chapter 1chapter 1 introduction: introduction

Chapter 1: IntroductionChapter 1 IntroductionOur goal: Overview:

get “feel” and terminologymore depth detail

what’s the Internetwhat’s a protocol?network edgemore depth, detail

later in courseapproach:

network edgenetwork coreaccess net physical media

use Internet as example

access net, physical mediaInternet/ISP structureperformance: loss, delayp yprotocol layers, service modelsnetwork modeling

Introduction 1-1

Chapter 1: roadmapChapter roadmap

1.1 What is the Internet?1.1 What is the Internet?1.2 Network edge1 3 Network core1.3 Network core1.4 Network access and physical media1 5 Internet structure and ISPs1.5 Internet structure and ISPs1.6 Delay & loss in packet-switched networks1 7 Protocol layers service models1.7 Protocol layers, service models1.8 History

Introduction 1-2

What’s the Internet: “nuts and bolts” viewmillions of connected computing devices: hosts

router workstationcomputing devices hosts = end systemsrunning network apps local ISP

servermobile

communication linksfiber, copper, radio, satellite regional ISPtransmission rate = bandwidth

routers: forward packets

regional ISP

routers: forward packets (chunks of data)

company

Introduction 1-3

network

What’s the Internet: “nuts and bolts” view

protocols control sending, receiving of msgs

router workstationreceiving of msgs

e.g., TCP, IP, HTTP, FTP, PPPInternet: “network of local ISP

servermobile

networks”loosely hierarchicalpublic Internet versus regional ISPpublic Internet versus private intranet

Internet standards

regional ISP

RFC: Request for commentsIETF: Internet Engineering Task Force company

Introduction 1-4

network

What’s the Internet: a service viewcommunication infrastructure enables fdistributed applications:

Web, email, games, e-commerce file sharingcommerce, file sharing

communication services provided to apps:

Connectionless unreliableconnection-oriented reliable

Introduction 1-5

What’s a protocol?What s a protocol?human protocols:

“ h t’ th ti ?”network protocols:

hi th th “what’s the time?”“I have a question”introductions

machines rather than humansall communication introductions

… specific msgs sent

all communication activity in Internet governed by protocols

… specific actions taken when msgs received, or other events

protocols define format, order of msgs sent and received among network or other events received among network

entities, and actions taken on msg

Introduction 1-6

transmission, receipt

What’s a protocol?What s a protocol?a human protocol and a computer network protocol:

Hi TCP connection

HiGot the

TCP connectionreq

TCP connectionresponseGot the

time?2:00

responseGet http://www.awl.com/kurose-ross

<file><file>time

Introduction 1-7

Q: Other human protocols?

Introduction 1-8

A closer look at network structure:

network edge:network edge:applications and hostsnetwork core:

routersnetwork of networks

t k access networks, physical media:communication links

Introduction 1-9

communication links

The network edge:The network edgeend systems (hosts):

l run application programse.g. Web, emailat “edge of network”g

client/server modelclient host requests, receives

i f l service from always-on servere.g. Web browser/server; email client/server

peer-peer model:minimal (or no) use of dedicated servers

Introduction 1-10

dedicated serverse.g. Gnutella, KaZaA

Network edge: connection-oriented serviceg

Goal: data transfer TCP service [RFC 793]Goal: data transfer between end systemshandshaking: setup ( f ) d

TCP service [RFC 793]reliable, in-order byte-stream data transfer

(prepare for) data transfer ahead of time

Hello, hello back human

loss: acknowledgements and retransmissions

flow control:H o, h o ac human protocolset up “state” in two communicating hosts

flow controlsender won’t overwhelm receiver

congestion control:mmu gTCP - Transmission Control Protocol

I ’ i

congestion control:senders “slow down sending rate” when network

n st d

Introduction 1-11

Internet’s connection-oriented service

congested

Network edge: connectionless serviceg

Goal: data transfer App’s using TCP:Goal: data transfer between end systems

same as before!DP D

App s using TCP:HTTP (Web), FTP (file transfer), Telnet ( l ) P UDP - User Datagram

Protocol [RFC 768]: connectionless

(remote login), SMTP (email)

connectionless unreliable data transfer

App’s using UDP:streaming media

no flow controlno congestion control

streaming media, teleconferencing, DNS, Internet telephony

Introduction 1-12

Introduction 1-13

The Network CoreThe Network Core

mesh of interconnected froutersthe fundamental

sti h is d t question: how is data transferred through net?

