mid-point discussion lecture tdts06 computer...
TRANSCRIPT
Mid-point discussion lecture hellip
TDTS06 Computer Networking
Niklas Carlsson Associate Professor httpwwwidaliuse~nikca
Kick starting science
hellip well cable into wall hellip
What happens there
Hosts the Internet architecture and the E2E arguments hellip
Network Stack in Practice
8
Application
Presentation
Session
Transport
Network
Data Link
Physical
Network
Data Link
Application
Presentation
Session
Transport
Network
Data Link
Physical
Host 1 Switch Host 2
Physical
Video Client
UDP
Video Server
UDP
FTP Client
TCP
IP
Ethernet
IP
Ethernet
FTP Server
TCP
IP
Ethernet 80211n 80211n 80211n
Encapsulation Revisited
9
Web Server
TCP
IP
Ethernet
HTTP Header
TCP Header
IP Header
Ethernet Header
Ethernet Trailer
Web Page
HTTP Header
Web Page
TCP Header
HTTP Header
Web Page
IP Header
TCP Header
HTTP Header
Web Page
TCP Segment
IP Datagram
Ethernet Frame
The Hourglass
10
IPv4
TCP UDP ICMP
HTTP FTP RTP IMAP Jabber hellip
Ethernet 80211x DOCSIS hellip
Fiber Coax Twisted Pair Radio hellip
Holding the Internet Together
bull Distributed cooperation for resource allocation
ndash BGP what end-to-end paths to take (for ~50K ASes)
ndash TCP what rate to send over each path (for ~3B hosts)
12
AS 1
AS 2
AS 3
AS 4
How do we find a path
Routing on a Graph
bull Goal determine a ldquogoodrdquo path through the network from source to destination
bull What is a good path ndash Usually means the shortest path
ndash Load balanced
ndash Lowest $$$ cost
bull Network modeled as a graph ndash Routers nodes
ndash Link edges bull Edge cost delay congestion level etc
A
B C
D E
F
5
2
3 5
2 1
1
2 3
1
14
Intra-domain Routing Protocols bull Distance vector
ndash Routing Information Protocol (RIP) based on Bellman-Ford
ndash Routers periodically exchange reachability info with neighbors
bull Link state
ndash Open Shortest Path First (OSPF) based on Dijkstra
ndash Each network periodically floods neighbor information to all routers
ndash Routers locally compute routes
15
16
Hierarchical addressing route aggregation
ldquoSend me anything with addresses beginning 2002316020rdquo
2002316023
2002318023
2002330023
Fly-By-Night-ISP
Organization 0
Organization 7 Internet
Organization 1
ISPs-R-Us ldquoSend me anything with addresses beginning 199310016rdquo
2002320023 Organization 2
ISP has an address block it can further divide this block into sub blocks and assign them to subscriber organizations
Example CIDR Routing Table
17
Address Netmask Third Byte Byte Range
2074600 19 000xxxxx 0 ndash 31
20746320 19 001xxxxx 32 ndash 63
20746640 19 010xxxxx 64 ndash 95
207461280 18 10xxxxxx 128 ndash 191
207461920 18 11xxxxxx 192 ndash 255
Hole in the Routing Table No coverage for 96 ndash 127 2074696019
Network of networks BGP and ASes 18
AS-1
AS-2
AS-3
Interior Routers
BGP Routers
BGP Relationships 19
Customer
Provider
Customer pays provider
Peer 1 Peer 2 Peer 3
Peers do not pay each other
Peer 2 has no incentive to route 1 3
Customer Customer
Provider
$
20
Importing Routes
From Provider
From Peer
From Peer
From Customer
ISP Routes
21
Exporting Routes
To Customer
To Peer
To Peer
To Provider
Customers get all routes
Customer and ISP routes only
$$$ generating routes
A new Internet model
22
How do we avoid sending too much for the receiver and network to handle
25
TCP Tahoe Summary bull Basic ideas
ndash Gently probe network for spare capacity ndash Drastically reduce rate on congestion ndash Windowing self-clocking ndash Other functions round trip time estimation error
recovery for every ACK if (W lt ssthresh) then W++ (SS) else W += 1W (CA) for every loss ssthresh = W2 W = 1
Congestion Avoidance Example
26
0
2
4
6
8
10
12
14
t=0
t=2
t=4
t=6
Round Trip Times
cwn
d (
in s
egm
en
ts)
Slow Start
cwnd gt= ssthresh
cwnd = 1
cwnd = 2
cwnd = 4
cwnd = 8
cwnd = 9
ssthresh = 8
27
TCP Tahoe
Window
Time
W1
W12
W2
W22
ssthresh=W12
ssthresh=W22
Slow Start
Reached initial ssthresh value switch to CA mode
28
bull Can we do better than TCP Tahoe
29
TCP Reno
Window
Time Slow Start
Reached initial ssthresh value switch to CA mode
Note how there is ldquoFast Recoveryrdquo after cutting Window in half
30
TCP Reno Fast Recovery bull Objective prevent `pipersquo from emptying after
fast retransmit ndash each dup ACK represents a packet having left the
pipe (successfully received)
ndash Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs
ssthresh W2 retransmit lost packet W ssthresh + ndup (window inflation) Wait till W is large enough transmit new packet(s) On non-dup ACK (1 RTT later) W ssthresh (window deflation) enter CA mode
31
TCP Reno Summary
bull Fast Recovery along with Fast Retransmit used to avoid slow start
bull On 3 duplicate ACKs
ndash Fast retransmit and fast recovery
bull On timeout
ndash Fast retransmit and slow start
Fast Retransmit and Fast Recovery
bull At steady state cwnd oscillates around the optimal window size
bull TCP always forces packet drops
32
Time
cwn
d
Timeout
Slow Start
Congestion Avoidance Fast RetransmitRecovery
ssthresh
Timeout
34
TCP Throughput
bull Whatrsquos the average throughout ot TCP as a function of window size and RTT
ndash Ignore slow start
bull Let W be the window size when loss occurs
bull When window is W throughput is WRTT
bull Just after loss window drops to W2 throughput to W2RTT
bull Average throughout 75 WRTT
35
TCP Futures
bull Example 1500 byte segments 100ms RTT want 10 Gbps throughput
bull Requires window size W = 83333 in-flight segments
bull Throughput in terms of loss rate
bull L = 210-10 Wow
bull New versions of TCP for high-speed needed
LRTT
MSS221
36
Fairness goal if K TCP sessions share same bottleneck link of bandwidth R each should have average rate of RK
TCP connection 1
bottleneck router
capacity R
TCP connection 2
TCP Fairness
37
Fairness (more)
bull TCP fairness dependency on RTT
ndash Connections with long RTT get less throughput
bull Parallel TCP connections
bull TCP friendliness for UDP streams
ndash Similar throughput (and behavior) as TCP eg
LRTTthroughput
1
39
TCP+HTTP refresher
bull TCP is a connection-oriented protocol
SYN
SYNACK
ACK GET URL
YOUR DATA HERE
FIN FINACK
ACK
Web Client Web Server
40
Example Web Page
Harry Potter Movies
As you all know the new HP book will be out in June and then there will be a new movie shortly after thathellip ldquoHarry Potter and the Bathtub Ringrdquo
pagehtml
hpfacejpg
castlegif
41
Client Server
The ldquoclassicrdquo approach in HTTP10 is to use one HTTP request per TCP connection serially
TCP SYN
TCP FIN
pagehtml G
TCP SYN
TCP FIN
hpfacejpg G
TCP SYN
TCP FIN
castlegif G
42
Client Server Concurrent (parallel) TCP connections can be used to make things faster
TCP SYN
TCP FIN
pagehtml G
castlegif G
F
S
G hpfacejpg
S
F
C S C S
43
Client Server
The ldquopersistent HTTPrdquo approach can re-use the same TCP connection for Multiple HTTP transfers one after another serially Amortizes TCP overhead but maintains TCP state longer at server
TCP FIN
Timeout
TCP SYN
pagehtml G
hpfacejpg G
castlegif G
44
Client Server
The ldquopipeliningrdquo feature in HTTP11 allows requests to be issued asynchronously on a persistent connection Requests must be processed in proper order Can do clever packaging
TCP FIN
Timeout
TCP SYN
pagehtml G
castlegif
hpfacejpg GG
Kick starting science
hellip well cable into wall hellip
What happens there
Hosts the Internet architecture and the E2E arguments hellip
Network Stack in Practice
8
Application
Presentation
Session
Transport
Network
Data Link
Physical
Network
Data Link
Application
Presentation
Session
Transport
Network
Data Link
Physical
Host 1 Switch Host 2
Physical
Video Client
UDP
Video Server
UDP
FTP Client
TCP
IP
Ethernet
IP
Ethernet
FTP Server
TCP
IP
Ethernet 80211n 80211n 80211n
Encapsulation Revisited
9
Web Server
TCP
IP
Ethernet
HTTP Header
TCP Header
IP Header
Ethernet Header
Ethernet Trailer
Web Page
HTTP Header
Web Page
TCP Header
HTTP Header
Web Page
IP Header
TCP Header
HTTP Header
Web Page
TCP Segment
IP Datagram
Ethernet Frame
The Hourglass
10
IPv4
TCP UDP ICMP
HTTP FTP RTP IMAP Jabber hellip
Ethernet 80211x DOCSIS hellip
Fiber Coax Twisted Pair Radio hellip
Holding the Internet Together
bull Distributed cooperation for resource allocation
ndash BGP what end-to-end paths to take (for ~50K ASes)
ndash TCP what rate to send over each path (for ~3B hosts)
12
AS 1
AS 2
AS 3
AS 4
How do we find a path
Routing on a Graph
bull Goal determine a ldquogoodrdquo path through the network from source to destination
bull What is a good path ndash Usually means the shortest path
ndash Load balanced
ndash Lowest $$$ cost
bull Network modeled as a graph ndash Routers nodes
ndash Link edges bull Edge cost delay congestion level etc
A
B C
D E
F
5
2
3 5
2 1
1
2 3
1
14
Intra-domain Routing Protocols bull Distance vector
ndash Routing Information Protocol (RIP) based on Bellman-Ford
ndash Routers periodically exchange reachability info with neighbors
bull Link state
ndash Open Shortest Path First (OSPF) based on Dijkstra
ndash Each network periodically floods neighbor information to all routers
ndash Routers locally compute routes
15
16
Hierarchical addressing route aggregation
ldquoSend me anything with addresses beginning 2002316020rdquo
2002316023
2002318023
2002330023
Fly-By-Night-ISP
Organization 0
Organization 7 Internet
Organization 1
ISPs-R-Us ldquoSend me anything with addresses beginning 199310016rdquo
2002320023 Organization 2
ISP has an address block it can further divide this block into sub blocks and assign them to subscriber organizations
Example CIDR Routing Table
17
Address Netmask Third Byte Byte Range
2074600 19 000xxxxx 0 ndash 31
20746320 19 001xxxxx 32 ndash 63
20746640 19 010xxxxx 64 ndash 95
207461280 18 10xxxxxx 128 ndash 191
207461920 18 11xxxxxx 192 ndash 255
Hole in the Routing Table No coverage for 96 ndash 127 2074696019
Network of networks BGP and ASes 18
AS-1
AS-2
AS-3
Interior Routers
BGP Routers
BGP Relationships 19
Customer
Provider
Customer pays provider
Peer 1 Peer 2 Peer 3
Peers do not pay each other
Peer 2 has no incentive to route 1 3
Customer Customer
Provider
$
20
Importing Routes
From Provider
From Peer
From Peer
From Customer
ISP Routes
21
Exporting Routes
To Customer
To Peer
To Peer
To Provider
Customers get all routes
Customer and ISP routes only
$$$ generating routes
A new Internet model
22
How do we avoid sending too much for the receiver and network to handle
25
TCP Tahoe Summary bull Basic ideas
ndash Gently probe network for spare capacity ndash Drastically reduce rate on congestion ndash Windowing self-clocking ndash Other functions round trip time estimation error
recovery for every ACK if (W lt ssthresh) then W++ (SS) else W += 1W (CA) for every loss ssthresh = W2 W = 1
Congestion Avoidance Example
26
0
2
4
6
8
10
12
14
t=0
t=2
t=4
t=6
Round Trip Times
cwn
d (
in s
egm
en
ts)
Slow Start
cwnd gt= ssthresh
cwnd = 1
cwnd = 2
cwnd = 4
cwnd = 8
cwnd = 9
ssthresh = 8
27
TCP Tahoe
Window
Time
W1
W12
W2
W22
ssthresh=W12
ssthresh=W22
Slow Start
Reached initial ssthresh value switch to CA mode
28
bull Can we do better than TCP Tahoe
29
TCP Reno
Window
Time Slow Start
Reached initial ssthresh value switch to CA mode
Note how there is ldquoFast Recoveryrdquo after cutting Window in half
30
TCP Reno Fast Recovery bull Objective prevent `pipersquo from emptying after
fast retransmit ndash each dup ACK represents a packet having left the
pipe (successfully received)
ndash Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs
ssthresh W2 retransmit lost packet W ssthresh + ndup (window inflation) Wait till W is large enough transmit new packet(s) On non-dup ACK (1 RTT later) W ssthresh (window deflation) enter CA mode
31
TCP Reno Summary
bull Fast Recovery along with Fast Retransmit used to avoid slow start
bull On 3 duplicate ACKs
ndash Fast retransmit and fast recovery
bull On timeout
ndash Fast retransmit and slow start
Fast Retransmit and Fast Recovery
bull At steady state cwnd oscillates around the optimal window size
bull TCP always forces packet drops
32
Time
cwn
d
Timeout
Slow Start
Congestion Avoidance Fast RetransmitRecovery
ssthresh
Timeout
34
TCP Throughput
bull Whatrsquos the average throughout ot TCP as a function of window size and RTT
ndash Ignore slow start
bull Let W be the window size when loss occurs
bull When window is W throughput is WRTT
bull Just after loss window drops to W2 throughput to W2RTT
bull Average throughout 75 WRTT
35
TCP Futures
bull Example 1500 byte segments 100ms RTT want 10 Gbps throughput
bull Requires window size W = 83333 in-flight segments
bull Throughput in terms of loss rate
bull L = 210-10 Wow
bull New versions of TCP for high-speed needed
LRTT
MSS221
36
Fairness goal if K TCP sessions share same bottleneck link of bandwidth R each should have average rate of RK
TCP connection 1
bottleneck router
capacity R
TCP connection 2
TCP Fairness
37
Fairness (more)
bull TCP fairness dependency on RTT
ndash Connections with long RTT get less throughput
bull Parallel TCP connections
bull TCP friendliness for UDP streams
ndash Similar throughput (and behavior) as TCP eg
LRTTthroughput
1
39
TCP+HTTP refresher
bull TCP is a connection-oriented protocol
SYN
SYNACK
ACK GET URL
YOUR DATA HERE
FIN FINACK
ACK
Web Client Web Server
40
Example Web Page
Harry Potter Movies
As you all know the new HP book will be out in June and then there will be a new movie shortly after thathellip ldquoHarry Potter and the Bathtub Ringrdquo
pagehtml
hpfacejpg
castlegif
41
Client Server
The ldquoclassicrdquo approach in HTTP10 is to use one HTTP request per TCP connection serially
TCP SYN
TCP FIN
pagehtml G
TCP SYN
TCP FIN
hpfacejpg G
TCP SYN
TCP FIN
castlegif G
42
Client Server Concurrent (parallel) TCP connections can be used to make things faster
TCP SYN
TCP FIN
pagehtml G
castlegif G
F
S
G hpfacejpg
S
F
C S C S
43
Client Server
The ldquopersistent HTTPrdquo approach can re-use the same TCP connection for Multiple HTTP transfers one after another serially Amortizes TCP overhead but maintains TCP state longer at server
TCP FIN
Timeout
TCP SYN
pagehtml G
hpfacejpg G
castlegif G
44
Client Server
The ldquopipeliningrdquo feature in HTTP11 allows requests to be issued asynchronously on a persistent connection Requests must be processed in proper order Can do clever packaging
TCP FIN
Timeout
TCP SYN
pagehtml G
castlegif
hpfacejpg GG
hellip well cable into wall hellip
What happens there
Hosts the Internet architecture and the E2E arguments hellip
Network Stack in Practice
8
Application
Presentation
Session
Transport
Network
Data Link
Physical
Network
Data Link
Application
Presentation
Session
Transport
Network
Data Link
Physical
Host 1 Switch Host 2
Physical
Video Client
UDP
Video Server
UDP
FTP Client
TCP
IP
Ethernet
IP
Ethernet
FTP Server
TCP
IP
Ethernet 80211n 80211n 80211n
Encapsulation Revisited
9
Web Server
TCP
IP
Ethernet
HTTP Header
TCP Header
IP Header
Ethernet Header
Ethernet Trailer
Web Page
HTTP Header
Web Page
TCP Header
HTTP Header
Web Page
IP Header
TCP Header
HTTP Header
Web Page
TCP Segment
IP Datagram
Ethernet Frame
The Hourglass
10
IPv4
TCP UDP ICMP
HTTP FTP RTP IMAP Jabber hellip
Ethernet 80211x DOCSIS hellip
Fiber Coax Twisted Pair Radio hellip
Holding the Internet Together
bull Distributed cooperation for resource allocation
ndash BGP what end-to-end paths to take (for ~50K ASes)
ndash TCP what rate to send over each path (for ~3B hosts)
12
AS 1
AS 2
AS 3
AS 4
How do we find a path
Routing on a Graph
bull Goal determine a ldquogoodrdquo path through the network from source to destination
bull What is a good path ndash Usually means the shortest path
ndash Load balanced
ndash Lowest $$$ cost
bull Network modeled as a graph ndash Routers nodes
ndash Link edges bull Edge cost delay congestion level etc
A
B C
D E
F
5
2
3 5
2 1
1
2 3
1
14
Intra-domain Routing Protocols bull Distance vector
ndash Routing Information Protocol (RIP) based on Bellman-Ford
ndash Routers periodically exchange reachability info with neighbors
bull Link state
ndash Open Shortest Path First (OSPF) based on Dijkstra
ndash Each network periodically floods neighbor information to all routers
ndash Routers locally compute routes
15
16
Hierarchical addressing route aggregation
ldquoSend me anything with addresses beginning 2002316020rdquo
2002316023
2002318023
2002330023
Fly-By-Night-ISP
Organization 0
Organization 7 Internet
Organization 1
ISPs-R-Us ldquoSend me anything with addresses beginning 199310016rdquo
2002320023 Organization 2
ISP has an address block it can further divide this block into sub blocks and assign them to subscriber organizations
Example CIDR Routing Table
17
Address Netmask Third Byte Byte Range
2074600 19 000xxxxx 0 ndash 31
20746320 19 001xxxxx 32 ndash 63
20746640 19 010xxxxx 64 ndash 95
207461280 18 10xxxxxx 128 ndash 191
207461920 18 11xxxxxx 192 ndash 255
Hole in the Routing Table No coverage for 96 ndash 127 2074696019
Network of networks BGP and ASes 18
AS-1
AS-2
AS-3
Interior Routers
BGP Routers
BGP Relationships 19
Customer
Provider
Customer pays provider
Peer 1 Peer 2 Peer 3
Peers do not pay each other
Peer 2 has no incentive to route 1 3
Customer Customer
Provider
$
20
Importing Routes
From Provider
From Peer
From Peer
From Customer
ISP Routes
21
Exporting Routes
To Customer
To Peer
To Peer
To Provider
Customers get all routes
Customer and ISP routes only
$$$ generating routes
A new Internet model
22
How do we avoid sending too much for the receiver and network to handle
25
TCP Tahoe Summary bull Basic ideas
ndash Gently probe network for spare capacity ndash Drastically reduce rate on congestion ndash Windowing self-clocking ndash Other functions round trip time estimation error
recovery for every ACK if (W lt ssthresh) then W++ (SS) else W += 1W (CA) for every loss ssthresh = W2 W = 1
Congestion Avoidance Example
26
0
2
4
6
8
10
12
14
t=0
t=2
t=4
t=6
Round Trip Times
cwn
d (
in s
egm
en
ts)
Slow Start
cwnd gt= ssthresh
cwnd = 1
cwnd = 2
cwnd = 4
cwnd = 8
cwnd = 9
ssthresh = 8
27
TCP Tahoe
Window
Time
W1
W12
W2
W22
ssthresh=W12
ssthresh=W22
Slow Start
Reached initial ssthresh value switch to CA mode
28
bull Can we do better than TCP Tahoe
29
TCP Reno
Window
Time Slow Start
Reached initial ssthresh value switch to CA mode
Note how there is ldquoFast Recoveryrdquo after cutting Window in half
30
TCP Reno Fast Recovery bull Objective prevent `pipersquo from emptying after
fast retransmit ndash each dup ACK represents a packet having left the
pipe (successfully received)
ndash Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs
ssthresh W2 retransmit lost packet W ssthresh + ndup (window inflation) Wait till W is large enough transmit new packet(s) On non-dup ACK (1 RTT later) W ssthresh (window deflation) enter CA mode
31
TCP Reno Summary
bull Fast Recovery along with Fast Retransmit used to avoid slow start
bull On 3 duplicate ACKs
ndash Fast retransmit and fast recovery
bull On timeout
ndash Fast retransmit and slow start
Fast Retransmit and Fast Recovery
bull At steady state cwnd oscillates around the optimal window size
