a top-10 problem







Host B

λout






Host B

λout





λin

λout=

λin

λoutgtλ

inλout


R2

R2λin

λ out

b

R2

R2λin

λ out

a

R2

R2λin

λ out

c

R4

R3



λin


in



Host B

λout





Host A

Host B

λou

t










le CongWin









X

X

XX


send

ing

rate

time







roughly




cwndbytes

RTT

ACK(s)

















Host A

one segment

RTT

Host B

time

two segments

four segments





segment 1

ACK for segment 1

cwnd = 1


ACK for segments 2


ACK for segments 4

cwnd = 7

ACK for segments 3

ACK for segments 5

ACK for segments 6

cwnd = 3

cwnd = 5


cwnd = 8

segment 7






AIMD










ssthresh = 8

cwnd = 1

cwnd = 2

cwnd = 4

cwnd = 8

cwnd = 9

cwnd = 10

02468

101214

t=0

t=2

t=4

t=6

Roundtrip times

Cw

nd(in

seg

men

ts)

ssthresh

cwnd = 3





SS

CA

ssthresh













Philosophy

3-90











ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







Slow Start (SS)












Enter slow start

Duplicate ACK




TCP throughput








LRTTMSSsdot221



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness




R

R



Conn

ecti

on 2

thr

ough

p ut
















number)













client

FIN

server

ACK

ACK

FIN

close

close

closed

tim

ed w

ait






client

FIN

server

ACK

ACK

FIN

closing

closing

closed

tim

ed w

ait

closed



TCP clientlifecycle

TCP serverlifecycle






























UDP more

UDP checksum












rdt21 discussion




rdt30 sender

rdt30 in action

rdt30 in action



Pipelined protocols


Go-Back-N



GBN inaction

Selective Repeat


Selective repeat

















TCP sender events





Fast Retransmit

Fast Retransmit


TCP Flow Control















Slow Start Example











TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)









rdt30 in action


rdt30 in action






U sender=

008 30008

= 000027 L RRTT + L R

=





sender receiver

RTT




U sender=

00830008

= 000027 L RRTT + L R

=








sender receiver

RTT





U sender=

024 30008

= 000083 L RRTT + L R

=





Go-Back-NSender







timeout

rdt_send(data)





stop_timerelse

start_timer


base=1nextseqnum=1


Λ

Λ






Wait






Λ


GBN inaction


Selective Repeat









Selective repeat








ACK(n)otherwise

ignore

receiver










sender

receiver

Go-Back-N

expectedSN

snd_base=expectedSN



senderrsquos window



sender

receiver

Go-Back-N

expectedSN




senderrsquos window



sender

receiver

Go-Back-N

expectedSN






sender

receiver

Selective Repeat

rcv_base

snd_base=rcv_base



senderrsquos window


rcv_base+N-1



sender

receiver

Selective Repeat

rcv_base

snd_base=rcv_base-N



senderrsquos window

rcv_base


rcv_base+N-1



sender

receiver

Selective Repeat

snd_base=rcv_base-N



rcv_basercv_base


rcv_base+N-1











socketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment






32 bits

applicationdata

(variable length)



FSRPAUheadlen

notused



ACK ACK valid



commands)


Internetchecksum

(as in UDP)






















100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

iseco

nds)

































start timer

end of loop forever





ACK=100


Host B

Seq=92 8 bytes data

ACK=120

Seq=92 8 bytes data

Seq=

92 t

imeo

ut

ACK=120

Host A

Seq=92 8 bytes data

ACK=100

loss

tim

eout

lost ACK scenario

Host B

X

Seq=92 8 bytes data

ACK=100

time

Seq=

92 t

imeo

utSendBase

= 100

SendBase= 120

SendBase= 120

Sendbase= 100



Seq=92 8 bytes data

ACK=100

loss

tim

eout


Host B

X


ACK=120

time

SendBase= 120



Event at Receiver





TCP Receiver action






Fast Retransmit









Host A

tim

eout

Host B

time

X

resend seq X2


ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer





fast retransmit


TCP Flow Control






flow control




= RcvWin






3K

2K SeqNo=0

ReceiverBuffer


2K


4K

AckNo=4096 RcvWin=0


Sender blocked





a top-10 problem







Host B

λout






Host B

λout





λin

λout=

λin

λoutgtλ

inλout


R2

R2λin

λ out

b

R2

R2λin

λ out

a

R2

R2λin

λ out

c

R4

R3



λin


in



Host B

λout





Host A

Host B

λou

t










le CongWin









X

X

XX


send

ing

rate

time







roughly




cwndbytes

RTT

ACK(s)

















Host A

one segment

RTT

Host B

time

two segments

four segments





segment 1

ACK for segment 1

cwnd = 1


ACK for segments 2


ACK for segments 4

cwnd = 7

ACK for segments 3

ACK for segments 5

ACK for segments 6

cwnd = 3

cwnd = 5


cwnd = 8

segment 7






AIMD










ssthresh = 8

cwnd = 1

cwnd = 2

cwnd = 4

cwnd = 8

cwnd = 9

cwnd = 10

02468

101214

t=0

t=2

t=4

t=6

Roundtrip times

Cw

nd(in

seg

men

ts)

ssthresh

cwnd = 3





SS

CA

ssthresh













Philosophy

3-90











ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







Slow Start (SS)












Enter slow start

Duplicate ACK




TCP throughput








LRTTMSSsdot221



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness




R

R



Conn

ecti

on 2

thr

ough

p ut
















number)













client

FIN

server

ACK

ACK

FIN

close

close

closed

tim

ed w

ait






client

FIN

server

ACK

ACK

FIN

closing

closing

closed

tim

ed w

ait

closed



TCP clientlifecycle

TCP serverlifecycle






























UDP more

UDP checksum












rdt21 discussion




rdt30 sender

rdt30 in action

rdt30 in action



Pipelined protocols


Go-Back-N



GBN inaction

Selective Repeat


Selective repeat

















TCP sender events





Fast Retransmit

Fast Retransmit


TCP Flow Control















Slow Start Example











TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)









rdt30 in action






U sender=

008 30008

= 000027 L RRTT + L R

=





sender receiver

RTT




U sender=

00830008

= 000027 L RRTT + L R

=








sender receiver

RTT





U sender=

024 30008

= 000083 L RRTT + L R

=





Go-Back-NSender







timeout

rdt_send(data)





stop_timerelse

start_timer


base=1nextseqnum=1


Λ

Λ






Wait






Λ


GBN inaction


Selective Repeat









Selective repeat








ACK(n)otherwise

ignore

receiver










sender

receiver

Go-Back-N

expectedSN

snd_base=expectedSN



senderrsquos window



sender

receiver

Go-Back-N

expectedSN




senderrsquos window



sender

receiver

Go-Back-N

expectedSN






sender

receiver

Selective Repeat

rcv_base

snd_base=rcv_base



senderrsquos window


rcv_base+N-1



sender

receiver

Selective Repeat

rcv_base

snd_base=rcv_base-N



senderrsquos window

rcv_base


rcv_base+N-1



sender

receiver

Selective Repeat

snd_base=rcv_base-N



rcv_basercv_base


rcv_base+N-1











socketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment






32 bits

applicationdata

(variable length)



FSRPAUheadlen

notused



ACK ACK valid



commands)


Internetchecksum

(as in UDP)






















100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

iseco

nds)

































start timer

end of loop forever





ACK=100


Host B

Seq=92 8 bytes data

ACK=120

Seq=92 8 bytes data

Seq=

92 t

imeo

ut

ACK=120

Host A

Seq=92 8 bytes data

ACK=100

loss

tim

eout

lost ACK scenario

Host B

X

Seq=92 8 bytes data

ACK=100

time

Seq=

92 t

imeo

utSendBase

= 100

SendBase= 120

SendBase= 120

Sendbase= 100



Seq=92 8 bytes data

ACK=100

loss

tim

eout


Host B

X


ACK=120

time

SendBase= 120



Event at Receiver





TCP Receiver action






Fast Retransmit









Host A

tim

eout

Host B

time

X

resend seq X2


ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer





fast retransmit


TCP Flow Control






flow control




= RcvWin






3K

2K SeqNo=0

ReceiverBuffer


2K


4K

AckNo=4096 RcvWin=0


Sender blocked





a top-10 problem







Host B

λout






Host B

λout





λin

λout=

λin

λoutgtλ

inλout


R2

R2λin

λ out

b

R2

R2λin

λ out

a

R2

R2λin

λ out

c

R4

R3



λin


in



Host B

λout





Host A

Host B

λou

t










le CongWin









X

X

XX


send

ing

rate

time







roughly




cwndbytes

RTT

ACK(s)

















Host A

one segment

RTT

Host B

time

two segments

four segments





segment 1

ACK for segment 1

cwnd = 1


ACK for segments 2


ACK for segments 4

cwnd = 7

ACK for segments 3

ACK for segments 5

ACK for segments 6

cwnd = 3

cwnd = 5


cwnd = 8

segment 7






AIMD










ssthresh = 8

cwnd = 1

cwnd = 2

cwnd = 4

cwnd = 8

cwnd = 9

cwnd = 10

02468

101214

t=0

t=2

t=4

t=6

Roundtrip times

Cw

nd(in

seg

men

ts)

ssthresh

cwnd = 3





SS

CA

ssthresh













Philosophy

3-90











ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







Slow Start (SS)












Enter slow start

Duplicate ACK




TCP throughput








LRTTMSSsdot221



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness




R

R



Conn

ecti

on 2

thr

ough

p ut
















number)













client

FIN

server

ACK

ACK

FIN

close

close

closed

tim

ed w

ait






client

FIN

server

ACK

ACK

FIN

closing

closing

closed

tim

ed w

ait

closed



TCP clientlifecycle

TCP serverlifecycle






























UDP more

UDP checksum












rdt21 discussion




rdt30 sender

rdt30 in action

rdt30 in action



Pipelined protocols


Go-Back-N



GBN inaction

Selective Repeat


Selective repeat

















TCP sender events





Fast Retransmit

Fast Retransmit


TCP Flow Control















Slow Start Example











TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)













U sender=

008 30008

= 000027 L RRTT + L R

=





sender receiver

RTT




U sender=

00830008

= 000027 L RRTT + L R

=








sender receiver

RTT





U sender=

024 30008

= 000083 L RRTT + L R

=





Go-Back-NSender







timeout

rdt_send(data)





stop_timerelse

start_timer


base=1nextseqnum=1


Λ

Λ






Wait






Λ


GBN inaction


Selective Repeat









Selective repeat








ACK(n)otherwise

ignore

receiver










sender

receiver

Go-Back-N

expectedSN

snd_base=expectedSN



senderrsquos window



sender

receiver

Go-Back-N

expectedSN




senderrsquos window



sender

receiver

Go-Back-N

expectedSN






sender

receiver

Selective Repeat

rcv_base

snd_base=rcv_base



senderrsquos window


rcv_base+N-1



sender

receiver

Selective Repeat

rcv_base

snd_base=rcv_base-N



senderrsquos window

rcv_base


rcv_base+N-1



sender

receiver

Selective Repeat

snd_base=rcv_base-N



rcv_basercv_base


rcv_base+N-1











socketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment






32 bits

applicationdata

(variable length)



FSRPAUheadlen

notused



ACK ACK valid



commands)


Internetchecksum

(as in UDP)






















100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

iseco

nds)

































start timer

end of loop forever





ACK=100


Host B

Seq=92 8 bytes data

ACK=120

Seq=92 8 bytes data

Seq=

92 t

imeo

ut

ACK=120

Host A

Seq=92 8 bytes data

ACK=100

loss

tim

eout

lost ACK scenario

Host B

X

Seq=92 8 bytes data

ACK=100

time

Seq=

92 t

imeo

utSendBase

= 100

SendBase= 120

SendBase= 120

Sendbase= 100



Seq=92 8 bytes data

ACK=100

loss

tim

eout


Host B

X


ACK=120

time

SendBase= 120



Event at Receiver





TCP Receiver action






Fast Retransmit









Host A

tim

eout

Host B

time

X

resend seq X2


ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer





fast retransmit


TCP Flow Control






flow control




= RcvWin






3K

2K SeqNo=0

ReceiverBuffer


2K


4K

AckNo=4096 RcvWin=0


Sender blocked





a top-10 problem







Host B

λout






Host B

λout





λin

λout=

λin

λoutgtλ

inλout


R2

R2λin

λ out

b

R2

R2λin

λ out

a

R2

R2λin

λ out

c

R4

R3



λin


in



Host B

λout





Host A

Host B

λou

t










le CongWin









X

X

XX


send

ing

rate

time







roughly




cwndbytes

RTT

ACK(s)

















Host A

one segment

RTT

Host B

time

two segments

four segments





segment 1

ACK for segment 1

cwnd = 1


ACK for segments 2


ACK for segments 4

cwnd = 7

ACK for segments 3

ACK for segments 5

ACK for segments 6

cwnd = 3

cwnd = 5


cwnd = 8

segment 7






AIMD










ssthresh = 8

cwnd = 1

cwnd = 2

cwnd = 4

cwnd = 8

cwnd = 9

cwnd = 10

02468

101214

t=0

t=2

t=4

t=6

Roundtrip times

Cw

nd(in

seg

men

ts)

ssthresh

cwnd = 3





SS

CA

ssthresh













Philosophy

3-90











ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







Slow Start (SS)












Enter slow start

Duplicate ACK




TCP throughput








LRTTMSSsdot221



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness




R

R



Conn

ecti

on 2

thr

ough

p ut
















number)













client

FIN

server

ACK

ACK

FIN

close

close

closed

tim

ed w

ait






client

FIN

server

ACK

ACK

FIN

closing

closing

closed

tim

ed w

ait

closed



TCP clientlifecycle

TCP serverlifecycle






























UDP more

UDP checksum












rdt21 discussion




rdt30 sender

rdt30 in action

rdt30 in action



Pipelined protocols


Go-Back-N



GBN inaction

Selective Repeat


Selective repeat

















TCP sender events





Fast Retransmit

Fast Retransmit


TCP Flow Control















Slow Start Example











TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)











sender receiver

RTT




U sender=

00830008

= 000027 L RRTT + L R

=








sender receiver

RTT





U sender=

024 30008

= 000083 L RRTT + L R

=





Go-Back-NSender







timeout

rdt_send(data)





stop_timerelse

start_timer


base=1nextseqnum=1


Λ

Λ






Wait






Λ


GBN inaction


Selective Repeat









Selective repeat








ACK(n)otherwise

ignore

receiver










sender

receiver

Go-Back-N

expectedSN

snd_base=expectedSN



senderrsquos window



sender

receiver

Go-Back-N

expectedSN




senderrsquos window



sender

receiver

Go-Back-N

expectedSN






sender

receiver

Selective Repeat

rcv_base

snd_base=rcv_base



senderrsquos window


rcv_base+N-1



sender

receiver

Selective Repeat

rcv_base

snd_base=rcv_base-N



senderrsquos window

rcv_base


rcv_base+N-1



sender

receiver

Selective Repeat

snd_base=rcv_base-N



rcv_basercv_base


rcv_base+N-1











socketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment






32 bits

applicationdata

(variable length)



FSRPAUheadlen

notused



ACK ACK valid



commands)


Internetchecksum

(as in UDP)






















