Data Communications. From Basics to Broadband. Third Edition. William J. Beyda

Transcription

1 Data Communications From Basics to Broadband Third Edition William J. Beyda University of California Extension, Berkeley Siemens Information and Communication Networks, Inc. Prentice Hall Upper Saddle River, New Jersey 07458

2 Contents PREFACE Acknowledgments xv xiii 1 OVERVIEW AND INTRODUCTION 1 A Logical Progression 2 Using this Book 4 2 UNDERSTANDING TELECOMMUNICATIONS 5 The Importance of Telecommunications 5 The Public Network 5 Central Offices and Local Loops, 6 Signaling on a Voice Network, 8 Divestiture 10 Intra-LATA Call Routing 13 Inter-LATA Call Routing 15 Regulation 16 Increased Competition 17 Voice Communications Service Offerings 18 Echo Suppressors and Cancellers, 20 TASIvs. Voice Call Multiplexing, 21 Leasing Services vs. Buying Customer-Premises Equipment 22 Centrex, 22 Key Systems, 23 Private Branch Exchange, 23 Wireless Communications 27

3 vi Contents Summary 30 Terms for Review 30 Exercises 32 3 BASIC DATA COMMUNICATIONS CONCEPTS 33 Defining Data Communications 33 Host Computers and Terminals 33 Bits and Bytes 34 Character Codes 35 Morse Code, 35 Baudot Code, 36 Extended Binary Coded Decimal Interchange Code, 38 American National Standard Code for Information Interchange, 38 Equipment Compatibility and Character Code Comparisons, 41 Character Code Design and Terminal Implementation, 42 Parallel vs. Serial Transmission 43 Asynchronous vs. Synchronous Transmission 45 Asynchronous vs. Synchronous Transmission Efficiency, 48 Simplex, Half Duplex, and Full Duplex Communications 49 Summary 52 Terms for Review 52 Exercises 53 4 DATA INTERFACES AND TRANSMISSION 55 Standards Organizations 55 Digital Interface Standards 56 The RS-232-C Standard, 57 RS-232-C Handshaking, 64 Connecting a DTE to Another DTE in RS-232-C, 66 RS-449, RS-422-A, andrs-423-a, 67 High-speed Desktop Serial Interfaces, 70 Remote Digital Transmission 70 Dataphone Digital Service, 72 T-l Carrier, 72 Integrated Services Digital Network, 73 Packet Data Networks, 73 Digital Access, 73 Digital and Analog Bandwidth, 73

4 Contents vii Transmission Media 75 Baseband vs. Broadband 81 Modulation 81 Amplitude Modulation, 83 Frequency Modulation, 84 Phase Modulation, 84 Bits Per Second vs. Baud, 85 Multispeed Modems, 87 High-Speed Modems, 87 Error Correcting Modems, 89 Data Compression in Modems, 90 Short-Haul Modems, 90 Facsimile and Fax Modems, 90 Summary 91 Terms for Review 92 Exercises 94 5 IMPROVING DATA COMMUNICATIONS EFFICIENCY 97 Front-End Processors 97 Port-Sharing Devices 100 Line Splitters and Remote Intelligent Controllers 101 Multiplexers 103 Time-Division Multiplexing, 104 Character and Bit Interleaving, 105 Statistical Time-Division Multiplexing, 107 Frequency-Division Multiplexing, 109 Data Compression Devices 111 Inverse Multiplexers 111 Multidrop Configurations 112 Summary 114 Terms for Review 115 Exercises DATA INTEGRITY AND SECURITY 117 Data Integrity 117 Sources of Errors 117