circuit switching:c rcu t sw tch ngdedicated circuit per call: telephone net

k t it hi d t packet-switching: data sent thru net in discrete “chunks”

Introduction 1-14

Network Core: Circuit Switchingg

End-end resources End end resources reserved for “call”link bandwidth, switch capacitydedicated resources: no sharingno sharingcircuit-like (guaranteed) (g )performancecall setup required

Introduction 1-15

Network Core: Circuit Switchinggnetwork resources

( b d idth) dividing link bandwidth

“ ”(e.g., bandwidth) divided into “pieces”pieces allocated to calls

into “pieces”frequency divisiontime divisionpieces allocated to calls

resource piece idle if not used by owning call

time division

y g(no sharing)

Introduction 1-16

Circuit Switching: FDM and TDMC rcu t Sw tch ng FDM and DM

FDM 4 usersExample:

frequency

4 users

frequency

timeTDM

frequency

Introduction 1-17time

Numerical exampleNumer cal example

How long does it take to send a file of How long does it take to send a file of 640,000 bits from host A to host B over a circuit-switched network?

All links are 1.536 MbpsEach link uses TDM with 24 slots500 msec to establish end-to-end circuit

W k it t!Work it out!

Introduction 1-18

Network Core: Packet Switchinggeach end-end data stream

divided into packetsresource contention:

t divided into packetsuser A, B packets sharenetwork resources

aggregate resource demand can exceed amount available

each packet uses full link bandwidth

congestion: packets queue, wait for link uset d f d resources used as needed store and forward:

packets move one hop at a time

Node receives complete packet before forwarding

Bandwidth division into “pieces”Dedicated allocationResource reservation

Introduction 1-19

Resource reservation

Packet Switching: Statistical Multiplexingg p g

A C10 Mb/sEthernet statistical multiplexing

B1.5 Mb/s

Bqueue of packetswaiting for output

Sequence of A & B packets does not have fixed pattern statistical multiplexing.

In TDM each host gets same slot in revolving TDM

Introduction 1-20

In TDM each host gets same slot in revolving TDM frame.

Packet switching versus circuit switchingg g

Packet switching allows more users to use network!

1 Mb/s linkeach user:

k / h “100 kb/s when “active”active 10% of time

N userscircuit-switching:

10 usersk t it hi

N users1 Mbps link

packet switching: with 35 users, probability > 10 active

Introduction 1-21

less than .0004

Packet switching versus circuit switchingg g

Is packet switching a “slam dunk winner?”

Great for bursty dataresource sharingsimpler, no call setup

Excessive congestion: packet delay and losspr t c ls needed f r reli ble d t tr nsfer protocols needed for reliable data transfer, congestion control

Q: How to provide circuit-like behavior?Q pbandwidth guarantees needed for audio/video apps

Introduction 1-22

still an unsolved problem (chapter 6)

Packet-switching: store-and-forwardg f

R R RL

Takes L/R seconds to transmit (push out)

Example:L = 7 5 Mbits

transmit (push out) packet of L bits on to link with capacity of R bps

L = 7.5 MbitsR = 1.5 Mbpsdelay = 15 secbps

Entire packet must arrive at router before it can be transmitted it can be transmitted on next link: store and forwardd l 3L/R

Introduction 1-23

delay = 3L/R

Packet-switched networks: forwardingg

Goal: move packets through routers from source to destinationdestination

we’ll study several path selection (i.e. routing) algorithms (chapter 4)

d kdatagram network:destination address in packet determines next hoproutes may change during sessionroutes may change during sessionanalogy: driving, asking directions

virtual circuit network:h k ( l D) each packet carries tag (virtual circuit ID), tag

determines next hopfixed path determined at call setup time, remains fixed h ll

Introduction 1-24

thru callrouters maintain per-call state

Network TaxonomyTelecommunication

networks

Circuit-switched Packet-switchednetworks networks

DFDM TDM Networkswith VCs

DatagramNetworks

• Datagram network is not either connection-oriented or connectionless.• Internet provides both connection-oriented (TCP) and

Introduction 1-25

Internet provides both connection oriented (TCP) and connectionless services (UDP) to apps.

