'

Computer Networks Protocols, Standards,

and Interfaces

Second Edition

Uyless Black Bell Atlantic Education Services

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PRENTICE HALL PTR Englewood Cliffs, New Jersey 07632

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Preface, ix Organization of this Book, xi Acknowledgments, xii Introduction to Computer Networks Introduction, 1 Advantages of Networks, 1 Structure of the Communications Network, 2 Point-to-point and Multidrop Circuits, 4 Data Flow and Physical Circuits, A Network Topologies, 6 Topologies and Design Goals, 6 Hierarchical Topology, 7 Horizontal Topology (Bus), 9 Star Topology, 9 Ring Topology, 9 Mesh Topology, 9 The Telephone Network, 10 Switched and Nonswitched Options, 12 Fundamentals of Communications Theory, 13 Channel Speed and Bit Rate, 13 Voice Communications and Analog Waveforms, 14 Bandwidth and the Frequency Spectrum, 14 Connecting the Analog and Digital Worlds, 18 Digital Signals, 18 The Modem, 18 Synchronizing Network Components, 19 Synchronization Codes, 20 Asynchronous and Synchronous Transmission, 22 Message Formats, 24 The Communications Port, 24 Additional Network Components, 25 Summary, 27

Communications Between and Among Computers and Terminals, 28 Introduction, 28 Traffic Control and Accountability, 28 Checking for Errors, 30 Wide Area and Local Networks, 30 Connection-oriented and Connectionless Networks, 34 Classification of Communications Protocols, 36 Polling/Selection Systems, 38 Selective and Group Polling, 40 Stop-and-Wait Polling/Selection, 41 Continuous ARQ (Sliding Windows), 43 Nonpolling Systems, 46 Request to Send/Clear to Send, Al Xon/Xoff, Al Time Division Multiple Access (TDMA), 48 Peer-to-Peer Nonpriority Systems, 49 Time Division Multiplexing (TDM) or Slot, 49 Register Insertion, 50 Carrier Sense (Collision) Systems, 50 Token Passing, 52 Peer-to-Peer Priority Systems, 54 Priority Slot, 54 Carrier Sense (Collision-free) Systems, 54 Token-passing (Priority) Systems, 55 Summary, 55

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Chapter Three Layered Protocols, Networks, and the OSI Model, 56 Introduction, 56 Goals of Layered Protocols, 56 Network Design Problems, 57 Communication Between Layers, 58 A Pragmatic Illustration, 61 Introduction to Standards Organizations and the OSI Model, 63 Standards Organizations, 63 The Layers of OSI, 64 OSI Status, 66 GOSIP, 67 GOSIP, Version 1, 68 GOSIP, Version 2,11 Summary, 71

Chapter Four Polling/Selection Protocols, 72 Introduction, 72 Character and Bit Protocols, 72 Binary Synchronous Control (BSC), 73 BSC Formats and Control Codes, 73 Line Modes, 74 Line Control, 75 Problems with BSC, 76 HDLC, 76 HDLC Options, 11 HDLC Frame Format, 79 Code Transparency and Synchronization, 81 HDLC Control Field, 83 Commands and Responses, 85 The HDLC Transmission Process, 89 HDLC Subsets, 95 SDLC, 97 Protocol Conversion, 100 Summary, 100

Chapter Rve Satellite Networks, 101 Introduction, 101 Satellite Components, 101 Pros and Cons of Satellite Networks, 102 Brief History, 103 Using Satellites to Communicate, 104 Conventional Multiplexing, 104 Polling/Selection, 105 Nonpolling Peer/Peer Systems, 108 Nonpolling Primary/Secondary Systems, 111 Satellite Delay Units (SDUs), 114 The Teleport, 115 Summary, 116

Chapter Six Local Area Networks, 117 Introduction, 117 Why LANs?, 117 Primary Attributes of a LAN, 118 Broadband and Baseband LANs, 118 IEEE LAN Standards, 119 Relationship of the 802 Standards to the ISO/CCITT Model, 120 Connection Options with LANs, 120 LLC and MAC Protocol Data Units, 123 LAN Topologies and Protocols, 125 CSMA/CD and IEEE 802.3, 125 Token Ring (Priority), 130 Token Bus and IEEE 802.4, 134 Metropolitan Area Networks (MANs), 137 Summary of the 802 Specifications, 137 Other Systems, 138 AT&T Information System Network (ISN), 138 IBM Token Ring, 139 ANSI Fiber Distributed Data Interface, 145 Summary, 148

Chapter Seven Switching and Routing in Networks, 149 Introduction, 149 Telephone Switching Systems, 149 Electromechanical Systems, 152 Stored Program Control Systems, 153 Message Switching, 156 Packet Switching, 157 When and When Not to Use Packet Switching, 159 Packet Routing, 161 Packet-Switching Support to Circuit-Switching Networks, 170 Summary, 172

