Data Communications Eighth Edition by William Stallings Chapter 1 – Data Communications, Data Networks, and the Internet.

Data CommunicationsData Communications

Eighth EditionEighth Edition

by William Stallingsby William Stallings

Chapter 1 – Chapter 1 – Data Communications, Data Communications, Data Networks, and the InternetData Networks, and the Internet

Data Communications, Data Data Communications, Data Networks, and the InternetNetworks, and the Internet

The fundamental problem of The fundamental problem of communication is that of communication is that of reproducing at reproducing at one point either exactly or approximately a one point either exactly or approximately a message selected at another point message selected at another point - - The The Mathematical Theory of CommunicationMathematical Theory of Communication, , Claude ShannonClaude Shannon

Contemporary Data CommsContemporary Data Comms

Trends influenced by:Trends influenced by: traffic growth traffic growth at a high & steady rateat a high & steady rate Requirement / development of Requirement / development of new servicesnew services advances in technologyadvances in technology

significant change in requirements led to:significant change in requirements led to: emergence of high-speed LANsemergence of high-speed LANs corporate WAN needscorporate WAN needs Use of digital electronicsUse of digital electronics

A Communications ModelA Communications Model

Key Communications TasksKey Communications Tasks

Transmission system utilization Addressing

Interfacing Routing

Signal generation Recovery

Synchronization Message formatting

Exchange management Security

Error detection and correction Network management

Flow control

Data Communications ModelData Communications Model

Transmission MediumTransmission Medium selection is a basic choiceselection is a basic choice

internal use entirely up to businessinternal use entirely up to business long-distance links made by carrierlong-distance links made by carrier

rapid technology advances affects choicerapid technology advances affects choice fiber optic – high capacity, getting cheaperfiber optic – high capacity, getting cheaper Wireless - mobilityWireless - mobility

transmission cost is still transmission cost is still highhigh hence interest in efficiency improvements hence interest in efficiency improvements

– – multiplexingmultiplexing and and compressioncompression

NetworkingNetworking

growth of number & power of computers is growth of number & power of computers is driving need for interconnectiondriving need for interconnection

also seeing rapid integration of voice, also seeing rapid integration of voice, data, image & video technologiesdata, image & video technologies

two broad categories of communications two broad categories of communications networks:networks: Local Area Network (LAN)Local Area Network (LAN) Wide Area Network (WAN)Wide Area Network (WAN)

Wide Area NetworksWide Area Networks span a large geographical areaspan a large geographical area rely in part on common carrier circuitsrely in part on common carrier circuits alternative WAN technologies used alternative WAN technologies used

include:include: circuit switchingcircuit switching packet switchingpacket switching frame relayframe relay Asynchronous Transfer Mode (ATM)Asynchronous Transfer Mode (ATM)

Circuit SwitchingCircuit Switching

uses a dedicated communications path uses a dedicated communications path established for duration of communicationestablished for duration of communication

comprising a sequence of physical linkscomprising a sequence of physical links with a dedicated logical channelwith a dedicated logical channel eg. telephone networkeg. telephone network

Packet SwitchingPacket Switching

data sent out in sequencedata sent out in sequence small chunks (packets) of data at a timesmall chunks (packets) of data at a time packets passed from node to node packets passed from node to node

between source and destinationbetween source and destination used for terminal to computer and used for terminal to computer and

computer to computer communicationscomputer to computer communications

Frame RelayFrame Relay

packet switching systems have large packet switching systems have large overheads to compensate for errorsoverheads to compensate for errors

modern systems are more modern systems are more reliablereliable errors can be caught in end systemerrors can be caught in end system Frame Relay provides higher speedsFrame Relay provides higher speeds with most error control overhead removedwith most error control overhead removed

Asynchronous Transfer ModeAsynchronous Transfer Mode

ATM - evolution of frame relayATM - evolution of frame relay fixed packet (called cell) lengthfixed packet (called cell) length with little overhead for error controlwith little overhead for error control anything from 10Mbps to Gbpsanything from 10Mbps to Gbps constant data rate using packet switching constant data rate using packet switching

technique with multiple virtual circuitstechnique with multiple virtual circuits

Local Area NetworksLocal Area Networks

smaller scopesmaller scope Building or small campusBuilding or small campus

usually owned by same organization as usually owned by same organization as the attached devicesthe attached devices

data rates much higher withindata rates much higher within switched LANs, eg Ethernetswitched LANs, eg Ethernet wireless LANswireless LANs

Metropolitan Area NetworksMetropolitan Area Networks

MANMAN middle ground between LAN and WANmiddle ground between LAN and WAN private or public networkprivate or public network high speedhigh speed large area – city or metrolarge area – city or metro

1.1.1616

Types of connections: point-to-point and multipoint

1.1.1717

Categories of topology

1.1.1818

A fully connected mesh topology (five devices)

1.1.1919

A star topology connecting four stations

1.1.2020

A bus topology connecting three stations

1.1.2121

A ring topology connecting six stations

1.1.2222

A hybrid topology: a star backbone with three bus networks

## In a network with 25 computers, which In a network with 25 computers, which topology would require the least extensive topology would require the least extensive cabling?cabling? MeshMesh StarStar BusBus RingRing## For six devices connected in mesh, how many For six devices connected in mesh, how many

cables are needed? How many ports are cables are needed? How many ports are needed for each device?needed for each device?

## What is the consequence if a connection fails What is the consequence if a connection fails for five devices arranged in:for five devices arranged in:

a) Mesh b) Star (excluding hub) c) Bus d) Ringa) Mesh b) Star (excluding hub) c) Bus d) Ring

The InternetThe Internet

Internet evolved from ARPANETInternet evolved from ARPANET first operational packet networkfirst operational packet network applied to tactical radio & satellite nets alsoapplied to tactical radio & satellite nets also had a need for interoperabilityhad a need for interoperability led to standardized TCP/IP protocolsled to standardized TCP/IP protocols

Internet ElementsInternet Elements

Internet ArchitectureInternet Architecture

Example ConfigurationExample Configuration

MCQMCQ The The protocol/medium/signal/all the above protocol/medium/signal/all the above is is

the physical path over which message travels.the physical path over which message travels. The information to be communicated in a data The information to be communicated in a data

communications system is the communications system is the medium/protocol/message/transmission.medium/protocol/message/transmission.

Frequency of failure and network recovery Frequency of failure and network recovery time after a failure are measures of the time after a failure are measures of the performance/reliability/security/feasibilityperformance/reliability/security/feasibility of a of a network.network.

SummarySummary

introduced data communications needsintroduced data communications needs communications modelcommunications model defined data communicationsdefined data communications overview of networksoverview of networks introduce Internetintroduce Internet