Introduction 1-26

Access networks and physical mediap y

Q: How to connect end systems to edge router?systems to edge router?residential access netsinstitutional access institutional access networks (school, company)

bil t kmobile access networks

Keep in mind: b d id h (bi bandwidth (bits per second) of access network?

Introduction 1-27

shared or dedicated?

Residential access: point to point accessp p

Dialup via modemD a up a mo mup to 56Kbps direct access to router (often less)Can’t surf and phone at same time: can’t be “always on”

d l lADSL: asymmetric digital subscriber lineup to 1 Mbps upstream (today typically < 256 kbps)up to 8 Mbps downstream (today typically < 1 Mbps)up to 8 Mbps downstream (today typically < 1 Mbps)FDM: 50 kHz - 1 MHz for downstream

4 kHz - 50 kHz for upstream

Introduction 1-28

p0 kHz - 4 kHz for ordinary telephone

Residential access: cable modems

HFC: hybrid fiber coaxHFC: hybrid fiber coaxasymmetric: up to 30Mbps downstream, 2 Mbps upstream

network of cable and fiber attaches homes to ISP router

h m s sh ss t t homes share access to router deployment: available via cable TV companies

Introduction 1-29

Residential access: cable modems

Introduction 1-30Diagram: http://www.cabledatacomnews.com/cmic/diagram.html

Cable Network Architecture: Overview

Typically 500 to 5,000 homes

cable headend

cable distribution

Introduction 1-31

cable distributionnetwork (simplified)

cable headend

cable distribution

Introduction 1-32

cable distributionnetwork (simplified)

server(s)

cable headend

cable distribution

Introduction 1-33

cable distributionnetwork

CONTROL

Channels

O O O O O O A A L

1 2 3 4 5 6 7 8 9

cable headend

cable distribution

Introduction 1-34

cable distributionnetwork

Company access: local area networksp y

company/univ local area network (LAN) connects network (LAN) connects end system to edge routerEthernet:

shared or dedicated link connects end system and routerand router10 Mbs, 100Mbps, Gigabit Ethernetg

LANs: chapter 5

Introduction 1-35

Wireless access networksshared wireless access network connects end system network connects end system to router

via base station aka “access p int”

router

point”wireless LANs:

802.11b (WiFi): 11 Mbps

basestation

( ) pwider-area wireless access

provided by telco operator3G 384 kb3G ~ 384 kbps

• Will it happen??WAP/GPRS in Europe

mobilehosts

Introduction 1-36

Home networksTypical home network components:

ADSL or cable modemADSL or cable modemrouter/firewall/NATEthernetwireless accesspoint

wirelesslaptops

router/f ll

cabled

to/fromcable

wirelessaccess

firewallmodemcableheadend

Ethernet

Introduction 1-37

pointEthernet

Physical Mediay

Bit: propagates betweenTwisted Pair (TP)

two insulated copper p p gtransmitter/rcvr pairsphysical link: what lies b t t s itt &

two insulated copper wires

Category 3: traditional h i 10 Mb between transmitter &

receiverguided media:

phone wires, 10 Mbps EthernetCategory 5: 100Mb Eth tgu ded med a

signals propagate in solid media: copper, fiber, coax

unguided media:

100Mbps Ethernet

unguided media:signals propagate freely, e.g., radio

Introduction 1-38

Physical Media: coax, fibery ,

Coaxial cable: Fiber optic cable:glass fiber carrying light two concentric copper

conductorsbidirectional

glass fiber carrying light pulses, each pulse a bithigh-speed operation:bidirectional

baseband:single channel on cable

high-speed point-to-point transmission (e.g., 5 Gps)

low error rate: repeaters legacy Ethernet

broadband:multiple channel on cable

low error rate: repeaters spaced far apart ; immune to electromagnetic noise

multiple channel on cableHFC

Introduction 1-39

Physical media: radioy

signal carried in electromagnetic

Radio link types:terrestrial microwaveelectromagnetic

spectrumno physical “wire”

terrestrial microwavee.g. up to 45 Mbps channels

LAN (e.g., Wifi)p ybidirectionalpropagation

i t ff t

( g )2Mbps, 11Mbps

wide-area (e.g., cellular) 3G h d d f kbenvironment effects:

reflection obstruction by objects

e.g. 3G: hundreds of kbpssatellite

up to 50Mbps channel (or y jinterference

p p (multiple smaller channels)270 msec end-end delaygeosynchronous versus low

Introduction 1-40

geosynchronous versus low altitude

Introduction 1-41

Internet structure: network of networks

roughly hierarchicalat center: “tier-1” ISPs (e.g., UUNet, BBN/Genuity/level3, Sprint, AT&T, QWest), national/international coveragenat onal/ nternat onal coverage

treat each other as equals

Tier-1 providers also interconnect

Tier 1 ISPTier-1 providers interconnect (peer)