100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

iseco

nds)

































start timer

end of loop forever





ACK=100


Host B

Seq=92 8 bytes data

ACK=120

Seq=92 8 bytes data

Seq=

92 t

imeo

ut

ACK=120

Host A

Seq=92 8 bytes data

ACK=100

loss

tim

eout

lost ACK scenario

Host B

X

Seq=92 8 bytes data

ACK=100

time

Seq=

92 t

imeo

utSendBase

= 100

SendBase= 120

SendBase= 120

Sendbase= 100



Seq=92 8 bytes data

ACK=100

loss

tim

eout


Host B

X


ACK=120

time

SendBase= 120



Event at Receiver





TCP Receiver action






Fast Retransmit









Host A

tim

eout

Host B

time

X

resend seq X2


ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer





fast retransmit


TCP Flow Control






flow control




= RcvWin






3K

2K SeqNo=0

ReceiverBuffer


2K


4K

AckNo=4096 RcvWin=0


Sender blocked





a top-10 problem







Host B

λout






Host B

λout





λin

λout=

λin

λoutgtλ

inλout


R2

R2λin

λ out

b

R2

R2λin

λ out

a

R2

R2λin

λ out

c

R4

R3



λin


in



Host B

λout





Host A

Host B

λou

t










le CongWin









X

X

XX


send

ing

rate

time







roughly




cwndbytes

RTT

ACK(s)

















Host A

one segment

RTT

Host B

time

two segments

four segments





segment 1

ACK for segment 1

cwnd = 1


ACK for segments 2


ACK for segments 4

cwnd = 7

ACK for segments 3

ACK for segments 5

ACK for segments 6

cwnd = 3

cwnd = 5


cwnd = 8

segment 7






AIMD










ssthresh = 8

cwnd = 1

cwnd = 2

cwnd = 4

cwnd = 8

cwnd = 9

cwnd = 10

02468

101214

t=0

t=2

t=4

t=6

Roundtrip times

Cw

nd(in

seg

men

ts)

ssthresh

cwnd = 3





SS

CA

ssthresh













Philosophy

3-90











ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







Slow Start (SS)












Enter slow start

Duplicate ACK




TCP throughput








LRTTMSSsdot221



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness




R

R



Conn

ecti

on 2

thr

ough

p ut
















number)













client

FIN

server

ACK

ACK

FIN

close

close

closed

tim

ed w

ait






client

FIN

server

ACK

ACK

FIN

closing

closing

closed

tim

ed w

ait

closed



TCP clientlifecycle

TCP serverlifecycle






























UDP more

UDP checksum












rdt21 discussion




rdt30 sender

rdt30 in action

rdt30 in action



Pipelined protocols


Go-Back-N



GBN inaction

Selective Repeat


Selective repeat

















TCP sender events





Fast Retransmit

Fast Retransmit


TCP Flow Control















Slow Start Example











TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)















sender receiver

RTT





U sender=

024 30008

= 000083 L RRTT + L R

=





Go-Back-NSender







timeout

rdt_send(data)





stop_timerelse

start_timer


base=1nextseqnum=1


Λ

Λ






Wait






Λ


GBN inaction


Selective Repeat









Selective repeat








ACK(n)otherwise

ignore

receiver










sender

receiver

Go-Back-N

expectedSN

snd_base=expectedSN



senderrsquos window



sender

receiver

Go-Back-N

expectedSN




senderrsquos window



sender

receiver

Go-Back-N

expectedSN






sender

receiver

Selective Repeat

rcv_base

snd_base=rcv_base



senderrsquos window


rcv_base+N-1



sender

receiver

Selective Repeat

rcv_base

snd_base=rcv_base-N



senderrsquos window

rcv_base


rcv_base+N-1



sender

receiver

Selective Repeat

snd_base=rcv_base-N



rcv_basercv_base


rcv_base+N-1











socketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment






32 bits

applicationdata

(variable length)



FSRPAUheadlen

notused



ACK ACK valid



commands)


Internetchecksum

(as in UDP)






















100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

iseco

nds)

































start timer

end of loop forever





ACK=100


Host B

Seq=92 8 bytes data

ACK=120

Seq=92 8 bytes data

Seq=

92 t

imeo

ut

ACK=120

Host A

Seq=92 8 bytes data

ACK=100

loss

tim

eout

lost ACK scenario

Host B

X

Seq=92 8 bytes data

ACK=100

time

Seq=

92 t

imeo

utSendBase

= 100

SendBase= 120

SendBase= 120

Sendbase= 100



Seq=92 8 bytes data

ACK=100

loss

tim

eout


Host B

X


ACK=120

time

SendBase= 120



Event at Receiver





TCP Receiver action






Fast Retransmit









Host A

tim

eout

Host B

time

X

resend seq X2


ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer





fast retransmit


TCP Flow Control






flow control




= RcvWin






3K

2K SeqNo=0

ReceiverBuffer


2K


4K

AckNo=4096 RcvWin=0


Sender blocked





a top-10 problem







Host B

λout






Host B

λout





λin

λout=

λin

λoutgtλ

inλout


R2

R2λin

λ out

b

R2

R2λin

λ out

a

R2

R2λin

λ out

c

R4

R3



λin


in



Host B

λout





Host A

Host B

λou

t










le CongWin









X

X

XX


send

ing

rate

time







roughly




cwndbytes

RTT

ACK(s)

















Host A

one segment

RTT

Host B

time

two segments

four segments





segment 1

ACK for segment 1

cwnd = 1


ACK for segments 2


ACK for segments 4

cwnd = 7

ACK for segments 3

ACK for segments 5

ACK for segments 6

cwnd = 3

cwnd = 5


cwnd = 8

segment 7






AIMD










ssthresh = 8

cwnd = 1

cwnd = 2

cwnd = 4

cwnd = 8

cwnd = 9

cwnd = 10

02468

101214

t=0

t=2

t=4

t=6

Roundtrip times

Cw

nd(in

seg

men

ts)

ssthresh

cwnd = 3





SS

CA

ssthresh













Philosophy

3-90











ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







Slow Start (SS)












Enter slow start

Duplicate ACK




TCP throughput








LRTTMSSsdot221



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness




R

R



Conn

ecti

on 2

thr

ough

p ut
















number)













client

FIN

server

ACK

ACK

FIN

close

close

closed

tim

ed w

ait






client

FIN

server

ACK

ACK

FIN

closing

closing

closed

tim

ed w

ait

closed



TCP clientlifecycle

TCP serverlifecycle






























UDP more

UDP checksum












rdt21 discussion




rdt30 sender

rdt30 in action

rdt30 in action



Pipelined protocols


Go-Back-N



GBN inaction

Selective Repeat


Selective repeat

















TCP sender events





Fast Retransmit

Fast Retransmit


TCP Flow Control















Slow Start Example











TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)











Go-Back-NSender







timeout

rdt_send(data)





stop_timerelse

start_timer


base=1nextseqnum=1


Λ

Λ






Wait






Λ


GBN inaction


Selective Repeat









Selective repeat








ACK(n)otherwise

ignore

receiver










sender

receiver

Go-Back-N

expectedSN

snd_base=expectedSN



senderrsquos window



sender

receiver

Go-Back-N

expectedSN




senderrsquos window



sender

receiver

Go-Back-N

expectedSN






sender

receiver

Selective Repeat

rcv_base

snd_base=rcv_base



senderrsquos window


rcv_base+N-1



sender

receiver

Selective Repeat

rcv_base

snd_base=rcv_base-N



senderrsquos window

rcv_base


rcv_base+N-1



sender

receiver

Selective Repeat

snd_base=rcv_base-N



rcv_basercv_base


rcv_base+N-1











socketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment






32 bits

applicationdata

(variable length)



FSRPAUheadlen

notused



ACK ACK valid



commands)


Internetchecksum

(as in UDP)






















100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

iseco

nds)

































start timer

end of loop forever





ACK=100


Host B

Seq=92 8 bytes data

ACK=120

Seq=92 8 bytes data

Seq=

92 t

imeo

ut

ACK=120

Host A

Seq=92 8 bytes data

ACK=100

loss

tim

eout

lost ACK scenario

Host B

X

Seq=92 8 bytes data

ACK=100

time

Seq=

92 t

imeo

utSendBase

= 100

SendBase= 120

SendBase= 120

Sendbase= 100



Seq=92 8 bytes data

ACK=100

loss

tim

eout


Host B

X


ACK=120

time

SendBase= 120



Event at Receiver





TCP Receiver action






Fast Retransmit









Host A

tim

eout

Host B

time

X

resend seq X2


ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer





fast retransmit


TCP Flow Control






flow control




= RcvWin






3K

2K SeqNo=0

ReceiverBuffer


2K


4K

AckNo=4096 RcvWin=0


Sender blocked





a top-10 problem







Host B

λout






Host B

λout





λin

λout=

λin

λoutgtλ

inλout


R2

R2λin

λ out

b

R2

R2λin

λ out

a

R2

R2λin

λ out

c

R4

R3



λin


in



Host B

λout





Host A

Host B

λou

t










le CongWin









X

X

XX


send

ing

rate

time







roughly




cwndbytes

RTT

ACK(s)

















Host A

one segment

RTT

Host B

time

two segments

four segments





segment 1

ACK for segment 1

cwnd = 1


ACK for segments 2


ACK for segments 4

cwnd = 7

ACK for segments 3

ACK for segments 5

ACK for segments 6

cwnd = 3

cwnd = 5


cwnd = 8

segment 7






AIMD










ssthresh = 8

cwnd = 1

cwnd = 2

cwnd = 4

cwnd = 8

cwnd = 9

cwnd = 10

02468

101214

t=0

t=2

t=4

t=6

Roundtrip times

Cw

nd(in

seg

men

ts)

ssthresh

cwnd = 3





SS

CA

ssthresh













Philosophy

3-90











ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







Slow Start (SS)












Enter slow start

Duplicate ACK




TCP throughput








LRTTMSSsdot221



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness




R

R



Conn

ecti

on 2

thr

ough

p ut
















number)













client

FIN

server

ACK

ACK

FIN

close

close

closed

tim

ed w

ait






client

FIN

server

ACK

ACK

FIN

closing

closing

closed

tim

ed w

ait

closed



TCP clientlifecycle

TCP serverlifecycle






























UDP more

UDP checksum












rdt21 discussion




rdt30 sender

rdt30 in action

rdt30 in action



Pipelined protocols


Go-Back-N



GBN inaction

Selective Repeat


Selective repeat

















TCP sender events





Fast Retransmit

Fast Retransmit


TCP Flow Control















Slow Start Example











TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)











timeout

rdt_send(data)





stop_timerelse

start_timer


base=1nextseqnum=1


Λ

Λ






Wait






Λ


GBN inaction


Selective Repeat









Selective repeat








ACK(n)otherwise

ignore

receiver










sender

receiver

Go-Back-N

expectedSN

snd_base=expectedSN



senderrsquos window



sender

receiver

Go-Back-N

expectedSN




senderrsquos window



sender

receiver

Go-Back-N

expectedSN






sender

receiver

Selective Repeat

rcv_base

snd_base=rcv_base



senderrsquos window


rcv_base+N-1



sender

receiver

Selective Repeat

rcv_base

snd_base=rcv_base-N



senderrsquos window

rcv_base


rcv_base+N-1



sender

receiver

Selective Repeat

snd_base=rcv_base-N



rcv_basercv_base


rcv_base+N-1











socketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment






32 bits

applicationdata

(variable length)



FSRPAUheadlen

notused



ACK ACK valid



commands)


Internetchecksum

(as in UDP)






















100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

iseco

nds)

































start timer

end of loop forever





ACK=100


Host B

Seq=92 8 bytes data

ACK=120

Seq=92 8 bytes data

Seq=

92 t

imeo

ut

ACK=120

Host A

Seq=92 8 bytes data

ACK=100

loss

tim

eout

lost ACK scenario

Host B

X

Seq=92 8 bytes data

ACK=100

time

Seq=

92 t

imeo

utSendBase

= 100

SendBase= 120

SendBase= 120

Sendbase= 100



Seq=92 8 bytes data

ACK=100

loss

tim

eout


Host B

X


ACK=120

time

SendBase= 120



Event at Receiver





TCP Receiver action






Fast Retransmit









Host A

tim

eout

Host B

time

X

resend seq X2


ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer





fast retransmit


TCP Flow Control






flow control




= RcvWin






3K

2K SeqNo=0

ReceiverBuffer


2K


4K

AckNo=4096 RcvWin=0


Sender blocked





a top-10 problem







Host B

λout






Host B

λout





λin

λout=

λin

λoutgtλ

inλout


R2

R2λin

λ out

b

R2

R2λin

λ out

a

R2

R2λin

λ out

c

R4

R3



λin


in



Host B

λout





Host A

Host B

λou

t










le CongWin









X

X

XX


send

ing

rate

time







roughly




cwndbytes

RTT

ACK(s)

















Host A

one segment

RTT

Host B

time

two segments

four segments





segment 1

ACK for segment 1

cwnd = 1


ACK for segments 2


ACK for segments 4

cwnd = 7

ACK for segments 3

ACK for segments 5

ACK for segments 6

cwnd = 3

cwnd = 5


cwnd = 8

segment 7






AIMD










ssthresh = 8

cwnd = 1

cwnd = 2

cwnd = 4

cwnd = 8

cwnd = 9

cwnd = 10

02468

101214

t=0

t=2

t=4

t=6

Roundtrip times

Cw

nd(in

seg

men

ts)

ssthresh

cwnd = 3





SS

CA

ssthresh













Philosophy

3-90











ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







Slow Start (SS)












Enter slow start

Duplicate ACK




TCP throughput








LRTTMSSsdot221



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness




R

R



Conn

ecti

on 2

thr

ough

p ut
















number)













client

FIN

server

ACK

ACK

FIN

close

close

closed

tim

ed w

ait






client

FIN

server

ACK

ACK

FIN

closing

closing

closed

tim

ed w

ait

closed



TCP clientlifecycle

TCP serverlifecycle






























UDP more

UDP checksum












rdt21 discussion




rdt30 sender

rdt30 in action

rdt30 in action



Pipelined protocols


Go-Back-N



GBN inaction

Selective Repeat


Selective repeat

















TCP sender events





Fast Retransmit

Fast Retransmit


TCP Flow Control















Slow Start Example











TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)













Wait






Λ


GBN inaction


Selective Repeat









Selective repeat








ACK(n)otherwise

ignore

receiver










sender

receiver

Go-Back-N

expectedSN

snd_base=expectedSN



senderrsquos window



sender

receiver

Go-Back-N

expectedSN




senderrsquos window



sender

receiver

Go-Back-N

expectedSN






sender

receiver

Selective Repeat

rcv_base

snd_base=rcv_base



senderrsquos window


rcv_base+N-1



sender

receiver

Selective Repeat

rcv_base

snd_base=rcv_base-N



senderrsquos window

rcv_base


rcv_base+N-1



sender

receiver

Selective Repeat

snd_base=rcv_base-N



rcv_basercv_base


rcv_base+N-1











socketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment






32 bits

applicationdata

(variable length)



FSRPAUheadlen

notused



ACK ACK valid



commands)


Internetchecksum

(as in UDP)






















100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

iseco

nds)

































start timer

end of loop forever





ACK=100


Host B

Seq=92 8 bytes data

ACK=120

Seq=92 8 bytes data

Seq=

92 t

imeo

ut

ACK=120

Host A

Seq=92 8 bytes data

ACK=100

loss

tim

eout

lost ACK scenario

Host B

X

Seq=92 8 bytes data

ACK=100

time

Seq=

92 t

imeo

utSendBase

= 100

SendBase= 120

SendBase= 120

Sendbase= 100



Seq=92 8 bytes data

ACK=100

loss

tim

eout


Host B

X


ACK=120

time

SendBase= 120



Event at Receiver





TCP Receiver action






Fast Retransmit









Host A

tim

eout

Host B

time

X

resend seq X2


ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer





fast retransmit


TCP Flow Control






flow control




= RcvWin






3K

2K SeqNo=0

ReceiverBuffer


2K


4K

AckNo=4096 RcvWin=0


Sender blocked





a top-10 problem







Host B

λout






Host B

λout





λin

λout=

λin

λoutgtλ

inλout


R2

R2λin

λ out

b

R2

R2λin

λ out

a

R2

R2λin

λ out

c

R4

R3



λin


in



Host B

λout





Host A

Host B

λou

t










le CongWin









X

X

XX


send

ing

rate

time







roughly




cwndbytes

RTT

ACK(s)

