5 viii Contents Error Control Approaches 118 Implementing Error Control: The Technical Details, 119 Echo Checking, 119 Parity Checking, 119 Cyclical Parity, 121 Hamming Code, 121 Checksums, 122 Cyclical Redundancy Check, 123 Security 123 The Importance of Security 123 Security Concerns 123 Security Goals 124 Security Measures 124 Secure Transmission Facilities, 124 Passwords, 125 Historical and Statistical Logging, 125 Closed User Groups, 126 Firewalls, 126 Encryption and Decryption, 128 Data Confidentiality and Identity Verification, 132 Summary 133 Terms for Review 134 Exercises ARCHITECTURES AND PROTOCOLS 137 Architectures 137 The Open Systems Interconnection Model 138 OSI in Action 141 Traditional Communications Architectures 143 Systems Network Architecture, 144 Other Communications Architectures, 150 Protocols 152 Polling and Selecting, 152 Automatic Repeat Request, 152 Common Link-level Protocols 153 Binary Synchronous Communications, 154 Characters in a BSC Frame, 155 Synchronous Data Link Control, 157 Bits in an SDLC Frame, 158

6 Contents ix Protocol Converters and Code Converters, 160 The TCP/IP Protocol Suite and Related Protocols 160 The IP Header, 161 Summary 165 Terms for Review 167 Exercises DATA TRANSPORT NETWORKS 171 Packet Switching Networks 171 Public Packet Switching Networks, 173 The X.25 Standard, 174 Packet Switching Network Services, 176 Routing Data in a Packet Switching Network, 176 Frame Relay Networks, 177 The Internet, 178 Local Area Networks 180 Local Area Network Topologies, 182 Baseband vs. Broadband Transmission, 184 Local Area Network Access Methods, 184 Priority and Random Backoff, 186 Local Area Network Standards, 189 Widely Used Local Area Networks, 190 The Ethernet Frame, 190 Higher Speed Local Area Networks, 193 Internetworking 194 Repeaters, 194 Bridges, 194 Routers, 199 Gateways, 200 Internetworking Transmission Options, 201 Wireless Data Transport Networks, 202 Summary 204 Terms for Review 205 Exercises NETWORK MANAGEMENT 209 Network Management Functions 209 Service Levels 210

7 x Contents Availability, 210 Reliability, 211 Response Time, 212 Throughput, 213 Network Management Approaches 213 Nonautomated Network Management, 214 Semiautomated Network Management, 214 Integrated Network Management, 214 Network Management Protocols, 215 Diagnostic Methods 217 Analog and Digital Modem Loopback Testing, 218 Data Communications Test Equipment 220 The Breakout Box, 220 The Datascope or Protocol Analyzer, 221 Analog Test Equipment, 222 Summary 222 Terms for Review 223 Exercises DIGITAL TELECOMMUNICATIONS 225 Digital Customer-Premises Equipment 225 Digitizing Voice Using Pulse Code Modulation, 227 High-Bandwidth Digital Transmission Facilities, 227 T-l Signaling, 229 Digital Networks, 231 Integrated Services Digital Network 232 ISDN Channels, 232 The Basic-Rate Interface, 233 The Primary-Rate Interface, 234 Other Channel Arrangements, 234 ISDN Equipment Functions and Reference Points, 235 Circuit and Packet Switching in ISDN, 237 PBXs, LANs, and ISDN, 237 ISDN Services, 238 National ISDN, 239 Video and ISDN, 240 The Realities of ISDN, 241 Digital Subscriber Line Services, 242 Cable Modems, 243 Broadband ISDN, 244 Broadband ISDN Transmission Media, 245 Asynchronous Transfer Mode 246 ATM Cells, 247

8 Contents xi Physical Transmission in ATM, 247 Routing Cells in an ATM Network, 248 Video Transmission and ATM, 249 ATM and the OSI Model, 250 ATM Layers, 250 ATM Capacity Issues, 250 ATM Tariff Issues, 251 The Information Superhighway 252 Summary 253 Terms for Review 256 Exercises 257 APPENDIX: THE BINARY NUMBER SYSTEM 259 GLOSSARY 265 BIBLIOGRAPHY 303 INDEX 313