NAPat public network access points (NAPs)

Tier 1 ISP Tier 1 ISP(p )privately

Introduction 1-42

Tier-1 ISP: e.g., SprintT er ISP e.g., Spr ntSprint US backbone network

Introduction 1-43

“Tier-2” ISPs: smaller (often regional) ISPsC i 1 I P ibl h i 2 I PConnect to one or more tier-1 ISPs, possibly other tier-2 ISPs

Tier-2 ISPTier-2 ISPTier-2 ISP pays tier-1 ISP for

Tier-2 ISPs also peer privately with

Tier 1 ISPNAP

tier 1 ISP for connectivity to rest of Internet

tier-2 ISP is t f

each other, interconnect at NAP

Tier 1 ISP Tier 1 ISP

Tier-2 ISP Tier-2 ISP

Tier-2 ISPcustomer oftier-1 provider

Introduction 1-44

“Tier-3” ISPs and local ISPs l h (“ ”) k ( l d )last hop (“access”) network (closest to end systems)

local l llocalISP Tier 3

Tier-2 ISPTier-2 ISP

localISPlocal

ISPlocalISP

ISP Tier 3ISP

Local and tier-3 ISPs are

Tier 1 ISPNAP

customers ofhigher tier ISPsconnecting

Tier-2 ISPlocal

connecting them to rest of Internet

Introduction 1-45

Tier 2 ISP Tier 2 ISPlocalISP

localISP

a packet passes through many networks!

local l llocalISP Tier 3

Tier-2 ISPTier-2 ISP

localISPlocal

ISPlocalISP

ISP Tier 3ISP

Tier 1 ISPNAP

Tier-2 ISPlocal

Introduction 1-46

Tier 2 ISP Tier 2 ISPlocalISP

localISP

Introduction 1-47

How do loss and delay occur?How do loss and delay occur?packets queue in router buffers

packet arrival rate to link exceeds output link capacitypackets queue, wait for turn

packet being transmitted (delay)

Bpackets queueing (delay)

Introduction 1-48

free (available) buffers: arriving packets dropped (loss) if no free buffers

Four sources of packet delayFour sources of packet delay

1. nodal processing: 2. queueing1. nodal processingcheck bit errorsdetermine output link

2. queueingtime waiting at output link for transmission depends on congestion depends on congestion level of router

A propagation

transmission

Bnodal

Introduction 1-49

processing queueing

Delay in packet-switched networksDelay in packet switched networks3. Transmission delay:

R li k b d idth (b )4. Propagation delay:

d l th f h i l li kR=link bandwidth (bps)L=packet length (bits)time to send bits into

d = length of physical links = propagation speed in medium (~2x108 m/sec)time to send bits into

link = L/Rmedium ( 2x10 m/sec)propagation delay = d/s

Atransmission

Note: s and R are very different quantities!

propagation

Introduction 1-50

Bnodal

processing queueing

Nodal delayNodal delayproptransqueueprocnodal ddddd +++=

dproc = processing delayproc p g ytypically a few microsecs or less

dqueue = queuing delayd d tidepends on congestion

dtrans = transmission delay= L/R, significant for low-speed links, g p

dprop = propagation delaya few microsecs to hundreds of msecs

Introduction 1-51

Queueing delay (revisited)Queueing delay (revisited)

R=link bandwidth (bps)R link bandwidth (bps)L=packet length (bits)a=average packet parrival rate

traffic intensity = La/Ry

La/R ~ 0: average queueing delay smallLa/R -> 1: delays become largeLa/R > 1: more “work” arriving than can be serviced average delay infinite!

Introduction 1-52

serviced, average delay infinite!

