OPEN SYSTEMS NETWORKING TCP/IP AND OSI David M. Piscitello and A. Lyman Chapin Addison-Wesley Publishing Company Reading, Massachusetts Menlo Park, California New York Don Mills, Ontariao Wokingham, England Amsterdam Bonn Sydney Singapore Tokyo Madrid San Juan Paris Seoul Milan Mexico City Taipei OPEN SYSTEMS NETWORKING Addison-Wesley Professional Computing Series Brian W. Kernighan, Consulting Editor Ken Arnold/John Peyton, A C User’s Guide to ANSI C Tom Cargill, C++ Programming Style David A. Curry, UNIX® System Security: A Guide for Users and System Administrators Scott Meyers, Effective C++: 50 Specific Ways to Improve Your Programs and Designs Robert B. Murray, C++ Strategies and Tactics Craig Partridge, Gigabit Networking Radia Perlman, Interconnections: Bridges and Routers David M. Piscitello/A. Lyman Chapin, Open Systems Networking: TCP/IP and OSI Stephen A. Rago, UNIX® System V Network Programming W. Richard Stevens, Advanced Programming in the UNIX® Environment W. Richard Stevens, TCP/IP Illustrated, Volume 1 The publisher offers discounts on this book when ordered in quantity for special sales. For more information please contact: Corporate & Professional Publishing Group Addison-Wesley Publishing Company One Jacob Way Reading, Massachusetts 01867 Library of Congress Cataloging-in-Publication Data Piscitello, David M. Open systems networking : TCP/IP and OSI / David M. Piscitello and A. Lyman Chapin. p. cm. - - (Addison-Wesley professional computing series) Includes bibliographical references and index. ISBN 0-201-56334-7 (alk. paper) 1. OSI (Computer network standard) 2. TCP/IP (Computer network proto- col) 3. Computer networks. I. Chapin, A. Lyman. II. Title. III. Series. TK5105.55.P57 1993 004.6'2 - - dc20 93-17791 CIP Copyright © 1993 by Addison-Wesley Publishing Company All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form, or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior consent of the publisher. Printed in the United States of America. Published simultaneously in Canada. Cover photo by Steven Hunt, The Image Bank Text design by Carol Keller ISBN 0-201-56334-7 Text printed on recycled and acid-free paper. 1 2 3 4 5 6 7 8 9 10 MU 96959493 First printing, August 1993 CONTENTS PREFACE xiii Why This Book, Now? xiii Demystifying Open Systems xvii Equal Treatment xvii Opinions Are Good! xix Historical Asides and Authors’ Insights xix Who Should Read This Book? xx Contributors xxi Acknowledgments xxi PART ONE INTRODUCTION TO OPEN SYSTEMS 1 CHAPTER 1 INTRODUCTION 3 Organization of This Book 9 CHAPTER 2 OPEN SYSTEMS STANDARDS 13 OSI Standards 13 Internet Standards 21 Parting Comments on Open Systems Standards Processes 26 v vi OPEN SYSTEMS NETWORKING: TCP/IP AND OSI PART TWO OPEN NETWORK ARCHITECTURES 31 CHAPTER 3 CONCEPTS AND TERMINOLOGY OF OPEN SYSTEMS 33 Introduction 33 Architectures 34 Open Systems 35 Architecture Wars 37 Layers 37 Terminology 45 Entities 46 Notation 47 Services 47 The Queue Model 50 Connections and Connectionless 51 What about Protocols? 54 Protocol Headers and User Data 57 Relating Service to Protocol 58 Time-Sequence Diagrams 59 A Final Fling with OSI Fundamentals 60 Conclusion 61 CHAPTER 4 THE LANGUAGES OF OPEN SYSTEMS 63 Introduction 63 “Open” Languages—Breaking Language Barriers 64 Data Representation 65 Abstract Syntax Notation 68 ASN.1 Data Types and Tags 69 Modules 72 Transfer Syntax—Basic Encoding Rules (BER) for ASN.1 73 Do I Really Have to Deal with All This? 75 Languages and the TCP/IP Community 76 Conclusion 79 CONTENTS vii CHAPTER 5 NAMES AND ADDRESSES 81 Names 82 Addresses 88 Registration Authorities 88 Object Identifiers 