Host A

one segment

RTT

Host B

time

two segments

four segments





segment 1

ACK for segment 1

cwnd = 1


ACK for segments 2


ACK for segments 4

cwnd = 7

ACK for segments 3

ACK for segments 5

ACK for segments 6

cwnd = 3

cwnd = 5


cwnd = 8

segment 7






AIMD










ssthresh = 8

cwnd = 1

cwnd = 2

cwnd = 4

cwnd = 8

cwnd = 9

cwnd = 10

02468

101214

t=0

t=2

t=4

t=6

Roundtrip times

Cw

nd(in

seg

men

ts)

ssthresh

cwnd = 3





SS

CA

ssthresh













Philosophy

3-90











ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







Slow Start (SS)












Enter slow start

Duplicate ACK




TCP throughput








LRTTMSSsdot221



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness




R

R



Conn

ecti

on 2

thr

ough

p ut
















number)













client

FIN

server

ACK

ACK

FIN

close

close

closed

tim

ed w

ait






client

FIN

server

ACK

ACK

FIN

closing

closing

closed

tim

ed w

ait

closed



TCP clientlifecycle

TCP serverlifecycle






























UDP more

UDP checksum












rdt21 discussion




rdt30 sender

rdt30 in action

rdt30 in action



Pipelined protocols


Go-Back-N



GBN inaction

Selective Repeat


Selective repeat

















TCP sender events





Fast Retransmit

Fast Retransmit


TCP Flow Control















Slow Start Example











TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)









GBN inaction


Selective Repeat









Selective repeat








ACK(n)otherwise

ignore

receiver










sender

receiver

Go-Back-N

expectedSN

snd_base=expectedSN



senderrsquos window



sender

receiver

Go-Back-N

expectedSN




senderrsquos window



sender

receiver

Go-Back-N

expectedSN






sender

receiver

Selective Repeat

rcv_base

snd_base=rcv_base



senderrsquos window


rcv_base+N-1



sender

receiver

Selective Repeat

rcv_base

snd_base=rcv_base-N



senderrsquos window

rcv_base


rcv_base+N-1



sender

receiver

Selective Repeat

snd_base=rcv_base-N



rcv_basercv_base


rcv_base+N-1











socketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment






32 bits

applicationdata

(variable length)



FSRPAUheadlen

notused



ACK ACK valid



commands)


Internetchecksum

(as in UDP)






















100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

iseco

nds)

































start timer

end of loop forever





ACK=100


Host B

Seq=92 8 bytes data

ACK=120

Seq=92 8 bytes data

Seq=

92 t

imeo

ut

ACK=120

Host A

Seq=92 8 bytes data

ACK=100

loss

tim

eout

lost ACK scenario

Host B

X

Seq=92 8 bytes data

ACK=100

time

Seq=

92 t

imeo

utSendBase

= 100

SendBase= 120

SendBase= 120

Sendbase= 100



Seq=92 8 bytes data

ACK=100

loss

tim

eout


Host B

X


ACK=120

time

SendBase= 120



Event at Receiver





TCP Receiver action






Fast Retransmit









Host A

tim

eout

Host B

time

X

resend seq X2


ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer





fast retransmit


TCP Flow Control






flow control




= RcvWin






3K

2K SeqNo=0

ReceiverBuffer


2K


4K

AckNo=4096 RcvWin=0


Sender blocked





a top-10 problem







Host B

λout






Host B

λout





λin

λout=

λin

λoutgtλ

inλout


R2

R2λin

λ out

b

R2

R2λin

λ out

a

R2

R2λin

λ out

c

R4

R3



λin


in



Host B

λout





Host A

Host B

λou

t










le CongWin









X

X

XX


send

ing

rate

time







roughly




cwndbytes

RTT

ACK(s)

















Host A

one segment

RTT

Host B

time

two segments

four segments





segment 1

ACK for segment 1

cwnd = 1


ACK for segments 2


ACK for segments 4

cwnd = 7

ACK for segments 3

ACK for segments 5

ACK for segments 6

cwnd = 3

cwnd = 5


cwnd = 8

segment 7






AIMD










ssthresh = 8

cwnd = 1

cwnd = 2

cwnd = 4

cwnd = 8

cwnd = 9

cwnd = 10

02468

101214

t=0

t=2

t=4

t=6

Roundtrip times

Cw

nd(in

seg

men

ts)

ssthresh

cwnd = 3





SS

CA

ssthresh













Philosophy

3-90











ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







Slow Start (SS)












Enter slow start

Duplicate ACK




TCP throughput








LRTTMSSsdot221



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness




R

R



Conn

ecti

on 2

thr

ough

p ut
















number)













client

FIN

server

ACK

ACK

FIN

close

close

closed

tim

ed w

ait






client

FIN

server

ACK

ACK

FIN

closing

closing

closed

tim

ed w

ait

closed



TCP clientlifecycle

TCP serverlifecycle






























UDP more

UDP checksum












rdt21 discussion




rdt30 sender

rdt30 in action

rdt30 in action



Pipelined protocols


Go-Back-N



GBN inaction

Selective Repeat


Selective repeat

















TCP sender events





Fast Retransmit

Fast Retransmit


TCP Flow Control















Slow Start Example











TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)









Selective Repeat









Selective repeat








ACK(n)otherwise

ignore

receiver










sender

receiver

Go-Back-N

expectedSN

snd_base=expectedSN



senderrsquos window



sender

receiver

Go-Back-N

expectedSN




senderrsquos window



sender

receiver

Go-Back-N

expectedSN






sender

receiver

Selective Repeat

rcv_base

snd_base=rcv_base



senderrsquos window


rcv_base+N-1



sender

receiver

Selective Repeat

rcv_base

snd_base=rcv_base-N



senderrsquos window

rcv_base


rcv_base+N-1



sender

receiver

Selective Repeat

snd_base=rcv_base-N



rcv_basercv_base


rcv_base+N-1











socketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment






32 bits

applicationdata

(variable length)



FSRPAUheadlen

notused



ACK ACK valid



commands)


Internetchecksum

(as in UDP)






















100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

iseco

nds)

































start timer

end of loop forever





ACK=100


Host B

Seq=92 8 bytes data

ACK=120

Seq=92 8 bytes data

Seq=

92 t

imeo

ut

ACK=120

Host A

Seq=92 8 bytes data

ACK=100

loss

tim

eout

lost ACK scenario

Host B

X

Seq=92 8 bytes data

ACK=100

time

Seq=

92 t

imeo

utSendBase

= 100

SendBase= 120

SendBase= 120

Sendbase= 100



Seq=92 8 bytes data

ACK=100

loss

tim

eout


Host B

X


ACK=120

time

SendBase= 120



Event at Receiver





TCP Receiver action






Fast Retransmit









Host A

tim

eout

Host B

time

X

resend seq X2


ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer





fast retransmit


TCP Flow Control






flow control




= RcvWin






3K

2K SeqNo=0

ReceiverBuffer


2K


4K

AckNo=4096 RcvWin=0


Sender blocked





a top-10 problem







Host B

λout






Host B

λout





λin

λout=

λin

λoutgtλ

inλout


R2

R2λin

λ out

b

R2

R2λin

λ out

a

R2

R2λin

λ out

c

R4

R3



λin


in



Host B

λout





Host A

Host B

λou

t










le CongWin









X

X

XX


send

ing

rate

time







roughly




cwndbytes

RTT

ACK(s)

















Host A

one segment

RTT

Host B

time

two segments

four segments





segment 1

ACK for segment 1

cwnd = 1


ACK for segments 2


ACK for segments 4

cwnd = 7

ACK for segments 3

ACK for segments 5

ACK for segments 6

cwnd = 3

cwnd = 5


cwnd = 8

segment 7






AIMD










ssthresh = 8

cwnd = 1

cwnd = 2

cwnd = 4

cwnd = 8

cwnd = 9

cwnd = 10

02468

101214

t=0

t=2

t=4

t=6

Roundtrip times

Cw

nd(in

seg

men

ts)

ssthresh

cwnd = 3





SS

CA

ssthresh













Philosophy

3-90











ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







Slow Start (SS)












Enter slow start

Duplicate ACK




TCP throughput








LRTTMSSsdot221



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness




R

R



Conn

ecti

on 2

thr

ough

p ut
















number)













client

FIN

server

ACK

ACK

FIN

close

close

closed

tim

ed w

ait






client

FIN

server

ACK

ACK

FIN

closing

closing

closed

tim

ed w

ait

closed



TCP clientlifecycle

TCP serverlifecycle






























UDP more

UDP checksum












rdt21 discussion




rdt30 sender

rdt30 in action

rdt30 in action



Pipelined protocols


Go-Back-N



GBN inaction

Selective Repeat


Selective repeat

















TCP sender events





Fast Retransmit

Fast Retransmit


TCP Flow Control















Slow Start Example











TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)











Selective repeat








ACK(n)otherwise

ignore

receiver










sender

receiver

Go-Back-N

expectedSN

snd_base=expectedSN



senderrsquos window



sender

receiver

Go-Back-N

expectedSN




senderrsquos window



sender

receiver

Go-Back-N

expectedSN






sender

receiver

Selective Repeat

rcv_base

snd_base=rcv_base



senderrsquos window


rcv_base+N-1



sender

receiver

Selective Repeat

rcv_base

snd_base=rcv_base-N



senderrsquos window

rcv_base


rcv_base+N-1



sender

receiver

Selective Repeat

snd_base=rcv_base-N



rcv_basercv_base


rcv_base+N-1











socketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment






32 bits

applicationdata

(variable length)



FSRPAUheadlen

notused



ACK ACK valid



commands)


Internetchecksum

(as in UDP)






















100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

iseco

nds)

































start timer

end of loop forever





ACK=100


Host B

Seq=92 8 bytes data

ACK=120

Seq=92 8 bytes data

Seq=

92 t

imeo

ut

ACK=120

Host A

Seq=92 8 bytes data

ACK=100

loss

tim

eout

lost ACK scenario

Host B

X

Seq=92 8 bytes data

ACK=100

time

Seq=

92 t

imeo

utSendBase

= 100

SendBase= 120

SendBase= 120

Sendbase= 100



Seq=92 8 bytes data

ACK=100

loss

tim

eout


Host B

X


ACK=120

time

SendBase= 120



Event at Receiver





TCP Receiver action






Fast Retransmit









Host A

tim

eout

Host B

time

X

resend seq X2


ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer





fast retransmit


TCP Flow Control






flow control




= RcvWin






3K

2K SeqNo=0

ReceiverBuffer


2K


4K

AckNo=4096 RcvWin=0


Sender blocked





a top-10 problem







Host B

λout






Host B

λout





λin

λout=

λin

λoutgtλ

inλout


R2

R2λin

λ out

b

R2

R2λin

λ out

a

R2

R2λin

λ out

c

R4

R3



λin


in



Host B

λout





Host A

Host B

λou

t










le CongWin









X

X

XX


send

ing

rate

time







roughly




cwndbytes

RTT

ACK(s)

















Host A

one segment

RTT

Host B

time

two segments

four segments





segment 1

ACK for segment 1

cwnd = 1


ACK for segments 2


ACK for segments 4

cwnd = 7

ACK for segments 3

ACK for segments 5

ACK for segments 6

cwnd = 3

cwnd = 5


cwnd = 8

segment 7






AIMD










ssthresh = 8

cwnd = 1

cwnd = 2

cwnd = 4

cwnd = 8

cwnd = 9

cwnd = 10

02468

101214

t=0

t=2

t=4

t=6

Roundtrip times

Cw

nd(in

seg

men

ts)

ssthresh

cwnd = 3





SS

CA

ssthresh













Philosophy

3-90











ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







Slow Start (SS)












Enter slow start

Duplicate ACK




TCP throughput








LRTTMSSsdot221



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness




R

R



Conn

ecti

on 2

thr

ough

p ut
















number)













client

FIN

server

ACK

ACK

FIN

close

close

closed

tim

ed w

ait






client

FIN

server

ACK

ACK

FIN

closing

closing

closed

tim

ed w

ait

closed



TCP clientlifecycle

TCP serverlifecycle






























UDP more

UDP checksum












rdt21 discussion




rdt30 sender

rdt30 in action

rdt30 in action



Pipelined protocols


Go-Back-N



GBN inaction

Selective Repeat


Selective repeat

















TCP sender events





Fast Retransmit

Fast Retransmit


TCP Flow Control















Slow Start Example











TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)

















sender

receiver

Go-Back-N

expectedSN

snd_base=expectedSN



senderrsquos window



sender

receiver

Go-Back-N

expectedSN




senderrsquos window



sender

receiver

Go-Back-N

expectedSN






sender

receiver

Selective Repeat

rcv_base

snd_base=rcv_base



senderrsquos window


rcv_base+N-1



sender

receiver

Selective Repeat

rcv_base

snd_base=rcv_base-N



senderrsquos window

rcv_base


rcv_base+N-1



sender

receiver

Selective Repeat

snd_base=rcv_base-N



rcv_basercv_base


rcv_base+N-1











socketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment






32 bits

applicationdata

(variable length)



FSRPAUheadlen

notused



ACK ACK valid



commands)


Internetchecksum

(as in UDP)






















100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

iseco

nds)

































start timer

end of loop forever





ACK=100


Host B

Seq=92 8 bytes data

ACK=120

Seq=92 8 bytes data

Seq=

92 t

imeo

ut

ACK=120

Host A

Seq=92 8 bytes data

ACK=100

loss

tim

eout

lost ACK scenario

Host B

X

Seq=92 8 bytes data

ACK=100

time

Seq=

92 t

imeo

utSendBase

= 100

SendBase= 120

SendBase= 120

Sendbase= 100



Seq=92 8 bytes data

ACK=100

loss

tim

eout


Host B

X


ACK=120

time

SendBase= 120



Event at Receiver





TCP Receiver action






Fast Retransmit









Host A

tim

eout

Host B

time

X

resend seq X2


ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer





fast retransmit


TCP Flow Control






flow control




= RcvWin






3K

2K SeqNo=0

ReceiverBuffer


2K


4K

AckNo=4096 RcvWin=0


Sender blocked





a top-10 problem







Host B

λout






Host B

λout





λin

λout=

λin

λoutgtλ

inλout


R2

R2λin

λ out

b

R2

R2λin

λ out

a

R2

R2λin

λ out

c

R4

R3



λin


in



Host B

λout





Host A

Host B

λou

t










le CongWin









X

X

XX


send

ing

rate

time







roughly




cwndbytes

RTT

ACK(s)

















Host A

one segment

RTT

Host B

time

two segments

four segments





segment 1

ACK for segment 1

cwnd = 1


ACK for segments 2


ACK for segments 4

cwnd = 7

ACK for segments 3

ACK for segments 5

ACK for segments 6

cwnd = 3

cwnd = 5


cwnd = 8

segment 7






AIMD










ssthresh = 8

cwnd = 1

cwnd = 2

cwnd = 4

cwnd = 8

cwnd = 9

cwnd = 10

02468

101214

t=0

t=2

t=4

t=6

Roundtrip times

Cw

nd(in

seg

men

ts)

ssthresh

cwnd = 3





SS

CA

ssthresh













Philosophy

3-90











ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







Slow Start (SS)