“Real” Internet delays and routesy

What do “real” Internet delay & loss look like? yTraceroute program: provides delay measurement from source to router along end-end I t t th t ds d sti ti F ll iInternet path towards destination. For all i:

sends three packets that will reach router i on path towards destinationrouter i will return packets to sendersender times interval between transmission and reply.

3 probes

Introduction 1-53

“Real” Internet delays and routesytraceroute: gaia.cs.umass.edu to www.eurecom.fr

Three delay measements from

1 cs-gw (128.119.240.254) 1 ms 1 ms 2 ms2 border1-rt-fa5-1-0.gw.umass.edu (128.119.3.145) 1 ms 1 ms 2 ms3 cht-vbns.gw.umass.edu (128.119.3.130) 6 ms 5 ms 5 ms

Three delay measements from gaia.cs.umass.edu to cs-gw.cs.umass.edu

g ( )4 jn1-at1-0-0-19.wor.vbns.net (204.147.132.129) 16 ms 11 ms 13 ms 5 jn1-so7-0-0-0.wae.vbns.net (204.147.136.136) 21 ms 18 ms 18 ms 6 abilene-vbns.abilene.ucaid.edu (198.32.11.9) 22 ms 18 ms 22 ms7 nycm-wash.abilene.ucaid.edu (198.32.8.46) 22 ms 22 ms 22 ms8 62.40.103.253 (62.40.103.253) 104 ms 109 ms 106 ms

trans-oceaniclink( )

9 de2-1.de1.de.geant.net (62.40.96.129) 109 ms 102 ms 104 ms10 de.fr1.fr.geant.net (62.40.96.50) 113 ms 121 ms 114 ms11 renater-gw.fr1.fr.geant.net (62.40.103.54) 112 ms 114 ms 112 ms12 nio-n2.cssi.renater.fr (193.51.206.13) 111 ms 114 ms 116 ms13 nice.cssi.renater.fr (195.220.98.102) 123 ms 125 ms 124 ms

( )14 r3t2-nice.cssi.renater.fr (195.220.98.110) 126 ms 126 ms 124 ms15 eurecom-valbonne.r3t2.ft.net (193.48.50.54) 135 ms 128 ms 133 ms16 194.214.211.25 (194.214.211.25) 126 ms 128 ms 126 ms17 * * *18 * * * * means no reponse (probe lost, router not replying)

Introduction 1-54

19 fantasia.eurecom.fr (193.55.113.142) 132 ms 128 ms 136 msp (p p y g)

Packet lossPacket loss

queue (aka buffer) preceding link in buffer queue (aka buffer) preceding link in buffer has finite capacitywhen packet arrives to full queue, packet is p f q , pdropped (aka lost)lost packet may be retransmitted by p y yprevious node, by source end system, or not retransmitted at all

Introduction 1-55

Introduction 1-56

Network ModelsNetwork Models

Using a formal model allows us to deal with g f m mvarious aspects of Networks abstractly.We will look at two popular models

• OSI reference model• TCP/IP model

Both models are based on the concept of Both models are based on the concept of layering.

1-57Introduction

LayeringLayeringDivide a task into sub-tasks and then solve Divide a task into sub tasks and then solve each sub-task independently.Establishing a well defined interface E g f fbetween layers makes porting easier. Major Advantages:j g♦ Code Reuse♦ Extensibility

1-58Introduction

L i E l F d l ELayering Example: Federal ExpressLetter in envelope address on outsideLetter in envelope, address on outsideFedX guy adds addressing information, barcodebarcode.Local office drives to airport and delivers to hub to hub. Sent via airplane to nearest city.Delivered to right officeDelivered to right officeDelivered to right person

1-59Introduction

FedX LayersyLetter Addressed

Envelope

Letter Addressed EnvelopeEnvelope

1-60Introduction

Protocol “Layers”Protocol LayersNetworks are complex!

“ i ”many “pieces”:hostsrouters

Question:Is th h f routers

links of various media

Is there any hope of organizing structure of

network?applicationsprotocols Or at least our discussion

f t k ?hardware, software

of networks?

Introduction 1-61

Why layering?Why layer ng?Dealing with complex systems:

l ll d f explicit structure allows identification, relationship of complex system’s pieces

layered reference model for discussionlayered reference model for discussionmodularization eases maintenance, updating of system

change of implementation of layer’s service transparent to rest of systeme g change in one procedure doesn’t affect e.g., change in one procedure doesn t affect rest of system

layering considered harmful?

