Spring 2000John Kristoff1 Introduction Computer Networks

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Introduction

Computer Networks

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Motivation and Scope

Computer networks and internets: an overview of concepts, terminology

and technologies that form the basis for digital communication in private corporate networks the the global

Internet.

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Motivation for Networks

Information AccessSharing of ResourcesFacilitate Communications

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What a Network Includes

Transmission hardwareSpecial-purpose hardware devices

interconnect transmission media control transmission run protocol software

Protocol software encodes and formats data detects and corrects problems

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What a Network Does

Provides communication that is Reliable Fair Efficient From one application to another

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What a Network Does [continued]

Automatically detects and corrects Data corruption Data loss Duplication Out-of-order delivery

Automatically finds optimal path from source to destination

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Data Communication versus Networking

With only two nodes, mostly EE issues.

With more than two nodes, lot more issues!

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Direction of Transmission

Point to Point Broadcast

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Network Topologies

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Transmission Media

Wireline String Garden Hose Copper

Twisted PairCoax

Optical Fiber

Wireless Sound Light and mirrors Infrared RF Microwave

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Network Scope

Local Area Network (LAN)Metropolitan Area Network (MAN)Wide Area Network (WAN)

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Data Transmission

Serial

Parallel

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Multiplexing

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Communication Modes

SimplexHalf-duplexFull-duplex

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Connection-oriented versus Connectionless

Connection SetupData TransferConnection

Termination

Data Transfer

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Circuit Switching versus Packet Switching

Dedicated fixed bandwidth route fixed at setup idle capacity

wasted network state

Best Effort end-to-end control multiplexing

technique re-route capability congestion

problems

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Examples

Public Switched Telephone NetworkInternetPostal ServiceTrainCar and highway system

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Standards

HardwareSoftwareProtocolsAdvantages and DisadvantagesProprietary, De Facto, De JureStandards Bodies

IETF, IEEE, OSI, ANSI, ATM Forum, etc.

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Protocols

Rules, standards and etiquetteMetric SystemEnglishDinner partyMorse CodeTCP/IPHTML

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Layering

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Headers, Data and Trailers

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Encapsulation

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ISO OSI Reference Model

7: Application Layer6: Presentation Layer5: Session Layer4: Transport Layer3: Network Layer2: Data link Layer1: Physical Layer

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Interfaces and Services

PDUsSDUsSAPsPeer communicationsService Primitivesetc... read Tanenbaum 1.3.3 and

1.3.5

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TCP/IP Model

5: Application Layer4: Transport Layer3: Network Layer2: Data link Layer1: Physical Layer

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OSI versus TCP/IP

“Rough consensus and running code”

SimplicityTime to marketAvailability

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Network Classification

Physical medium: copper, fiber, wireless

Scope: LAN, MAN, WANTopology: bus, star, ring, meshSwitching style: circuit, packetApplication: voice, data, videoProtocol: IP, OSI, Ethernet, ATMTransmission rate: 10Mb/s, Gigabit

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Terms I (we) Often Use

Frames: think data link layerPackets: think network layerDatagrams: think IPSegments: think TCPCells: think ATMLayer <x>: refer to reference

models

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The End-to-End Argument

“End-to-End Arguments in System Design” J.H. Saltzer, D.P. Reed, and D.D. Clark http://web.mit.edu/Saltzer/www/

publications/