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Chapter 1 Introduction 1. 1 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required 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 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 Data Flow 1. 2

Criteria of Effectiveness of Data Communication Delivery: Data must arrive at the correct destination. Criteria of Effectiveness of Data Communication Delivery: Data must arrive at the correct destination. Data only arrive at the right destination. Accuracy: Data must be correct without any error. Timeliness: Data must be delivered in timely manner Jitter: Variation in the data arrival time at the detonation Different applications have different requirements on these criteria 1. 3

Figure 1. 1 Five components of data communication • Message • • 1. 4 Figure 1. 1 Five components of data communication • Message • • 1. 4 Sender Receiver Transmission medium Protocol

Data Representation • Text • Numbers • Images • Audio • Video 1. 5 Data Representation • Text • Numbers • Images • Audio • Video 1. 5

Data Representation: Text q ASCII code: includes definitions for 128 characters v 33 are Data Representation: Text q ASCII code: includes definitions for 128 characters v 33 are non-printing control characters (now mostly obsolete) that affect how text and space is processed v 95 printable characters, including the space q Unicode: current prevalent coding system for text q 32 bits to represent a symbol or char in any language in the world q First 127 characters are ASCII code q Details can be found at Appendix A in the textbook 1. 6

Figure 1. 2 Data flow (simplex, half-duplex, and full-duplex) 1. 7 Figure 1. 2 Data flow (simplex, half-duplex, and full-duplex) 1. 7

Data Flow Examples q Simplex mode q Keyboard, mouse, traditional monitor q GPS device Data Flow Examples q Simplex mode q Keyboard, mouse, traditional monitor q GPS device q Half duplex q q Walkie-talkie Citizen band radio Advantage: entire bandwidth can be used for transmission Cons: not suitable for high interactive application q Full duplex 1. 8

1 -2 NETWORKS A network is a set of devices (often referred to as 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. 9

Communication Devices: Examples Common communication devices Non-common communication devices Bluetooth watches switch Wireless router Communication Devices: Examples Common communication devices Non-common communication devices Bluetooth watches switch Wireless router 1. 10 Bluetooth alarm clock

Network Criteria • Performance: • Throughput: average rate of successful message delivery • Delay Network Criteria • Performance: • Throughput: average rate of successful message delivery • Delay • Other criteria • Reliability: frequency of failure, recover time, robustness • Security • becoming more important now 1. 11

Figure 1. 3 Types of connections: point-to-point and multipoint Whether the link capacity is Figure 1. 3 Types of connections: point-to-point and multipoint Whether the link capacity is shared or not 1. 12

Figure 1. 4 Categories of topology 1. 13 Figure 1. 4 Categories of topology 1. 13

Figure 1. 5 A fully connected mesh topology (five devices) 2 3 1 5 Figure 1. 5 A fully connected mesh topology (five devices) 2 3 1 5 n(n-1) half-duplex links n(n-1)/2 duplex links 4 Pro: robustness Con: many cabling/installation and need many I/O ports on nodes 1. 14

Figure 1. 6 A star topology connecting four stations Example: Ethernet switch/hub, Wifi access Figure 1. 6 A star topology connecting four stations Example: Ethernet switch/hub, Wifi access point Pro: robust against a node’s failure or a link failure Con: single point of failure at the hub 1. 15

Figure 1. 7 A bus topology connecting three stations Example: first generation Ethernet that Figure 1. 7 A bus topology connecting three stations Example: first generation Ethernet that using cable for wiring Con: any tap device failure will cause the whole system fail 1. 16

Figure 1. 8 A ring topology connecting six stations Example: IBM token ring LAN Figure 1. 8 A ring topology connecting six stations Example: IBM token ring LAN (less popular now). 1. 17

Figure 1. 9 A hybrid topology: a star backbone with three bus networks 1. Figure 1. 9 A hybrid topology: a star backbone with three bus networks 1. 18

Categories of Networks Local Area Networks (LAN) Metropolitan Area Networks (MAN) IEEE 802. 3 Categories of Networks Local Area Networks (LAN) Metropolitan Area Networks (MAN) IEEE 802. 3 IEEE 802. 4 IEEE 802. 5 1. 19 High-speed DSL Cable TV network Wide Area Networks (WAN) Frame Relay ATM

Figure 1. 10 An isolated LAN connecting 12 computers to a hub in a Figure 1. 10 An isolated LAN connecting 12 computers to a hub in a closet 1. 20

Figure 1. 11 WANs: a switched WAN and a point-to-point WAN 1. 21 Figure 1. 11 WANs: a switched WAN and a point-to-point WAN 1. 21

Figure 1. 12 A heterogeneous network made of four WANs and two LANs 1. Figure 1. 12 A heterogeneous network made of four WANs and two LANs 1. 22

1 -3 THE INTERNET Internet: Interconnection of Networks Before Internet: § Many isolated Local 1 -3 THE INTERNET Internet: Interconnection of Networks Before Internet: § Many isolated Local Area Networks (LANs) existed § Those LANs had very different hardware and network protocols § Protocol example: TCP/IP, IPX (from Novell) Topics discussed in this section: A Brief History The Internet Today (ISPs-Internet Service Providers) 1. 23

A Brief History 1961: Kleinrock - queueing theory shows effectiveness of packet-switching 1964: Baran A Brief History 1961: Kleinrock - queueing theory shows effectiveness of packet-switching 1964: Baran - packet-switching in military nets 1967: ARPAnet conceived by Advanced Research Projects Agency 1969: first ARPAnet node operational 1972: ARPAnet demonstrated publicly NCP (Network Control Protocol) first host-host protocol first e-mail program ARPAnet has 15 nodes 1. 24

Figure 1. 13 Hierarchical organization of the Internet now 1. 25 Figure 1. 13 Hierarchical organization of the Internet now 1. 25

1 -4 PROTOCOLS AND STANDARDS In this section, we define two widely used terms: 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 – similar to human language (syntax, semantics, timing) Standards – public recognized protocols for open market Standards Organizations Internet Standards – Internet draft (work in progress) Request for Comment (RFC) (published, final standard) 1. 26