Enter slow start

Duplicate ACK




TCP throughput








LRTTMSSsdot221



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness




R

R



Conn

ecti

on 2

thr

ough

p ut
















number)













client

FIN

server

ACK

ACK

FIN

close

close

closed

tim

ed w

ait






client

FIN

server

ACK

ACK

FIN

closing

closing

closed

tim

ed w

ait

closed



TCP clientlifecycle

TCP serverlifecycle






























UDP more

UDP checksum












rdt21 discussion




rdt30 sender

rdt30 in action

rdt30 in action



Pipelined protocols


Go-Back-N



GBN inaction

Selective Repeat


Selective repeat

















TCP sender events





Fast Retransmit

Fast Retransmit


TCP Flow Control















Slow Start Example











TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)










sender

receiver

Go-Back-N

expectedSN




senderrsquos window



sender

receiver

Go-Back-N

expectedSN






sender

receiver

Selective Repeat

rcv_base

snd_base=rcv_base



senderrsquos window


rcv_base+N-1



sender

receiver

Selective Repeat

rcv_base

snd_base=rcv_base-N



senderrsquos window

rcv_base


rcv_base+N-1



sender

receiver

Selective Repeat

snd_base=rcv_base-N



rcv_basercv_base


rcv_base+N-1











socketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment






32 bits

applicationdata

(variable length)



FSRPAUheadlen

notused



ACK ACK valid



commands)


Internetchecksum

(as in UDP)






















100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

iseco

nds)

































start timer

end of loop forever





ACK=100


Host B

Seq=92 8 bytes data

ACK=120

Seq=92 8 bytes data

Seq=

92 t

imeo

ut

ACK=120

Host A

Seq=92 8 bytes data

ACK=100

loss

tim

eout

lost ACK scenario

Host B

X

Seq=92 8 bytes data

ACK=100

time

Seq=

92 t

imeo

utSendBase

= 100

SendBase= 120

SendBase= 120

Sendbase= 100



Seq=92 8 bytes data

ACK=100

loss

tim

eout


Host B

X


ACK=120

time

SendBase= 120



Event at Receiver





TCP Receiver action






Fast Retransmit









Host A

tim

eout

Host B

time

X

resend seq X2


ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer





fast retransmit


TCP Flow Control






flow control




= RcvWin






3K

2K SeqNo=0

ReceiverBuffer


2K


4K

AckNo=4096 RcvWin=0


Sender blocked





a top-10 problem







Host B

λout






Host B

λout





λin

λout=

λin

λoutgtλ

inλout


R2

R2λin

λ out

b

R2

R2λin

λ out

a

R2

R2λin

λ out

c

R4

R3



λin


in



Host B

λout





Host A

Host B

λou

t










le CongWin









X

X

XX


send

ing

rate

time







roughly




cwndbytes

RTT

ACK(s)

















Host A

one segment

RTT

Host B

time

two segments

four segments





segment 1

ACK for segment 1

cwnd = 1


ACK for segments 2


ACK for segments 4

cwnd = 7

ACK for segments 3

ACK for segments 5

ACK for segments 6

cwnd = 3

cwnd = 5


cwnd = 8

segment 7






AIMD










ssthresh = 8

cwnd = 1

cwnd = 2

cwnd = 4

cwnd = 8

cwnd = 9

cwnd = 10

02468

101214

t=0

t=2

t=4

t=6

Roundtrip times

Cw

nd(in

seg

men

ts)

ssthresh

cwnd = 3





SS

CA

ssthresh













Philosophy

3-90











ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







Slow Start (SS)












Enter slow start

Duplicate ACK




TCP throughput








LRTTMSSsdot221



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness




R

R



Conn

ecti

on 2

thr

ough

p ut
















number)













client

FIN

server

ACK

ACK

FIN

close

close

closed

tim

ed w

ait






client

FIN

server

ACK

ACK

FIN

closing

closing

closed

tim

ed w

ait

closed



TCP clientlifecycle

TCP serverlifecycle






























UDP more

UDP checksum












rdt21 discussion




rdt30 sender

rdt30 in action

rdt30 in action



Pipelined protocols


Go-Back-N



GBN inaction

Selective Repeat


Selective repeat

















TCP sender events





Fast Retransmit

Fast Retransmit


TCP Flow Control















Slow Start Example











TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)










sender

receiver

Go-Back-N

expectedSN






sender

receiver

Selective Repeat

rcv_base

snd_base=rcv_base



senderrsquos window


rcv_base+N-1



sender

receiver

Selective Repeat

rcv_base

snd_base=rcv_base-N



senderrsquos window

rcv_base


rcv_base+N-1



sender

receiver

Selective Repeat

snd_base=rcv_base-N



rcv_basercv_base


rcv_base+N-1











socketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment






32 bits

applicationdata

(variable length)



FSRPAUheadlen

notused



ACK ACK valid



commands)


Internetchecksum

(as in UDP)






















100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

iseco

nds)

































start timer

end of loop forever





ACK=100


Host B

Seq=92 8 bytes data

ACK=120

Seq=92 8 bytes data

Seq=

92 t

imeo

ut

ACK=120

Host A

Seq=92 8 bytes data

ACK=100

loss

tim

eout

lost ACK scenario

Host B

X

Seq=92 8 bytes data

ACK=100

time

Seq=

92 t

imeo

utSendBase

= 100

SendBase= 120

SendBase= 120

Sendbase= 100



Seq=92 8 bytes data

ACK=100

loss

tim

eout


Host B

X


ACK=120

time

SendBase= 120



Event at Receiver





TCP Receiver action






Fast Retransmit









Host A

tim

eout

Host B

time

X

resend seq X2


ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer





fast retransmit


TCP Flow Control






flow control




= RcvWin






3K

2K SeqNo=0

ReceiverBuffer


2K


4K

AckNo=4096 RcvWin=0


Sender blocked





a top-10 problem







Host B

λout






Host B

λout





λin

λout=

λin

λoutgtλ

inλout


R2

R2λin

λ out

b

R2

R2λin

λ out

a

R2

R2λin

λ out

c

R4

R3



λin


in



Host B

λout





Host A

Host B

λou

t










le CongWin









X

X

XX


send

ing

rate

time







roughly




cwndbytes

RTT

ACK(s)

















Host A

one segment

RTT

Host B

time

two segments

four segments





segment 1

ACK for segment 1

cwnd = 1


ACK for segments 2


ACK for segments 4

cwnd = 7

ACK for segments 3

ACK for segments 5

ACK for segments 6

cwnd = 3

cwnd = 5


cwnd = 8

segment 7






AIMD










ssthresh = 8

cwnd = 1

cwnd = 2

cwnd = 4

cwnd = 8

cwnd = 9

cwnd = 10

02468

101214

t=0

t=2

t=4

t=6

Roundtrip times

Cw

nd(in

seg

men

ts)

ssthresh

cwnd = 3





SS

CA

ssthresh













Philosophy

3-90











ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







Slow Start (SS)












Enter slow start

Duplicate ACK




TCP throughput








LRTTMSSsdot221



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness




R

R



Conn

ecti

on 2

thr

ough

p ut
















number)













client

FIN

server

ACK

ACK

FIN

close

close

closed

tim

ed w

ait






client

FIN

server

ACK

ACK

FIN

closing

closing

closed

tim

ed w

ait

closed



TCP clientlifecycle

TCP serverlifecycle






























UDP more

UDP checksum












rdt21 discussion




rdt30 sender

rdt30 in action

rdt30 in action



Pipelined protocols


Go-Back-N



GBN inaction

Selective Repeat


Selective repeat

















TCP sender events





Fast Retransmit

Fast Retransmit


TCP Flow Control















Slow Start Example











TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)










sender

receiver

Selective Repeat

rcv_base

snd_base=rcv_base



senderrsquos window


rcv_base+N-1



sender

receiver

Selective Repeat

rcv_base

snd_base=rcv_base-N



senderrsquos window

rcv_base


rcv_base+N-1



sender

receiver

Selective Repeat

snd_base=rcv_base-N



rcv_basercv_base


rcv_base+N-1











socketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment






32 bits

applicationdata

(variable length)



FSRPAUheadlen

notused



ACK ACK valid



commands)


Internetchecksum

(as in UDP)






















100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

iseco

nds)

































start timer

end of loop forever





ACK=100


Host B

Seq=92 8 bytes data

ACK=120

Seq=92 8 bytes data

Seq=

92 t

imeo

ut

ACK=120

Host A

Seq=92 8 bytes data

ACK=100

loss

tim

eout

lost ACK scenario

Host B

X

Seq=92 8 bytes data

ACK=100

time

Seq=

92 t

imeo

utSendBase

= 100

SendBase= 120

SendBase= 120

Sendbase= 100



Seq=92 8 bytes data

ACK=100

loss

tim

eout


Host B

X


ACK=120

time

SendBase= 120



Event at Receiver





TCP Receiver action






Fast Retransmit









Host A

tim

eout

Host B

time

X

resend seq X2


ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer





fast retransmit


TCP Flow Control






flow control




= RcvWin






3K

2K SeqNo=0

ReceiverBuffer


2K


4K

AckNo=4096 RcvWin=0


Sender blocked





a top-10 problem







Host B

λout






Host B

λout





λin

λout=

λin

λoutgtλ

inλout


R2

R2λin

λ out

b

R2

R2λin

λ out

a

R2

R2λin

λ out

c

R4

R3



λin


in



Host B

λout





Host A

Host B

λou

t










le CongWin









X

X

XX


send

ing

rate

time







roughly




cwndbytes

RTT

ACK(s)

















Host A

one segment

RTT

Host B

time

two segments

four segments





segment 1

ACK for segment 1

cwnd = 1


ACK for segments 2


ACK for segments 4

cwnd = 7

ACK for segments 3

ACK for segments 5

ACK for segments 6

cwnd = 3

cwnd = 5


cwnd = 8

segment 7






AIMD










ssthresh = 8

cwnd = 1

cwnd = 2

cwnd = 4

cwnd = 8

cwnd = 9

cwnd = 10

02468

101214

t=0

t=2

t=4

t=6

Roundtrip times

Cw

nd(in

seg

men

ts)

ssthresh

cwnd = 3





SS

CA

ssthresh













Philosophy

3-90











ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







Slow Start (SS)












Enter slow start

Duplicate ACK




TCP throughput








LRTTMSSsdot221



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness




R

R



Conn

ecti

on 2

thr

ough

p ut
















number)













client

FIN

server

ACK

ACK

FIN

close

close

closed

tim

ed w

ait






client

FIN

server

ACK

ACK

FIN

closing

closing

closed

tim

ed w

ait

closed



TCP clientlifecycle

TCP serverlifecycle






























UDP more

UDP checksum












rdt21 discussion




rdt30 sender

rdt30 in action

rdt30 in action



Pipelined protocols


Go-Back-N



GBN inaction

Selective Repeat


Selective repeat

















TCP sender events





Fast Retransmit

Fast Retransmit


TCP Flow Control















Slow Start Example











TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)










sender

receiver

Selective Repeat

rcv_base

snd_base=rcv_base-N



senderrsquos window

rcv_base


rcv_base+N-1



sender

receiver

Selective Repeat

snd_base=rcv_base-N



rcv_basercv_base


rcv_base+N-1











socketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment






32 bits

applicationdata

(variable length)



FSRPAUheadlen

notused



ACK ACK valid



commands)


Internetchecksum

(as in UDP)






















100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

iseco

nds)

































start timer

end of loop forever





ACK=100


Host B

Seq=92 8 bytes data

ACK=120

Seq=92 8 bytes data

Seq=

92 t

imeo

ut

ACK=120

Host A

Seq=92 8 bytes data

ACK=100

loss

tim

eout

lost ACK scenario

Host B

X

Seq=92 8 bytes data

ACK=100

time

Seq=

92 t

imeo

utSendBase

= 100

SendBase= 120

SendBase= 120

Sendbase= 100



Seq=92 8 bytes data

ACK=100

loss

tim

eout


Host B

X


ACK=120

time

SendBase= 120



Event at Receiver





TCP Receiver action






Fast Retransmit









Host A

tim

eout

Host B

time

X

resend seq X2


ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer





fast retransmit


TCP Flow Control






flow control




= RcvWin






3K

2K SeqNo=0

ReceiverBuffer


2K


4K

AckNo=4096 RcvWin=0


Sender blocked





a top-10 problem







Host B

λout






Host B

λout





λin

λout=

λin

λoutgtλ

inλout


R2

R2λin

λ out

b

R2

R2λin

λ out

a

R2

R2λin

λ out

c

R4

R3



λin


in



Host B

λout





Host A

Host B

λou

t










le CongWin









X

X

XX


send

ing

rate

time







roughly




cwndbytes

RTT

ACK(s)

















Host A

one segment

RTT

Host B

time

two segments

four segments





segment 1

ACK for segment 1

cwnd = 1


ACK for segments 2


ACK for segments 4

cwnd = 7

ACK for segments 3

ACK for segments 5

ACK for segments 6

cwnd = 3

cwnd = 5


cwnd = 8

segment 7






AIMD










ssthresh = 8

cwnd = 1

cwnd = 2

cwnd = 4

cwnd = 8

cwnd = 9

cwnd = 10

02468

101214

t=0

t=2

t=4

t=6

Roundtrip times

Cw

nd(in

seg

men

ts)

ssthresh

cwnd = 3





SS

CA

ssthresh













Philosophy

3-90











ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







Slow Start (SS)












Enter slow start

Duplicate ACK




TCP throughput








LRTTMSSsdot221



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness




R

R



Conn

ecti

on 2

thr

ough

p ut
















number)













client

FIN

server

ACK

ACK

FIN

close

close

closed

tim

ed w

ait






client

FIN

server

ACK

ACK

FIN

closing

closing

closed

tim

ed w

ait

closed



TCP clientlifecycle

TCP serverlifecycle






























UDP more

UDP checksum












rdt21 discussion




rdt30 sender

rdt30 in action

rdt30 in action



Pipelined protocols


Go-Back-N



GBN inaction

Selective Repeat


Selective repeat

















TCP sender events





Fast Retransmit

Fast Retransmit


TCP Flow Control















Slow Start Example











TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)










sender

receiver

Selective Repeat

snd_base=rcv_base-N



rcv_basercv_base


rcv_base+N-1











socketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment






32 bits

applicationdata

(variable length)



FSRPAUheadlen

notused



ACK ACK valid



commands)


Internetchecksum

(as in UDP)






















100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

iseco

nds)

































start timer

end of loop forever





ACK=100


Host B

Seq=92 8 bytes data

ACK=120

Seq=92 8 bytes data

Seq=

92 t

imeo

ut

ACK=120

Host A

Seq=92 8 bytes data

ACK=100

loss

tim

eout

lost ACK scenario

Host B

X

Seq=92 8 bytes data

ACK=100

time

Seq=

92 t

imeo

utSendBase

= 100

SendBase= 120

SendBase= 120

Sendbase= 100



Seq=92 8 bytes data

ACK=100

loss

tim

eout


Host B

X


ACK=120

time

SendBase= 120



Event at Receiver





TCP Receiver action






Fast Retransmit









Host A

tim

eout

Host B

time

X

resend seq X2


ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer





fast retransmit


TCP Flow Control






flow control




= RcvWin






3K

2K SeqNo=0

ReceiverBuffer


2K


4K

AckNo=4096 RcvWin=0


Sender blocked





a top-10 problem







Host B

λout






Host B

λout





λin

λout=

λin

λoutgtλ

inλout


R2

R2λin

λ out

b

R2

R2λin

λ out

a

R2

R2λin

λ out

c

R4

R3



λin


in



Host B

λout





Host A

Host B

λou

t










le CongWin









X

X

XX


send

ing

rate

time







roughly




cwndbytes

RTT

ACK(s)

