Introduction 1-62

Internet protocol stackInternet protocol stackapplication: supporting network

li ti sapplicationsFTP, SMTP

transport: host-host data transfer

application

transporttran p rt h t h t ata tran f rTCP, UDP

network: routing of datagrams from t d ti ti

transport

networksource to destination

IP, routing protocolslink: data transfer between

linklink data transfer between neighboring network elements

PPP, Etherneth i l bit “ th i ”

physical

Introduction 1-63

physical: bits “on the wire”

message

sourceapplicationM

Encapsulationgsegment

datagramframe

pptransportnetwork

linkHtHnHl MHtHn M

physicallink

physicalHtHnHl M HtHnHl M

switch

destinationapplicationM

networklinkHtHnHl M

HtHn M

HtHnHl MHtHn M

pptransportnetwork

linkHtHnHl MHtHn M

Ht M physical

router

Introduction 1-64

physical

OSI Reference ModelOSI Reference ModelThe International Standards OrganizationThe International Standards Organization(ISO) proposal for the standardization ofthe various protocols used in computernetworks (specifically those networks usedto connect open systems) is called the OpenS t I t ti R f M d lSystems Interconnection Reference Model(1984), or simply the OSI model.

1-65Introduction

Why a Layered Model?Why a Layered Model?

All People Seem To Need Data Processing1-66Introduction

Layers with Functions Layers w th Funct ons

1-67Introduction

The Seven Layers of the OSI R f M d l Reference Model

The application (upper) layersLayer 7: ApplicationLayer 6: PresentationLayer 5: Session

Th d t fl (l ) lThe data-flow (lower) layersLayer 4: TransportLayer 3: NetworkLayer 3: NetworkLayer 2: Data linkLayer 1: Physicaly y

1-68Introduction

The Application (Upper) LayersThe Application (Upper) LayersApplication

User interfaceUser interfaceExamples – Telnet, HTTP

PresentationHow data is presentedSpecial processing, such as encryptionEx mples ASCIIExamples – ASCII

SessionKeeping different applications’ data separateKeeping different applications data separateestablishes, manages, and terminates sessions between applications.

1-69Introduction

The Data-Flow (Lower) LayersThe Data Flow (Lower) Layers

Transport Reliable or unreliable deliveryError correction before transmitError correction before transmitExamples: TCP, UDP

NetworkProvide logical addressing which routers use for path determinationExamples: IPExamples: IP

1-70Introduction

The Lower Layers (cont )The Lower Layers (cont.)

Data linkCombines bits into bytes and bytes into framesAccess to media using MAC addressAccess to media using MAC addressError detection not correctionExamples: 802.3 (defining the physical layer and

'p g p y y

data link layer's media access control (MAC) of wired Ethernet)

PhysicalPhysicalMoves bits between devicesSpecifies voltage, wire speed, and pinout cablesE l RS 232Examples: RS-232

1-71Introduction

Layering & Headers Layer ng & Headers Each layer needs to add some control information to the data in order to do it’s job. Thi i f i i i ll dd d h This information is typically added to the data before being given to the lower layer.O th l l d li th d t d Once the lower layers deliver the data and control information - the peer layer uses the control informationthe control information.

1-72Introduction

Packet PropagationPacket Propagation

Each router provides its services to support upper-layer functions.pp pp y

1-73Introduction

AddressesAddresses

Each communication endpoint must have an Each communication endpoint must have an address.Consider 2 processes communicating over p mm gan internet:

the network must be specifiedthe host (end-system) must be specifiedthe process must be specified.

1-74Introduction

Addresses at LayersAddresses at Layers

Physical Layer: no address necessaryPhysical Layer: no address necessaryData Link Layer - address must be able to select any host on the network (MAC)select any host on the network (MAC).Network Layer - address must be able to provide information to enable routing (IP)provide information to enable routing (IP).Transport Layer - address must identify the destination process (PORT)the destination process (PORT).

1-75Introduction

Broadcasts

Many networks support the notion of Many networks support the notion of sending a message from one host to all other hosts on the network.A special address called the “broadcast address” is often used.