bull TCP always forces packet drops
32
Time
cwn
d
Timeout
Slow Start
Congestion Avoidance Fast RetransmitRecovery
ssthresh
Timeout
34
TCP Throughput
bull Whatrsquos the average throughout ot TCP as a function of window size and RTT
ndash Ignore slow start
bull Let W be the window size when loss occurs
bull When window is W throughput is WRTT
bull Just after loss window drops to W2 throughput to W2RTT
bull Average throughout 75 WRTT
35
TCP Futures
bull Example 1500 byte segments 100ms RTT want 10 Gbps throughput
bull Requires window size W = 83333 in-flight segments
bull Throughput in terms of loss rate
bull L = 210-10 Wow
bull New versions of TCP for high-speed needed
LRTT
MSS221
36
Fairness goal if K TCP sessions share same bottleneck link of bandwidth R each should have average rate of RK
TCP connection 1
bottleneck router
capacity R
TCP connection 2
TCP Fairness
37
Fairness (more)
bull TCP fairness dependency on RTT
ndash Connections with long RTT get less throughput
bull Parallel TCP connections
bull TCP friendliness for UDP streams
ndash Similar throughput (and behavior) as TCP eg
LRTTthroughput
1
39
TCP+HTTP refresher
bull TCP is a connection-oriented protocol
SYN
SYNACK
ACK GET URL
YOUR DATA HERE
FIN FINACK
ACK
Web Client Web Server
40
Example Web Page
Harry Potter Movies
As you all know the new HP book will be out in June and then there will be a new movie shortly after thathellip ldquoHarry Potter and the Bathtub Ringrdquo
pagehtml
hpfacejpg
castlegif
41
Client Server
The ldquoclassicrdquo approach in HTTP10 is to use one HTTP request per TCP connection serially
TCP SYN
TCP FIN
pagehtml G
TCP SYN
TCP FIN
hpfacejpg G
TCP SYN
TCP FIN
castlegif G
42
Client Server Concurrent (parallel) TCP connections can be used to make things faster
TCP SYN
TCP FIN
pagehtml G
castlegif G
F
S
G hpfacejpg
S
F
C S C S
43
Client Server
The ldquopersistent HTTPrdquo approach can re-use the same TCP connection for Multiple HTTP transfers one after another serially Amortizes TCP overhead but maintains TCP state longer at server
TCP FIN
Timeout
TCP SYN
pagehtml G
hpfacejpg G
castlegif G
44
Client Server
The ldquopipeliningrdquo feature in HTTP11 allows requests to be issued asynchronously on a persistent connection Requests must be processed in proper order Can do clever packaging
TCP FIN
Timeout
TCP SYN
pagehtml G
castlegif
hpfacejpg GG
What happens there
Hosts the Internet architecture and the E2E arguments hellip
Network Stack in Practice
8
Application
Presentation
Session
Transport
Network
Data Link
Physical
Network
Data Link
Application
Presentation
Session
Transport
Network
Data Link
Physical
Host 1 Switch Host 2
Physical
Video Client
UDP
Video Server
UDP
FTP Client
TCP
IP
Ethernet
IP
Ethernet
FTP Server
TCP
IP
Ethernet 80211n 80211n 80211n
Encapsulation Revisited
9
Web Server
TCP
IP
Ethernet
HTTP Header
TCP Header
IP Header
Ethernet Header
Ethernet Trailer
Web Page
HTTP Header
Web Page
TCP Header
HTTP Header
Web Page
IP Header
TCP Header
HTTP Header
Web Page
TCP Segment
IP Datagram
Ethernet Frame
The Hourglass
10
IPv4
TCP UDP ICMP
HTTP FTP RTP IMAP Jabber hellip
Ethernet 80211x DOCSIS hellip
Fiber Coax Twisted Pair Radio hellip
Holding the Internet Together
bull Distributed cooperation for resource allocation
ndash BGP what end-to-end paths to take (for ~50K ASes)
ndash TCP what rate to send over each path (for ~3B hosts)
12
AS 1
AS 2
AS 3
AS 4
How do we find a path
Routing on a Graph
bull Goal determine a ldquogoodrdquo path through the network from source to destination
bull What is a good path ndash Usually means the shortest path
ndash Load balanced
ndash Lowest $$$ cost
bull Network modeled as a graph ndash Routers nodes
ndash Link edges bull Edge cost delay congestion level etc
A
B C
D E
F
5
2
3 5
2 1
1
2 3
1
14
Intra-domain Routing Protocols bull Distance vector
ndash Routing Information Protocol (RIP) based on Bellman-Ford
ndash Routers periodically exchange reachability info with neighbors
bull Link state
ndash Open Shortest Path First (OSPF) based on Dijkstra
ndash Each network periodically floods neighbor information to all routers
ndash Routers locally compute routes
15
16
Hierarchical addressing route aggregation
ldquoSend me anything with addresses beginning 2002316020rdquo
2002316023
2002318023
2002330023
Fly-By-Night-ISP
Organization 0
Organization 7 Internet
Organization 1
ISPs-R-Us ldquoSend me anything with addresses beginning 199310016rdquo
2002320023 Organization 2
ISP has an address block it can further divide this block into sub blocks and assign them to subscriber organizations
Example CIDR Routing Table
17
Address Netmask Third Byte Byte Range
2074600 19 000xxxxx 0 ndash 31
20746320 19 001xxxxx 32 ndash 63
20746640 19 010xxxxx 64 ndash 95
207461280 18 10xxxxxx 128 ndash 191
207461920 18 11xxxxxx 192 ndash 255
Hole in the Routing Table No coverage for 96 ndash 127 2074696019
Network of networks BGP and ASes 18
AS-1
AS-2
AS-3
Interior Routers
BGP Routers
BGP Relationships 19
Customer
Provider
Customer pays provider
Peer 1 Peer 2 Peer 3
Peers do not pay each other
Peer 2 has no incentive to route 1 3
Customer Customer
Provider
$
20
Importing Routes
From Provider
From Peer
From Peer
From Customer
ISP Routes
21
Exporting Routes
To Customer
To Peer
To Peer
To Provider
Customers get all routes
Customer and ISP routes only
$$$ generating routes
A new Internet model
22
How do we avoid sending too much for the receiver and network to handle
25
TCP Tahoe Summary bull Basic ideas
ndash Gently probe network for spare capacity ndash Drastically reduce rate on congestion ndash Windowing self-clocking ndash Other functions round trip time estimation error
recovery for every ACK if (W lt ssthresh) then W++ (SS) else W += 1W (CA) for every loss ssthresh = W2 W = 1
Congestion Avoidance Example
26
0
2
4
6
8
10
12
14
t=0
t=2
t=4
t=6
Round Trip Times
cwn
d (
in s
egm
en
ts)
Slow Start
cwnd gt= ssthresh
cwnd = 1
cwnd = 2
cwnd = 4
cwnd = 8
cwnd = 9
ssthresh = 8
27
TCP Tahoe
Window
Time
W1
W12
W2
W22
ssthresh=W12
ssthresh=W22
Slow Start
Reached initial ssthresh value switch to CA mode
28
bull Can we do better than TCP Tahoe
29
TCP Reno
Window
Time Slow Start
Reached initial ssthresh value switch to CA mode
Note how there is ldquoFast Recoveryrdquo after cutting Window in half
30
TCP Reno Fast Recovery bull Objective prevent `pipersquo from emptying after
fast retransmit ndash each dup ACK represents a packet having left the
pipe (successfully received)
ndash Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs
ssthresh W2 retransmit lost packet W ssthresh + ndup (window inflation) Wait till W is large enough transmit new packet(s) On non-dup ACK (1 RTT later) W ssthresh (window deflation) enter CA mode
31
TCP Reno Summary
bull Fast Recovery along with Fast Retransmit used to avoid slow start
bull On 3 duplicate ACKs
ndash Fast retransmit and fast recovery
bull On timeout
ndash Fast retransmit and slow start
Fast Retransmit and Fast Recovery
bull At steady state cwnd oscillates around the optimal window size
bull TCP always forces packet drops
32
Time
cwn
d
Timeout
Slow Start
Congestion Avoidance Fast RetransmitRecovery
ssthresh
Timeout
34
TCP Throughput
bull Whatrsquos the average throughout ot TCP as a function of window size and RTT
ndash Ignore slow start
bull Let W be the window size when loss occurs
bull When window is W throughput is WRTT
bull Just after loss window drops to W2 throughput to W2RTT
bull Average throughout 75 WRTT
35
TCP Futures
bull Example 1500 byte segments 100ms RTT want 10 Gbps throughput
bull Requires window size W = 83333 in-flight segments
bull Throughput in terms of loss rate
bull L = 210-10 Wow
bull New versions of TCP for high-speed needed
LRTT
MSS221
36
Fairness goal if K TCP sessions share same bottleneck link of bandwidth R each should have average rate of RK
TCP connection 1
bottleneck router
capacity R
TCP connection 2
TCP Fairness
37
Fairness (more)
bull TCP fairness dependency on RTT
ndash Connections with long RTT get less throughput
bull Parallel TCP connections
bull TCP friendliness for UDP streams
ndash Similar throughput (and behavior) as TCP eg
LRTTthroughput
1
39
TCP+HTTP refresher
bull TCP is a connection-oriented protocol
SYN
SYNACK
ACK GET URL
YOUR DATA HERE
FIN FINACK
ACK
Web Client Web Server
40
Example Web Page
Harry Potter Movies
As you all know the new HP book will be out in June and then there will be a new movie shortly after thathellip ldquoHarry Potter and the Bathtub Ringrdquo
pagehtml
hpfacejpg
castlegif
41
Client Server
The ldquoclassicrdquo approach in HTTP10 is to use one HTTP request per TCP connection serially
TCP SYN
TCP FIN
pagehtml G
TCP SYN
TCP FIN
hpfacejpg G
TCP SYN
TCP FIN
castlegif G
42
Client Server Concurrent (parallel) TCP connections can be used to make things faster
TCP SYN
TCP FIN
pagehtml G
castlegif G
F
S
G hpfacejpg
S
F
C S C S
43
Client Server
The ldquopersistent HTTPrdquo approach can re-use the same TCP connection for Multiple HTTP transfers one after another serially Amortizes TCP overhead but maintains TCP state longer at server
TCP FIN
Timeout
TCP SYN
pagehtml G
hpfacejpg G
castlegif G
44
Client Server
The ldquopipeliningrdquo feature in HTTP11 allows requests to be issued asynchronously on a persistent connection Requests must be processed in proper order Can do clever packaging
TCP FIN
Timeout
TCP SYN
pagehtml G
castlegif
hpfacejpg GG
Hosts the Internet architecture and the E2E arguments hellip
Network Stack in Practice
8
Application
Presentation
Session
Transport
Network
Data Link
Physical
Network
Data Link
Application
Presentation
Session
Transport
Network
Data Link
Physical
Host 1 Switch Host 2
Physical
Video Client
UDP
Video Server
UDP
FTP Client
TCP
IP
Ethernet
IP
Ethernet
FTP Server
TCP
IP
Ethernet 80211n 80211n 80211n
Encapsulation Revisited
9
Web Server
TCP
IP
Ethernet
HTTP Header
TCP Header
IP Header
Ethernet Header
Ethernet Trailer
Web Page
HTTP Header
Web Page
TCP Header
HTTP Header
Web Page
IP Header
TCP Header
HTTP Header
Web Page
TCP Segment
IP Datagram
Ethernet Frame
The Hourglass
10
IPv4
TCP UDP ICMP
HTTP FTP RTP IMAP Jabber hellip
Ethernet 80211x DOCSIS hellip
Fiber Coax Twisted Pair Radio hellip
Holding the Internet Together
bull Distributed cooperation for resource allocation
ndash BGP what end-to-end paths to take (for ~50K ASes)
ndash TCP what rate to send over each path (for ~3B hosts)
12
AS 1
AS 2
AS 3
AS 4
How do we find a path
Routing on a Graph
bull Goal determine a ldquogoodrdquo path through the network from source to destination
bull What is a good path ndash Usually means the shortest path
ndash Load balanced
ndash Lowest $$$ cost
bull Network modeled as a graph ndash Routers nodes
ndash Link edges bull Edge cost delay congestion level etc
A
B C
D E
F
5
2
3 5
2 1
1
2 3
1
14
Intra-domain Routing Protocols bull Distance vector
ndash Routing Information Protocol (RIP) based on Bellman-Ford
ndash Routers periodically exchange reachability info with neighbors
bull Link state
ndash Open Shortest Path First (OSPF) based on Dijkstra
ndash Each network periodically floods neighbor information to all routers
ndash Routers locally compute routes
15
16
Hierarchical addressing route aggregation
ldquoSend me anything with addresses beginning 2002316020rdquo
2002316023
2002318023
2002330023
Fly-By-Night-ISP
Organization 0
Organization 7 Internet
Organization 1
ISPs-R-Us ldquoSend me anything with addresses beginning 199310016rdquo
2002320023 Organization 2
ISP has an address block it can further divide this block into sub blocks and assign them to subscriber organizations
Example CIDR Routing Table
17
Address Netmask Third Byte Byte Range
2074600 19 000xxxxx 0 ndash 31
20746320 19 001xxxxx 32 ndash 63
20746640 19 010xxxxx 64 ndash 95
207461280 18 10xxxxxx 128 ndash 191
207461920 18 11xxxxxx 192 ndash 255
Hole in the Routing Table No coverage for 96 ndash 127 2074696019
Network of networks BGP and ASes 18
AS-1
AS-2
AS-3
Interior Routers
BGP Routers
BGP Relationships 19
Customer
Provider
Customer pays provider
Peer 1 Peer 2 Peer 3
Peers do not pay each other
Peer 2 has no incentive to route 1 3
Customer Customer
Provider
$
20
Importing Routes
From Provider
From Peer
From Peer
From Customer
ISP Routes
21
Exporting Routes
To Customer
To Peer
To Peer
To Provider
Customers get all routes
Customer and ISP routes only
$$$ generating routes
A new Internet model
22
How do we avoid sending too much for the receiver and network to handle
25
TCP Tahoe Summary bull Basic ideas
ndash Gently probe network for spare capacity ndash Drastically reduce rate on congestion ndash Windowing self-clocking ndash Other functions round trip time estimation error
recovery for every ACK if (W lt ssthresh) then W++ (SS) else W += 1W (CA) for every loss ssthresh = W2 W = 1
Congestion Avoidance Example
26
0
2
4
6
8
10
12
14
t=0
t=2
t=4
t=6
Round Trip Times
cwn
d (
in s
egm
en
ts)
Slow Start
cwnd gt= ssthresh
cwnd = 1
cwnd = 2
cwnd = 4
cwnd = 8
cwnd = 9
ssthresh = 8
27
TCP Tahoe
Window
Time
W1
W12
W2
W22
ssthresh=W12
ssthresh=W22
Slow Start
Reached initial ssthresh value switch to CA mode
28
bull Can we do better than TCP Tahoe
29
TCP Reno
Window
Time Slow Start
Reached initial ssthresh value switch to CA mode
Note how there is ldquoFast Recoveryrdquo after cutting Window in half
30
TCP Reno Fast Recovery bull Objective prevent `pipersquo from emptying after
fast retransmit ndash each dup ACK represents a packet having left the
pipe (successfully received)
ndash Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs
ssthresh W2 retransmit lost packet W ssthresh + ndup (window inflation) Wait till W is large enough transmit new packet(s) On non-dup ACK (1 RTT later) W ssthresh (window deflation) enter CA mode
31
TCP Reno Summary
bull Fast Recovery along with Fast Retransmit used to avoid slow start
bull On 3 duplicate ACKs
ndash Fast retransmit and fast recovery
bull On timeout
ndash Fast retransmit and slow start
Fast Retransmit and Fast Recovery
bull At steady state cwnd oscillates around the optimal window size
bull TCP always forces packet drops
32
Time
cwn
d
Timeout
Slow Start
Congestion Avoidance Fast RetransmitRecovery
ssthresh
Timeout
34
TCP Throughput
bull Whatrsquos the average throughout ot TCP as a function of window size and RTT
ndash Ignore slow start
bull Let W be the window size when loss occurs
bull When window is W throughput is WRTT
bull Just after loss window drops to W2 throughput to W2RTT
bull Average throughout 75 WRTT
35
TCP Futures
bull Example 1500 byte segments 100ms RTT want 10 Gbps throughput
bull Requires window size W = 83333 in-flight segments
bull Throughput in terms of loss rate
bull L = 210-10 Wow
bull New versions of TCP for high-speed needed
LRTT
MSS221
36
Fairness goal if K TCP sessions share same bottleneck link of bandwidth R each should have average rate of RK
TCP connection 1
bottleneck router
capacity R
TCP connection 2
TCP Fairness
37
Fairness (more)
bull TCP fairness dependency on RTT
ndash Connections with long RTT get less throughput
bull Parallel TCP connections
bull TCP friendliness for UDP streams
ndash Similar throughput (and behavior) as TCP eg
LRTTthroughput
1
39
TCP+HTTP refresher
bull TCP is a connection-oriented protocol
SYN
SYNACK
ACK GET URL
YOUR DATA HERE
FIN FINACK
ACK
Web Client Web Server
40
Example Web Page
Harry Potter Movies
As you all know the new HP book will be out in June and then there will be a new movie shortly after thathellip ldquoHarry Potter and the Bathtub Ringrdquo
pagehtml
hpfacejpg
castlegif
41
Client Server
The ldquoclassicrdquo approach in HTTP10 is to use one HTTP request per TCP connection serially
TCP SYN
TCP FIN
pagehtml G
TCP SYN
TCP FIN
hpfacejpg G
TCP SYN
TCP FIN
castlegif G
42
Client Server Concurrent (parallel) TCP connections can be used to make things faster
TCP SYN
TCP FIN
pagehtml G
castlegif G
F
S
G hpfacejpg
S
F
C S C S
43
Client Server
The ldquopersistent HTTPrdquo approach can re-use the same TCP connection for Multiple HTTP transfers one after another serially Amortizes TCP overhead but maintains TCP state longer at server
TCP FIN
Timeout
TCP SYN
pagehtml G
hpfacejpg G
castlegif G
44
Client Server
The ldquopipeliningrdquo feature in HTTP11 allows requests to be issued asynchronously on a persistent connection Requests must be processed in proper order Can do clever packaging
TCP FIN
Timeout
TCP SYN
pagehtml G
castlegif
hpfacejpg GG
Network Stack in Practice
8
Application
Presentation
Session
Transport
Network
Data Link
Physical
Network
Data Link
Application
Presentation
Session
Transport
Network
Data Link
Physical
Host 1 Switch Host 2
Physical
Video Client
UDP
Video Server
UDP
FTP Client
TCP
IP
Ethernet
IP
Ethernet
FTP Server
TCP
IP
Ethernet 80211n 80211n 80211n
Encapsulation Revisited
9
Web Server
TCP
IP
Ethernet
HTTP Header
TCP Header
IP Header
Ethernet Header
Ethernet Trailer
Web Page
HTTP Header
Web Page
TCP Header
HTTP Header
Web Page
IP Header
TCP Header
HTTP Header
Web Page
TCP Segment
IP Datagram
Ethernet Frame
The Hourglass
10
IPv4
TCP UDP ICMP
HTTP FTP RTP IMAP Jabber hellip
Ethernet 80211x DOCSIS hellip
Fiber Coax Twisted Pair Radio hellip
Holding the Internet Together
bull Distributed cooperation for resource allocation
ndash BGP what end-to-end paths to take (for ~50K ASes)
ndash TCP what rate to send over each path (for ~3B hosts)
12
AS 1
AS 2
AS 3
AS 4
How do we find a path
Routing on a Graph
bull Goal determine a ldquogoodrdquo path through the network from source to destination
bull What is a good path ndash Usually means the shortest path
ndash Load balanced
ndash Lowest $$$ cost
bull Network modeled as a graph ndash Routers nodes
ndash Link edges bull Edge cost delay congestion level etc
A
B C
D E
F
5
2
3 5
2 1
1
2 3
1
14
Intra-domain Routing Protocols bull Distance vector
ndash Routing Information Protocol (RIP) based on Bellman-Ford
ndash Routers periodically exchange reachability info with neighbors
bull Link state
ndash Open Shortest Path First (OSPF) based on Dijkstra
ndash Each network periodically floods neighbor information to all routers
ndash Routers locally compute routes
15
16
Hierarchical addressing route aggregation
ldquoSend me anything with addresses beginning 2002316020rdquo
2002316023
2002318023
2002330023
Fly-By-Night-ISP
Organization 0
Organization 7 Internet
Organization 1
ISPs-R-Us ldquoSend me anything with addresses beginning 199310016rdquo
2002320023 Organization 2
ISP has an address block it can further divide this block into sub blocks and assign them to subscriber organizations
Example CIDR Routing Table
17
Address Netmask Third Byte Byte Range
2074600 19 000xxxxx 0 ndash 31
20746320 19 001xxxxx 32 ndash 63
20746640 19 010xxxxx 64 ndash 95
207461280 18 10xxxxxx 128 ndash 191
207461920 18 11xxxxxx 192 ndash 255
Hole in the Routing Table No coverage for 96 ndash 127 2074696019
Network of networks BGP and ASes 18
AS-1
AS-2
AS-3
Interior Routers
BGP Routers
BGP Relationships 19
Customer
Provider
Customer pays provider
Peer 1 Peer 2 Peer 3
Peers do not pay each other
Peer 2 has no incentive to route 1 3
