1

Data and Computer Communications

Seventh Editionby William Stallings

2

Chapter 1 – Data Communications and Networks overview

3

Types of information systems

Storage systemTransport information in time without altering the message.

Processing system.Process input information to generate different output.

Communication system.Transport information from one point in time and space to another point in time and space without altering the message.

4

storage system

Information source

Recorder f

destination n

Playback device

Memory m

5

Processing system

Information source

Input device

destination n

Output device

memory

Processor k

6

Communication system

Information source

Input transducer

destination n

Output transducer

Comm. system

Transmitter Channel Receiver

7

Comm. System cont.

Transmitterconsist of one or more of the following components: filters, amplifiers, A/D ,encoders, modulator, …..etc.Channeldegradation of transmitted signal during propagation due to distortion, noise, interference.

8

Comm. System cont.

Receiverconsist of one or more of the following components: filters, amplifiers, D/A, decoders, demodulator, …..etc.

9

Types of comm. systemsAnalog comm. system

Transport analog information using analog modulation techniques (AM,FM,PM).

Digital comm. system.Transport digital information using digital modulation techniques (ASK,FSK,PSK).

Hybrid comm. system.Transport digitized analog information using one of the following digital techniques:

1. Analog pulse modulation schemes (PAM,PDM,PPM). 2. digital modulation schemes (ASK,FSK,PSK).3. Pulse code modulation schemes (PCM,DPCM, δ).

10

Analysis and Design of comm. system

AnalysisTransmission rate, quality of transmission,

robustness to noise.

DesignType of comm. System for given application,

performance requirements, resources, constraints ( Time-bandwidth, noise limitation, equipment limitation).

11

Analysis and Design of comm. System cont.

Design efficient utilization of the two primary

resources of comm. System, namely: transmitted power (SNR) and channel bandwidth.

12

Analysis and Design of comm. System cont.

Limitation imposed on the transmission rate by channel bandwidth B, and SNR is given by

C: channel capacity (maximum rate at no error)M: #of signaling levels

2

2

log (1 ) bps (Shannon equation)2 log bps (Nyquist equation)

C B SNRC B M= +=

13

Types of transmission

Base-band transmission:Short distance.No modulation is needed.

Band-pass transmission:long distance.Modulation is needed.

14

Why modulation?

For ease of radiation.Modulation for multiplexing.For exchange of SNR with B.To over come equipment limitation.To match channel characteristics.

15

Types of modulation

Continuous wave (CW) modulation.RF sinusoidal carrier wave.

Pulse modulation.RF pulse carrier wave.

16

Digital versus analog transmission

Immunity to noise and distortion.Viability of regenerative repeaters.Digital hardware implementation is flexible and scalable.Digital signals can be encoded to yield low BER.Multiplexing is easier and more efficient.Realization of exchange SNR and B is more efficient.Digital storage easier and cheaper.cost of digital hardware is cheaper.

17

A Communications Model

18

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

19

Data communication system

Data Communications Model

Data communication : concern with exchange of information between two directly connected devices.

20

Computer Networks

Computer Network: An interconnected collection of computers which are:Cooperative

Cooperative action is required between componentsNo master-slave relationships

AutonomousAll components are capable of independent actionAny resource is capable of refusing requests

Mutually Suspicious–Components verify requests

21

Cont.Computer network: concern with the exchange of information among several devices (computers, serversrouters, data processing devices,...etc. )

22

Cont.Role of Computers in Communication

As users - main sources and sinks for info and dataAs providers - used to implement switching nodes, controllers, concentrators, protocol translators, etc.

Three General Types of Computer Communication

Computer-to-computer - including intra-computer communication.Human-to-computer - user interface protocols, etc.Computer-aided human-to-human – electronic mail, bboard, publishing, etc.

23

Cont.

Factors lead to fast growing of computer-communication networks:Hardware and software technologies of computerDigital transmissionFiber opticsDigital signal processingVLSI technologies, etc

24

Cont.Network Goals

Resource (and Load) SharingReduced CostHigh Reliability

Applications of Computer NetworksReservation systemsElectronic mail systemsRemote teller banking systemsCredit verification systemsAccess to remote data systems

25

Cont.

Trends in Computer Networks– Higher speed network > 100 Mbps– Wider geographic coverage– Integrated services: text, graphics,

voice, audio, image, video,...

26

Types of comm. networks

two broad categories of communications networks:

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

27

Wide Area Networks

span a large geographical areacross public right-of-waysrely in part on common carrier circuitsalternative technologies used include:

circuit switchingpacket switchingframe relayAsynchronous Transfer Mode (ATM)

28

Circuit Switching

uses a dedicated communications path established for duration of conversationPath consists of a sequence of physical links.Each link has a dedicated logical channel.E.g. telephone network

29

Packet Switching

data sent out of sequencesmall chunks (packets) of data at a timepackets passed from node to node between source and destination.used for terminal to computer and computer to computer communicationsData rate about 64kbps.

30

Frame Relay

packet switching systems have large overheads to compensate for errorsmodern systems are more reliableerrors can be caught in end systemFrame Relay provides higher speeds up to 2 Mbps.with most error control overhead removed

31

Asynchronous Transfer Mode

ATMevolution of frame relayfixed packet (called cell) lengthwith little overhead for error controlanything from 10Mbps to Gbpsconstant data rate using packet switching technique with multiple virtual circuits

32

Local Area Networks

smaller scopeBuilding or small campus

usually owned by same organization as attached devicesdata rates much higherswitched LANs, eg Ethernetwireless LANs

33

Metropolitan Area Networks

MANmiddle ground between LAN and WANprivate or public networkhigh speedlarge area

34

Distance-Speed in Networks

35

The Internet

Internet evolved from ARPANETfirst operational packet networkapplied to tactical radio & satellite nets alsohad a need for interoperabilityled to standardized TCP/IP protocols

36

Internet Elements

37

Internet Architecture

38

Example: Network Configuration

39

Summary

introduced data communications needscommunications modeldefined data communicationsoverview of networksintroduce Internet

40

Topics to be covered in following chapters

Protocol architecture (ch2).Transmission and Transmission Media (ch3-4)Communication Techniques (ch5-6)Flow and Error control (ch7)Transmission efficiency ( ch8)Switching Techniques (ch10)