1-76Introduction

TCP/IP Network Model

Process Process

Interface Protocols

Transport TransportPeer-to-peer

Network Network

pProtocols

Data Link Data LinkData Link Data Link

1-77Introduction

Headers(Encapsulation De-Encapsulation)

DATAProcess ProcessDATA

Transport TransportDATAH

Network NetworkDATAHH

Data Data LinkDATAHHHData Link

Data LinkDATAHH

1-78Introduction

OSI Model and TCP/IP Model OSI Model and TCP/IP Model

1-79Introduction

Differences of the OSI and TCP/IP d l TCP/IP models

TCP/IP combines the presentation and TCP/IP combines the presentation and session layer into its application layer.TCP/IP combines the OSI data link and / mphysical layers into one layer.TCP/IP appears simpler because it has pp pfewer layers.TCP/IP transport layer using UDP does not p y galways guarantee reliable delivery of packets as the transport layer in the OSI

d l dmodel does.1-80Introduction

TCP/IP Protocol GraphTCP/IP Protocol Graph

ICMPICMP&

RARPRARP

1-81Introduction

PortsPorts

TCP/IP uses an abstract destination point called a protocol port.P id ifi d b i i iPorts are identified by a positive integer.Operating systems provide some mechanism th t t if t that processes use to specify a port.

1-82Introduction

PortsHost AHost A Host BHost B

Process Process

Process ProcessProcess Process

Process Process

1-83Introduction

Port NumbersPort Numbers

1-84Introduction

Introduction 1-85

Internet History

1961: Kleinrock queueing 1972:

1961-1972: Early packet-switching principles

1961: Kleinrock - queueing theory shows effectiveness of packet-switching

1972:ARPAnet demonstrated publiclyNCP (N k C l switching

1964: Baran - packet-switching in military nets1967: ARPAnet conceived

NCP (Network Control Protocol) first host-host protocol fi il 1967: ARPAnet conceived

by Advanced Research Projects Agency1969: first ARPAnet node

first e-mail programARPAnet has 15 nodes

1969: first ARPAnet node operational

Introduction 1-86

Internet History

1970: ALOHAnet satellite Cerf and Kahn’s

1972-1980: Internetworking, new and proprietary nets1970: ALOHAnet satellite network in Hawaii1973: Metcalfe’s PhD thesis proposes Ethernet

Cerf and Kahn s internetworking principles:

minimalism, autonomy -no internal changes proposes Ethernet

1974: Cerf and Kahn -architecture for interconnecting networks

no internal changes required to interconnect networksbest effort service interconnecting networks

late70’s: proprietary architectures: DECnet, SNA, XNA

best effort service modelstateless routersd li d lXNA

late 70’s: switching fixed length packets (ATM precursor)

decentralized controldefine today’s Internet

architecture

Introduction 1-87

precursor)1979: ARPAnet has 200 nodes

Internet History

Early 1990’s: ARPAnet L t 1990’ 2000’

1990, 2000’s: commercialization, the Web, new apps

Early 1990 s: ARPAnet decommissioned1991: NSF lifts restrictions on commercial use of NSFnet

Late 1990’s – 2000’s:more killer apps: instant messaging, P2P file sharing

commercial use of NSFnet (decommissioned, 1995)early 1990s: Web

h t t [B h 1945 N l

network security to forefrontest. 50 million host, 100

hypertext [Bush 1945, Nelson 1960’s]HTML, HTTP: Berners-Lee

million+ usersbackbone links running at Gbps

1994: Mosaic, later Netscapelate 1990’s: commercialization of the Web

Introduction 1-88

Introduction: SummaryIntroduct on SummaryCovered a “ton” of material! You now have:

Internet overviewwhat’s a protocol?network edge core access

context, overview, “feel” of networkingmore depth detail to network edge, core, access

networkpacket-switching versus i i i hi

more depth, detail to follow!

circuit-switchingInternet/ISP structureperformance: loss delayperformance: loss, delaylayering and service modelshi t

Introduction 1-89

history

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chapter 9 – software evolution and maintenance 1chapter 9...

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chapter 9 – software evolution lecture 1 1chapter 9...

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chapter 1chapter 1 square roots and pythagorean...

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chapter 5 – system modeling lecture 1 1chapter 5 system...

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chapter 4 – requirements engineering lecture 1 1chapter 4...

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