Customer Customer
Provider
$
20
Importing Routes
From Provider
From Peer
From Peer
From Customer
ISP Routes
21
Exporting Routes
To Customer
To Peer
To Peer
To Provider
Customers get all routes
Customer and ISP routes only
$$$ generating routes
A new Internet model
22
How do we avoid sending too much for the receiver and network to handle
25
TCP Tahoe Summary bull Basic ideas
ndash Gently probe network for spare capacity ndash Drastically reduce rate on congestion ndash Windowing self-clocking ndash Other functions round trip time estimation error
recovery for every ACK if (W lt ssthresh) then W++ (SS) else W += 1W (CA) for every loss ssthresh = W2 W = 1
Congestion Avoidance Example
26
0
2
4
6
8
10
12
14
t=0
t=2
t=4
t=6
Round Trip Times
cwn
d (
in s
egm
en
ts)
Slow Start
cwnd gt= ssthresh
cwnd = 1
cwnd = 2
cwnd = 4
cwnd = 8
cwnd = 9
ssthresh = 8
27
TCP Tahoe
Window
Time
W1
W12
W2
W22
ssthresh=W12
ssthresh=W22
Slow Start
Reached initial ssthresh value switch to CA mode
28
bull Can we do better than TCP Tahoe
29
TCP Reno
Window
Time Slow Start
Reached initial ssthresh value switch to CA mode
Note how there is ldquoFast Recoveryrdquo after cutting Window in half
30
TCP Reno Fast Recovery bull Objective prevent `pipersquo from emptying after
fast retransmit ndash each dup ACK represents a packet having left the
pipe (successfully received)
ndash Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs
ssthresh W2 retransmit lost packet W ssthresh + ndup (window inflation) Wait till W is large enough transmit new packet(s) On non-dup ACK (1 RTT later) W ssthresh (window deflation) enter CA mode
31
TCP Reno Summary
bull Fast Recovery along with Fast Retransmit used to avoid slow start
bull On 3 duplicate ACKs
ndash Fast retransmit and fast recovery
bull On timeout
ndash Fast retransmit and slow start
Fast Retransmit and Fast Recovery
bull At steady state cwnd oscillates around the optimal window size
bull TCP always forces packet drops
32
Time
cwn
d
Timeout
Slow Start
Congestion Avoidance Fast RetransmitRecovery
ssthresh
Timeout
34
TCP Throughput
bull Whatrsquos the average throughout ot TCP as a function of window size and RTT
ndash Ignore slow start
bull Let W be the window size when loss occurs
bull When window is W throughput is WRTT
bull Just after loss window drops to W2 throughput to W2RTT
bull Average throughout 75 WRTT
35
TCP Futures
bull Example 1500 byte segments 100ms RTT want 10 Gbps throughput
bull Requires window size W = 83333 in-flight segments
bull Throughput in terms of loss rate
bull L = 210-10 Wow
bull New versions of TCP for high-speed needed
LRTT
MSS221
36
Fairness goal if K TCP sessions share same bottleneck link of bandwidth R each should have average rate of RK
TCP connection 1
bottleneck router
capacity R
TCP connection 2
TCP Fairness
37
Fairness (more)
bull TCP fairness dependency on RTT
ndash Connections with long RTT get less throughput
bull Parallel TCP connections
bull TCP friendliness for UDP streams
ndash Similar throughput (and behavior) as TCP eg
LRTTthroughput
1
39
TCP+HTTP refresher
bull TCP is a connection-oriented protocol
SYN
SYNACK
ACK GET URL
YOUR DATA HERE
FIN FINACK
ACK
Web Client Web Server
40
Example Web Page
Harry Potter Movies
As you all know the new HP book will be out in June and then there will be a new movie shortly after thathellip ldquoHarry Potter and the Bathtub Ringrdquo
pagehtml
hpfacejpg
castlegif
41
Client Server
The ldquoclassicrdquo approach in HTTP10 is to use one HTTP request per TCP connection serially
TCP SYN
TCP FIN
pagehtml G
TCP SYN
TCP FIN
hpfacejpg G
TCP SYN
TCP FIN
castlegif G
42
Client Server Concurrent (parallel) TCP connections can be used to make things faster
TCP SYN
TCP FIN
pagehtml G
castlegif G
F
S
G hpfacejpg
S
F
C S C S
43
Client Server
The ldquopersistent HTTPrdquo approach can re-use the same TCP connection for Multiple HTTP transfers one after another serially Amortizes TCP overhead but maintains TCP state longer at server
TCP FIN
Timeout
TCP SYN
pagehtml G
hpfacejpg G
castlegif G
44
Client Server
The ldquopipeliningrdquo feature in HTTP11 allows requests to be issued asynchronously on a persistent connection Requests must be processed in proper order Can do clever packaging
TCP FIN
Timeout
TCP SYN
pagehtml G
castlegif
hpfacejpg GG
Encapsulation Revisited
9
Web Server
TCP
IP
Ethernet
HTTP Header
TCP Header
IP Header
Ethernet Header
Ethernet Trailer
Web Page
HTTP Header
Web Page
TCP Header
HTTP Header
Web Page
IP Header
TCP Header
HTTP Header
Web Page
TCP Segment
IP Datagram
Ethernet Frame
The Hourglass
10
IPv4
TCP UDP ICMP
HTTP FTP RTP IMAP Jabber hellip
Ethernet 80211x DOCSIS hellip
Fiber Coax Twisted Pair Radio hellip
Holding the Internet Together
bull Distributed cooperation for resource allocation
ndash BGP what end-to-end paths to take (for ~50K ASes)
ndash TCP what rate to send over each path (for ~3B hosts)
12
AS 1
AS 2
AS 3
AS 4
How do we find a path
Routing on a Graph
bull Goal determine a ldquogoodrdquo path through the network from source to destination
bull What is a good path ndash Usually means the shortest path
ndash Load balanced
ndash Lowest $$$ cost
bull Network modeled as a graph ndash Routers nodes
ndash Link edges bull Edge cost delay congestion level etc
A
B C
D E
F
5
2
3 5
2 1
1
2 3
1
14
Intra-domain Routing Protocols bull Distance vector
ndash Routing Information Protocol (RIP) based on Bellman-Ford
ndash Routers periodically exchange reachability info with neighbors
bull Link state
ndash Open Shortest Path First (OSPF) based on Dijkstra
ndash Each network periodically floods neighbor information to all routers
ndash Routers locally compute routes
15
16
Hierarchical addressing route aggregation
ldquoSend me anything with addresses beginning 2002316020rdquo
2002316023
2002318023
2002330023
Fly-By-Night-ISP
Organization 0
Organization 7 Internet
Organization 1
ISPs-R-Us ldquoSend me anything with addresses beginning 199310016rdquo
2002320023 Organization 2
ISP has an address block it can further divide this block into sub blocks and assign them to subscriber organizations
Example CIDR Routing Table
17
Address Netmask Third Byte Byte Range
2074600 19 000xxxxx 0 ndash 31
20746320 19 001xxxxx 32 ndash 63
20746640 19 010xxxxx 64 ndash 95
207461280 18 10xxxxxx 128 ndash 191
207461920 18 11xxxxxx 192 ndash 255
Hole in the Routing Table No coverage for 96 ndash 127 2074696019
Network of networks BGP and ASes 18
AS-1
AS-2
AS-3
Interior Routers
BGP Routers
BGP Relationships 19
Customer
Provider
Customer pays provider
Peer 1 Peer 2 Peer 3
Peers do not pay each other
Peer 2 has no incentive to route 1 3
Customer Customer
Provider
$
20
Importing Routes
From Provider
From Peer
From Peer
From Customer
ISP Routes
21
Exporting Routes
To Customer
To Peer
To Peer
To Provider
Customers get all routes
Customer and ISP routes only
$$$ generating routes
A new Internet model
22
How do we avoid sending too much for the receiver and network to handle
25
TCP Tahoe Summary bull Basic ideas
ndash Gently probe network for spare capacity ndash Drastically reduce rate on congestion ndash Windowing self-clocking ndash Other functions round trip time estimation error
recovery for every ACK if (W lt ssthresh) then W++ (SS) else W += 1W (CA) for every loss ssthresh = W2 W = 1
Congestion Avoidance Example
26
0
2
4
6
8
10
12
14
t=0
t=2
t=4
t=6
Round Trip Times
cwn
d (
in s
egm
en
ts)
Slow Start
cwnd gt= ssthresh
cwnd = 1
cwnd = 2
cwnd = 4
cwnd = 8
cwnd = 9
ssthresh = 8
27
TCP Tahoe
Window
Time
W1
W12
W2
W22
ssthresh=W12
ssthresh=W22
Slow Start
Reached initial ssthresh value switch to CA mode
28
bull Can we do better than TCP Tahoe
29
TCP Reno
Window
Time Slow Start
Reached initial ssthresh value switch to CA mode
Note how there is ldquoFast Recoveryrdquo after cutting Window in half
30
TCP Reno Fast Recovery bull Objective prevent `pipersquo from emptying after
fast retransmit ndash each dup ACK represents a packet having left the
pipe (successfully received)
ndash Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs
ssthresh W2 retransmit lost packet W ssthresh + ndup (window inflation) Wait till W is large enough transmit new packet(s) On non-dup ACK (1 RTT later) W ssthresh (window deflation) enter CA mode
31
TCP Reno Summary
bull Fast Recovery along with Fast Retransmit used to avoid slow start
bull On 3 duplicate ACKs
ndash Fast retransmit and fast recovery
bull On timeout
ndash Fast retransmit and slow start
Fast Retransmit and Fast Recovery
bull At steady state cwnd oscillates around the optimal window size
bull TCP always forces packet drops
32
Time
cwn
d
Timeout
Slow Start
Congestion Avoidance Fast RetransmitRecovery
ssthresh
Timeout
34
TCP Throughput
bull Whatrsquos the average throughout ot TCP as a function of window size and RTT
ndash Ignore slow start
bull Let W be the window size when loss occurs
bull When window is W throughput is WRTT
bull Just after loss window drops to W2 throughput to W2RTT
bull Average throughout 75 WRTT
35
TCP Futures
bull Example 1500 byte segments 100ms RTT want 10 Gbps throughput
bull Requires window size W = 83333 in-flight segments
bull Throughput in terms of loss rate
bull L = 210-10 Wow
bull New versions of TCP for high-speed needed
LRTT
MSS221
36
Fairness goal if K TCP sessions share same bottleneck link of bandwidth R each should have average rate of RK
TCP connection 1
bottleneck router
capacity R
TCP connection 2
TCP Fairness
37
Fairness (more)
bull TCP fairness dependency on RTT
ndash Connections with long RTT get less throughput
bull Parallel TCP connections
bull TCP friendliness for UDP streams
ndash Similar throughput (and behavior) as TCP eg
LRTTthroughput
1
39
TCP+HTTP refresher
bull TCP is a connection-oriented protocol
SYN
SYNACK
ACK GET URL
YOUR DATA HERE
FIN FINACK
ACK
Web Client Web Server
40
Example Web Page
Harry Potter Movies
As you all know the new HP book will be out in June and then there will be a new movie shortly after thathellip ldquoHarry Potter and the Bathtub Ringrdquo
pagehtml
hpfacejpg
castlegif
41
Client Server
The ldquoclassicrdquo approach in HTTP10 is to use one HTTP request per TCP connection serially
TCP SYN
TCP FIN
pagehtml G
TCP SYN
TCP FIN
hpfacejpg G
TCP SYN
TCP FIN
castlegif G
42
Client Server Concurrent (parallel) TCP connections can be used to make things faster
TCP SYN
TCP FIN
pagehtml G
castlegif G
F
S
G hpfacejpg
S
F
C S C S
43
Client Server
The ldquopersistent HTTPrdquo approach can re-use the same TCP connection for Multiple HTTP transfers one after another serially Amortizes TCP overhead but maintains TCP state longer at server
TCP FIN
Timeout
TCP SYN
pagehtml G
hpfacejpg G
castlegif G
44
Client Server
The ldquopipeliningrdquo feature in HTTP11 allows requests to be issued asynchronously on a persistent connection Requests must be processed in proper order Can do clever packaging
TCP FIN
Timeout
TCP SYN
pagehtml G
castlegif
hpfacejpg GG
The Hourglass
10
IPv4
TCP UDP ICMP
HTTP FTP RTP IMAP Jabber hellip
Ethernet 80211x DOCSIS hellip
Fiber Coax Twisted Pair Radio hellip
Holding the Internet Together
bull Distributed cooperation for resource allocation
ndash BGP what end-to-end paths to take (for ~50K ASes)
ndash TCP what rate to send over each path (for ~3B hosts)
12
AS 1
AS 2
AS 3
AS 4
How do we find a path
Routing on a Graph
bull Goal determine a ldquogoodrdquo path through the network from source to destination
bull What is a good path ndash Usually means the shortest path
ndash Load balanced
ndash Lowest $$$ cost
bull Network modeled as a graph ndash Routers nodes
ndash Link edges bull Edge cost delay congestion level etc
A
B C
D E
F
5
2
3 5
2 1
1
2 3
1
14
Intra-domain Routing Protocols bull Distance vector
ndash Routing Information Protocol (RIP) based on Bellman-Ford
ndash Routers periodically exchange reachability info with neighbors
bull Link state
ndash Open Shortest Path First (OSPF) based on Dijkstra
ndash Each network periodically floods neighbor information to all routers
ndash Routers locally compute routes
15
16
Hierarchical addressing route aggregation
ldquoSend me anything with addresses beginning 2002316020rdquo
2002316023
2002318023
2002330023
Fly-By-Night-ISP
Organization 0
Organization 7 Internet
Organization 1
ISPs-R-Us ldquoSend me anything with addresses beginning 199310016rdquo
2002320023 Organization 2
ISP has an address block it can further divide this block into sub blocks and assign them to subscriber organizations
Example CIDR Routing Table
17
Address Netmask Third Byte Byte Range
2074600 19 000xxxxx 0 ndash 31
20746320 19 001xxxxx 32 ndash 63
20746640 19 010xxxxx 64 ndash 95
207461280 18 10xxxxxx 128 ndash 191
207461920 18 11xxxxxx 192 ndash 255
Hole in the Routing Table No coverage for 96 ndash 127 2074696019
Network of networks BGP and ASes 18
AS-1
AS-2
AS-3
Interior Routers
BGP Routers
BGP Relationships 19
Customer
Provider
Customer pays provider
Peer 1 Peer 2 Peer 3
Peers do not pay each other
Peer 2 has no incentive to route 1 3
Customer Customer
Provider
$
20
Importing Routes
From Provider
From Peer
From Peer
From Customer
ISP Routes
21
Exporting Routes
To Customer
To Peer
To Peer
To Provider
Customers get all routes
Customer and ISP routes only
$$$ generating routes
A new Internet model
22
How do we avoid sending too much for the receiver and network to handle
25
TCP Tahoe Summary bull Basic ideas
ndash Gently probe network for spare capacity ndash Drastically reduce rate on congestion ndash Windowing self-clocking ndash Other functions round trip time estimation error
recovery for every ACK if (W lt ssthresh) then W++ (SS) else W += 1W (CA) for every loss ssthresh = W2 W = 1
Congestion Avoidance Example
26
0
2
4
6
8
10
12
14
t=0
t=2
t=4
t=6
Round Trip Times
cwn
d (
in s
egm
en
ts)
Slow Start
cwnd gt= ssthresh
cwnd = 1
cwnd = 2
cwnd = 4
cwnd = 8
cwnd = 9
ssthresh = 8
27
TCP Tahoe
Window
Time
W1
W12
W2
W22
ssthresh=W12
ssthresh=W22
Slow Start
Reached initial ssthresh value switch to CA mode
28
bull Can we do better than TCP Tahoe
29
TCP Reno
Window
Time Slow Start
Reached initial ssthresh value switch to CA mode
Note how there is ldquoFast Recoveryrdquo after cutting Window in half
30
TCP Reno Fast Recovery bull Objective prevent `pipersquo from emptying after
fast retransmit ndash each dup ACK represents a packet having left the
pipe (successfully received)
ndash Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs
ssthresh W2 retransmit lost packet W ssthresh + ndup (window inflation) Wait till W is large enough transmit new packet(s) On non-dup ACK (1 RTT later) W ssthresh (window deflation) enter CA mode
31
TCP Reno Summary
bull Fast Recovery along with Fast Retransmit used to avoid slow start
bull On 3 duplicate ACKs
ndash Fast retransmit and fast recovery
bull On timeout
ndash Fast retransmit and slow start
Fast Retransmit and Fast Recovery
bull At steady state cwnd oscillates around the optimal window size
bull TCP always forces packet drops
32
Time
cwn
d
Timeout
Slow Start
Congestion Avoidance Fast RetransmitRecovery
ssthresh
Timeout
34
TCP Throughput
bull Whatrsquos the average throughout ot TCP as a function of window size and RTT
ndash Ignore slow start
bull Let W be the window size when loss occurs
bull When window is W throughput is WRTT
bull Just after loss window drops to W2 throughput to W2RTT
bull Average throughout 75 WRTT
35
TCP Futures
bull Example 1500 byte segments 100ms RTT want 10 Gbps throughput
bull Requires window size W = 83333 in-flight segments
bull Throughput in terms of loss rate
bull L = 210-10 Wow
bull New versions of TCP for high-speed needed
LRTT
MSS221
36
Fairness goal if K TCP sessions share same bottleneck link of bandwidth R each should have average rate of RK
TCP connection 1
bottleneck router
capacity R
TCP connection 2
TCP Fairness
37
Fairness (more)
bull TCP fairness dependency on RTT
ndash Connections with long RTT get less throughput
bull Parallel TCP connections
bull TCP friendliness for UDP streams
ndash Similar throughput (and behavior) as TCP eg
LRTTthroughput
1
39
TCP+HTTP refresher
bull TCP is a connection-oriented protocol
SYN
SYNACK
ACK GET URL
YOUR DATA HERE
FIN FINACK
ACK
Web Client Web Server
40
Example Web Page
Harry Potter Movies
As you all know the new HP book will be out in June and then there will be a new movie shortly after thathellip ldquoHarry Potter and the Bathtub Ringrdquo
pagehtml
hpfacejpg
castlegif
41
Client Server
The ldquoclassicrdquo approach in HTTP10 is to use one HTTP request per TCP connection serially
TCP SYN
TCP FIN
pagehtml G
TCP SYN
TCP FIN
hpfacejpg G
TCP SYN
TCP FIN
castlegif G
42
Client Server Concurrent (parallel) TCP connections can be used to make things faster
TCP SYN
TCP FIN
pagehtml G
castlegif G
F
S
G hpfacejpg
S
F
C S C S
43
Client Server
The ldquopersistent HTTPrdquo approach can re-use the same TCP connection for Multiple HTTP transfers one after another serially Amortizes TCP overhead but maintains TCP state longer at server
TCP FIN
Timeout
TCP SYN
pagehtml G
hpfacejpg G
castlegif G
44
Client Server
The ldquopipeliningrdquo feature in HTTP11 allows requests to be issued asynchronously on a persistent connection Requests must be processed in proper order Can do clever packaging
TCP FIN
Timeout
TCP SYN
pagehtml G
castlegif
hpfacejpg GG
Holding the Internet Together
bull Distributed cooperation for resource allocation
ndash BGP what end-to-end paths to take (for ~50K ASes)
ndash TCP what rate to send over each path (for ~3B hosts)
12
AS 1
AS 2
AS 3
AS 4
How do we find a path
Routing on a Graph
bull Goal determine a ldquogoodrdquo path through the network from source to destination
bull What is a good path ndash Usually means the shortest path
ndash Load balanced
ndash Lowest $$$ cost
bull Network modeled as a graph ndash Routers nodes
ndash Link edges bull Edge cost delay congestion level etc
A
B C
D E
F
5
2
3 5
2 1
1
2 3
1
14
Intra-domain Routing Protocols bull Distance vector
ndash Routing Information Protocol (RIP) based on Bellman-Ford
ndash Routers periodically exchange reachability info with neighbors
bull Link state
ndash Open Shortest Path First (OSPF) based on Dijkstra
ndash Each network periodically floods neighbor information to all routers
ndash Routers locally compute routes
15
16
Hierarchical addressing route aggregation
ldquoSend me anything with addresses beginning 2002316020rdquo
2002316023
2002318023
2002330023
Fly-By-Night-ISP
Organization 0
Organization 7 Internet
Organization 1
ISPs-R-Us ldquoSend me anything with addresses beginning 199310016rdquo
2002320023 Organization 2
ISP has an address block it can further divide this block into sub blocks and assign them to subscriber organizations
Example CIDR Routing Table
17
Address Netmask Third Byte Byte Range
2074600 19 000xxxxx 0 ndash 31
20746320 19 001xxxxx 32 ndash 63
20746640 19 010xxxxx 64 ndash 95
207461280 18 10xxxxxx 128 ndash 191
207461920 18 11xxxxxx 192 ndash 255
Hole in the Routing Table No coverage for 96 ndash 127 2074696019
Network of networks BGP and ASes 18
AS-1
AS-2
AS-3
Interior Routers
BGP Routers
BGP Relationships 19
