1. William Stallings Data and Computer Communications Chapter 1 Introduction

2. A Communications Model zSource ygenerates data to be transmitted zTransmitter yConverts data into transmittable signals zTransmission System yCarries data zReceiver yConverts received signal into data zDestination yTakes incoming data

3. Simplified Communications Model - Diagram

4. Key Communications Tasks zTransmission System Utilization zInterfacing zSignal Generation zSynchronization zExchange Management zError detection and correction zAddressing and routing zRecovery zMessage formatting zSecurity zNetwork Management

5. Simplified Data Communications Model

6. Networking zPoint to point communication not usually practical yDevices are too far apart yLarge set of devices would need impractical number of connections zSolution is a communications network

7. Simplified Network Model

8. Wide Area Networks zLarge geographical area zCrossing public rights of way zRely in part on common carrier circuits zAlternative technologies yCircuit switching yPacket switching yFrame relay yAsynchronous Transfer Mode (ATM)

9. Circuit Switching zDedicated communications path established for the duration of the conversation ze.g. telephone network

10. Packet Switching zData sent out of sequence zSmall chunks (packets) of data at a time zPackets passed from node to node between source and destination zUsed for terminal to computer and computer to computer communications

11. Frame Relay zPacket switching systems have large overheads to compensate for errors zModern systems are more reliable zErrors can be caught in end system zMost overhead for error control is stripped out

12. Asynchronous Transfer Mode zATM zEvolution of frame relay zLittle overhead for error control zFixed packet (called cell) length zAnything from 10Mbps to Gbps zConstant data rate using packet switching technique

13. Integrated Services Digital Network zISDN zDesigned to replace public telecom system zWide variety of services zEntirely digital domain

14. Local Area Networks zSmaller scope yBuilding or small campus zUsually owned by same organization as attached devices zData rates much higher zUsually broadcast systems zNow some switched systems and ATM are being introduced