Host A

one segment

RTT

Host B

time

two segments

four segments





segment 1

ACK for segment 1

cwnd = 1


ACK for segments 2


ACK for segments 4

cwnd = 7

ACK for segments 3

ACK for segments 5

ACK for segments 6

cwnd = 3

cwnd = 5


cwnd = 8

segment 7






AIMD










ssthresh = 8

cwnd = 1

cwnd = 2

cwnd = 4

cwnd = 8

cwnd = 9

cwnd = 10

02468

101214

t=0

t=2

t=4

t=6

Roundtrip times

Cw

nd(in

seg

men

ts)

ssthresh

cwnd = 3





SS

CA

ssthresh













Philosophy

3-90











ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







Slow Start (SS)












Enter slow start

Duplicate ACK




TCP throughput








LRTTMSSsdot221



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness




R

R



Conn

ecti

on 2

thr

ough

p ut
















number)













client

FIN

server

ACK

ACK

FIN

close

close

closed

tim

ed w

ait






client

FIN

server

ACK

ACK

FIN

closing

closing

closed

tim

ed w

ait

closed



TCP clientlifecycle

TCP serverlifecycle






























UDP more

UDP checksum












rdt21 discussion




rdt30 sender

rdt30 in action

rdt30 in action



Pipelined protocols


Go-Back-N



GBN inaction

Selective Repeat


Selective repeat

















TCP sender events





Fast Retransmit

Fast Retransmit


TCP Flow Control















Slow Start Example











TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)


















socketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment






32 bits

applicationdata

(variable length)



FSRPAUheadlen

notused



ACK ACK valid



commands)


Internetchecksum

(as in UDP)






















100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

iseco

nds)

































start timer

end of loop forever





ACK=100


Host B

Seq=92 8 bytes data

ACK=120

Seq=92 8 bytes data

Seq=

92 t

imeo

ut

ACK=120

Host A

Seq=92 8 bytes data

ACK=100

loss

tim

eout

lost ACK scenario

Host B

X

Seq=92 8 bytes data

ACK=100

time

Seq=

92 t

imeo

utSendBase

= 100

SendBase= 120

SendBase= 120

Sendbase= 100



Seq=92 8 bytes data

ACK=100

loss

tim

eout


Host B

X


ACK=120

time

SendBase= 120



Event at Receiver





TCP Receiver action






Fast Retransmit









Host A

tim

eout

Host B

time

X

resend seq X2


ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer





fast retransmit


TCP Flow Control






flow control




= RcvWin






3K

2K SeqNo=0

ReceiverBuffer


2K


4K

AckNo=4096 RcvWin=0


Sender blocked





a top-10 problem







Host B

λout






Host B

λout





λin

λout=

λin

λoutgtλ

inλout


R2

R2λin

λ out

b

R2

R2λin

λ out

a

R2

R2λin

λ out

c

R4

R3



λin


in



Host B

λout





Host A

Host B

λou

t










le CongWin









X

X

XX


send

ing

rate

time







roughly




cwndbytes

RTT

ACK(s)

















Host A

one segment

RTT

Host B

time

two segments

four segments





segment 1

ACK for segment 1

cwnd = 1


ACK for segments 2


ACK for segments 4

cwnd = 7

ACK for segments 3

ACK for segments 5

ACK for segments 6

cwnd = 3

cwnd = 5


cwnd = 8

segment 7






AIMD










ssthresh = 8

cwnd = 1

cwnd = 2

cwnd = 4

cwnd = 8

cwnd = 9

cwnd = 10

02468

101214

t=0

t=2

t=4

t=6

Roundtrip times

Cw

nd(in

seg

men

ts)

ssthresh

cwnd = 3





SS

CA

ssthresh













Philosophy

3-90











ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







Slow Start (SS)












Enter slow start

Duplicate ACK




TCP throughput








LRTTMSSsdot221



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness




R

R



Conn

ecti

on 2

thr

ough

p ut
















number)













client

FIN

server

ACK

ACK

FIN

close

close

closed

tim

ed w

ait






client

FIN

server

ACK

ACK

FIN

closing

closing

closed

tim

ed w

ait

closed



TCP clientlifecycle

TCP serverlifecycle






























UDP more

UDP checksum












rdt21 discussion




rdt30 sender

rdt30 in action

rdt30 in action



Pipelined protocols


Go-Back-N



GBN inaction

Selective Repeat


Selective repeat

















TCP sender events





Fast Retransmit

Fast Retransmit


TCP Flow Control















Slow Start Example











TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)











32 bits

applicationdata

(variable length)



FSRPAUheadlen

notused



ACK ACK valid



commands)


Internetchecksum

(as in UDP)






















100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

iseco

nds)

































start timer

end of loop forever





ACK=100


Host B

Seq=92 8 bytes data

ACK=120

Seq=92 8 bytes data

Seq=

92 t

imeo

ut

ACK=120

Host A

Seq=92 8 bytes data

ACK=100

loss

tim

eout

lost ACK scenario

Host B

X

Seq=92 8 bytes data

ACK=100

time

Seq=

92 t

imeo

utSendBase

= 100

SendBase= 120

SendBase= 120

Sendbase= 100



Seq=92 8 bytes data

ACK=100

loss

tim

eout


Host B

X


ACK=120

time

SendBase= 120



Event at Receiver





TCP Receiver action






Fast Retransmit









Host A

tim

eout

Host B

time

X

resend seq X2


ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer





fast retransmit


TCP Flow Control






flow control




= RcvWin






3K

2K SeqNo=0

ReceiverBuffer


2K


4K

AckNo=4096 RcvWin=0


Sender blocked





a top-10 problem







Host B

λout






Host B

λout





λin

λout=

λin

λoutgtλ

inλout


R2

R2λin

λ out

b

R2

R2λin

λ out

a

R2

R2λin

λ out

c

R4

R3



λin


in



Host B

λout





Host A

Host B

λou

t










le CongWin









X

X

XX


send

ing

rate

time







roughly




cwndbytes

RTT

ACK(s)

















Host A

one segment

RTT

Host B

time

two segments

four segments





segment 1

ACK for segment 1

cwnd = 1


ACK for segments 2


ACK for segments 4

cwnd = 7

ACK for segments 3

ACK for segments 5

ACK for segments 6

cwnd = 3

cwnd = 5


cwnd = 8

segment 7






AIMD










ssthresh = 8

cwnd = 1

cwnd = 2

cwnd = 4

cwnd = 8

cwnd = 9

cwnd = 10

02468

101214

t=0

t=2

t=4

t=6

Roundtrip times

Cw

nd(in

seg

men

ts)

ssthresh

cwnd = 3





SS

CA

ssthresh













Philosophy

3-90











ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







Slow Start (SS)












Enter slow start

Duplicate ACK




TCP throughput








LRTTMSSsdot221



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness




R

R



Conn

ecti

on 2

thr

ough

p ut
















number)













client

FIN

server

ACK

ACK

FIN

close

close

closed

tim

ed w

ait






client

FIN

server

ACK

ACK

FIN

closing

closing

closed

tim

ed w

ait

closed



TCP clientlifecycle

TCP serverlifecycle






























UDP more

UDP checksum












rdt21 discussion




rdt30 sender

rdt30 in action

rdt30 in action



Pipelined protocols


Go-Back-N



GBN inaction

Selective Repeat


Selective repeat

















TCP sender events





Fast Retransmit

Fast Retransmit


TCP Flow Control















Slow Start Example











TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)




























100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

RTT

(mill

iseco

nds)

































start timer

end of loop forever





ACK=100


Host B

Seq=92 8 bytes data

ACK=120

Seq=92 8 bytes data

Seq=

92 t

imeo

ut

ACK=120

Host A

Seq=92 8 bytes data

ACK=100

loss

tim

eout

lost ACK scenario

Host B

X

Seq=92 8 bytes data

ACK=100

time

Seq=

92 t

imeo

utSendBase

= 100

SendBase= 120

SendBase= 120

Sendbase= 100



Seq=92 8 bytes data

ACK=100

loss

tim

eout


Host B

X


ACK=120

time

SendBase= 120



Event at Receiver





TCP Receiver action






Fast Retransmit









Host A

tim

eout

Host B

time

X

resend seq X2


ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer





fast retransmit


TCP Flow Control






flow control




= RcvWin






3K

2K SeqNo=0

ReceiverBuffer


2K


4K

AckNo=4096 RcvWin=0


Sender blocked





a top-10 problem







Host B

λout






Host B

λout





λin

λout=

λin

λoutgtλ

inλout


R2

R2λin

λ out

b

R2

R2λin

λ out

a

R2

R2λin

λ out

c

R4

R3



λin


in



Host B

λout





Host A

Host B

λou

t










le CongWin









X

X

XX


send

ing

rate

time







roughly




cwndbytes

RTT

ACK(s)

















Host A

one segment

RTT

Host B

time

two segments

four segments





segment 1

ACK for segment 1

cwnd = 1


ACK for segments 2


ACK for segments 4

cwnd = 7

ACK for segments 3

ACK for segments 5

ACK for segments 6

cwnd = 3

cwnd = 5


cwnd = 8

segment 7






AIMD










ssthresh = 8

cwnd = 1

cwnd = 2

cwnd = 4

cwnd = 8

cwnd = 9

cwnd = 10

02468

101214

t=0

t=2

t=4

t=6

Roundtrip times

Cw

nd(in

seg

men

ts)

ssthresh

cwnd = 3





SS

CA

ssthresh













Philosophy

3-90











ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







Slow Start (SS)












Enter slow start

Duplicate ACK




TCP throughput








LRTTMSSsdot221



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness




R

R



Conn

ecti

on 2

thr

ough

p ut
















number)













client

FIN

server

ACK

ACK

FIN

close

close

closed

tim

ed w

ait






client

FIN

server

ACK

ACK

FIN

closing

closing

closed

tim

ed w

ait

closed



TCP clientlifecycle

TCP serverlifecycle






























UDP more

UDP checksum












rdt21 discussion




rdt30 sender

rdt30 in action

rdt30 in action



Pipelined protocols


Go-Back-N



GBN inaction

Selective Repeat


Selective repeat

















TCP sender events





Fast Retransmit

Fast Retransmit


TCP Flow Control















Slow Start Example











TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)







































start timer

end of loop forever





ACK=100


Host B

Seq=92 8 bytes data

ACK=120

Seq=92 8 bytes data

Seq=

92 t

imeo

ut

ACK=120

Host A

Seq=92 8 bytes data

ACK=100

loss

tim

eout

lost ACK scenario

Host B

X

Seq=92 8 bytes data

ACK=100

time

Seq=

92 t

imeo

utSendBase

= 100

SendBase= 120

SendBase= 120

Sendbase= 100



Seq=92 8 bytes data

ACK=100

loss

tim

eout


Host B

X


ACK=120

time

SendBase= 120



Event at Receiver





TCP Receiver action






Fast Retransmit









Host A

tim

eout

Host B

time

X

resend seq X2


ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer





fast retransmit


TCP Flow Control






flow control




= RcvWin






3K

2K SeqNo=0

ReceiverBuffer


2K


4K

AckNo=4096 RcvWin=0


Sender blocked





a top-10 problem







Host B

λout






Host B

λout





λin

λout=

λin

λoutgtλ

inλout


R2

R2λin

λ out

b

R2

R2λin

λ out

a

R2

R2λin

λ out

c

R4

R3



λin


in



Host B

λout





Host A

Host B

λou

t










le CongWin









X

X

XX


send

ing

rate

time







roughly




cwndbytes

RTT

ACK(s)

















Host A

one segment

RTT

Host B

time

two segments

four segments





segment 1

ACK for segment 1

cwnd = 1


ACK for segments 2


ACK for segments 4

cwnd = 7

ACK for segments 3

ACK for segments 5

ACK for segments 6

cwnd = 3

cwnd = 5


cwnd = 8

segment 7






AIMD










ssthresh = 8

cwnd = 1

cwnd = 2

cwnd = 4

cwnd = 8

cwnd = 9

cwnd = 10

02468

101214

t=0

t=2

t=4

t=6

Roundtrip times

Cw

nd(in

seg

men

ts)

ssthresh

cwnd = 3





SS

CA

ssthresh













Philosophy

3-90











ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







Slow Start (SS)












Enter slow start

Duplicate ACK




TCP throughput








LRTTMSSsdot221



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness




R

R



Conn

ecti

on 2

thr

ough

p ut
















number)













client

FIN

server

ACK

ACK

FIN

close

close

closed

tim

ed w

ait






client

FIN

server

ACK

ACK

FIN

closing

closing

closed

tim

ed w

ait

closed



TCP clientlifecycle

TCP serverlifecycle






























UDP more

UDP checksum












rdt21 discussion




rdt30 sender

rdt30 in action

rdt30 in action



Pipelined protocols


Go-Back-N



GBN inaction

Selective Repeat


Selective repeat

















TCP sender events





Fast Retransmit

Fast Retransmit


TCP Flow Control















Slow Start Example











TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)











ACK=100


Host B

Seq=92 8 bytes data

ACK=120

Seq=92 8 bytes data

Seq=

92 t

imeo

ut

ACK=120

Host A

Seq=92 8 bytes data

ACK=100

loss

tim

eout

lost ACK scenario

Host B

X

Seq=92 8 bytes data

ACK=100

time

Seq=

92 t

imeo

utSendBase

= 100

SendBase= 120

SendBase= 120

Sendbase= 100



Seq=92 8 bytes data

ACK=100

loss

tim

eout


Host B

X


ACK=120

time

SendBase= 120



Event at Receiver





TCP Receiver action






Fast Retransmit









Host A

tim

eout

Host B

time

X

resend seq X2


ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer





fast retransmit


TCP Flow Control






flow control




= RcvWin






3K

2K SeqNo=0

ReceiverBuffer


2K


4K

AckNo=4096 RcvWin=0


Sender blocked





a top-10 problem







Host B

λout






Host B

λout





λin

λout=

λin

λoutgtλ

inλout


R2

R2λin

λ out

b

R2

R2λin

λ out

a

R2

R2λin

λ out

c

R4

R3



λin


in



Host B

λout





Host A

Host B

λou

t










le CongWin









X

X

XX


send

ing

rate

time







roughly




cwndbytes

RTT

ACK(s)

















Host A

one segment

RTT

Host B

time

two segments

four segments





segment 1

ACK for segment 1

cwnd = 1


ACK for segments 2


ACK for segments 4

cwnd = 7

ACK for segments 3

ACK for segments 5

ACK for segments 6

cwnd = 3

cwnd = 5


cwnd = 8

segment 7






AIMD










ssthresh = 8

cwnd = 1

cwnd = 2

cwnd = 4

cwnd = 8

cwnd = 9

cwnd = 10

02468

101214

t=0

t=2

t=4

t=6

Roundtrip times

Cw

nd(in

seg

men

ts)

ssthresh

cwnd = 3





SS

CA

ssthresh













Philosophy

3-90











ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







Slow Start (SS)