Customer
Provider
Customer pays provider
Peer 1 Peer 2 Peer 3
Peers do not pay each other
Peer 2 has no incentive to route 1 3
Customer Customer
Provider
$
20
Importing Routes
From Provider
From Peer
From Peer
From Customer
ISP Routes
21
Exporting Routes
To Customer
To Peer
To Peer
To Provider
Customers get all routes
Customer and ISP routes only
$$$ generating routes
A new Internet model
22
How do we avoid sending too much for the receiver and network to handle
25
TCP Tahoe Summary bull Basic ideas
ndash Gently probe network for spare capacity ndash Drastically reduce rate on congestion ndash Windowing self-clocking ndash Other functions round trip time estimation error
recovery for every ACK if (W lt ssthresh) then W++ (SS) else W += 1W (CA) for every loss ssthresh = W2 W = 1
Congestion Avoidance Example
26
0
2
4
6
8
10
12
14
t=0
t=2
t=4
t=6
Round Trip Times
cwn
d (
in s
egm
en
ts)
Slow Start
cwnd gt= ssthresh
cwnd = 1
cwnd = 2
cwnd = 4
cwnd = 8
cwnd = 9
ssthresh = 8
27
TCP Tahoe
Window
Time
W1
W12
W2
W22
ssthresh=W12
ssthresh=W22
Slow Start
Reached initial ssthresh value switch to CA mode
28
bull Can we do better than TCP Tahoe
29
TCP Reno
Window
Time Slow Start
Reached initial ssthresh value switch to CA mode
Note how there is ldquoFast Recoveryrdquo after cutting Window in half
30
TCP Reno Fast Recovery bull Objective prevent `pipersquo from emptying after
fast retransmit ndash each dup ACK represents a packet having left the
pipe (successfully received)
ndash Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs
ssthresh W2 retransmit lost packet W ssthresh + ndup (window inflation) Wait till W is large enough transmit new packet(s) On non-dup ACK (1 RTT later) W ssthresh (window deflation) enter CA mode
31
TCP Reno Summary
bull Fast Recovery along with Fast Retransmit used to avoid slow start
bull On 3 duplicate ACKs
ndash Fast retransmit and fast recovery
bull On timeout
ndash Fast retransmit and slow start
Fast Retransmit and Fast Recovery
bull At steady state cwnd oscillates around the optimal window size
bull TCP always forces packet drops
32
Time
cwn
d
Timeout
Slow Start
Congestion Avoidance Fast RetransmitRecovery
ssthresh
Timeout
34
TCP Throughput
bull Whatrsquos the average throughout ot TCP as a function of window size and RTT
ndash Ignore slow start
bull Let W be the window size when loss occurs
bull When window is W throughput is WRTT
bull Just after loss window drops to W2 throughput to W2RTT
bull Average throughout 75 WRTT
35
TCP Futures
bull Example 1500 byte segments 100ms RTT want 10 Gbps throughput
bull Requires window size W = 83333 in-flight segments
bull Throughput in terms of loss rate
bull L = 210-10 Wow
bull New versions of TCP for high-speed needed
LRTT
MSS221
36
Fairness goal if K TCP sessions share same bottleneck link of bandwidth R each should have average rate of RK
TCP connection 1
bottleneck router
capacity R
TCP connection 2
TCP Fairness
37
Fairness (more)
bull TCP fairness dependency on RTT
ndash Connections with long RTT get less throughput
bull Parallel TCP connections
bull TCP friendliness for UDP streams
ndash Similar throughput (and behavior) as TCP eg
LRTTthroughput
1
39
TCP+HTTP refresher
bull TCP is a connection-oriented protocol
SYN
SYNACK
ACK GET URL
YOUR DATA HERE
FIN FINACK
ACK
Web Client Web Server
40
Example Web Page
Harry Potter Movies
As you all know the new HP book will be out in June and then there will be a new movie shortly after thathellip ldquoHarry Potter and the Bathtub Ringrdquo
pagehtml
hpfacejpg
castlegif
41
Client Server
The ldquoclassicrdquo approach in HTTP10 is to use one HTTP request per TCP connection serially
TCP SYN
TCP FIN
pagehtml G
TCP SYN
TCP FIN
hpfacejpg G
TCP SYN
TCP FIN
castlegif G
42
Client Server Concurrent (parallel) TCP connections can be used to make things faster
TCP SYN
TCP FIN
pagehtml G
castlegif G
F
S
G hpfacejpg
S
F
C S C S
43
Client Server
The ldquopersistent HTTPrdquo approach can re-use the same TCP connection for Multiple HTTP transfers one after another serially Amortizes TCP overhead but maintains TCP state longer at server
TCP FIN
Timeout
TCP SYN
pagehtml G
hpfacejpg G
castlegif G
44
Client Server
The ldquopipeliningrdquo feature in HTTP11 allows requests to be issued asynchronously on a persistent connection Requests must be processed in proper order Can do clever packaging
TCP FIN
Timeout
TCP SYN
pagehtml G
castlegif
hpfacejpg GG
How do we find a path
Routing on a Graph
bull Goal determine a ldquogoodrdquo path through the network from source to destination
bull What is a good path ndash Usually means the shortest path
ndash Load balanced
ndash Lowest $$$ cost
bull Network modeled as a graph ndash Routers nodes
ndash Link edges bull Edge cost delay congestion level etc
A
B C
D E
F
5
2
3 5
2 1
1
2 3
1
14
Intra-domain Routing Protocols bull Distance vector
ndash Routing Information Protocol (RIP) based on Bellman-Ford
ndash Routers periodically exchange reachability info with neighbors
bull Link state
ndash Open Shortest Path First (OSPF) based on Dijkstra
ndash Each network periodically floods neighbor information to all routers
ndash Routers locally compute routes
15
16
Hierarchical addressing route aggregation
ldquoSend me anything with addresses beginning 2002316020rdquo
2002316023
2002318023
2002330023
Fly-By-Night-ISP
Organization 0
Organization 7 Internet
Organization 1
ISPs-R-Us ldquoSend me anything with addresses beginning 199310016rdquo
2002320023 Organization 2
ISP has an address block it can further divide this block into sub blocks and assign them to subscriber organizations
Example CIDR Routing Table
17
Address Netmask Third Byte Byte Range
2074600 19 000xxxxx 0 ndash 31
20746320 19 001xxxxx 32 ndash 63
20746640 19 010xxxxx 64 ndash 95
207461280 18 10xxxxxx 128 ndash 191
207461920 18 11xxxxxx 192 ndash 255
Hole in the Routing Table No coverage for 96 ndash 127 2074696019
Network of networks BGP and ASes 18
AS-1
AS-2
AS-3
Interior Routers
BGP Routers
BGP Relationships 19
Customer
Provider
Customer pays provider
Peer 1 Peer 2 Peer 3
Peers do not pay each other
Peer 2 has no incentive to route 1 3
Customer Customer
Provider
$
20
Importing Routes
From Provider
From Peer
From Peer
From Customer
ISP Routes
21
Exporting Routes
To Customer
To Peer
To Peer
To Provider
Customers get all routes
Customer and ISP routes only
$$$ generating routes
A new Internet model
22
How do we avoid sending too much for the receiver and network to handle
25
TCP Tahoe Summary bull Basic ideas
ndash Gently probe network for spare capacity ndash Drastically reduce rate on congestion ndash Windowing self-clocking ndash Other functions round trip time estimation error
recovery for every ACK if (W lt ssthresh) then W++ (SS) else W += 1W (CA) for every loss ssthresh = W2 W = 1
Congestion Avoidance Example
26
0
2
4
6
8
10
12
14
t=0
t=2
t=4
t=6
Round Trip Times
cwn
d (
in s
egm
en
ts)
Slow Start
cwnd gt= ssthresh
cwnd = 1
cwnd = 2
cwnd = 4
cwnd = 8
cwnd = 9
ssthresh = 8
27
TCP Tahoe
Window
Time
W1
W12
W2
W22
ssthresh=W12
ssthresh=W22
Slow Start
Reached initial ssthresh value switch to CA mode
28
bull Can we do better than TCP Tahoe
29
TCP Reno
Window
Time Slow Start
Reached initial ssthresh value switch to CA mode
Note how there is ldquoFast Recoveryrdquo after cutting Window in half
30
TCP Reno Fast Recovery bull Objective prevent `pipersquo from emptying after
fast retransmit ndash each dup ACK represents a packet having left the
pipe (successfully received)
ndash Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs
ssthresh W2 retransmit lost packet W ssthresh + ndup (window inflation) Wait till W is large enough transmit new packet(s) On non-dup ACK (1 RTT later) W ssthresh (window deflation) enter CA mode
31
TCP Reno Summary
bull Fast Recovery along with Fast Retransmit used to avoid slow start
bull On 3 duplicate ACKs
ndash Fast retransmit and fast recovery
bull On timeout
ndash Fast retransmit and slow start
Fast Retransmit and Fast Recovery
bull At steady state cwnd oscillates around the optimal window size
bull TCP always forces packet drops
32
Time
cwn
d
Timeout
Slow Start
Congestion Avoidance Fast RetransmitRecovery
ssthresh
Timeout
34
TCP Throughput
bull Whatrsquos the average throughout ot TCP as a function of window size and RTT
ndash Ignore slow start
bull Let W be the window size when loss occurs
bull When window is W throughput is WRTT
bull Just after loss window drops to W2 throughput to W2RTT
bull Average throughout 75 WRTT
35
TCP Futures
bull Example 1500 byte segments 100ms RTT want 10 Gbps throughput
bull Requires window size W = 83333 in-flight segments
bull Throughput in terms of loss rate
bull L = 210-10 Wow
bull New versions of TCP for high-speed needed
LRTT
MSS221
36
Fairness goal if K TCP sessions share same bottleneck link of bandwidth R each should have average rate of RK
TCP connection 1
bottleneck router
capacity R
TCP connection 2
TCP Fairness
37
Fairness (more)
bull TCP fairness dependency on RTT
ndash Connections with long RTT get less throughput
bull Parallel TCP connections
bull TCP friendliness for UDP streams
ndash Similar throughput (and behavior) as TCP eg
LRTTthroughput
1
39
TCP+HTTP refresher
bull TCP is a connection-oriented protocol
SYN
SYNACK
ACK GET URL
YOUR DATA HERE
FIN FINACK
ACK
Web Client Web Server
40
Example Web Page
Harry Potter Movies
As you all know the new HP book will be out in June and then there will be a new movie shortly after thathellip ldquoHarry Potter and the Bathtub Ringrdquo
pagehtml
hpfacejpg
castlegif
41
Client Server
The ldquoclassicrdquo approach in HTTP10 is to use one HTTP request per TCP connection serially
TCP SYN
TCP FIN
pagehtml G
TCP SYN
TCP FIN
hpfacejpg G
TCP SYN
TCP FIN
castlegif G
42
Client Server Concurrent (parallel) TCP connections can be used to make things faster
TCP SYN
TCP FIN
pagehtml G
castlegif G
F
S
G hpfacejpg
S
F
C S C S
43
Client Server
The ldquopersistent HTTPrdquo approach can re-use the same TCP connection for Multiple HTTP transfers one after another serially Amortizes TCP overhead but maintains TCP state longer at server
TCP FIN
Timeout
TCP SYN
pagehtml G
hpfacejpg G
castlegif G
44
Client Server
The ldquopipeliningrdquo feature in HTTP11 allows requests to be issued asynchronously on a persistent connection Requests must be processed in proper order Can do clever packaging
TCP FIN
Timeout
TCP SYN
pagehtml G
castlegif
hpfacejpg GG
Routing on a Graph
bull Goal determine a ldquogoodrdquo path through the network from source to destination
bull What is a good path ndash Usually means the shortest path
ndash Load balanced
ndash Lowest $$$ cost
bull Network modeled as a graph ndash Routers nodes
ndash Link edges bull Edge cost delay congestion level etc
A
B C
D E
F
5
2
3 5
2 1
1
2 3
1
14
Intra-domain Routing Protocols bull Distance vector
ndash Routing Information Protocol (RIP) based on Bellman-Ford
ndash Routers periodically exchange reachability info with neighbors
bull Link state
ndash Open Shortest Path First (OSPF) based on Dijkstra
ndash Each network periodically floods neighbor information to all routers
ndash Routers locally compute routes
15
16
Hierarchical addressing route aggregation
ldquoSend me anything with addresses beginning 2002316020rdquo
2002316023
2002318023
2002330023
Fly-By-Night-ISP
Organization 0
Organization 7 Internet
Organization 1
ISPs-R-Us ldquoSend me anything with addresses beginning 199310016rdquo
2002320023 Organization 2
ISP has an address block it can further divide this block into sub blocks and assign them to subscriber organizations
Example CIDR Routing Table
17
Address Netmask Third Byte Byte Range
2074600 19 000xxxxx 0 ndash 31
20746320 19 001xxxxx 32 ndash 63
20746640 19 010xxxxx 64 ndash 95
207461280 18 10xxxxxx 128 ndash 191
207461920 18 11xxxxxx 192 ndash 255
Hole in the Routing Table No coverage for 96 ndash 127 2074696019
Network of networks BGP and ASes 18
AS-1
AS-2
AS-3
Interior Routers
BGP Routers
BGP Relationships 19
Customer
Provider
Customer pays provider
Peer 1 Peer 2 Peer 3
Peers do not pay each other
Peer 2 has no incentive to route 1 3
Customer Customer
Provider
$
20
Importing Routes
From Provider
From Peer
From Peer
From Customer
ISP Routes
21
Exporting Routes
To Customer
To Peer
To Peer
To Provider
Customers get all routes
Customer and ISP routes only
$$$ generating routes
A new Internet model
22
How do we avoid sending too much for the receiver and network to handle
25
TCP Tahoe Summary bull Basic ideas
ndash Gently probe network for spare capacity ndash Drastically reduce rate on congestion ndash Windowing self-clocking ndash Other functions round trip time estimation error
recovery for every ACK if (W lt ssthresh) then W++ (SS) else W += 1W (CA) for every loss ssthresh = W2 W = 1
Congestion Avoidance Example
26
0
2
4
6
8
10
12
14
t=0
t=2
t=4
t=6
Round Trip Times
cwn
d (
in s
egm
en
ts)
Slow Start
cwnd gt= ssthresh
cwnd = 1
cwnd = 2
cwnd = 4
cwnd = 8
cwnd = 9
ssthresh = 8
27
TCP Tahoe
Window
Time
W1
W12
W2
W22
ssthresh=W12
ssthresh=W22
Slow Start
Reached initial ssthresh value switch to CA mode
28
bull Can we do better than TCP Tahoe
29
TCP Reno
Window
Time Slow Start
Reached initial ssthresh value switch to CA mode
Note how there is ldquoFast Recoveryrdquo after cutting Window in half
30
TCP Reno Fast Recovery bull Objective prevent `pipersquo from emptying after
fast retransmit ndash each dup ACK represents a packet having left the
pipe (successfully received)
ndash Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs
ssthresh W2 retransmit lost packet W ssthresh + ndup (window inflation) Wait till W is large enough transmit new packet(s) On non-dup ACK (1 RTT later) W ssthresh (window deflation) enter CA mode
31
TCP Reno Summary
bull Fast Recovery along with Fast Retransmit used to avoid slow start
bull On 3 duplicate ACKs
ndash Fast retransmit and fast recovery
bull On timeout
ndash Fast retransmit and slow start
Fast Retransmit and Fast Recovery
bull At steady state cwnd oscillates around the optimal window size
bull TCP always forces packet drops
32
Time
cwn
d
Timeout
Slow Start
Congestion Avoidance Fast RetransmitRecovery
ssthresh
Timeout
34
TCP Throughput
bull Whatrsquos the average throughout ot TCP as a function of window size and RTT
ndash Ignore slow start
bull Let W be the window size when loss occurs
bull When window is W throughput is WRTT
bull Just after loss window drops to W2 throughput to W2RTT
bull Average throughout 75 WRTT
35
TCP Futures
bull Example 1500 byte segments 100ms RTT want 10 Gbps throughput
bull Requires window size W = 83333 in-flight segments
bull Throughput in terms of loss rate
bull L = 210-10 Wow
bull New versions of TCP for high-speed needed
LRTT
MSS221
36
Fairness goal if K TCP sessions share same bottleneck link of bandwidth R each should have average rate of RK
TCP connection 1
bottleneck router
capacity R
TCP connection 2
TCP Fairness
37
Fairness (more)
bull TCP fairness dependency on RTT
ndash Connections with long RTT get less throughput
bull Parallel TCP connections
bull TCP friendliness for UDP streams
ndash Similar throughput (and behavior) as TCP eg
LRTTthroughput
1
39
TCP+HTTP refresher
bull TCP is a connection-oriented protocol
SYN
SYNACK
ACK GET URL
YOUR DATA HERE
FIN FINACK
ACK
Web Client Web Server
40
Example Web Page
Harry Potter Movies
As you all know the new HP book will be out in June and then there will be a new movie shortly after thathellip ldquoHarry Potter and the Bathtub Ringrdquo
pagehtml
hpfacejpg
castlegif
41
Client Server
The ldquoclassicrdquo approach in HTTP10 is to use one HTTP request per TCP connection serially
TCP SYN
TCP FIN
pagehtml G
TCP SYN
TCP FIN
hpfacejpg G
TCP SYN
TCP FIN
castlegif G
42
Client Server Concurrent (parallel) TCP connections can be used to make things faster
TCP SYN
TCP FIN
pagehtml G
castlegif G
F
S
G hpfacejpg
S
F
C S C S
43
Client Server
The ldquopersistent HTTPrdquo approach can re-use the same TCP connection for Multiple HTTP transfers one after another serially Amortizes TCP overhead but maintains TCP state longer at server
TCP FIN
Timeout
TCP SYN
pagehtml G
hpfacejpg G
castlegif G
44
Client Server
The ldquopipeliningrdquo feature in HTTP11 allows requests to be issued asynchronously on a persistent connection Requests must be processed in proper order Can do clever packaging
TCP FIN
Timeout
TCP SYN
pagehtml G
castlegif
hpfacejpg GG
Intra-domain Routing Protocols bull Distance vector
ndash Routing Information Protocol (RIP) based on Bellman-Ford
ndash Routers periodically exchange reachability info with neighbors
bull Link state
ndash Open Shortest Path First (OSPF) based on Dijkstra
ndash Each network periodically floods neighbor information to all routers
ndash Routers locally compute routes
15
16
Hierarchical addressing route aggregation
ldquoSend me anything with addresses beginning 2002316020rdquo
2002316023
2002318023
2002330023
Fly-By-Night-ISP
Organization 0
Organization 7 Internet
Organization 1
ISPs-R-Us ldquoSend me anything with addresses beginning 199310016rdquo
2002320023 Organization 2
ISP has an address block it can further divide this block into sub blocks and assign them to subscriber organizations
Example CIDR Routing Table
17
Address Netmask Third Byte Byte Range
2074600 19 000xxxxx 0 ndash 31
20746320 19 001xxxxx 32 ndash 63
20746640 19 010xxxxx 64 ndash 95
207461280 18 10xxxxxx 128 ndash 191
207461920 18 11xxxxxx 192 ndash 255
Hole in the Routing Table No coverage for 96 ndash 127 2074696019
Network of networks BGP and ASes 18
AS-1
AS-2
AS-3
Interior Routers
BGP Routers
BGP Relationships 19
Customer
Provider
Customer pays provider
Peer 1 Peer 2 Peer 3
Peers do not pay each other
Peer 2 has no incentive to route 1 3
Customer Customer
Provider
$
20
Importing Routes
From Provider
From Peer
From Peer
From Customer
ISP Routes
21
Exporting Routes
To Customer
To Peer
To Peer
To Provider
Customers get all routes
Customer and ISP routes only
$$$ generating routes
A new Internet model
22
How do we avoid sending too much for the receiver and network to handle
25
TCP Tahoe Summary bull Basic ideas
ndash Gently probe network for spare capacity ndash Drastically reduce rate on congestion ndash Windowing self-clocking ndash Other functions round trip time estimation error
recovery for every ACK if (W lt ssthresh) then W++ (SS) else W += 1W (CA) for every loss ssthresh = W2 W = 1
Congestion Avoidance Example
26
0
2
4
6
8
10
12
14
t=0
t=2
t=4
t=6
Round Trip Times
cwn
d (
in s
egm
en
ts)
Slow Start
cwnd gt= ssthresh
cwnd = 1
cwnd = 2
cwnd = 4
cwnd = 8
cwnd = 9
ssthresh = 8
27
TCP Tahoe
Window
Time
W1
W12
W2
W22
ssthresh=W12
ssthresh=W22
Slow Start
Reached initial ssthresh value switch to CA mode
28
bull Can we do better than TCP Tahoe
29
TCP Reno
Window
Time Slow Start
Reached initial ssthresh value switch to CA mode
Note how there is ldquoFast Recoveryrdquo after cutting Window in half
30
TCP Reno Fast Recovery bull Objective prevent `pipersquo from emptying after
fast retransmit ndash each dup ACK represents a packet having left the
pipe (successfully received)