Chapter Eight

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vii The X.25 Network and Supporting Protocols, 173 Introduction, 173 Features of X.25, 173 Why X.25?, 175 Layers of X.25, 175 X.25 and the Physical Layer, 175 X.25 and the Data Link Layer, 176 Companion Standards to X.25, 111 Features of X.25, 178 X.25 Channel Options, 178 Flow-Control Principles, 182 Other Packet Types, 182 X.25 Logical Channel States, 186 Timeouts and Time Limits, 187 Packet Formats, 188 The D Bit, 192 The M Bit, 192 A and B Packets, 193 The Q Bit, 193 The A Bit, 194 Flow Control and Windows, 194 X.25 Facilities, 195 Other Standards and Layers, 198 The Pad, 198 PAD: Packet Formats and Packet Flow, 204 The Transport Layer, 204 Internetworking, 209 Connectionless-mode Networks, 211 X.75, 211 Communications Between the Layers, 214 Frame Relay and X.25, 224 The Frame Relay and X.25 Stacks, 225 International X.25 Networks, 226 Does a Standard Assure Compatability?, 226 Summary, 227

Chapter Nine

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Chapter Ten

Digital Networks, 228 Introduction, 228 Advantages of Digital Systems, 228 Signal Conversion, 230 Digital Carrier Systems, 232 Channel and Data Service Units, 234 Analog-to-Digital Techniques, 234 Waveform Analysis, 234 Parameter Coding (Vocoders), 237 Future Digital Systems, 238 Integrated Digital Networks, 239 SBS Integrated Network, 239 The Integrated Services Digital Network (ISDN), 241 Digital Switching, 255 Voice Transmission by Packet, 257 Bell Labs' Packet-Switched Voice-Data Patent, 260 Summary, 260

TCP/IP, 261 Introduction, 261 TCP/IP and Internetworking, 261 Example of TCP/IP Operations, 263 Related Protocols 264 Ports and Sockets, 264 The IP Address Structure, 265 Major Features of IP, 265 IP Datagram, 267 Major IP Services, 269 IP Source Routing, 269 Route-Recording Option, 271 The Time stamp Option, 271 ICMP, 271 ICMP Message Format, 271 ICMP Error- and Status-Reporting Procedures, 272 Value of the Transport Layer, 273 TCP, 274 Major Features of TCP, 21A Passive and Active Opens, 276 The Transmission Control Block (TCB), 277 The TCP Segment, 277 User Datagram Protocol (UDP), 279 Format of the UDP Message, 279 Route Discovery Protocols, 280 Examples of Route Discovery Protocols, 282 The Application Layer Protocols, 285 Summary, 285

Chapter Eleven Personal Computer Networks, 287 Personal Computer Introduction, 287 Growth in the Personal Computer Industry, 287 Personal Computer Communications Characteristics, 288 Error Handling, 289 Using the Personal Computer as a Server, 291 Linking the Personal Computer to Mainframe Computers, 292 File Transfer on Personal Computers,

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294 Personal Computers and Local Area Networks, 298 Network Operating Systems (NOSs), 300 Common IBM PC LAN Protocol Stacks, 301 AppleTalk and EtherTalk, 303 Summary, 305

Chapter Twelve The PBX and Data Communications Networks, 306 Introduction, 306 Why Use a PBX in Data Communications?, 306 Evolution of the PBX, 307 Issue of Voice/Data Integration, 310 Issue of Using a PBX in a LAN, 311 Wiring Costs, 312 The Fourth-Generation PBX, 313 Examples of Modern PBXs, 314 The Digital Multiplexed Interface (DMI) and Computer-to-PBX Interface (CPI) Proposals, 315 Summary, 318

Chapter Thirteen

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Upper-Layer Protocols, 319 Introduction, 319 Network Security, 319 Encryption with Private Keys, 321 The Data Encryption Standard (DES), 323 Encryption with Public Keys, 326 ISO Security Recommendations, 328 The Session Layer, 328 Session Layer Operations, 329 The Graceful Close, 329 Synchronization Services, 329 Session Layer Activities, 331 The Presentation Layer, 331 ASN. 1,331 ASN. 1 Coding Rules, 333 Some Examples of ASN. 1 Coding, 333 Transfer Syntax, 337 The Application Layer, 338 ACSE, 340 RTSE, 340 ROSE, 342 CCR, 344 Terminal Systems and Protocols, 346 Telematics, 346 Teletex, 347 Electronic Mail, 348 X.400, 349 X.500 Directory Services, 353 Protocols for File Management, 353 FTAM, 356 Virtual Terminal Protocols, 360 Distributed Transaction Processing, 363 RDA, 364 EDI, 365 Summary, 365 Final Thoughts, 366

Appendix A A Data Communications Tutorial, 367 Appendix B Translation Tables, 380 Appendix C Physical Level Interfaces, 383 Appendix D Commonly Used Standards, 400 Appendix E Supporting Standards to X.25/X.75 Networks, 412

Index, 425