Enter slow start

Duplicate ACK




TCP throughput








LRTTMSSsdot221



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness




R

R



Conn

ecti

on 2

thr

ough

p ut
















number)













client

FIN

server

ACK

ACK

FIN

close

close

closed

tim

ed w

ait






client

FIN

server

ACK

ACK

FIN

closing

closing

closed

tim

ed w

ait

closed



TCP clientlifecycle

TCP serverlifecycle






























UDP more

UDP checksum












rdt21 discussion




rdt30 sender

rdt30 in action

rdt30 in action



Pipelined protocols


Go-Back-N



GBN inaction

Selective Repeat


Selective repeat

















TCP sender events





Fast Retransmit

Fast Retransmit


TCP Flow Control















Slow Start Example











TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)










Seq=92 8 bytes data

ACK=100

loss

tim

eout


Host B

X


ACK=120

time

SendBase= 120



Event at Receiver





TCP Receiver action






Fast Retransmit









Host A

tim

eout

Host B

time

X

resend seq X2


ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer





fast retransmit


TCP Flow Control






flow control




= RcvWin






3K

2K SeqNo=0

ReceiverBuffer


2K


4K

AckNo=4096 RcvWin=0


Sender blocked





a top-10 problem







Host B

λout






Host B

λout





λin

λout=

λin

λoutgtλ

inλout


R2

R2λin

λ out

b

R2

R2λin

λ out

a

R2

R2λin

λ out

c

R4

R3



λin


in



Host B

λout





Host A

Host B

λou

t










le CongWin









X

X

XX


send

ing

rate

time







roughly




cwndbytes

RTT

ACK(s)

















Host A

one segment

RTT

Host B

time

two segments

four segments





segment 1

ACK for segment 1

cwnd = 1


ACK for segments 2


ACK for segments 4

cwnd = 7

ACK for segments 3

ACK for segments 5

ACK for segments 6

cwnd = 3

cwnd = 5


cwnd = 8

segment 7






AIMD










ssthresh = 8

cwnd = 1

cwnd = 2

cwnd = 4

cwnd = 8

cwnd = 9

cwnd = 10

02468

101214

t=0

t=2

t=4

t=6

Roundtrip times

Cw

nd(in

seg

men

ts)

ssthresh

cwnd = 3





SS

CA

ssthresh













Philosophy

3-90











ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







Slow Start (SS)












Enter slow start

Duplicate ACK




TCP throughput








LRTTMSSsdot221



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness




R

R



Conn

ecti

on 2

thr

ough

p ut
















number)













client

FIN

server

ACK

ACK

FIN

close

close

closed

tim

ed w

ait






client

FIN

server

ACK

ACK

FIN

closing

closing

closed

tim

ed w

ait

closed



TCP clientlifecycle

TCP serverlifecycle






























UDP more

UDP checksum












rdt21 discussion




rdt30 sender

rdt30 in action

rdt30 in action



Pipelined protocols


Go-Back-N



GBN inaction

Selective Repeat


Selective repeat

















TCP sender events





Fast Retransmit

Fast Retransmit


TCP Flow Control















Slow Start Example











TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)










Event at Receiver





TCP Receiver action






Fast Retransmit









Host A

tim

eout

Host B

time

X

resend seq X2


ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer





fast retransmit


TCP Flow Control






flow control




= RcvWin






3K

2K SeqNo=0

ReceiverBuffer


2K


4K

AckNo=4096 RcvWin=0


Sender blocked





a top-10 problem







Host B

λout






Host B

λout





λin

λout=

λin

λoutgtλ

inλout


R2

R2λin

λ out

b

R2

R2λin

λ out

a

R2

R2λin

λ out

c

R4

R3



λin


in



Host B

λout





Host A

Host B

λou

t










le CongWin









X

X

XX


send

ing

rate

time







roughly




cwndbytes

RTT

ACK(s)

















Host A

one segment

RTT

Host B

time

two segments

four segments





segment 1

ACK for segment 1

cwnd = 1


ACK for segments 2


ACK for segments 4

cwnd = 7

ACK for segments 3

ACK for segments 5

ACK for segments 6

cwnd = 3

cwnd = 5


cwnd = 8

segment 7






AIMD










ssthresh = 8

cwnd = 1

cwnd = 2

cwnd = 4

cwnd = 8

cwnd = 9

cwnd = 10

02468

101214

t=0

t=2

t=4

t=6

Roundtrip times

Cw

nd(in

seg

men

ts)

ssthresh

cwnd = 3





SS

CA

ssthresh













Philosophy

3-90











ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







Slow Start (SS)












Enter slow start

Duplicate ACK




TCP throughput








LRTTMSSsdot221



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness




R

R



Conn

ecti

on 2

thr

ough

p ut
















number)













client

FIN

server

ACK

ACK

FIN

close

close

closed

tim

ed w

ait






client

FIN

server

ACK

ACK

FIN

closing

closing

closed

tim

ed w

ait

closed



TCP clientlifecycle

TCP serverlifecycle






























UDP more

UDP checksum












rdt21 discussion




rdt30 sender

rdt30 in action

rdt30 in action



Pipelined protocols


Go-Back-N



GBN inaction

Selective Repeat


Selective repeat

















TCP sender events





Fast Retransmit

Fast Retransmit


TCP Flow Control















Slow Start Example











TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)









Fast Retransmit









Host A

tim

eout

Host B

time

X

resend seq X2


ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer





fast retransmit


TCP Flow Control






flow control




= RcvWin






3K

2K SeqNo=0

ReceiverBuffer


2K


4K

AckNo=4096 RcvWin=0


Sender blocked





a top-10 problem







Host B

λout






Host B

λout





λin

λout=

λin

λoutgtλ

inλout


R2

R2λin

λ out

b

R2

R2λin

λ out

a

R2

R2λin

λ out

c

R4

R3



λin


in



Host B

λout





Host A

Host B

λou

t










le CongWin









X

X

XX


send

ing

rate

time







roughly




cwndbytes

RTT

ACK(s)

















Host A

one segment

RTT

Host B

time

two segments

four segments





segment 1

ACK for segment 1

cwnd = 1


ACK for segments 2


ACK for segments 4

cwnd = 7

ACK for segments 3

ACK for segments 5

ACK for segments 6

cwnd = 3

cwnd = 5


cwnd = 8

segment 7






AIMD










ssthresh = 8

cwnd = 1

cwnd = 2

cwnd = 4

cwnd = 8

cwnd = 9

cwnd = 10

02468

101214

t=0

t=2

t=4

t=6

Roundtrip times

Cw

nd(in

seg

men

ts)

ssthresh

cwnd = 3





SS

CA

ssthresh













Philosophy

3-90











ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







Slow Start (SS)












Enter slow start

Duplicate ACK




TCP throughput








LRTTMSSsdot221



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness




R

R



Conn

ecti

on 2

thr

ough

p ut
















number)













client

FIN

server

ACK

ACK

FIN

close

close

closed

tim

ed w

ait






client

FIN

server

ACK

ACK

FIN

closing

closing

closed

tim

ed w

ait

closed



TCP clientlifecycle

TCP serverlifecycle






























UDP more

UDP checksum












rdt21 discussion




rdt30 sender

rdt30 in action

rdt30 in action



Pipelined protocols


Go-Back-N



GBN inaction

Selective Repeat


Selective repeat

















TCP sender events





Fast Retransmit

Fast Retransmit


TCP Flow Control















Slow Start Example











TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)










Host A

tim

eout

Host B

time

X

resend seq X2


ACK x1

ACK x1ACK x1ACK x1

tripleduplicate

ACKs




start timer





fast retransmit


TCP Flow Control






flow control




= RcvWin






3K

2K SeqNo=0

ReceiverBuffer


2K


4K

AckNo=4096 RcvWin=0


Sender blocked





a top-10 problem







Host B

λout






Host B

λout





λin

λout=

λin

λoutgtλ

inλout


R2

R2λin

λ out

b

R2

R2λin

λ out

a

R2

R2λin

λ out

c

R4

R3



λin


in



Host B

λout





Host A

Host B

λou

t










le CongWin









X

X

XX


send

ing

rate

time







roughly




cwndbytes

RTT

ACK(s)

















Host A

one segment

RTT

Host B

time

two segments

four segments





segment 1

ACK for segment 1

cwnd = 1


ACK for segments 2


ACK for segments 4

cwnd = 7

ACK for segments 3

ACK for segments 5

ACK for segments 6

cwnd = 3

cwnd = 5


cwnd = 8

segment 7






AIMD










ssthresh = 8

cwnd = 1

cwnd = 2

cwnd = 4

cwnd = 8

cwnd = 9

cwnd = 10

02468

101214

t=0

t=2

t=4

t=6

Roundtrip times

Cw

nd(in

seg

men

ts)

ssthresh

cwnd = 3





SS

CA

ssthresh













Philosophy

3-90











ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







Slow Start (SS)












Enter slow start

Duplicate ACK




TCP throughput








LRTTMSSsdot221



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness




R

R



Conn

ecti

on 2

thr

ough

p ut
















number)













client

FIN

server

ACK

ACK

FIN

close

close

closed

tim

ed w

ait






client

FIN

server

ACK

ACK

FIN

closing

closing

closed

tim

ed w

ait

closed



TCP clientlifecycle

TCP serverlifecycle






























UDP more

UDP checksum












rdt21 discussion




rdt30 sender

rdt30 in action

rdt30 in action



Pipelined protocols


Go-Back-N



GBN inaction

Selective Repeat


Selective repeat

















TCP sender events





Fast Retransmit

Fast Retransmit


TCP Flow Control















Slow Start Example











TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)











start timer





fast retransmit


TCP Flow Control






flow control




= RcvWin






3K

2K SeqNo=0

ReceiverBuffer


2K


4K

AckNo=4096 RcvWin=0


Sender blocked





a top-10 problem







Host B

λout






Host B

λout





λin

λout=

λin

λoutgtλ

inλout


R2

R2λin

λ out

b

R2

R2λin

λ out

a

R2

R2λin

λ out

c

R4

R3



λin


in



Host B

λout





Host A

Host B

λou

t










le CongWin









X

X

XX


send

ing

rate

time







roughly




cwndbytes

RTT

ACK(s)

















Host A

one segment

RTT

Host B

time

two segments

four segments





segment 1

ACK for segment 1

cwnd = 1


ACK for segments 2


ACK for segments 4

cwnd = 7

ACK for segments 3

ACK for segments 5

ACK for segments 6

cwnd = 3

cwnd = 5


cwnd = 8

segment 7






AIMD










ssthresh = 8

cwnd = 1

cwnd = 2

cwnd = 4

cwnd = 8

cwnd = 9

cwnd = 10

02468

101214

t=0

t=2

t=4

t=6

Roundtrip times

Cw

nd(in

seg

men

ts)

ssthresh

cwnd = 3





SS

CA

ssthresh













Philosophy

3-90











ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







Slow Start (SS)












Enter slow start

Duplicate ACK




TCP throughput








LRTTMSSsdot221



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness




R

R



Conn

ecti

on 2

thr

ough

p ut
















number)













client

FIN

server

ACK

ACK

FIN

close

close

closed

tim

ed w

ait






client

FIN

server

ACK

ACK

FIN

closing

closing

closed

tim

ed w

ait

closed



TCP clientlifecycle

TCP serverlifecycle






























UDP more

UDP checksum












rdt21 discussion




rdt30 sender

rdt30 in action

rdt30 in action



Pipelined protocols


Go-Back-N



GBN inaction

Selective Repeat


Selective repeat

















TCP sender events





Fast Retransmit

Fast Retransmit


TCP Flow Control















Slow Start Example











TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)









TCP Flow Control






flow control




= RcvWin






3K

2K SeqNo=0

ReceiverBuffer


2K


4K

AckNo=4096 RcvWin=0


Sender blocked





a top-10 problem







Host B

λout






Host B

λout





λin

λout=

λin

λoutgtλ

inλout


R2

R2λin

λ out

b

R2

R2λin

λ out

a

R2

R2λin

λ out

c

R4

R3



λin


in



Host B

λout





Host A

Host B

λou

t










le CongWin









X

X

XX


send

ing

rate

time







roughly




cwndbytes

RTT

ACK(s)

















Host A

one segment

RTT

Host B

time

two segments

four segments





segment 1

ACK for segment 1

cwnd = 1


ACK for segments 2


ACK for segments 4

cwnd = 7

ACK for segments 3

ACK for segments 5

ACK for segments 6

cwnd = 3

cwnd = 5


cwnd = 8

segment 7






AIMD










ssthresh = 8

cwnd = 1

cwnd = 2

cwnd = 4

cwnd = 8

cwnd = 9

cwnd = 10

02468

101214

t=0

t=2

t=4

t=6

Roundtrip times

Cw

nd(in

seg

men

ts)

ssthresh

cwnd = 3





SS

CA

ssthresh













Philosophy

3-90











ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







Slow Start (SS)












Enter slow start

Duplicate ACK




TCP throughput








LRTTMSSsdot221



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness




R

R



Conn

ecti

on 2

thr

ough

p ut
















number)













client

FIN

server

ACK

ACK

FIN

close

close

closed

tim

ed w

ait






client

FIN

server

ACK

ACK

FIN

closing

closing

closed

tim

ed w

ait

closed



TCP clientlifecycle

TCP serverlifecycle






























UDP more

UDP checksum












rdt21 discussion




rdt30 sender

rdt30 in action

rdt30 in action



Pipelined protocols


Go-Back-N



GBN inaction

Selective Repeat


Selective repeat

















TCP sender events





Fast Retransmit

Fast Retransmit


TCP Flow Control















Slow Start Example











TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)











= RcvWin






3K

2K SeqNo=0

ReceiverBuffer


2K


4K

AckNo=4096 RcvWin=0


Sender blocked





a top-10 problem







Host B

λout






Host B

λout





λin

λout=

λin

λoutgtλ

inλout


R2

R2λin

λ out

b

R2

R2λin

λ out

a

R2

R2λin

λ out

c

R4

R3



λin


in



Host B

λout





Host A

Host B

λou

t










le CongWin









X

X

XX


send

ing

rate

time







roughly




cwndbytes

RTT

ACK(s)

















Host A

one segment

RTT

Host B

time

two segments

four segments





segment 1

ACK for segment 1

cwnd = 1


ACK for segments 2


ACK for segments 4

cwnd = 7

ACK for segments 3

ACK for segments 5

ACK for segments 6

cwnd = 3

cwnd = 5


cwnd = 8

segment 7






AIMD










ssthresh = 8

cwnd = 1

cwnd = 2

cwnd = 4

cwnd = 8

cwnd = 9

cwnd = 10

02468

101214

t=0

t=2

t=4

t=6

Roundtrip times

Cw

nd(in

seg

men

ts)

ssthresh

cwnd = 3





SS

CA

ssthresh













Philosophy

3-90











ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







Slow Start (SS)












Enter slow start

Duplicate ACK




TCP throughput








LRTTMSSsdot221



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness




R

R



Conn

ecti

on 2

thr

ough

p ut
















number)













client

FIN

server

ACK

ACK

FIN

close

close

closed

tim

ed w

ait






client

FIN

server

ACK

ACK

FIN

closing

closing

closed

tim

ed w

ait

closed



TCP clientlifecycle

TCP serverlifecycle






























UDP more

UDP checksum












rdt21 discussion




rdt30 sender

rdt30 in action

rdt30 in action



Pipelined protocols


Go-Back-N



GBN inaction

Selective Repeat


Selective repeat

















TCP sender events





Fast Retransmit

Fast Retransmit


TCP Flow Control















Slow Start Example











TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)










