Chapter 1 Introduction 1 1 Copyright The

Chapter 1 Introduction 1. 1 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

1 -1 DATA COMMUNICATIONS The term telecommunication means communication at a distance. The word data refers to information presented in whatever form is agreed upon by the parties creating and using the data. Data communications are the exchange of data between two devices via some form of transmission medium such as a wire cable. Topics discussed in this section: Components Data Representation (texts, numbers, images, audio and vidéo) Data Flow 1. 2

Figure 1. 1 Five components of data communication 1. 3

Figure 1. 2 Data flow (simplex, half-duplex, and full-duplex) 1. 4

1 -2 NETWORKS A network is a set of devices (often referred to as nodes) connected by communication links. A node can be a computer, printer, or any other device capable of sending and/or receiving data generated by other nodes on the network. Topics discussed in this section: Distributed Processing Network Criteria Physical Structures Network Models Categories of Networks Interconnection of Networks: Internetwork 1. 5

Figure 1. 3 Types of connections: point-to-point and multipoint 1. 6

Figure 1. 4 Categories of topology 1. 7

Figure 1. 5 A fully connected mesh topology (five devices) 1. 8

Figure 1. 6 A star topology connecting four stations 1. 9

Figure 1. 7 A bus topology connecting three stations 1. 10

Figure 1. 8 A ring topology connecting six stations 1. 11

Figure 1. 9 A hybrid topology: a star backbone with three bus networks 1. 12

Local Area Networks n Smaller scope n n n Building 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

Figure 1. 10 An isolated LAN connecting 12 computers to a hub in a closet 1. 14

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

Figure 1. 11 WANs: a switched WAN and a point-to-point WAN 1. 16

Metropolitan Area Networks n n n MAN Middle ground between LAN and WAN Private or public network High speed Large area

Figure 1. 12 A heterogeneous network made of four WANs and two LANs 1. 18

1 -3 THE INTERNET The Internet has revolutionized many aspects of our daily lives. It has affected the way we do business as well as the way we spend our leisure time. The Internet is a communication system that has brought a wealth of information to our fingertips and organized it for our use. Topics discussed in this section: A Brief History The Internet Today (ISPs) 1. 19

A Quick Timeline n http: //www. internet-story. com/index. htm n ARPANET developed in 1969 n n Designed to connect computers at four locations Designed to be resistant to disruption © Prentice. Hall, Inc

Figure 1. 13 Hierarchical organization of the Internet 1. 21

1 -4 PROTOCOLS AND STANDARDS In this section, we define two widely used terms: protocols and standards. First, we define protocol, which is synonymous with rule. Then we discuss standards, which are agreed-upon rules. Topics discussed in this section: Protocols Standards Organizations Internet Standards 1. 22

Protocol n n Set of conventions between two entities involved in a communication Elements n n n syntax : data format and signal levels concerns the format of the data blocks semantics : include control information for coordination and error handling timing : speed matching and sequencing

Protocol Architecture n n Software structure that implements the communication function Consists of a layered set of protocols Separate layers or protocols implemented in separate modules Different applications have different requirements at each layer