ndash Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs
ssthresh W2 retransmit lost packet W ssthresh + ndup (window inflation) Wait till W is large enough transmit new packet(s) On non-dup ACK (1 RTT later) W ssthresh (window deflation) enter CA mode
31
TCP Reno Summary
bull Fast Recovery along with Fast Retransmit used to avoid slow start
bull On 3 duplicate ACKs
ndash Fast retransmit and fast recovery
bull On timeout
ndash Fast retransmit and slow start
Fast Retransmit and Fast Recovery
bull At steady state cwnd oscillates around the optimal window size
bull TCP always forces packet drops
32
Time
cwn
d
Timeout
Slow Start
Congestion Avoidance Fast RetransmitRecovery
ssthresh
Timeout
34
TCP Throughput
bull Whatrsquos the average throughout ot TCP as a function of window size and RTT
ndash Ignore slow start
bull Let W be the window size when loss occurs
bull When window is W throughput is WRTT
bull Just after loss window drops to W2 throughput to W2RTT
bull Average throughout 75 WRTT
35
TCP Futures
bull Example 1500 byte segments 100ms RTT want 10 Gbps throughput
bull Requires window size W = 83333 in-flight segments
bull Throughput in terms of loss rate
bull L = 210-10 Wow
bull New versions of TCP for high-speed needed
LRTT
MSS221
36
Fairness goal if K TCP sessions share same bottleneck link of bandwidth R each should have average rate of RK
TCP connection 1
bottleneck router
capacity R
TCP connection 2
TCP Fairness
37
Fairness (more)
bull TCP fairness dependency on RTT
ndash Connections with long RTT get less throughput
bull Parallel TCP connections
bull TCP friendliness for UDP streams
ndash Similar throughput (and behavior) as TCP eg
LRTTthroughput
1
39
TCP+HTTP refresher
bull TCP is a connection-oriented protocol
SYN
SYNACK
ACK GET URL
YOUR DATA HERE
FIN FINACK
ACK
Web Client Web Server
40
Example Web Page
Harry Potter Movies
As you all know the new HP book will be out in June and then there will be a new movie shortly after thathellip ldquoHarry Potter and the Bathtub Ringrdquo
pagehtml
hpfacejpg
castlegif
41
Client Server
The ldquoclassicrdquo approach in HTTP10 is to use one HTTP request per TCP connection serially
TCP SYN
TCP FIN
pagehtml G
TCP SYN
TCP FIN
hpfacejpg G
TCP SYN
TCP FIN
castlegif G
42
Client Server Concurrent (parallel) TCP connections can be used to make things faster
TCP SYN
TCP FIN
pagehtml G
castlegif G
F
S
G hpfacejpg
S
F
C S C S
43
Client Server
The ldquopersistent HTTPrdquo approach can re-use the same TCP connection for Multiple HTTP transfers one after another serially Amortizes TCP overhead but maintains TCP state longer at server
TCP FIN
Timeout
TCP SYN
pagehtml G
hpfacejpg G
castlegif G
44
Client Server
The ldquopipeliningrdquo feature in HTTP11 allows requests to be issued asynchronously on a persistent connection Requests must be processed in proper order Can do clever packaging
TCP FIN
Timeout
TCP SYN
pagehtml G
castlegif
hpfacejpg GG
16
Hierarchical addressing route aggregation
ldquoSend me anything with addresses beginning 2002316020rdquo
2002316023
2002318023
2002330023
Fly-By-Night-ISP
Organization 0
Organization 7 Internet
Organization 1
ISPs-R-Us ldquoSend me anything with addresses beginning 199310016rdquo
2002320023 Organization 2
ISP has an address block it can further divide this block into sub blocks and assign them to subscriber organizations
Example CIDR Routing Table
17
Address Netmask Third Byte Byte Range
2074600 19 000xxxxx 0 ndash 31
20746320 19 001xxxxx 32 ndash 63
20746640 19 010xxxxx 64 ndash 95
207461280 18 10xxxxxx 128 ndash 191
207461920 18 11xxxxxx 192 ndash 255
Hole in the Routing Table No coverage for 96 ndash 127 2074696019
Network of networks BGP and ASes 18
AS-1
AS-2
AS-3
Interior Routers
BGP Routers
BGP Relationships 19
Customer
Provider
Customer pays provider
Peer 1 Peer 2 Peer 3
Peers do not pay each other
Peer 2 has no incentive to route 1 3
Customer Customer
Provider
$
20
Importing Routes
From Provider
From Peer
From Peer
From Customer
ISP Routes
21
Exporting Routes
To Customer
To Peer
To Peer
To Provider
Customers get all routes
Customer and ISP routes only
$$$ generating routes
A new Internet model
22
How do we avoid sending too much for the receiver and network to handle
25
TCP Tahoe Summary bull Basic ideas
ndash Gently probe network for spare capacity ndash Drastically reduce rate on congestion ndash Windowing self-clocking ndash Other functions round trip time estimation error
recovery for every ACK if (W lt ssthresh) then W++ (SS) else W += 1W (CA) for every loss ssthresh = W2 W = 1
Congestion Avoidance Example
26
0
2
4
6
8
10
12
14
t=0
t=2
t=4
t=6
Round Trip Times
cwn
d (
in s
egm
en
ts)
Slow Start
cwnd gt= ssthresh
cwnd = 1
cwnd = 2
cwnd = 4
cwnd = 8
cwnd = 9
ssthresh = 8
27
TCP Tahoe
Window
Time
W1
W12
W2
W22
ssthresh=W12
ssthresh=W22
Slow Start
Reached initial ssthresh value switch to CA mode
28
bull Can we do better than TCP Tahoe
29
TCP Reno
Window
Time Slow Start
Reached initial ssthresh value switch to CA mode
Note how there is ldquoFast Recoveryrdquo after cutting Window in half
30
TCP Reno Fast Recovery bull Objective prevent `pipersquo from emptying after
fast retransmit ndash each dup ACK represents a packet having left the
pipe (successfully received)
ndash Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs
ssthresh W2 retransmit lost packet W ssthresh + ndup (window inflation) Wait till W is large enough transmit new packet(s) On non-dup ACK (1 RTT later) W ssthresh (window deflation) enter CA mode
31
TCP Reno Summary
bull Fast Recovery along with Fast Retransmit used to avoid slow start
bull On 3 duplicate ACKs
ndash Fast retransmit and fast recovery
bull On timeout
ndash Fast retransmit and slow start
Fast Retransmit and Fast Recovery
bull At steady state cwnd oscillates around the optimal window size
bull TCP always forces packet drops
32
Time
cwn
d
Timeout
Slow Start
Congestion Avoidance Fast RetransmitRecovery
ssthresh
Timeout
34
TCP Throughput
bull Whatrsquos the average throughout ot TCP as a function of window size and RTT
ndash Ignore slow start
bull Let W be the window size when loss occurs
bull When window is W throughput is WRTT
bull Just after loss window drops to W2 throughput to W2RTT
bull Average throughout 75 WRTT
35
TCP Futures
bull Example 1500 byte segments 100ms RTT want 10 Gbps throughput
bull Requires window size W = 83333 in-flight segments
bull Throughput in terms of loss rate
bull L = 210-10 Wow
bull New versions of TCP for high-speed needed
LRTT
MSS221
36
Fairness goal if K TCP sessions share same bottleneck link of bandwidth R each should have average rate of RK
TCP connection 1
bottleneck router
capacity R
TCP connection 2
TCP Fairness
37
Fairness (more)
bull TCP fairness dependency on RTT
ndash Connections with long RTT get less throughput
bull Parallel TCP connections
bull TCP friendliness for UDP streams
ndash Similar throughput (and behavior) as TCP eg
LRTTthroughput
1
39
TCP+HTTP refresher
bull TCP is a connection-oriented protocol
SYN
SYNACK
ACK GET URL
YOUR DATA HERE
FIN FINACK
ACK
Web Client Web Server
40
Example Web Page
Harry Potter Movies
As you all know the new HP book will be out in June and then there will be a new movie shortly after thathellip ldquoHarry Potter and the Bathtub Ringrdquo
pagehtml
hpfacejpg
castlegif
41
Client Server
The ldquoclassicrdquo approach in HTTP10 is to use one HTTP request per TCP connection serially
TCP SYN
TCP FIN
pagehtml G
TCP SYN
TCP FIN
hpfacejpg G
TCP SYN
TCP FIN
castlegif G
42
Client Server Concurrent (parallel) TCP connections can be used to make things faster
TCP SYN
TCP FIN
pagehtml G
castlegif G
F
S
G hpfacejpg
S
F
C S C S
43
Client Server
The ldquopersistent HTTPrdquo approach can re-use the same TCP connection for Multiple HTTP transfers one after another serially Amortizes TCP overhead but maintains TCP state longer at server
TCP FIN
Timeout
TCP SYN
pagehtml G
hpfacejpg G
castlegif G
44
Client Server
The ldquopipeliningrdquo feature in HTTP11 allows requests to be issued asynchronously on a persistent connection Requests must be processed in proper order Can do clever packaging
TCP FIN
Timeout
TCP SYN
pagehtml G
castlegif
hpfacejpg GG
Example CIDR Routing Table
17
Address Netmask Third Byte Byte Range
2074600 19 000xxxxx 0 ndash 31
20746320 19 001xxxxx 32 ndash 63
20746640 19 010xxxxx 64 ndash 95
207461280 18 10xxxxxx 128 ndash 191
207461920 18 11xxxxxx 192 ndash 255
Hole in the Routing Table No coverage for 96 ndash 127 2074696019
Network of networks BGP and ASes 18
AS-1
AS-2
AS-3
Interior Routers
BGP Routers
BGP Relationships 19
Customer
Provider
Customer pays provider
Peer 1 Peer 2 Peer 3
Peers do not pay each other
Peer 2 has no incentive to route 1 3
Customer Customer
Provider
$
20
Importing Routes
From Provider
From Peer
From Peer
From Customer
ISP Routes
21
Exporting Routes
To Customer
To Peer
To Peer
To Provider
Customers get all routes
Customer and ISP routes only
$$$ generating routes
A new Internet model
22
How do we avoid sending too much for the receiver and network to handle
25
TCP Tahoe Summary bull Basic ideas
ndash Gently probe network for spare capacity ndash Drastically reduce rate on congestion ndash Windowing self-clocking ndash Other functions round trip time estimation error
recovery for every ACK if (W lt ssthresh) then W++ (SS) else W += 1W (CA) for every loss ssthresh = W2 W = 1
Congestion Avoidance Example
26
0
2
4
6
8
10
12
14
t=0
t=2
t=4
t=6
Round Trip Times
cwn
d (
in s
egm
en
ts)
Slow Start
cwnd gt= ssthresh
cwnd = 1
cwnd = 2
cwnd = 4
cwnd = 8
cwnd = 9
ssthresh = 8
27
TCP Tahoe
Window
Time
W1
W12
W2
W22
ssthresh=W12
ssthresh=W22
Slow Start
Reached initial ssthresh value switch to CA mode
28
bull Can we do better than TCP Tahoe
29
TCP Reno
Window
Time Slow Start
Reached initial ssthresh value switch to CA mode
Note how there is ldquoFast Recoveryrdquo after cutting Window in half
30
TCP Reno Fast Recovery bull Objective prevent `pipersquo from emptying after
fast retransmit ndash each dup ACK represents a packet having left the
pipe (successfully received)
ndash Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs
ssthresh W2 retransmit lost packet W ssthresh + ndup (window inflation) Wait till W is large enough transmit new packet(s) On non-dup ACK (1 RTT later) W ssthresh (window deflation) enter CA mode
31
TCP Reno Summary
bull Fast Recovery along with Fast Retransmit used to avoid slow start
bull On 3 duplicate ACKs
ndash Fast retransmit and fast recovery
bull On timeout
ndash Fast retransmit and slow start
Fast Retransmit and Fast Recovery
bull At steady state cwnd oscillates around the optimal window size
bull TCP always forces packet drops
32
Time
cwn
d
Timeout
Slow Start
Congestion Avoidance Fast RetransmitRecovery
ssthresh
Timeout
34
TCP Throughput
bull Whatrsquos the average throughout ot TCP as a function of window size and RTT
ndash Ignore slow start
bull Let W be the window size when loss occurs
bull When window is W throughput is WRTT
bull Just after loss window drops to W2 throughput to W2RTT
bull Average throughout 75 WRTT
35
TCP Futures
bull Example 1500 byte segments 100ms RTT want 10 Gbps throughput
bull Requires window size W = 83333 in-flight segments
bull Throughput in terms of loss rate
bull L = 210-10 Wow
bull New versions of TCP for high-speed needed
LRTT
MSS221
36
Fairness goal if K TCP sessions share same bottleneck link of bandwidth R each should have average rate of RK
TCP connection 1
bottleneck router
capacity R
TCP connection 2
TCP Fairness
37
Fairness (more)
bull TCP fairness dependency on RTT
ndash Connections with long RTT get less throughput
bull Parallel TCP connections
bull TCP friendliness for UDP streams
ndash Similar throughput (and behavior) as TCP eg
LRTTthroughput
1
39
TCP+HTTP refresher
bull TCP is a connection-oriented protocol
SYN
SYNACK
ACK GET URL
YOUR DATA HERE
FIN FINACK
ACK
Web Client Web Server
40
Example Web Page
Harry Potter Movies
As you all know the new HP book will be out in June and then there will be a new movie shortly after thathellip ldquoHarry Potter and the Bathtub Ringrdquo
pagehtml
hpfacejpg
castlegif
41
Client Server
The ldquoclassicrdquo approach in HTTP10 is to use one HTTP request per TCP connection serially
TCP SYN
TCP FIN
pagehtml G
TCP SYN
TCP FIN
hpfacejpg G
TCP SYN
TCP FIN
castlegif G
42
Client Server Concurrent (parallel) TCP connections can be used to make things faster
TCP SYN
TCP FIN
pagehtml G
castlegif G
F
S
G hpfacejpg
S
F
C S C S
43
Client Server
The ldquopersistent HTTPrdquo approach can re-use the same TCP connection for Multiple HTTP transfers one after another serially Amortizes TCP overhead but maintains TCP state longer at server
TCP FIN
Timeout
TCP SYN
pagehtml G
hpfacejpg G
castlegif G
44
Client Server
The ldquopipeliningrdquo feature in HTTP11 allows requests to be issued asynchronously on a persistent connection Requests must be processed in proper order Can do clever packaging
TCP FIN
Timeout
TCP SYN
pagehtml G
castlegif
hpfacejpg GG
Network of networks BGP and ASes 18
AS-1
AS-2
AS-3
Interior Routers
BGP Routers
BGP Relationships 19
Customer
Provider
Customer pays provider
Peer 1 Peer 2 Peer 3
Peers do not pay each other
Peer 2 has no incentive to route 1 3
Customer Customer
Provider
$
20
Importing Routes
From Provider
From Peer
From Peer
From Customer
ISP Routes
21
Exporting Routes
To Customer
To Peer
To Peer
To Provider
Customers get all routes
Customer and ISP routes only
$$$ generating routes
A new Internet model
22
How do we avoid sending too much for the receiver and network to handle
25
TCP Tahoe Summary bull Basic ideas
ndash Gently probe network for spare capacity ndash Drastically reduce rate on congestion ndash Windowing self-clocking ndash Other functions round trip time estimation error
recovery for every ACK if (W lt ssthresh) then W++ (SS) else W += 1W (CA) for every loss ssthresh = W2 W = 1
Congestion Avoidance Example
26
0
2
4
6
8
10
12
14
t=0
t=2
t=4
t=6
Round Trip Times
cwn
d (
in s
egm
en
ts)
Slow Start
cwnd gt= ssthresh
cwnd = 1
cwnd = 2
cwnd = 4
cwnd = 8
cwnd = 9
ssthresh = 8
27
TCP Tahoe
Window
Time
W1
W12
W2
W22
ssthresh=W12
ssthresh=W22
Slow Start
Reached initial ssthresh value switch to CA mode
28
bull Can we do better than TCP Tahoe
29
TCP Reno
Window
Time Slow Start
Reached initial ssthresh value switch to CA mode
Note how there is ldquoFast Recoveryrdquo after cutting Window in half
30
TCP Reno Fast Recovery bull Objective prevent `pipersquo from emptying after
fast retransmit ndash each dup ACK represents a packet having left the
pipe (successfully received)
ndash Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs
ssthresh W2 retransmit lost packet W ssthresh + ndup (window inflation) Wait till W is large enough transmit new packet(s) On non-dup ACK (1 RTT later) W ssthresh (window deflation) enter CA mode
31
TCP Reno Summary
bull Fast Recovery along with Fast Retransmit used to avoid slow start
bull On 3 duplicate ACKs
ndash Fast retransmit and fast recovery
bull On timeout
ndash Fast retransmit and slow start
Fast Retransmit and Fast Recovery
bull At steady state cwnd oscillates around the optimal window size
bull TCP always forces packet drops
32
Time
cwn
d
Timeout
Slow Start
Congestion Avoidance Fast RetransmitRecovery
ssthresh
Timeout
34
TCP Throughput
bull Whatrsquos the average throughout ot TCP as a function of window size and RTT
ndash Ignore slow start
bull Let W be the window size when loss occurs
bull When window is W throughput is WRTT
bull Just after loss window drops to W2 throughput to W2RTT
bull Average throughout 75 WRTT
35
TCP Futures
bull Example 1500 byte segments 100ms RTT want 10 Gbps throughput
bull Requires window size W = 83333 in-flight segments
bull Throughput in terms of loss rate
bull L = 210-10 Wow
bull New versions of TCP for high-speed needed
LRTT
MSS221
36
Fairness goal if K TCP sessions share same bottleneck link of bandwidth R each should have average rate of RK
TCP connection 1
bottleneck router
capacity R
TCP connection 2
TCP Fairness
37
Fairness (more)
bull TCP fairness dependency on RTT
ndash Connections with long RTT get less throughput
bull Parallel TCP connections
bull TCP friendliness for UDP streams
ndash Similar throughput (and behavior) as TCP eg
LRTTthroughput
1
39
TCP+HTTP refresher
bull TCP is a connection-oriented protocol
SYN
SYNACK
ACK GET URL
YOUR DATA HERE
FIN FINACK
ACK
Web Client Web Server
40
Example Web Page
Harry Potter Movies
As you all know the new HP book will be out in June and then there will be a new movie shortly after thathellip ldquoHarry Potter and the Bathtub Ringrdquo
pagehtml
hpfacejpg
castlegif
41
Client Server
The ldquoclassicrdquo approach in HTTP10 is to use one HTTP request per TCP connection serially
TCP SYN
TCP FIN
pagehtml G
TCP SYN
TCP FIN
hpfacejpg G
TCP SYN
TCP FIN
castlegif G
42
Client Server Concurrent (parallel) TCP connections can be used to make things faster
TCP SYN
TCP FIN
pagehtml G
castlegif G
F
S
G hpfacejpg
S
F
C S C S
43
Client Server
The ldquopersistent HTTPrdquo approach can re-use the same TCP connection for Multiple HTTP transfers one after another serially Amortizes TCP overhead but maintains TCP state longer at server
TCP FIN
Timeout
TCP SYN
pagehtml G
hpfacejpg G
castlegif G
44
Client Server
The ldquopipeliningrdquo feature in HTTP11 allows requests to be issued asynchronously on a persistent connection Requests must be processed in proper order Can do clever packaging
TCP FIN
Timeout
TCP SYN
pagehtml G
castlegif
hpfacejpg GG
BGP Relationships 19
Customer
Provider
Customer pays provider
Peer 1 Peer 2 Peer 3
Peers do not pay each other
Peer 2 has no incentive to route 1 3
Customer Customer
Provider
$
20
Importing Routes
From Provider
From Peer
From Peer
From Customer
ISP Routes
21
Exporting Routes
To Customer
To Peer
To Peer
To Provider
Customers get all routes
Customer and ISP routes only
$$$ generating routes
A new Internet model
22
How do we avoid sending too much for the receiver and network to handle
25
TCP Tahoe Summary bull Basic ideas
ndash Gently probe network for spare capacity ndash Drastically reduce rate on congestion ndash Windowing self-clocking ndash Other functions round trip time estimation error
recovery for every ACK if (W lt ssthresh) then W++ (SS) else W += 1W (CA) for every loss ssthresh = W2 W = 1
Congestion Avoidance Example
26
0
2
4
6
8
10
12
14
t=0
t=2
t=4
t=6
Round Trip Times
cwn
d (
in s
egm
en
ts)
Slow Start
cwnd gt= ssthresh
cwnd = 1
cwnd = 2
cwnd = 4
cwnd = 8
cwnd = 9
ssthresh = 8
27
TCP Tahoe
Window
Time
W1
W12
W2
W22
ssthresh=W12
ssthresh=W22
Slow Start
Reached initial ssthresh value switch to CA mode
28
bull Can we do better than TCP Tahoe
29
TCP Reno
Window
Time Slow Start
Reached initial ssthresh value switch to CA mode
Note how there is ldquoFast Recoveryrdquo after cutting Window in half
30
TCP Reno Fast Recovery bull Objective prevent `pipersquo from emptying after
fast retransmit ndash each dup ACK represents a packet having left the
pipe (successfully received)
ndash Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs
ssthresh W2 retransmit lost packet W ssthresh + ndup (window inflation) Wait till W is large enough transmit new packet(s) On non-dup ACK (1 RTT later) W ssthresh (window deflation) enter CA mode
31
TCP Reno Summary
bull Fast Recovery along with Fast Retransmit used to avoid slow start
bull On 3 duplicate ACKs
ndash Fast retransmit and fast recovery
bull On timeout
ndash Fast retransmit and slow start
Fast Retransmit and Fast Recovery
bull At steady state cwnd oscillates around the optimal window size
bull TCP always forces packet drops
32
Time
cwn
d
Timeout
Slow Start
Congestion Avoidance Fast RetransmitRecovery
ssthresh
Timeout
34
TCP Throughput
bull Whatrsquos the average throughout ot TCP as a function of window size and RTT
ndash Ignore slow start
bull Let W be the window size when loss occurs
bull When window is W throughput is WRTT
bull Just after loss window drops to W2 throughput to W2RTT
bull Average throughout 75 WRTT
35
TCP Futures
bull Example 1500 byte segments 100ms RTT want 10 Gbps throughput
bull Requires window size W = 83333 in-flight segments
bull Throughput in terms of loss rate
bull L = 210-10 Wow
bull New versions of TCP for high-speed needed
LRTT
MSS221
36
Fairness goal if K TCP sessions share same bottleneck link of bandwidth R each should have average rate of RK
TCP connection 1
bottleneck router
capacity R
TCP connection 2
TCP Fairness
37
Fairness (more)
bull TCP fairness dependency on RTT
ndash Connections with long RTT get less throughput
bull Parallel TCP connections
bull TCP friendliness for UDP streams
ndash Similar throughput (and behavior) as TCP eg
LRTTthroughput
1
39
TCP+HTTP refresher
bull TCP is a connection-oriented protocol
SYN
SYNACK
ACK GET URL
YOUR DATA HERE
FIN FINACK
ACK
Web Client Web Server
40
Example Web Page
Harry Potter Movies
As you all know the new HP book will be out in June and then there will be a new movie shortly after thathellip ldquoHarry Potter and the Bathtub Ringrdquo
pagehtml
hpfacejpg
castlegif
41
Client Server
The ldquoclassicrdquo approach in HTTP10 is to use one HTTP request per TCP connection serially
TCP SYN
TCP FIN
pagehtml G
TCP SYN
TCP FIN
hpfacejpg G
TCP SYN
TCP FIN
castlegif G
42
Client Server Concurrent (parallel) TCP connections can be used to make things faster
TCP SYN
TCP FIN
pagehtml G
castlegif G
F
S
G hpfacejpg
S
F
C S C S
43
Client Server
The ldquopersistent HTTPrdquo approach can re-use the same TCP connection for Multiple HTTP transfers one after another serially Amortizes TCP overhead but maintains TCP state longer at server
TCP FIN
Timeout
TCP SYN
pagehtml G
hpfacejpg G
castlegif G
44
Client Server
The ldquopipeliningrdquo feature in HTTP11 allows requests to be issued asynchronously on a persistent connection Requests must be processed in proper order Can do clever packaging
TCP FIN
Timeout
TCP SYN
pagehtml G
castlegif
hpfacejpg GG
20
Importing Routes
From Provider
From Peer
From Peer
From Customer
ISP Routes
21
Exporting Routes
To Customer
To Peer
To Peer
To Provider
Customers get all routes
Customer and ISP routes only
$$$ generating routes
A new Internet model
22
How do we avoid sending too much for the receiver and network to handle
25
TCP Tahoe Summary bull Basic ideas
ndash Gently probe network for spare capacity ndash Drastically reduce rate on congestion ndash Windowing self-clocking ndash Other functions round trip time estimation error
recovery for every ACK if (W lt ssthresh) then W++ (SS) else W += 1W (CA) for every loss ssthresh = W2 W = 1
Congestion Avoidance Example
26
0
2
4
6
8
10
12
14
t=0
t=2
t=4
t=6
Round Trip Times
cwn
d (
in s
egm
en
ts)
Slow Start
cwnd gt= ssthresh
cwnd = 1
cwnd = 2
cwnd = 4
cwnd = 8
cwnd = 9
ssthresh = 8
27
TCP Tahoe
Window
Time
W1
W12
W2
W22
ssthresh=W12
ssthresh=W22
Slow Start
Reached initial ssthresh value switch to CA mode
28
bull Can we do better than TCP Tahoe
29
TCP Reno
Window
Time Slow Start
Reached initial ssthresh value switch to CA mode
Note how there is ldquoFast Recoveryrdquo after cutting Window in half
30
TCP Reno Fast Recovery bull Objective prevent `pipersquo from emptying after
fast retransmit ndash each dup ACK represents a packet having left the
pipe (successfully received)
ndash Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs
ssthresh W2 retransmit lost packet W ssthresh + ndup (window inflation) Wait till W is large enough transmit new packet(s) On non-dup ACK (1 RTT later) W ssthresh (window deflation) enter CA mode
31
TCP Reno Summary
bull Fast Recovery along with Fast Retransmit used to avoid slow start
bull On 3 duplicate ACKs
ndash Fast retransmit and fast recovery
bull On timeout
ndash Fast retransmit and slow start
Fast Retransmit and Fast Recovery
bull At steady state cwnd oscillates around the optimal window size
bull TCP always forces packet drops
32
Time
cwn
d
Timeout
Slow Start
Congestion Avoidance Fast RetransmitRecovery
ssthresh
Timeout
34
TCP Throughput
bull Whatrsquos the average throughout ot TCP as a function of window size and RTT
ndash Ignore slow start
bull Let W be the window size when loss occurs
bull When window is W throughput is WRTT
bull Just after loss window drops to W2 throughput to W2RTT
bull Average throughout 75 WRTT
35
TCP Futures
bull Example 1500 byte segments 100ms RTT want 10 Gbps throughput
bull Requires window size W = 83333 in-flight segments
bull Throughput in terms of loss rate
bull L = 210-10 Wow
bull New versions of TCP for high-speed needed
LRTT
MSS221
36
Fairness goal if K TCP sessions share same bottleneck link of bandwidth R each should have average rate of RK
TCP connection 1
bottleneck router
capacity R
TCP connection 2
TCP Fairness
37
Fairness (more)
bull TCP fairness dependency on RTT
ndash Connections with long RTT get less throughput
bull Parallel TCP connections
bull TCP friendliness for UDP streams
ndash Similar throughput (and behavior) as TCP eg
LRTTthroughput
1
39
TCP+HTTP refresher
bull TCP is a connection-oriented protocol
SYN
SYNACK
ACK GET URL
YOUR DATA HERE
FIN FINACK
ACK
Web Client Web Server
40
Example Web Page
Harry Potter Movies
As you all know the new HP book will be out in June and then there will be a new movie shortly after thathellip ldquoHarry Potter and the Bathtub Ringrdquo
pagehtml
hpfacejpg
castlegif
41
Client Server
The ldquoclassicrdquo approach in HTTP10 is to use one HTTP request per TCP connection serially
TCP SYN
TCP FIN
pagehtml G
TCP SYN
TCP FIN
hpfacejpg G
TCP SYN
TCP FIN
castlegif G
42
Client Server Concurrent (parallel) TCP connections can be used to make things faster
TCP SYN
TCP FIN
pagehtml G
castlegif G
F
S
G hpfacejpg
S
F
C S C S
43
Client Server
The ldquopersistent HTTPrdquo approach can re-use the same TCP connection for Multiple HTTP transfers one after another serially Amortizes TCP overhead but maintains TCP state longer at server
TCP FIN
Timeout
TCP SYN
pagehtml G
hpfacejpg G
castlegif G
44
Client Server
The ldquopipeliningrdquo feature in HTTP11 allows requests to be issued asynchronously on a persistent connection Requests must be processed in proper order Can do clever packaging
TCP FIN
Timeout
TCP SYN
pagehtml G
castlegif
hpfacejpg GG
21
Exporting Routes
To Customer
To Peer
To Peer
To Provider
Customers get all routes
Customer and ISP routes only
$$$ generating routes
A new Internet model
22
How do we avoid sending too much for the receiver and network to handle
25
TCP Tahoe Summary bull Basic ideas
ndash Gently probe network for spare capacity ndash Drastically reduce rate on congestion ndash Windowing self-clocking ndash Other functions round trip time estimation error
recovery for every ACK if (W lt ssthresh) then W++ (SS) else W += 1W (CA) for every loss ssthresh = W2 W = 1
Congestion Avoidance Example
26
0
2
4
6
8
10
12
14
t=0
t=2
t=4
t=6
Round Trip Times
cwn
d (
in s
egm
en
ts)
Slow Start
cwnd gt= ssthresh
cwnd = 1
cwnd = 2
cwnd = 4
cwnd = 8
cwnd = 9
ssthresh = 8
27
TCP Tahoe
Window
Time
W1
W12
W2
W22
ssthresh=W12
ssthresh=W22
Slow Start
Reached initial ssthresh value switch to CA mode
28
bull Can we do better than TCP Tahoe
29
TCP Reno
Window
Time Slow Start
Reached initial ssthresh value switch to CA mode
Note how there is ldquoFast Recoveryrdquo after cutting Window in half
30
TCP Reno Fast Recovery bull Objective prevent `pipersquo from emptying after
fast retransmit ndash each dup ACK represents a packet having left the
pipe (successfully received)
ndash Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs
ssthresh W2 retransmit lost packet W ssthresh + ndup (window inflation) Wait till W is large enough transmit new packet(s) On non-dup ACK (1 RTT later) W ssthresh (window deflation) enter CA mode
31
TCP Reno Summary
bull Fast Recovery along with Fast Retransmit used to avoid slow start
bull On 3 duplicate ACKs
ndash Fast retransmit and fast recovery
bull On timeout
ndash Fast retransmit and slow start
Fast Retransmit and Fast Recovery
bull At steady state cwnd oscillates around the optimal window size
bull TCP always forces packet drops
32
Time
cwn
d
Timeout
Slow Start
Congestion Avoidance Fast RetransmitRecovery
ssthresh
Timeout
34
TCP Throughput
bull Whatrsquos the average throughout ot TCP as a function of window size and RTT
ndash Ignore slow start
bull Let W be the window size when loss occurs
bull When window is W throughput is WRTT
bull Just after loss window drops to W2 throughput to W2RTT
bull Average throughout 75 WRTT
35
TCP Futures
bull Example 1500 byte segments 100ms RTT want 10 Gbps throughput
bull Requires window size W = 83333 in-flight segments
bull Throughput in terms of loss rate
bull L = 210-10 Wow
bull New versions of TCP for high-speed needed
LRTT
MSS221
36
Fairness goal if K TCP sessions share same bottleneck link of bandwidth R each should have average rate of RK
TCP connection 1
bottleneck router
capacity R
TCP connection 2
TCP Fairness
37
Fairness (more)
bull TCP fairness dependency on RTT
ndash Connections with long RTT get less throughput
bull Parallel TCP connections
bull TCP friendliness for UDP streams
ndash Similar throughput (and behavior) as TCP eg
LRTTthroughput
1
39
TCP+HTTP refresher
bull TCP is a connection-oriented protocol
SYN
SYNACK
ACK GET URL
YOUR DATA HERE
FIN FINACK
ACK
Web Client Web Server
40
Example Web Page
Harry Potter Movies
As you all know the new HP book will be out in June and then there will be a new movie shortly after thathellip ldquoHarry Potter and the Bathtub Ringrdquo
pagehtml
hpfacejpg
castlegif
41
Client Server
The ldquoclassicrdquo approach in HTTP10 is to use one HTTP request per TCP connection serially
TCP SYN
TCP FIN
pagehtml G
TCP SYN
TCP FIN
hpfacejpg G
TCP SYN
TCP FIN
castlegif G
42
Client Server Concurrent (parallel) TCP connections can be used to make things faster
TCP SYN
TCP FIN
pagehtml G
castlegif G
F
S
G hpfacejpg
S
F
C S C S
43
Client Server
The ldquopersistent HTTPrdquo approach can re-use the same TCP connection for Multiple HTTP transfers one after another serially Amortizes TCP overhead but maintains TCP state longer at server
TCP FIN
Timeout
TCP SYN
pagehtml G
hpfacejpg G
castlegif G
44
Client Server
The ldquopipeliningrdquo feature in HTTP11 allows requests to be issued asynchronously on a persistent connection Requests must be processed in proper order Can do clever packaging
TCP FIN
Timeout
TCP SYN
pagehtml G
castlegif
hpfacejpg GG
A new Internet model
22
How do we avoid sending too much for the receiver and network to handle
25
TCP Tahoe Summary bull Basic ideas
ndash Gently probe network for spare capacity ndash Drastically reduce rate on congestion ndash Windowing self-clocking ndash Other functions round trip time estimation error
recovery for every ACK if (W lt ssthresh) then W++ (SS) else W += 1W (CA) for every loss ssthresh = W2 W = 1
Congestion Avoidance Example
26
0
2
4
6
8
10
12
14
t=0
t=2
t=4
t=6
Round Trip Times
cwn
d (
in s
egm
en
ts)
Slow Start
cwnd gt= ssthresh
cwnd = 1
cwnd = 2
cwnd = 4
cwnd = 8
cwnd = 9
ssthresh = 8
27
TCP Tahoe
Window
Time
W1
W12
W2
W22
ssthresh=W12
ssthresh=W22
Slow Start
Reached initial ssthresh value switch to CA mode
28
bull Can we do better than TCP Tahoe
29
TCP Reno
Window
Time Slow Start
Reached initial ssthresh value switch to CA mode
Note how there is ldquoFast Recoveryrdquo after cutting Window in half
30
TCP Reno Fast Recovery bull Objective prevent `pipersquo from emptying after
fast retransmit ndash each dup ACK represents a packet having left the
pipe (successfully received)
ndash Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs
ssthresh W2 retransmit lost packet W ssthresh + ndup (window inflation) Wait till W is large enough transmit new packet(s) On non-dup ACK (1 RTT later) W ssthresh (window deflation) enter CA mode
31
TCP Reno Summary
bull Fast Recovery along with Fast Retransmit used to avoid slow start
bull On 3 duplicate ACKs
ndash Fast retransmit and fast recovery
bull On timeout
ndash Fast retransmit and slow start
Fast Retransmit and Fast Recovery
bull At steady state cwnd oscillates around the optimal window size
bull TCP always forces packet drops
32
Time
cwn
d
Timeout
Slow Start
Congestion Avoidance Fast RetransmitRecovery
ssthresh
Timeout
34
TCP Throughput
bull Whatrsquos the average throughout ot TCP as a function of window size and RTT
ndash Ignore slow start
bull Let W be the window size when loss occurs
bull When window is W throughput is WRTT
bull Just after loss window drops to W2 throughput to W2RTT
bull Average throughout 75 WRTT
35
TCP Futures
bull Example 1500 byte segments 100ms RTT want 10 Gbps throughput
bull Requires window size W = 83333 in-flight segments
bull Throughput in terms of loss rate
bull L = 210-10 Wow
bull New versions of TCP for high-speed needed
LRTT
MSS221
36
Fairness goal if K TCP sessions share same bottleneck link of bandwidth R each should have average rate of RK
TCP connection 1
bottleneck router
capacity R
TCP connection 2
TCP Fairness
37
Fairness (more)
bull TCP fairness dependency on RTT
ndash Connections with long RTT get less throughput
bull Parallel TCP connections
bull TCP friendliness for UDP streams
ndash Similar throughput (and behavior) as TCP eg
LRTTthroughput
1
39
TCP+HTTP refresher
bull TCP is a connection-oriented protocol
SYN
SYNACK
ACK GET URL
YOUR DATA HERE
FIN FINACK
ACK
Web Client Web Server
40
Example Web Page
Harry Potter Movies
As you all know the new HP book will be out in June and then there will be a new movie shortly after thathellip ldquoHarry Potter and the Bathtub Ringrdquo
pagehtml
hpfacejpg
castlegif
41
Client Server
The ldquoclassicrdquo approach in HTTP10 is to use one HTTP request per TCP connection serially
TCP SYN
TCP FIN
pagehtml G
TCP SYN
TCP FIN
hpfacejpg G
TCP SYN
TCP FIN
castlegif G
42
Client Server Concurrent (parallel) TCP connections can be used to make things faster
TCP SYN
TCP FIN
pagehtml G
castlegif G
F
S
G hpfacejpg
S
F
C S C S
43
Client Server
The ldquopersistent HTTPrdquo approach can re-use the same TCP connection for Multiple HTTP transfers one after another serially Amortizes TCP overhead but maintains TCP state longer at server
TCP FIN
Timeout
TCP SYN
pagehtml G
hpfacejpg G
castlegif G
44
Client Server
The ldquopipeliningrdquo feature in HTTP11 allows requests to be issued asynchronously on a persistent connection Requests must be processed in proper order Can do clever packaging
TCP FIN
Timeout
TCP SYN
pagehtml G
castlegif
hpfacejpg GG
How do we avoid sending too much for the receiver and network to handle
25
TCP Tahoe Summary bull Basic ideas
ndash Gently probe network for spare capacity ndash Drastically reduce rate on congestion ndash Windowing self-clocking ndash Other functions round trip time estimation error
recovery for every ACK if (W lt ssthresh) then W++ (SS) else W += 1W (CA) for every loss ssthresh = W2 W = 1
Congestion Avoidance Example
26
0
2
4
6
8
10
12
14
t=0
t=2
t=4
t=6
Round Trip Times
cwn
d (
in s
egm
en
ts)
Slow Start
cwnd gt= ssthresh
cwnd = 1
cwnd = 2
cwnd = 4
cwnd = 8
cwnd = 9
ssthresh = 8
27
TCP Tahoe
Window
Time
W1
W12
W2
W22
ssthresh=W12
ssthresh=W22
Slow Start
Reached initial ssthresh value switch to CA mode
28
bull Can we do better than TCP Tahoe
29
TCP Reno
Window
Time Slow Start
Reached initial ssthresh value switch to CA mode
Note how there is ldquoFast Recoveryrdquo after cutting Window in half
30
TCP Reno Fast Recovery bull Objective prevent `pipersquo from emptying after
fast retransmit ndash each dup ACK represents a packet having left the
pipe (successfully received)
ndash Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs
ssthresh W2 retransmit lost packet W ssthresh + ndup (window inflation) Wait till W is large enough transmit new packet(s) On non-dup ACK (1 RTT later) W ssthresh (window deflation) enter CA mode
31
TCP Reno Summary
bull Fast Recovery along with Fast Retransmit used to avoid slow start
bull On 3 duplicate ACKs
ndash Fast retransmit and fast recovery
bull On timeout
ndash Fast retransmit and slow start
Fast Retransmit and Fast Recovery
bull At steady state cwnd oscillates around the optimal window size
bull TCP always forces packet drops
32
Time
cwn
d
Timeout
Slow Start
Congestion Avoidance Fast RetransmitRecovery
ssthresh
Timeout
34
TCP Throughput
bull Whatrsquos the average throughout ot TCP as a function of window size and RTT
ndash Ignore slow start
bull Let W be the window size when loss occurs
bull When window is W throughput is WRTT
bull Just after loss window drops to W2 throughput to W2RTT
bull Average throughout 75 WRTT
35
TCP Futures
bull Example 1500 byte segments 100ms RTT want 10 Gbps throughput
bull Requires window size W = 83333 in-flight segments
bull Throughput in terms of loss rate
bull L = 210-10 Wow
bull New versions of TCP for high-speed needed
LRTT
MSS221
36
Fairness goal if K TCP sessions share same bottleneck link of bandwidth R each should have average rate of RK
TCP connection 1
bottleneck router
capacity R
TCP connection 2
TCP Fairness
37
Fairness (more)
bull TCP fairness dependency on RTT
ndash Connections with long RTT get less throughput
bull Parallel TCP connections
bull TCP friendliness for UDP streams
ndash Similar throughput (and behavior) as TCP eg
LRTTthroughput
1
39
TCP+HTTP refresher
bull TCP is a connection-oriented protocol
SYN
SYNACK
ACK GET URL
YOUR DATA HERE
FIN FINACK
ACK
Web Client Web Server
40
Example Web Page
Harry Potter Movies
As you all know the new HP book will be out in June and then there will be a new movie shortly after thathellip ldquoHarry Potter and the Bathtub Ringrdquo
pagehtml
hpfacejpg
castlegif
41
Client Server
The ldquoclassicrdquo approach in HTTP10 is to use one HTTP request per TCP connection serially
TCP SYN
TCP FIN
pagehtml G
TCP SYN
TCP FIN
hpfacejpg G
TCP SYN
TCP FIN
castlegif G
42
Client Server Concurrent (parallel) TCP connections can be used to make things faster
TCP SYN
TCP FIN
pagehtml G
castlegif G
F
S
G hpfacejpg
S
F
C S C S
43
Client Server
The ldquopersistent HTTPrdquo approach can re-use the same TCP connection for Multiple HTTP transfers one after another serially Amortizes TCP overhead but maintains TCP state longer at server