3K

2K SeqNo=0

ReceiverBuffer


2K


4K

AckNo=4096 RcvWin=0


Sender blocked





a top-10 problem







Host B

λout






Host B

λout





λin

λout=

λin

λoutgtλ

inλout


R2

R2λin

λ out

b

R2

R2λin

λ out

a

R2

R2λin

λ out

c

R4

R3



λin


in



Host B

λout





Host A

Host B

λou

t










le CongWin









X

X

XX


send

ing

rate

time







roughly




cwndbytes

RTT

ACK(s)

















Host A

one segment

RTT

Host B

time

two segments

four segments





segment 1

ACK for segment 1

cwnd = 1


ACK for segments 2


ACK for segments 4

cwnd = 7

ACK for segments 3

ACK for segments 5

ACK for segments 6

cwnd = 3

cwnd = 5


cwnd = 8

segment 7






AIMD










ssthresh = 8

cwnd = 1

cwnd = 2

cwnd = 4

cwnd = 8

cwnd = 9

cwnd = 10

02468

101214

t=0

t=2

t=4

t=6

Roundtrip times

Cw

nd(in

seg

men

ts)

ssthresh

cwnd = 3





SS

CA

ssthresh













Philosophy

3-90











ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







Slow Start (SS)












Enter slow start

Duplicate ACK




TCP throughput








LRTTMSSsdot221



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness




R

R



Conn

ecti

on 2

thr

ough

p ut
















number)













client

FIN

server

ACK

ACK

FIN

close

close

closed

tim

ed w

ait






client

FIN

server

ACK

ACK

FIN

closing

closing

closed

tim

ed w

ait

closed



TCP clientlifecycle

TCP serverlifecycle






























UDP more

UDP checksum












rdt21 discussion




rdt30 sender

rdt30 in action

rdt30 in action



Pipelined protocols


Go-Back-N



GBN inaction

Selective Repeat


Selective repeat

















TCP sender events





Fast Retransmit

Fast Retransmit


TCP Flow Control















Slow Start Example











TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)












a top-10 problem







Host B

λout






Host B

λout





λin

λout=

λin

λoutgtλ

inλout


R2

R2λin

λ out

b

R2

R2λin

λ out

a

R2

R2λin

λ out

c

R4

R3



λin


in



Host B

λout





Host A

Host B

λou

t










le CongWin









X

X

XX


send

ing

rate

time







roughly




cwndbytes

RTT

ACK(s)

















Host A

one segment

RTT

Host B

time

two segments

four segments





segment 1

ACK for segment 1

cwnd = 1


ACK for segments 2


ACK for segments 4

cwnd = 7

ACK for segments 3

ACK for segments 5

ACK for segments 6

cwnd = 3

cwnd = 5


cwnd = 8

segment 7






AIMD










ssthresh = 8

cwnd = 1

cwnd = 2

cwnd = 4

cwnd = 8

cwnd = 9

cwnd = 10

02468

101214

t=0

t=2

t=4

t=6

Roundtrip times

Cw

nd(in

seg

men

ts)

ssthresh

cwnd = 3





SS

CA

ssthresh













Philosophy

3-90











ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







Slow Start (SS)












Enter slow start

Duplicate ACK




TCP throughput








LRTTMSSsdot221



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness




R

R



Conn

ecti

on 2

thr

ough

p ut
















number)













client

FIN

server

ACK

ACK

FIN

close

close

closed

tim

ed w

ait






client

FIN

server

ACK

ACK

FIN

closing

closing

closed

tim

ed w

ait

closed



TCP clientlifecycle

TCP serverlifecycle






























UDP more

UDP checksum












rdt21 discussion




rdt30 sender

rdt30 in action

rdt30 in action



Pipelined protocols


Go-Back-N



GBN inaction

Selective Repeat


Selective repeat

















TCP sender events





Fast Retransmit

Fast Retransmit


TCP Flow Control















Slow Start Example











TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)














Host B

λout






Host B

λout





λin

λout=

λin

λoutgtλ

inλout


R2

R2λin

λ out

b

R2

R2λin

λ out

a

R2

R2λin

λ out

c

R4

R3



λin


in



Host B

λout





Host A

Host B

λou

t










le CongWin









X

X

XX


send

ing

rate

time







roughly




cwndbytes

RTT

ACK(s)

















Host A

one segment

RTT

Host B

time

two segments

four segments





segment 1

ACK for segment 1

cwnd = 1


ACK for segments 2


ACK for segments 4

cwnd = 7

ACK for segments 3

ACK for segments 5

ACK for segments 6

cwnd = 3

cwnd = 5


cwnd = 8

segment 7






AIMD










ssthresh = 8

cwnd = 1

cwnd = 2

cwnd = 4

cwnd = 8

cwnd = 9

cwnd = 10

02468

101214

t=0

t=2

t=4

t=6

Roundtrip times

Cw

nd(in

seg

men

ts)

ssthresh

cwnd = 3





SS

CA

ssthresh













Philosophy

3-90











ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







Slow Start (SS)












Enter slow start

Duplicate ACK




TCP throughput








LRTTMSSsdot221



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness




R

R



Conn

ecti

on 2

thr

ough

p ut
















number)













client

FIN

server

ACK

ACK

FIN

close

close

closed

tim

ed w

ait






client

FIN

server

ACK

ACK

FIN

closing

closing

closed

tim

ed w

ait

closed



TCP clientlifecycle

TCP serverlifecycle






























UDP more

UDP checksum












rdt21 discussion




rdt30 sender

rdt30 in action

rdt30 in action



Pipelined protocols


Go-Back-N



GBN inaction

Selective Repeat


Selective repeat

















TCP sender events





Fast Retransmit

Fast Retransmit


TCP Flow Control















Slow Start Example











TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)













Host B

λout





λin

λout=

λin

λoutgtλ

inλout


R2

R2λin

λ out

b

R2

R2λin

λ out

a

R2

R2λin

λ out

c

R4

R3



λin


in



Host B

λout





Host A

Host B

λou

t










le CongWin









X

X

XX


send

ing

rate

time







roughly




cwndbytes

RTT

ACK(s)

















Host A

one segment

RTT

Host B

time

two segments

four segments





segment 1

ACK for segment 1

cwnd = 1


ACK for segments 2


ACK for segments 4

cwnd = 7

ACK for segments 3

ACK for segments 5

ACK for segments 6

cwnd = 3

cwnd = 5


cwnd = 8

segment 7






AIMD










ssthresh = 8

cwnd = 1

cwnd = 2

cwnd = 4

cwnd = 8

cwnd = 9

cwnd = 10

02468

101214

t=0

t=2

t=4

t=6

Roundtrip times

Cw

nd(in

seg

men

ts)

ssthresh

cwnd = 3





SS

CA

ssthresh













Philosophy

3-90











ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







Slow Start (SS)












Enter slow start

Duplicate ACK




TCP throughput








LRTTMSSsdot221



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness




R

R



Conn

ecti

on 2

thr

ough

p ut
















number)













client

FIN

server

ACK

ACK

FIN

close

close

closed

tim

ed w

ait






client

FIN

server

ACK

ACK

FIN

closing

closing

closed

tim

ed w

ait

closed



TCP clientlifecycle

TCP serverlifecycle






























UDP more

UDP checksum












rdt21 discussion




rdt30 sender

rdt30 in action

rdt30 in action



Pipelined protocols


Go-Back-N



GBN inaction

Selective Repeat


Selective repeat

















TCP sender events





Fast Retransmit

Fast Retransmit


TCP Flow Control















Slow Start Example











TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)











λin

λout=

λin

λoutgtλ

inλout


R2

R2λin

λ out

b

R2

R2λin

λ out

a

R2

R2λin

λ out

c

R4

R3



λin


in



Host B

λout





Host A

Host B

λou

t










le CongWin









X

X

XX


send

ing

rate

time







roughly




cwndbytes

RTT

ACK(s)

















Host A

one segment

RTT

Host B

time

two segments

four segments





segment 1

ACK for segment 1

cwnd = 1


ACK for segments 2


ACK for segments 4

cwnd = 7

ACK for segments 3

ACK for segments 5

ACK for segments 6

cwnd = 3

cwnd = 5


cwnd = 8

segment 7






AIMD










ssthresh = 8

cwnd = 1

cwnd = 2

cwnd = 4

cwnd = 8

cwnd = 9

cwnd = 10

02468

101214

t=0

t=2

t=4

t=6

Roundtrip times

Cw

nd(in

seg

men

ts)

ssthresh

cwnd = 3





SS

CA

ssthresh













Philosophy

3-90











ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







Slow Start (SS)












Enter slow start

Duplicate ACK




TCP throughput








LRTTMSSsdot221



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness




R

R



Conn

ecti

on 2

thr

ough

p ut
















number)













client

FIN

server

ACK

ACK

FIN

close

close

closed

tim

ed w

ait






client

FIN

server

ACK

ACK

FIN

closing

closing

closed

tim

ed w

ait

closed



TCP clientlifecycle

TCP serverlifecycle






























UDP more

UDP checksum












rdt21 discussion




rdt30 sender

rdt30 in action

rdt30 in action



Pipelined protocols


Go-Back-N



GBN inaction

Selective Repeat


Selective repeat

















TCP sender events





Fast Retransmit

Fast Retransmit


TCP Flow Control















Slow Start Example











TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)










λin


in



Host B

λout





Host A

Host B

λou

t










le CongWin









X

X

XX


send

ing

rate

time







roughly




cwndbytes

RTT

ACK(s)

















Host A

one segment

RTT

Host B

time

two segments

four segments





segment 1

ACK for segment 1

cwnd = 1


ACK for segments 2


ACK for segments 4

cwnd = 7

ACK for segments 3

ACK for segments 5

ACK for segments 6

cwnd = 3

cwnd = 5


cwnd = 8

segment 7






AIMD










ssthresh = 8

cwnd = 1

cwnd = 2

cwnd = 4

cwnd = 8

cwnd = 9

cwnd = 10

02468

101214

t=0

t=2

t=4

t=6

Roundtrip times

Cw

nd(in

seg

men

ts)

ssthresh

cwnd = 3





SS

CA

ssthresh













Philosophy

3-90











ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







Slow Start (SS)












Enter slow start

Duplicate ACK




TCP throughput








LRTTMSSsdot221



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness




R

R



Conn

ecti

on 2

thr

ough

p ut
















number)













client

FIN

server

ACK

ACK

FIN

close

close

closed

tim

ed w

ait






client

FIN

server

ACK

ACK

FIN

closing

closing

closed

tim

ed w

ait

closed



TCP clientlifecycle

TCP serverlifecycle






























UDP more

UDP checksum












rdt21 discussion




rdt30 sender

rdt30 in action

rdt30 in action



Pipelined protocols


Go-Back-N



GBN inaction

Selective Repeat


Selective repeat

















TCP sender events





Fast Retransmit

Fast Retransmit


TCP Flow Control















Slow Start Example











TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)











Host A

Host B

λou

t










le CongWin









X

X

XX


send

ing

rate

time







roughly




cwndbytes

RTT

ACK(s)

















Host A

one segment

RTT

Host B

time

two segments

four segments





segment 1

ACK for segment 1

cwnd = 1


ACK for segments 2


ACK for segments 4

cwnd = 7

ACK for segments 3

ACK for segments 5

ACK for segments 6

cwnd = 3

cwnd = 5


cwnd = 8

segment 7






AIMD










ssthresh = 8

cwnd = 1

cwnd = 2

cwnd = 4

cwnd = 8

cwnd = 9

cwnd = 10

02468

101214

t=0

t=2

t=4

t=6

Roundtrip times

Cw

nd(in

seg

men

ts)

ssthresh

cwnd = 3





SS

CA

ssthresh













Philosophy

3-90











ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







Slow Start (SS)












Enter slow start

Duplicate ACK




TCP throughput








LRTTMSSsdot221



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness




R

R



Conn

ecti

on 2

thr

ough

p ut
















number)













client

FIN

server

ACK

ACK

FIN

close

close

closed

tim

ed w

ait






client

FIN

server

ACK

ACK

FIN

closing

closing

closed

tim

ed w

ait

closed



TCP clientlifecycle

TCP serverlifecycle






























UDP more

UDP checksum












rdt21 discussion




rdt30 sender

rdt30 in action

rdt30 in action



Pipelined protocols


Go-Back-N



GBN inaction

Selective Repeat


Selective repeat

















TCP sender events





Fast Retransmit

Fast Retransmit


TCP Flow Control















Slow Start Example











TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)

















le CongWin









X

X

XX


send

ing

rate

time







roughly




cwndbytes

RTT

ACK(s)

















Host A

one segment

RTT

Host B

time

two segments

four segments





segment 1

ACK for segment 1

cwnd = 1


ACK for segments 2


ACK for segments 4

cwnd = 7

ACK for segments 3

ACK for segments 5

ACK for segments 6

cwnd = 3

cwnd = 5


cwnd = 8

segment 7






AIMD










ssthresh = 8

cwnd = 1

cwnd = 2

cwnd = 4

cwnd = 8

cwnd = 9

cwnd = 10

02468

101214

t=0

t=2

t=4

t=6

Roundtrip times

Cw

nd(in

seg

men

ts)

ssthresh

cwnd = 3





SS

CA

ssthresh













Philosophy

3-90











ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







Slow Start (SS)












Enter slow start

Duplicate ACK




TCP throughput








LRTTMSSsdot221



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness




R

R



Conn

ecti

on 2

thr

ough

p ut
















number)













client

FIN

server

ACK

ACK

FIN

close

close

closed

tim

ed w

ait






client

FIN

server

ACK

ACK

FIN

closing

closing

closed

tim

ed w

ait

closed



TCP clientlifecycle

TCP serverlifecycle






























UDP more

UDP checksum












rdt21 discussion




rdt30 sender

rdt30 in action

rdt30 in action



Pipelined protocols


Go-Back-N



GBN inaction

Selective Repeat


Selective repeat

















TCP sender events





Fast Retransmit

Fast Retransmit


TCP Flow Control















Slow Start Example











TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)













X

X

XX


send

ing

rate

time







roughly




cwndbytes

RTT

ACK(s)

















Host A

one segment

RTT

Host B

time

two segments

four segments





segment 1

ACK for segment 1

cwnd = 1


ACK for segments 2


ACK for segments 4

cwnd = 7

ACK for segments 3

ACK for segments 5

ACK for segments 6

cwnd = 3

cwnd = 5


cwnd = 8

segment 7






AIMD










ssthresh = 8

cwnd = 1

cwnd = 2

cwnd = 4

cwnd = 8

cwnd = 9

cwnd = 10

02468

101214

t=0

t=2

t=4

t=6

Roundtrip times

Cw

nd(in

seg

men

ts)

ssthresh

cwnd = 3





SS

CA

ssthresh













Philosophy

3-90











ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







Slow Start (SS)












Enter slow start

Duplicate ACK




TCP throughput








LRTTMSSsdot221



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness




R

R



Conn

ecti

on 2

thr

ough

p ut
















number)













client

FIN

server

ACK

ACK

FIN

close

close

closed

tim

ed w

ait






client

FIN

server

ACK

ACK

FIN

closing

closing

closed

tim

ed w

ait

closed



TCP clientlifecycle

TCP serverlifecycle






























UDP more

UDP checksum












rdt21 discussion




rdt30 sender

rdt30 in action

rdt30 in action



Pipelined protocols


Go-Back-N



GBN inaction

Selective Repeat


Selective repeat

















TCP sender events





Fast Retransmit

Fast Retransmit


TCP Flow Control















Slow Start Example











TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)












roughly




cwndbytes

RTT

ACK(s)

















