1 William Stallings Data and Computer Communications 7th EditionChapter 1 Data Communications and Networks Overview

2 A Communications ModelSource generates data to be transmitted Transmitter Converts data into transmittable signals Transmission System Carries data Receiver Converts received signal into data Destination Takes incoming data

3 Communications Tasks Transmission system utilization AddressingInterfacing Routing Signal generation Recovery Synchronization Message formatting Exchange management Security Error detection and correction Network management Flow control

4 Simplified Communications Model - Diagram

5 Simplified Data Communications Model

6 Networking Point to point communication not usually practicalDevices are too far apart Large set of devices would need impractical number of connections Solution is a communications network Wide Area Network (WAN) Local Area Network (LAN)

7 Wide Area Networks Large geographical areaCrossing public rights of way Rely in part on common carrier circuits Alternative technologies Circuit switching Packet switching Frame relay Asynchronous Transfer Mode (ATM)

8 Circuit Switching Dedicated communications path established for the duration of the conversation e.g. telephone network

9 Packet Switching Data sent out of sequenceSmall chunks (packets) of data at a time Packets passed from node to node between source and destination Used for terminal to computer and computer to computer communications

10 Frame Relay Packet switching systems have large overheads to compensate for errors Modern systems are more reliable Errors can be caught in end system Most overhead for error control is stripped out

11 Asynchronous Transfer ModeATM Evolution of frame relay Little overhead for error control Fixed packet (called cell) length Anything from 10Mbps to Gbps Constant data rate using packet switching technique

12 Local Area Networks Smaller scopeBuilding or small campus Usually owned by same organization as attached devices Data rates much higher Usually broadcast systems Now some switched systems and ATM are being introduced

13 LAN Configurations Switched Wireless Switched Ethernet ATM LANMay be single or multiple switches ATM LAN Fibre Channel Wireless Mobility Ease of installation

14 Metropolitan Area NetworksMAN Middle ground between LAN and WAN Private or public network High speed Large area

15 Networking Configuration

16 Further Reading Stallings, W. [2003] Data and Computer Communications (7th edition), Prentice Hall, Upper Saddle River NJ, chapter 1 Web site for Stallings book