TCP FIN
Timeout
TCP SYN
pagehtml G
hpfacejpg G
castlegif G
44
Client Server
The ldquopipeliningrdquo feature in HTTP11 allows requests to be issued asynchronously on a persistent connection Requests must be processed in proper order Can do clever packaging
TCP FIN
Timeout
TCP SYN
pagehtml G
castlegif
hpfacejpg GG
25
TCP Tahoe Summary bull Basic ideas
ndash Gently probe network for spare capacity ndash Drastically reduce rate on congestion ndash Windowing self-clocking ndash Other functions round trip time estimation error
recovery for every ACK if (W lt ssthresh) then W++ (SS) else W += 1W (CA) for every loss ssthresh = W2 W = 1
Congestion Avoidance Example
26
0
2
4
6
8
10
12
14
t=0
t=2
t=4
t=6
Round Trip Times
cwn
d (
in s
egm
en
ts)
Slow Start
cwnd gt= ssthresh
cwnd = 1
cwnd = 2
cwnd = 4
cwnd = 8
cwnd = 9
ssthresh = 8
27
TCP Tahoe
Window
Time
W1
W12
W2
W22
ssthresh=W12
ssthresh=W22
Slow Start
Reached initial ssthresh value switch to CA mode
28
bull Can we do better than TCP Tahoe
29
TCP Reno
Window
Time Slow Start
Reached initial ssthresh value switch to CA mode
Note how there is ldquoFast Recoveryrdquo after cutting Window in half
30
TCP Reno Fast Recovery bull Objective prevent `pipersquo from emptying after
fast retransmit ndash each dup ACK represents a packet having left the
pipe (successfully received)
ndash Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs
ssthresh W2 retransmit lost packet W ssthresh + ndup (window inflation) Wait till W is large enough transmit new packet(s) On non-dup ACK (1 RTT later) W ssthresh (window deflation) enter CA mode
31
TCP Reno Summary
bull Fast Recovery along with Fast Retransmit used to avoid slow start
bull On 3 duplicate ACKs
ndash Fast retransmit and fast recovery
bull On timeout
ndash Fast retransmit and slow start
Fast Retransmit and Fast Recovery
bull At steady state cwnd oscillates around the optimal window size
bull TCP always forces packet drops
32
Time
cwn
d
Timeout
Slow Start
Congestion Avoidance Fast RetransmitRecovery
ssthresh
Timeout
34
TCP Throughput
bull Whatrsquos the average throughout ot TCP as a function of window size and RTT
ndash Ignore slow start
bull Let W be the window size when loss occurs
bull When window is W throughput is WRTT
bull Just after loss window drops to W2 throughput to W2RTT
bull Average throughout 75 WRTT
35
TCP Futures
bull Example 1500 byte segments 100ms RTT want 10 Gbps throughput
bull Requires window size W = 83333 in-flight segments
bull Throughput in terms of loss rate
bull L = 210-10 Wow
bull New versions of TCP for high-speed needed
LRTT
MSS221
36
Fairness goal if K TCP sessions share same bottleneck link of bandwidth R each should have average rate of RK
TCP connection 1
bottleneck router
capacity R
TCP connection 2
TCP Fairness
37
Fairness (more)
bull TCP fairness dependency on RTT
ndash Connections with long RTT get less throughput
bull Parallel TCP connections
bull TCP friendliness for UDP streams
ndash Similar throughput (and behavior) as TCP eg
LRTTthroughput
1
39
TCP+HTTP refresher
bull TCP is a connection-oriented protocol
SYN
SYNACK
ACK GET URL
YOUR DATA HERE
FIN FINACK
ACK
Web Client Web Server
40
Example Web Page
Harry Potter Movies
As you all know the new HP book will be out in June and then there will be a new movie shortly after thathellip ldquoHarry Potter and the Bathtub Ringrdquo
pagehtml
hpfacejpg
castlegif
41
Client Server
The ldquoclassicrdquo approach in HTTP10 is to use one HTTP request per TCP connection serially
TCP SYN
TCP FIN
pagehtml G
TCP SYN
TCP FIN
hpfacejpg G
TCP SYN
TCP FIN
castlegif G
42
Client Server Concurrent (parallel) TCP connections can be used to make things faster
TCP SYN
TCP FIN
pagehtml G
castlegif G
F
S
G hpfacejpg
S
F
C S C S
43
Client Server
The ldquopersistent HTTPrdquo approach can re-use the same TCP connection for Multiple HTTP transfers one after another serially Amortizes TCP overhead but maintains TCP state longer at server
TCP FIN
Timeout
TCP SYN
pagehtml G
hpfacejpg G
castlegif G
44
Client Server
The ldquopipeliningrdquo feature in HTTP11 allows requests to be issued asynchronously on a persistent connection Requests must be processed in proper order Can do clever packaging
TCP FIN
Timeout
TCP SYN
pagehtml G
castlegif
hpfacejpg GG
Congestion Avoidance Example
26
0
2
4
6
8
10
12
14
t=0
t=2
t=4
t=6
Round Trip Times
cwn
d (
in s
egm
en
ts)
Slow Start
cwnd gt= ssthresh
cwnd = 1
cwnd = 2
cwnd = 4
cwnd = 8
cwnd = 9
ssthresh = 8
27
TCP Tahoe
Window
Time
W1
W12
W2
W22
ssthresh=W12
ssthresh=W22
Slow Start
Reached initial ssthresh value switch to CA mode
28
bull Can we do better than TCP Tahoe
29
TCP Reno
Window
Time Slow Start
Reached initial ssthresh value switch to CA mode
Note how there is ldquoFast Recoveryrdquo after cutting Window in half
30
TCP Reno Fast Recovery bull Objective prevent `pipersquo from emptying after
fast retransmit ndash each dup ACK represents a packet having left the
pipe (successfully received)
ndash Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs
ssthresh W2 retransmit lost packet W ssthresh + ndup (window inflation) Wait till W is large enough transmit new packet(s) On non-dup ACK (1 RTT later) W ssthresh (window deflation) enter CA mode
31
TCP Reno Summary
bull Fast Recovery along with Fast Retransmit used to avoid slow start
bull On 3 duplicate ACKs
ndash Fast retransmit and fast recovery
bull On timeout
ndash Fast retransmit and slow start
Fast Retransmit and Fast Recovery
bull At steady state cwnd oscillates around the optimal window size
bull TCP always forces packet drops
32
Time
cwn
d
Timeout
Slow Start
Congestion Avoidance Fast RetransmitRecovery
ssthresh
Timeout
34
TCP Throughput
bull Whatrsquos the average throughout ot TCP as a function of window size and RTT
ndash Ignore slow start
bull Let W be the window size when loss occurs
bull When window is W throughput is WRTT
bull Just after loss window drops to W2 throughput to W2RTT
bull Average throughout 75 WRTT
35
TCP Futures
bull Example 1500 byte segments 100ms RTT want 10 Gbps throughput
bull Requires window size W = 83333 in-flight segments
bull Throughput in terms of loss rate
bull L = 210-10 Wow
bull New versions of TCP for high-speed needed
LRTT
MSS221
36
Fairness goal if K TCP sessions share same bottleneck link of bandwidth R each should have average rate of RK
TCP connection 1
bottleneck router
capacity R
TCP connection 2
TCP Fairness
37
Fairness (more)
bull TCP fairness dependency on RTT
ndash Connections with long RTT get less throughput
bull Parallel TCP connections
bull TCP friendliness for UDP streams
ndash Similar throughput (and behavior) as TCP eg
LRTTthroughput
1
39
TCP+HTTP refresher
bull TCP is a connection-oriented protocol
SYN
SYNACK
ACK GET URL
YOUR DATA HERE
FIN FINACK
ACK
Web Client Web Server
40
Example Web Page
Harry Potter Movies
As you all know the new HP book will be out in June and then there will be a new movie shortly after thathellip ldquoHarry Potter and the Bathtub Ringrdquo
pagehtml
hpfacejpg
castlegif
41
Client Server
The ldquoclassicrdquo approach in HTTP10 is to use one HTTP request per TCP connection serially
TCP SYN
TCP FIN
pagehtml G
TCP SYN
TCP FIN
hpfacejpg G
TCP SYN
TCP FIN
castlegif G
42
Client Server Concurrent (parallel) TCP connections can be used to make things faster
TCP SYN
TCP FIN
pagehtml G
castlegif G
F
S
G hpfacejpg
S
F
C S C S
43
Client Server
The ldquopersistent HTTPrdquo approach can re-use the same TCP connection for Multiple HTTP transfers one after another serially Amortizes TCP overhead but maintains TCP state longer at server
TCP FIN
Timeout
TCP SYN
pagehtml G
hpfacejpg G
castlegif G
44
Client Server
The ldquopipeliningrdquo feature in HTTP11 allows requests to be issued asynchronously on a persistent connection Requests must be processed in proper order Can do clever packaging
TCP FIN
Timeout
TCP SYN
pagehtml G
castlegif
hpfacejpg GG
27
TCP Tahoe
Window
Time
W1
W12
W2
W22
ssthresh=W12
ssthresh=W22
Slow Start
Reached initial ssthresh value switch to CA mode
28
bull Can we do better than TCP Tahoe
29
TCP Reno
Window
Time Slow Start
Reached initial ssthresh value switch to CA mode
Note how there is ldquoFast Recoveryrdquo after cutting Window in half
30
TCP Reno Fast Recovery bull Objective prevent `pipersquo from emptying after
fast retransmit ndash each dup ACK represents a packet having left the
pipe (successfully received)
ndash Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs
ssthresh W2 retransmit lost packet W ssthresh + ndup (window inflation) Wait till W is large enough transmit new packet(s) On non-dup ACK (1 RTT later) W ssthresh (window deflation) enter CA mode
31
TCP Reno Summary
bull Fast Recovery along with Fast Retransmit used to avoid slow start
bull On 3 duplicate ACKs
ndash Fast retransmit and fast recovery
bull On timeout
ndash Fast retransmit and slow start
Fast Retransmit and Fast Recovery
bull At steady state cwnd oscillates around the optimal window size
bull TCP always forces packet drops
32
Time
cwn
d
Timeout
Slow Start
Congestion Avoidance Fast RetransmitRecovery
ssthresh
Timeout
34
TCP Throughput
bull Whatrsquos the average throughout ot TCP as a function of window size and RTT
ndash Ignore slow start
bull Let W be the window size when loss occurs
bull When window is W throughput is WRTT
bull Just after loss window drops to W2 throughput to W2RTT
bull Average throughout 75 WRTT
35
TCP Futures
bull Example 1500 byte segments 100ms RTT want 10 Gbps throughput
bull Requires window size W = 83333 in-flight segments
bull Throughput in terms of loss rate
bull L = 210-10 Wow
bull New versions of TCP for high-speed needed
LRTT
MSS221
36
Fairness goal if K TCP sessions share same bottleneck link of bandwidth R each should have average rate of RK
TCP connection 1
bottleneck router
capacity R
TCP connection 2
TCP Fairness
37
Fairness (more)
bull TCP fairness dependency on RTT
ndash Connections with long RTT get less throughput
bull Parallel TCP connections
bull TCP friendliness for UDP streams
ndash Similar throughput (and behavior) as TCP eg
LRTTthroughput
1
39
TCP+HTTP refresher
bull TCP is a connection-oriented protocol
SYN
SYNACK
ACK GET URL
YOUR DATA HERE
FIN FINACK
ACK
Web Client Web Server
40
Example Web Page
Harry Potter Movies
As you all know the new HP book will be out in June and then there will be a new movie shortly after thathellip ldquoHarry Potter and the Bathtub Ringrdquo
pagehtml
hpfacejpg
castlegif
41
Client Server
The ldquoclassicrdquo approach in HTTP10 is to use one HTTP request per TCP connection serially
TCP SYN
TCP FIN
pagehtml G
TCP SYN
TCP FIN
hpfacejpg G
TCP SYN
TCP FIN
castlegif G
42
Client Server Concurrent (parallel) TCP connections can be used to make things faster
TCP SYN
TCP FIN
pagehtml G
castlegif G
F
S
G hpfacejpg
S
F
C S C S
43
Client Server
The ldquopersistent HTTPrdquo approach can re-use the same TCP connection for Multiple HTTP transfers one after another serially Amortizes TCP overhead but maintains TCP state longer at server
TCP FIN
Timeout
TCP SYN
pagehtml G
hpfacejpg G
castlegif G
44
Client Server
The ldquopipeliningrdquo feature in HTTP11 allows requests to be issued asynchronously on a persistent connection Requests must be processed in proper order Can do clever packaging
TCP FIN
Timeout
TCP SYN
pagehtml G
castlegif
hpfacejpg GG
28
bull Can we do better than TCP Tahoe
29
TCP Reno
Window
Time Slow Start
Reached initial ssthresh value switch to CA mode
Note how there is ldquoFast Recoveryrdquo after cutting Window in half
30
TCP Reno Fast Recovery bull Objective prevent `pipersquo from emptying after
fast retransmit ndash each dup ACK represents a packet having left the
pipe (successfully received)
ndash Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs
ssthresh W2 retransmit lost packet W ssthresh + ndup (window inflation) Wait till W is large enough transmit new packet(s) On non-dup ACK (1 RTT later) W ssthresh (window deflation) enter CA mode
31
TCP Reno Summary
bull Fast Recovery along with Fast Retransmit used to avoid slow start
bull On 3 duplicate ACKs
ndash Fast retransmit and fast recovery
bull On timeout
ndash Fast retransmit and slow start
Fast Retransmit and Fast Recovery
bull At steady state cwnd oscillates around the optimal window size
bull TCP always forces packet drops
32
Time
cwn
d
Timeout
Slow Start
Congestion Avoidance Fast RetransmitRecovery
ssthresh
Timeout
34
TCP Throughput
bull Whatrsquos the average throughout ot TCP as a function of window size and RTT
ndash Ignore slow start
bull Let W be the window size when loss occurs
bull When window is W throughput is WRTT
bull Just after loss window drops to W2 throughput to W2RTT
bull Average throughout 75 WRTT
35
TCP Futures
bull Example 1500 byte segments 100ms RTT want 10 Gbps throughput
bull Requires window size W = 83333 in-flight segments
bull Throughput in terms of loss rate
bull L = 210-10 Wow
bull New versions of TCP for high-speed needed
LRTT
MSS221
36
Fairness goal if K TCP sessions share same bottleneck link of bandwidth R each should have average rate of RK
TCP connection 1
bottleneck router
capacity R
TCP connection 2
TCP Fairness
37
Fairness (more)
bull TCP fairness dependency on RTT
ndash Connections with long RTT get less throughput
bull Parallel TCP connections
bull TCP friendliness for UDP streams
ndash Similar throughput (and behavior) as TCP eg
LRTTthroughput
1
39
TCP+HTTP refresher
bull TCP is a connection-oriented protocol
SYN
SYNACK
ACK GET URL
YOUR DATA HERE
FIN FINACK
ACK
Web Client Web Server
40
Example Web Page
Harry Potter Movies
As you all know the new HP book will be out in June and then there will be a new movie shortly after thathellip ldquoHarry Potter and the Bathtub Ringrdquo
pagehtml
hpfacejpg
castlegif
41
Client Server
The ldquoclassicrdquo approach in HTTP10 is to use one HTTP request per TCP connection serially
TCP SYN
TCP FIN
pagehtml G
TCP SYN
TCP FIN
hpfacejpg G
TCP SYN
TCP FIN
castlegif G
42
Client Server Concurrent (parallel) TCP connections can be used to make things faster
TCP SYN
TCP FIN
pagehtml G
castlegif G
F
S
G hpfacejpg
S
F
C S C S
43
Client Server
The ldquopersistent HTTPrdquo approach can re-use the same TCP connection for Multiple HTTP transfers one after another serially Amortizes TCP overhead but maintains TCP state longer at server
TCP FIN
Timeout
TCP SYN
pagehtml G
hpfacejpg G
castlegif G
44
Client Server
The ldquopipeliningrdquo feature in HTTP11 allows requests to be issued asynchronously on a persistent connection Requests must be processed in proper order Can do clever packaging
TCP FIN
Timeout
TCP SYN
pagehtml G
castlegif
hpfacejpg GG
29
TCP Reno
Window
Time Slow Start
Reached initial ssthresh value switch to CA mode
Note how there is ldquoFast Recoveryrdquo after cutting Window in half
30
TCP Reno Fast Recovery bull Objective prevent `pipersquo from emptying after
fast retransmit ndash each dup ACK represents a packet having left the
pipe (successfully received)
ndash Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs
ssthresh W2 retransmit lost packet W ssthresh + ndup (window inflation) Wait till W is large enough transmit new packet(s) On non-dup ACK (1 RTT later) W ssthresh (window deflation) enter CA mode
31
TCP Reno Summary
bull Fast Recovery along with Fast Retransmit used to avoid slow start
bull On 3 duplicate ACKs
ndash Fast retransmit and fast recovery
bull On timeout
ndash Fast retransmit and slow start
Fast Retransmit and Fast Recovery
bull At steady state cwnd oscillates around the optimal window size
bull TCP always forces packet drops
32
Time
cwn
d
Timeout
Slow Start
Congestion Avoidance Fast RetransmitRecovery
ssthresh
Timeout
34
TCP Throughput
bull Whatrsquos the average throughout ot TCP as a function of window size and RTT
ndash Ignore slow start
bull Let W be the window size when loss occurs
bull When window is W throughput is WRTT
bull Just after loss window drops to W2 throughput to W2RTT
bull Average throughout 75 WRTT
35
TCP Futures
bull Example 1500 byte segments 100ms RTT want 10 Gbps throughput
bull Requires window size W = 83333 in-flight segments
bull Throughput in terms of loss rate
bull L = 210-10 Wow
bull New versions of TCP for high-speed needed
LRTT
MSS221
36
Fairness goal if K TCP sessions share same bottleneck link of bandwidth R each should have average rate of RK
TCP connection 1
bottleneck router
capacity R
TCP connection 2
TCP Fairness
37
Fairness (more)
bull TCP fairness dependency on RTT
ndash Connections with long RTT get less throughput
bull Parallel TCP connections
bull TCP friendliness for UDP streams
ndash Similar throughput (and behavior) as TCP eg
LRTTthroughput
1
39
TCP+HTTP refresher
bull TCP is a connection-oriented protocol
SYN
SYNACK
ACK GET URL
YOUR DATA HERE
FIN FINACK
ACK
Web Client Web Server
40
Example Web Page
Harry Potter Movies
As you all know the new HP book will be out in June and then there will be a new movie shortly after thathellip ldquoHarry Potter and the Bathtub Ringrdquo
pagehtml
hpfacejpg
castlegif
41
Client Server
The ldquoclassicrdquo approach in HTTP10 is to use one HTTP request per TCP connection serially
TCP SYN
TCP FIN
pagehtml G
TCP SYN
TCP FIN
hpfacejpg G
TCP SYN
TCP FIN
castlegif G
42
Client Server Concurrent (parallel) TCP connections can be used to make things faster
TCP SYN
TCP FIN
pagehtml G
castlegif G
F
S
G hpfacejpg
S
F
C S C S
43
Client Server
The ldquopersistent HTTPrdquo approach can re-use the same TCP connection for Multiple HTTP transfers one after another serially Amortizes TCP overhead but maintains TCP state longer at server
TCP FIN
Timeout
TCP SYN
pagehtml G
hpfacejpg G
castlegif G
44
Client Server
The ldquopipeliningrdquo feature in HTTP11 allows requests to be issued asynchronously on a persistent connection Requests must be processed in proper order Can do clever packaging
TCP FIN
Timeout
TCP SYN
pagehtml G
castlegif
hpfacejpg GG
30
TCP Reno Fast Recovery bull Objective prevent `pipersquo from emptying after
fast retransmit ndash each dup ACK represents a packet having left the
pipe (successfully received)
ndash Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs
ssthresh W2 retransmit lost packet W ssthresh + ndup (window inflation) Wait till W is large enough transmit new packet(s) On non-dup ACK (1 RTT later) W ssthresh (window deflation) enter CA mode
31
TCP Reno Summary
bull Fast Recovery along with Fast Retransmit used to avoid slow start
bull On 3 duplicate ACKs
ndash Fast retransmit and fast recovery
bull On timeout
ndash Fast retransmit and slow start
Fast Retransmit and Fast Recovery
bull At steady state cwnd oscillates around the optimal window size
bull TCP always forces packet drops
32
Time
cwn
d
Timeout
Slow Start
Congestion Avoidance Fast RetransmitRecovery
ssthresh
Timeout
34
TCP Throughput
bull Whatrsquos the average throughout ot TCP as a function of window size and RTT
ndash Ignore slow start
bull Let W be the window size when loss occurs
bull When window is W throughput is WRTT
bull Just after loss window drops to W2 throughput to W2RTT
bull Average throughout 75 WRTT