Host A

one segment

RTT

Host B

time

two segments

four segments





segment 1

ACK for segment 1

cwnd = 1


ACK for segments 2


ACK for segments 4

cwnd = 7

ACK for segments 3

ACK for segments 5

ACK for segments 6

cwnd = 3

cwnd = 5


cwnd = 8

segment 7






AIMD










ssthresh = 8

cwnd = 1

cwnd = 2

cwnd = 4

cwnd = 8

cwnd = 9

cwnd = 10

02468

101214

t=0

t=2

t=4

t=6

Roundtrip times

Cw

nd(in

seg

men

ts)

ssthresh

cwnd = 3





SS

CA

ssthresh













Philosophy

3-90











ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







Slow Start (SS)












Enter slow start

Duplicate ACK




TCP throughput








LRTTMSSsdot221



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness




R

R



Conn

ecti

on 2

thr

ough

p ut
















number)













client

FIN

server

ACK

ACK

FIN

close

close

closed

tim

ed w

ait






client

FIN

server

ACK

ACK

FIN

closing

closing

closed

tim

ed w

ait

closed



TCP clientlifecycle

TCP serverlifecycle






























UDP more

UDP checksum












rdt21 discussion




rdt30 sender

rdt30 in action

rdt30 in action



Pipelined protocols


Go-Back-N



GBN inaction

Selective Repeat


Selective repeat

















TCP sender events





Fast Retransmit

Fast Retransmit


TCP Flow Control















Slow Start Example











TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)
























Host A

one segment

RTT

Host B

time

two segments

four segments





segment 1

ACK for segment 1

cwnd = 1


ACK for segments 2


ACK for segments 4

cwnd = 7

ACK for segments 3

ACK for segments 5

ACK for segments 6

cwnd = 3

cwnd = 5


cwnd = 8

segment 7






AIMD










ssthresh = 8

cwnd = 1

cwnd = 2

cwnd = 4

cwnd = 8

cwnd = 9

cwnd = 10

02468

101214

t=0

t=2

t=4

t=6

Roundtrip times

Cw

nd(in

seg

men

ts)

ssthresh

cwnd = 3





SS

CA

ssthresh













Philosophy

3-90











ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







Slow Start (SS)












Enter slow start

Duplicate ACK




TCP throughput








LRTTMSSsdot221



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness




R

R



Conn

ecti

on 2

thr

ough

p ut
















number)













client

FIN

server

ACK

ACK

FIN

close

close

closed

tim

ed w

ait






client

FIN

server

ACK

ACK

FIN

closing

closing

closed

tim

ed w

ait

closed



TCP clientlifecycle

TCP serverlifecycle






























UDP more

UDP checksum












rdt21 discussion




rdt30 sender

rdt30 in action

rdt30 in action



Pipelined protocols


Go-Back-N



GBN inaction

Selective Repeat


Selective repeat

















TCP sender events





Fast Retransmit

Fast Retransmit


TCP Flow Control















Slow Start Example











TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)












segment 1

ACK for segment 1

cwnd = 1


ACK for segments 2


ACK for segments 4

cwnd = 7

ACK for segments 3

ACK for segments 5

ACK for segments 6

cwnd = 3

cwnd = 5


cwnd = 8

segment 7






AIMD










ssthresh = 8

cwnd = 1

cwnd = 2

cwnd = 4

cwnd = 8

cwnd = 9

cwnd = 10

02468

101214

t=0

t=2

t=4

t=6

Roundtrip times

Cw

nd(in

seg

men

ts)

ssthresh

cwnd = 3





SS

CA

ssthresh













Philosophy

3-90











ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







Slow Start (SS)












Enter slow start

Duplicate ACK




TCP throughput








LRTTMSSsdot221



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness




R

R



Conn

ecti

on 2

thr

ough

p ut
















number)













client

FIN

server

ACK

ACK

FIN

close

close

closed

tim

ed w

ait






client

FIN

server

ACK

ACK

FIN

closing

closing

closed

tim

ed w

ait

closed



TCP clientlifecycle

TCP serverlifecycle






























UDP more

UDP checksum












rdt21 discussion




rdt30 sender

rdt30 in action

rdt30 in action



Pipelined protocols


Go-Back-N



GBN inaction

Selective Repeat


Selective repeat

















TCP sender events





Fast Retransmit

Fast Retransmit


TCP Flow Control















Slow Start Example











TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)













AIMD










ssthresh = 8

cwnd = 1

cwnd = 2

cwnd = 4

cwnd = 8

cwnd = 9

cwnd = 10

02468

101214

t=0

t=2

t=4

t=6

Roundtrip times

Cw

nd(in

seg

men

ts)

ssthresh

cwnd = 3





SS

CA

ssthresh













Philosophy

3-90











ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







Slow Start (SS)












Enter slow start

Duplicate ACK




TCP throughput








LRTTMSSsdot221



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness




R

R



Conn

ecti

on 2

thr

ough

p ut
















number)













client

FIN

server

ACK

ACK

FIN

close

close

closed

tim

ed w

ait






client

FIN

server

ACK

ACK

FIN

closing

closing

closed

tim

ed w

ait

closed



TCP clientlifecycle

TCP serverlifecycle






























UDP more

UDP checksum












rdt21 discussion




rdt30 sender

rdt30 in action

rdt30 in action



Pipelined protocols


Go-Back-N



GBN inaction

Selective Repeat


Selective repeat

















TCP sender events





Fast Retransmit

Fast Retransmit


TCP Flow Control















Slow Start Example











TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)
















ssthresh = 8

cwnd = 1

cwnd = 2

cwnd = 4

cwnd = 8

cwnd = 9

cwnd = 10

02468

101214

t=0

t=2

t=4

t=6

Roundtrip times

Cw

nd(in

seg

men

ts)

ssthresh

cwnd = 3





SS

CA

ssthresh













Philosophy

3-90











ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







Slow Start (SS)












Enter slow start

Duplicate ACK




TCP throughput








LRTTMSSsdot221



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness




R

R



Conn

ecti

on 2

thr

ough

p ut
















number)













client

FIN

server

ACK

ACK

FIN

close

close

closed

tim

ed w

ait






client

FIN

server

ACK

ACK

FIN

closing

closing

closed

tim

ed w

ait

closed



TCP clientlifecycle

TCP serverlifecycle






























UDP more

UDP checksum












rdt21 discussion




rdt30 sender

rdt30 in action

rdt30 in action



Pipelined protocols


Go-Back-N



GBN inaction

Selective Repeat


Selective repeat

















TCP sender events





Fast Retransmit

Fast Retransmit


TCP Flow Control















Slow Start Example











TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)











SS

CA

ssthresh













Philosophy

3-90











ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







Slow Start (SS)












Enter slow start

Duplicate ACK




TCP throughput








LRTTMSSsdot221



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness




R

R



Conn

ecti

on 2

thr

ough

p ut
















number)













client

FIN

server

ACK

ACK

FIN

close

close

closed

tim

ed w

ait






client

FIN

server

ACK

ACK

FIN

closing

closing

closed

tim

ed w

ait

closed



TCP clientlifecycle

TCP serverlifecycle






























UDP more

UDP checksum












rdt21 discussion




rdt30 sender

rdt30 in action

rdt30 in action



Pipelined protocols


Go-Back-N



GBN inaction

Selective Repeat


Selective repeat

















TCP sender events





Fast Retransmit

Fast Retransmit


TCP Flow Control















Slow Start Example











TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)




















Philosophy

3-90











ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







Slow Start (SS)












Enter slow start

Duplicate ACK




TCP throughput








LRTTMSSsdot221



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness




R

R



Conn

ecti

on 2

thr

ough

p ut
















number)













client

FIN

server

ACK

ACK

FIN

close

close

closed

tim

ed w

ait






client

FIN

server

ACK

ACK

FIN

closing

closing

closed

tim

ed w

ait

closed



TCP clientlifecycle

TCP serverlifecycle






























UDP more

UDP checksum












rdt21 discussion




rdt30 sender

rdt30 in action

rdt30 in action



Pipelined protocols


Go-Back-N



GBN inaction

Selective Repeat


Selective repeat

















TCP sender events





Fast Retransmit

Fast Retransmit


TCP Flow Control















Slow Start Example











TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)








3-90











ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







Slow Start (SS)












Enter slow start

Duplicate ACK




TCP throughput








LRTTMSSsdot221



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness




R

R



Conn

ecti

on 2

thr

ough

p ut
















number)













client

FIN

server

ACK

ACK

FIN

close

close

closed

tim

ed w

ait






client

FIN

server

ACK

ACK

FIN

closing

closing

closed

tim

ed w

ait

closed



TCP clientlifecycle

TCP serverlifecycle






























UDP more

UDP checksum












rdt21 discussion




rdt30 sender

rdt30 in action

rdt30 in action



Pipelined protocols


Go-Back-N



GBN inaction

Selective Repeat


Selective repeat

















TCP sender events





Fast Retransmit

Fast Retransmit


TCP Flow Control















Slow Start Example











TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)










ssthresh

ssthresh

TCP Tahoe

TCP Reno

Transmission round

cwnd

win

dow

siz

e (in

seg

men

ts)







Slow Start (SS)












Enter slow start

Duplicate ACK




TCP throughput








LRTTMSSsdot221



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness




R

R



Conn

ecti

on 2

thr

ough

p ut
















number)













client

FIN

server

ACK

ACK

FIN

close

close

closed

tim

ed w

ait






client

FIN

server

ACK

ACK

FIN

closing

closing

closed

tim

ed w

ait

closed



TCP clientlifecycle

TCP serverlifecycle






























UDP more

UDP checksum












rdt21 discussion




rdt30 sender

rdt30 in action

rdt30 in action



Pipelined protocols


Go-Back-N



GBN inaction

Selective Repeat


Selective repeat

















TCP sender events





Fast Retransmit

Fast Retransmit


TCP Flow Control















Slow Start Example











TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)














Slow Start (SS)












Enter slow start

Duplicate ACK




TCP throughput








LRTTMSSsdot221



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness




R

R



Conn

ecti

on 2

thr

ough

p ut
















number)













client

FIN

server

ACK

ACK

FIN

close

close

closed

tim

ed w

ait






client

FIN

server

ACK

ACK

FIN

closing

closing

closed

tim

ed w

ait

closed



TCP clientlifecycle

TCP serverlifecycle






























UDP more

UDP checksum












rdt21 discussion




rdt30 sender

rdt30 in action

rdt30 in action



Pipelined protocols


Go-Back-N



GBN inaction

Selective Repeat


Selective repeat

















TCP sender events





Fast Retransmit

Fast Retransmit


TCP Flow Control















Slow Start Example











TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)









TCP throughput








LRTTMSSsdot221



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness




R

R



Conn

ecti

on 2

thr

ough

p ut
















number)













client

FIN

server

ACK

ACK

FIN

close

close

closed

tim

ed w

ait






client

FIN

server

ACK

ACK

FIN

closing

closing

closed

tim

ed w

ait

closed



TCP clientlifecycle

TCP serverlifecycle






























UDP more

UDP checksum












rdt21 discussion




rdt30 sender

rdt30 in action

rdt30 in action



Pipelined protocols


Go-Back-N



GBN inaction

Selective Repeat


Selective repeat

















TCP sender events





Fast Retransmit

Fast Retransmit


TCP Flow Control















Slow Start Example











TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)












LRTTMSSsdot221



TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness




R

R



Conn

ecti

on 2

thr

ough

p ut
















number)













client

FIN

server

ACK

ACK

FIN

close

close

closed

tim

ed w

ait






client

FIN

server

ACK

ACK

FIN

closing

closing

closed

tim

ed w

ait

closed



TCP clientlifecycle

TCP serverlifecycle






























UDP more

UDP checksum












rdt21 discussion




rdt30 sender

rdt30 in action

rdt30 in action



Pipelined protocols


Go-Back-N



GBN inaction

Selective Repeat


Selective repeat

















TCP sender events





Fast Retransmit

Fast Retransmit


TCP Flow Control















Slow Start Example











TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)










TCP connection 1

bottleneckrouter

capacity R

TCP connection 2

TCP Fairness




R

R



Conn

ecti

on 2

thr

ough

p ut
















number)













client

FIN

server

ACK

ACK

FIN

close

close

closed

tim

ed w

ait






client

FIN

server

ACK

ACK

FIN

closing

closing

closed

tim

ed w

ait

closed



TCP clientlifecycle

TCP serverlifecycle






























UDP more

UDP checksum












rdt21 discussion




rdt30 sender

rdt30 in action

rdt30 in action



Pipelined protocols


Go-Back-N



GBN inaction

Selective Repeat


Selective repeat

















TCP sender events





Fast Retransmit

Fast Retransmit


TCP Flow Control















Slow Start Example











TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)











R

R



Conn

ecti

on 2

thr

ough

p ut
















number)













client

FIN

server

ACK

ACK

FIN

close

close

closed

tim

ed w

ait






client

FIN

server

ACK

ACK

FIN

closing

closing

closed

tim

ed w

ait

closed



TCP clientlifecycle

TCP serverlifecycle






























UDP more

UDP checksum












rdt21 discussion




rdt30 sender

rdt30 in action

rdt30 in action



Pipelined protocols


Go-Back-N



GBN inaction

Selective Repeat


Selective repeat

















TCP sender events





Fast Retransmit

Fast Retransmit


TCP Flow Control















Slow Start Example











TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)





















number)













client

FIN

server

ACK

ACK

FIN

close

close

closed

tim

ed w

ait






client

FIN

server

ACK

ACK

FIN

closing

closing

closed

tim

ed w

ait

closed



TCP clientlifecycle

TCP serverlifecycle






























UDP more

UDP checksum












rdt21 discussion




rdt30 sender

rdt30 in action

rdt30 in action



Pipelined protocols


Go-Back-N



GBN inaction

Selective Repeat


Selective repeat

















TCP sender events





Fast Retransmit

Fast Retransmit


TCP Flow Control















Slow Start Example











TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)














client

FIN

server

ACK

ACK

FIN

close

close

closed

tim

ed w

ait






client

FIN

server

ACK

ACK

FIN

closing

closing

closed

tim

ed w

ait

closed



TCP clientlifecycle

TCP serverlifecycle






























UDP more

UDP checksum












rdt21 discussion




rdt30 sender

rdt30 in action

rdt30 in action



Pipelined protocols


Go-Back-N



GBN inaction

Selective Repeat


Selective repeat

















TCP sender events





Fast Retransmit

Fast Retransmit


TCP Flow Control















Slow Start Example











TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)













client

FIN

server

ACK

ACK

FIN

closing

closing

closed

tim

ed w

ait

closed



TCP clientlifecycle

TCP serverlifecycle






























UDP more

UDP checksum












rdt21 discussion




rdt30 sender

rdt30 in action

rdt30 in action



Pipelined protocols


Go-Back-N



GBN inaction

Selective Repeat


Selective repeat

















TCP sender events





Fast Retransmit

Fast Retransmit


TCP Flow Control















Slow Start Example











TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)










TCP clientlifecycle

TCP serverlifecycle






























UDP more

UDP checksum












rdt21 discussion




rdt30 sender

rdt30 in action

rdt30 in action



Pipelined protocols


Go-Back-N



GBN inaction

Selective Repeat


Selective repeat

















TCP sender events





Fast Retransmit

Fast Retransmit


TCP Flow Control















Slow Start Example











TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)





































UDP more

UDP checksum












rdt21 discussion




rdt30 sender

rdt30 in action

rdt30 in action



Pipelined protocols


Go-Back-N



GBN inaction

Selective Repeat


Selective repeat

















TCP sender events





Fast Retransmit

Fast Retransmit


TCP Flow Control















Slow Start Example











TCP throughput


TCP Fairness

Why is TCP fair

Fairness (more)








chapter 3: transport layer - bilkent...

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