35
TCP Futures
bull Example 1500 byte segments 100ms RTT want 10 Gbps throughput
bull Requires window size W = 83333 in-flight segments
bull Throughput in terms of loss rate
bull L = 210-10 Wow
bull New versions of TCP for high-speed needed
LRTT
MSS221
36
Fairness goal if K TCP sessions share same bottleneck link of bandwidth R each should have average rate of RK
TCP connection 1
bottleneck router
capacity R
TCP connection 2
TCP Fairness
37
Fairness (more)
bull TCP fairness dependency on RTT
ndash Connections with long RTT get less throughput
bull Parallel TCP connections
bull TCP friendliness for UDP streams
ndash Similar throughput (and behavior) as TCP eg
LRTTthroughput
1
39
TCP+HTTP refresher
bull TCP is a connection-oriented protocol
SYN
SYNACK
ACK GET URL
YOUR DATA HERE
FIN FINACK
ACK
Web Client Web Server
40
Example Web Page
Harry Potter Movies
As you all know the new HP book will be out in June and then there will be a new movie shortly after thathellip ldquoHarry Potter and the Bathtub Ringrdquo
pagehtml
hpfacejpg
castlegif
41
Client Server
The ldquoclassicrdquo approach in HTTP10 is to use one HTTP request per TCP connection serially
TCP SYN
TCP FIN
pagehtml G
TCP SYN
TCP FIN
hpfacejpg G
TCP SYN
TCP FIN
castlegif G
42
Client Server Concurrent (parallel) TCP connections can be used to make things faster
TCP SYN
TCP FIN
pagehtml G
castlegif G
F
S
G hpfacejpg
S
F
C S C S
43
Client Server
The ldquopersistent HTTPrdquo approach can re-use the same TCP connection for Multiple HTTP transfers one after another serially Amortizes TCP overhead but maintains TCP state longer at server
TCP FIN
Timeout
TCP SYN
pagehtml G
hpfacejpg G
castlegif G
44
Client Server
The ldquopipeliningrdquo feature in HTTP11 allows requests to be issued asynchronously on a persistent connection Requests must be processed in proper order Can do clever packaging
TCP FIN
Timeout
TCP SYN
pagehtml G
castlegif
hpfacejpg GG
31
TCP Reno Summary
bull Fast Recovery along with Fast Retransmit used to avoid slow start
bull On 3 duplicate ACKs
ndash Fast retransmit and fast recovery
bull On timeout
ndash Fast retransmit and slow start
Fast Retransmit and Fast Recovery
bull At steady state cwnd oscillates around the optimal window size
bull TCP always forces packet drops
32
Time
cwn
d
Timeout
Slow Start
Congestion Avoidance Fast RetransmitRecovery
ssthresh
Timeout
34
TCP Throughput
bull Whatrsquos the average throughout ot TCP as a function of window size and RTT
ndash Ignore slow start
bull Let W be the window size when loss occurs
bull When window is W throughput is WRTT
bull Just after loss window drops to W2 throughput to W2RTT
bull Average throughout 75 WRTT
35
TCP Futures
bull Example 1500 byte segments 100ms RTT want 10 Gbps throughput
bull Requires window size W = 83333 in-flight segments
bull Throughput in terms of loss rate
bull L = 210-10 Wow
bull New versions of TCP for high-speed needed
LRTT
MSS221
36
Fairness goal if K TCP sessions share same bottleneck link of bandwidth R each should have average rate of RK
TCP connection 1
bottleneck router
capacity R
TCP connection 2
TCP Fairness
37
Fairness (more)
bull TCP fairness dependency on RTT
ndash Connections with long RTT get less throughput
bull Parallel TCP connections
bull TCP friendliness for UDP streams
ndash Similar throughput (and behavior) as TCP eg
LRTTthroughput
1
39
TCP+HTTP refresher
bull TCP is a connection-oriented protocol
SYN
SYNACK
ACK GET URL
YOUR DATA HERE
FIN FINACK
ACK
Web Client Web Server
40
Example Web Page
Harry Potter Movies
As you all know the new HP book will be out in June and then there will be a new movie shortly after thathellip ldquoHarry Potter and the Bathtub Ringrdquo
pagehtml
hpfacejpg
castlegif
41
Client Server
The ldquoclassicrdquo approach in HTTP10 is to use one HTTP request per TCP connection serially
TCP SYN
TCP FIN
pagehtml G
TCP SYN
TCP FIN
hpfacejpg G
TCP SYN
TCP FIN
castlegif G
42
Client Server Concurrent (parallel) TCP connections can be used to make things faster
TCP SYN
TCP FIN
pagehtml G
castlegif G
F
S
G hpfacejpg
S
F
C S C S
43
Client Server
The ldquopersistent HTTPrdquo approach can re-use the same TCP connection for Multiple HTTP transfers one after another serially Amortizes TCP overhead but maintains TCP state longer at server
TCP FIN
Timeout
TCP SYN
pagehtml G
hpfacejpg G
castlegif G
44
Client Server
The ldquopipeliningrdquo feature in HTTP11 allows requests to be issued asynchronously on a persistent connection Requests must be processed in proper order Can do clever packaging
TCP FIN
Timeout
TCP SYN
pagehtml G
castlegif
hpfacejpg GG
Fast Retransmit and Fast Recovery
bull At steady state cwnd oscillates around the optimal window size
bull TCP always forces packet drops
32
Time
cwn
d
Timeout
Slow Start
Congestion Avoidance Fast RetransmitRecovery
ssthresh
Timeout
34
TCP Throughput
bull Whatrsquos the average throughout ot TCP as a function of window size and RTT
ndash Ignore slow start
bull Let W be the window size when loss occurs
bull When window is W throughput is WRTT
bull Just after loss window drops to W2 throughput to W2RTT
bull Average throughout 75 WRTT
35
TCP Futures
bull Example 1500 byte segments 100ms RTT want 10 Gbps throughput
bull Requires window size W = 83333 in-flight segments
bull Throughput in terms of loss rate
bull L = 210-10 Wow
bull New versions of TCP for high-speed needed
LRTT
MSS221
36
Fairness goal if K TCP sessions share same bottleneck link of bandwidth R each should have average rate of RK
TCP connection 1
bottleneck router
capacity R
TCP connection 2
TCP Fairness
37
Fairness (more)
bull TCP fairness dependency on RTT
ndash Connections with long RTT get less throughput
bull Parallel TCP connections
bull TCP friendliness for UDP streams
ndash Similar throughput (and behavior) as TCP eg
LRTTthroughput
1
39
TCP+HTTP refresher
bull TCP is a connection-oriented protocol
SYN
SYNACK
ACK GET URL
YOUR DATA HERE
FIN FINACK
ACK
Web Client Web Server
40
Example Web Page
Harry Potter Movies
As you all know the new HP book will be out in June and then there will be a new movie shortly after thathellip ldquoHarry Potter and the Bathtub Ringrdquo
pagehtml
hpfacejpg
castlegif
41
Client Server
The ldquoclassicrdquo approach in HTTP10 is to use one HTTP request per TCP connection serially
TCP SYN
TCP FIN
pagehtml G
TCP SYN
TCP FIN
hpfacejpg G
TCP SYN
TCP FIN
castlegif G
42
Client Server Concurrent (parallel) TCP connections can be used to make things faster
TCP SYN
TCP FIN
pagehtml G
castlegif G
F
S
G hpfacejpg
S
F
C S C S
43
Client Server
The ldquopersistent HTTPrdquo approach can re-use the same TCP connection for Multiple HTTP transfers one after another serially Amortizes TCP overhead but maintains TCP state longer at server
TCP FIN
Timeout
TCP SYN
pagehtml G
hpfacejpg G
castlegif G
44
Client Server
The ldquopipeliningrdquo feature in HTTP11 allows requests to be issued asynchronously on a persistent connection Requests must be processed in proper order Can do clever packaging
TCP FIN
Timeout
TCP SYN
pagehtml G
castlegif
hpfacejpg GG
34
TCP Throughput
bull Whatrsquos the average throughout ot TCP as a function of window size and RTT
ndash Ignore slow start
bull Let W be the window size when loss occurs
bull When window is W throughput is WRTT
bull Just after loss window drops to W2 throughput to W2RTT
bull Average throughout 75 WRTT
35
TCP Futures
bull Example 1500 byte segments 100ms RTT want 10 Gbps throughput
bull Requires window size W = 83333 in-flight segments
bull Throughput in terms of loss rate
bull L = 210-10 Wow
bull New versions of TCP for high-speed needed
LRTT
MSS221
36
Fairness goal if K TCP sessions share same bottleneck link of bandwidth R each should have average rate of RK
TCP connection 1
bottleneck router
capacity R
TCP connection 2
TCP Fairness
37
Fairness (more)
bull TCP fairness dependency on RTT
ndash Connections with long RTT get less throughput
bull Parallel TCP connections
bull TCP friendliness for UDP streams
ndash Similar throughput (and behavior) as TCP eg
LRTTthroughput
1
39
TCP+HTTP refresher
bull TCP is a connection-oriented protocol
SYN
SYNACK
ACK GET URL
YOUR DATA HERE
FIN FINACK
ACK
Web Client Web Server
40
Example Web Page
Harry Potter Movies
As you all know the new HP book will be out in June and then there will be a new movie shortly after thathellip ldquoHarry Potter and the Bathtub Ringrdquo
pagehtml
hpfacejpg
castlegif
41
Client Server
The ldquoclassicrdquo approach in HTTP10 is to use one HTTP request per TCP connection serially
TCP SYN
TCP FIN
pagehtml G
TCP SYN
TCP FIN
hpfacejpg G
TCP SYN
TCP FIN
castlegif G
42
Client Server Concurrent (parallel) TCP connections can be used to make things faster
TCP SYN
TCP FIN
pagehtml G
castlegif G
F
S
G hpfacejpg
S
F
C S C S
43
Client Server
The ldquopersistent HTTPrdquo approach can re-use the same TCP connection for Multiple HTTP transfers one after another serially Amortizes TCP overhead but maintains TCP state longer at server
TCP FIN
Timeout
TCP SYN
pagehtml G
hpfacejpg G
castlegif G
44
Client Server
The ldquopipeliningrdquo feature in HTTP11 allows requests to be issued asynchronously on a persistent connection Requests must be processed in proper order Can do clever packaging
TCP FIN
Timeout
TCP SYN
pagehtml G
castlegif
hpfacejpg GG
35
TCP Futures
bull Example 1500 byte segments 100ms RTT want 10 Gbps throughput
bull Requires window size W = 83333 in-flight segments
bull Throughput in terms of loss rate
bull L = 210-10 Wow
bull New versions of TCP for high-speed needed
LRTT
MSS221
36
Fairness goal if K TCP sessions share same bottleneck link of bandwidth R each should have average rate of RK
TCP connection 1
bottleneck router
capacity R
TCP connection 2
TCP Fairness
37
Fairness (more)
bull TCP fairness dependency on RTT
ndash Connections with long RTT get less throughput
bull Parallel TCP connections
bull TCP friendliness for UDP streams
ndash Similar throughput (and behavior) as TCP eg
LRTTthroughput
1
39
TCP+HTTP refresher
bull TCP is a connection-oriented protocol
SYN
SYNACK
ACK GET URL
YOUR DATA HERE
FIN FINACK
ACK
Web Client Web Server
40
Example Web Page
Harry Potter Movies
As you all know the new HP book will be out in June and then there will be a new movie shortly after thathellip ldquoHarry Potter and the Bathtub Ringrdquo
pagehtml
hpfacejpg
castlegif
41
Client Server
The ldquoclassicrdquo approach in HTTP10 is to use one HTTP request per TCP connection serially
TCP SYN
TCP FIN
pagehtml G
TCP SYN
TCP FIN
hpfacejpg G
TCP SYN
TCP FIN
castlegif G
42
Client Server Concurrent (parallel) TCP connections can be used to make things faster
TCP SYN
TCP FIN
pagehtml G
castlegif G
F
S
G hpfacejpg
S
F
C S C S
43
Client Server
The ldquopersistent HTTPrdquo approach can re-use the same TCP connection for Multiple HTTP transfers one after another serially Amortizes TCP overhead but maintains TCP state longer at server
TCP FIN
Timeout
TCP SYN
pagehtml G
hpfacejpg G
castlegif G
44
Client Server
The ldquopipeliningrdquo feature in HTTP11 allows requests to be issued asynchronously on a persistent connection Requests must be processed in proper order Can do clever packaging
TCP FIN
Timeout
TCP SYN
pagehtml G
castlegif
hpfacejpg GG
36
Fairness goal if K TCP sessions share same bottleneck link of bandwidth R each should have average rate of RK
TCP connection 1
bottleneck router
capacity R
TCP connection 2
TCP Fairness
37
Fairness (more)
bull TCP fairness dependency on RTT
ndash Connections with long RTT get less throughput
bull Parallel TCP connections
bull TCP friendliness for UDP streams
ndash Similar throughput (and behavior) as TCP eg
LRTTthroughput
1
39
TCP+HTTP refresher
bull TCP is a connection-oriented protocol
SYN
SYNACK
ACK GET URL
YOUR DATA HERE
FIN FINACK
ACK
Web Client Web Server
40
Example Web Page
Harry Potter Movies
As you all know the new HP book will be out in June and then there will be a new movie shortly after thathellip ldquoHarry Potter and the Bathtub Ringrdquo
pagehtml
hpfacejpg
castlegif
41
Client Server
The ldquoclassicrdquo approach in HTTP10 is to use one HTTP request per TCP connection serially
TCP SYN
TCP FIN
pagehtml G
TCP SYN
TCP FIN
hpfacejpg G
TCP SYN
TCP FIN
castlegif G
42
Client Server Concurrent (parallel) TCP connections can be used to make things faster
TCP SYN
TCP FIN
pagehtml G
castlegif G
F
S
G hpfacejpg
S
F
C S C S
43
Client Server
The ldquopersistent HTTPrdquo approach can re-use the same TCP connection for Multiple HTTP transfers one after another serially Amortizes TCP overhead but maintains TCP state longer at server
TCP FIN
Timeout
TCP SYN
pagehtml G
hpfacejpg G
castlegif G
44
Client Server
The ldquopipeliningrdquo feature in HTTP11 allows requests to be issued asynchronously on a persistent connection Requests must be processed in proper order Can do clever packaging
TCP FIN
Timeout
TCP SYN
pagehtml G
castlegif
hpfacejpg GG
37
Fairness (more)
bull TCP fairness dependency on RTT
ndash Connections with long RTT get less throughput
bull Parallel TCP connections
bull TCP friendliness for UDP streams
ndash Similar throughput (and behavior) as TCP eg
LRTTthroughput
1
39
TCP+HTTP refresher
bull TCP is a connection-oriented protocol
SYN
SYNACK
ACK GET URL
YOUR DATA HERE
FIN FINACK
ACK
Web Client Web Server
40
Example Web Page
Harry Potter Movies
As you all know the new HP book will be out in June and then there will be a new movie shortly after thathellip ldquoHarry Potter and the Bathtub Ringrdquo
pagehtml
hpfacejpg
castlegif
41
Client Server
The ldquoclassicrdquo approach in HTTP10 is to use one HTTP request per TCP connection serially
TCP SYN
TCP FIN
pagehtml G
TCP SYN
TCP FIN
hpfacejpg G
TCP SYN
TCP FIN
castlegif G
42
Client Server Concurrent (parallel) TCP connections can be used to make things faster
TCP SYN
TCP FIN
pagehtml G
castlegif G
F
S
G hpfacejpg
S
F
C S C S
43
Client Server
The ldquopersistent HTTPrdquo approach can re-use the same TCP connection for Multiple HTTP transfers one after another serially Amortizes TCP overhead but maintains TCP state longer at server
TCP FIN
Timeout
TCP SYN
pagehtml G
hpfacejpg G
castlegif G
44
Client Server
The ldquopipeliningrdquo feature in HTTP11 allows requests to be issued asynchronously on a persistent connection Requests must be processed in proper order Can do clever packaging
TCP FIN
Timeout
TCP SYN
pagehtml G
castlegif
hpfacejpg GG
39
TCP+HTTP refresher
bull TCP is a connection-oriented protocol
SYN
SYNACK
ACK GET URL
YOUR DATA HERE
FIN FINACK
ACK
Web Client Web Server
40
Example Web Page
Harry Potter Movies
As you all know the new HP book will be out in June and then there will be a new movie shortly after thathellip ldquoHarry Potter and the Bathtub Ringrdquo
pagehtml
hpfacejpg
castlegif
41
Client Server
The ldquoclassicrdquo approach in HTTP10 is to use one HTTP request per TCP connection serially
TCP SYN
TCP FIN
pagehtml G
TCP SYN
TCP FIN
hpfacejpg G
TCP SYN
TCP FIN
castlegif G
42
Client Server Concurrent (parallel) TCP connections can be used to make things faster
TCP SYN
TCP FIN
pagehtml G
castlegif G
F
S
G hpfacejpg
S
F
C S C S
43
Client Server
The ldquopersistent HTTPrdquo approach can re-use the same TCP connection for Multiple HTTP transfers one after another serially Amortizes TCP overhead but maintains TCP state longer at server
TCP FIN
Timeout
TCP SYN
pagehtml G
hpfacejpg G
castlegif G
44
Client Server
The ldquopipeliningrdquo feature in HTTP11 allows requests to be issued asynchronously on a persistent connection Requests must be processed in proper order Can do clever packaging
TCP FIN
Timeout
TCP SYN
pagehtml G
castlegif
hpfacejpg GG
40
Example Web Page
Harry Potter Movies
As you all know the new HP book will be out in June and then there will be a new movie shortly after thathellip ldquoHarry Potter and the Bathtub Ringrdquo
pagehtml
hpfacejpg
castlegif
41
Client Server
The ldquoclassicrdquo approach in HTTP10 is to use one HTTP request per TCP connection serially
TCP SYN
TCP FIN
pagehtml G
TCP SYN
TCP FIN
hpfacejpg G
TCP SYN
TCP FIN
castlegif G
42
Client Server Concurrent (parallel) TCP connections can be used to make things faster
TCP SYN
TCP FIN
pagehtml G
castlegif G
F
S
G hpfacejpg
S
F
C S C S
43
Client Server
The ldquopersistent HTTPrdquo approach can re-use the same TCP connection for Multiple HTTP transfers one after another serially Amortizes TCP overhead but maintains TCP state longer at server
TCP FIN
Timeout
TCP SYN
pagehtml G
hpfacejpg G
castlegif G
44
Client Server
The ldquopipeliningrdquo feature in HTTP11 allows requests to be issued asynchronously on a persistent connection Requests must be processed in proper order Can do clever packaging
TCP FIN
Timeout
TCP SYN
pagehtml G
castlegif
hpfacejpg GG
41
Client Server
The ldquoclassicrdquo approach in HTTP10 is to use one HTTP request per TCP connection serially
TCP SYN
TCP FIN
pagehtml G
TCP SYN
TCP FIN
hpfacejpg G
TCP SYN
TCP FIN
castlegif G
42
Client Server Concurrent (parallel) TCP connections can be used to make things faster
TCP SYN
TCP FIN
pagehtml G
castlegif G
F
S
G hpfacejpg
S
F
C S C S
43
Client Server
The ldquopersistent HTTPrdquo approach can re-use the same TCP connection for Multiple HTTP transfers one after another serially Amortizes TCP overhead but maintains TCP state longer at server
TCP FIN
Timeout
TCP SYN
pagehtml G
hpfacejpg G
castlegif G
44
Client Server
The ldquopipeliningrdquo feature in HTTP11 allows requests to be issued asynchronously on a persistent connection Requests must be processed in proper order Can do clever packaging
TCP FIN
Timeout
TCP SYN
pagehtml G
castlegif
hpfacejpg GG
42
Client Server Concurrent (parallel) TCP connections can be used to make things faster
TCP SYN
TCP FIN
pagehtml G
castlegif G
F
S
G hpfacejpg
S
F
C S C S
43
Client Server
The ldquopersistent HTTPrdquo approach can re-use the same TCP connection for Multiple HTTP transfers one after another serially Amortizes TCP overhead but maintains TCP state longer at server
TCP FIN
Timeout
TCP SYN
pagehtml G
hpfacejpg G
castlegif G
44
Client Server
The ldquopipeliningrdquo feature in HTTP11 allows requests to be issued asynchronously on a persistent connection Requests must be processed in proper order Can do clever packaging
TCP FIN
Timeout
TCP SYN
pagehtml G
castlegif
hpfacejpg GG
43
Client Server
The ldquopersistent HTTPrdquo approach can re-use the same TCP connection for Multiple HTTP transfers one after another serially Amortizes TCP overhead but maintains TCP state longer at server
TCP FIN
Timeout
TCP SYN
pagehtml G
hpfacejpg G
castlegif G
44
Client Server
The ldquopipeliningrdquo feature in HTTP11 allows requests to be issued asynchronously on a persistent connection Requests must be processed in proper order Can do clever packaging
TCP FIN
Timeout
TCP SYN
pagehtml G
castlegif
hpfacejpg GG
44
Client Server
The ldquopipeliningrdquo feature in HTTP11 allows requests to be issued asynchronously on a persistent connection Requests must be processed in proper order Can do clever packaging
TCP FIN
Timeout
TCP SYN
pagehtml G
castlegif
hpfacejpg GG