96 Conclusion 97 PART THREE UPPER LAYERS 99 CHAPTER 6 OPEN SYSTEMS APPLICATIONS 101 Distributed Applications Services 106 Conclusion 109 CHAPTER 7 DIRECTORIES 111 The Telephony Model 112 Directory System Principles 113 Open System Directories 114 The Domain Name System 115 The OSI Directory 122 The Directory Model129 The Relationship Between the OSI Directory and Message Handling Services 135 The OSI Directory in the Internet 137 Other Internet Directory Utilities 139 Resource Location 141 Conclusion 145 CHAPTER 8 OPEN SYSTEMS MESSAGING: ELECTRONIC MAIL 147 OSI Message Handling System (X.400 MHS, MOTIS) 148 viii OPEN SYSTEMS NETWORKING: TCP/IP AND OSI Internet Mail 163 Interworking between MHS and Internet Mail172 Conclusion 174 CHAPTER 9 NETWORK MANAGEMENT 177 The Internet Approach: Keep It Simple 178 OSI Common Management: Flexibility, At A Price 189 Putting It All Together 205 Where To from Here? 208 Conclusion 211 CHAPTER 10 “CORE” APPLICATION SERVICE ELEMENTS 213 Association-Control Service Element 214 Reliable Transfer Service Element 223 Remote Operations Service Element 232 “Core ASE Wanna-bes” 243 Conclusion 245 CHAPTER 11 THE PRESENTATION AND SESSION LAYERS 247 Presentation Layer 247 Session Layer 261 Putting It All Together 281 The Future of OSI Upper Layers 284 Conclusion 285 PART FOUR MIDDLE LAYERS 287 CHAPTER 12 THE TRANSPORT LAYER 289 OSI’s Connection-oriented Transport Service 290 CONTENTS ix TCP/IP’s Reliable Stream Service 291 Interfaces to Transport Services 292 Transport Addressing 300 Five Classes of OSI Transport Protocol 301 Conformance 309 Comparing TP4 to TCP 310 OSI Transport Connection Establishment 311 Setting It All to UNIX 317 Frozen References 320 TCP Connection Establishment 320 Normal Data Transfer in OSI Transport Protocol 325 Reliability Mechanisms to Deal with the Real World 328 Data Transfer in TCP—More of the Same 334 Window Considerations for TP4 and TCP 337 OSI’s Expedited Data 340 TCP’s Urgent Data 341 Timers and Open Transport Protocols 342 Connection Release (Connection Refusal) in the OSI Transport Protocol 354 Connection Release (Refusal) in TCP 356 Datagram Transport Protocols—CLTP and UDP 358 Conclusion 360 CHAPTER 13 THE NETWORK LAYER 361 Architecture: The Internal Organization of the Network Layer 362 Connection-oriented Network Service 372 Connectionless Network Service 379 Internetworking Protocols 383 NL Protocol Identification in TCP/IP and Multiprotocol Environments 397 Network Layer Addresses 398 Conclusion 411 CHAPTER 14 ROUTING 413 Source Routing and “Hop-by-Hop” Routing 414 Routing Principles 415 Routing Protocols 424 Conclusion 465 x OPEN SYSTEMS NETWORKING: OSI & TCP CHAPTER 15 DATA LINK AND PHYSICAL LAYERS 467 Taxonomy of Data Link Standards 468 Point-to-Point Connection Standards 469 Multiaccess Channel Standards 471 Metropolitan Area Networks: FDDI and IEEE 802.6 DQDB 473 Fast Packet Services and Technologies 482 Very High Bandwidth as an Enabling Vehicle for OSI 500 Conclusion 500 PART FIVE THE FUTURE OF OPEN SYSTEMS NETWORKING 503 CHAPTER 16 MULTIPROTOCOL OPEN SYSTEMS 505 The Myth of “OSI Migration” 505 OSI Is an Alternative, Not a Substitute 507 OSI and TCP/IP Coexistence: Networking Détente 510 Bringing OSI into a Network 520 Are the Instrumentation and Expertise Available to Operate OSI Networks? 522 Conclusion 522 CHAPTER 17 AN ARCHITECTURAL ALTERNATIVE FOR THE INTERNET 525 What Is “the Internet”? 525 A Naming-based Concept of Internet Connectivity 527 CHAPTER 18 A READING FROM THE BOOK OF GENEBITS 533 APPENDIX A NETWORKING ACRONYMS 537 CONTENTS xi APPENDIX B SOURCES 559 How and Where to Obtain Useful Information 559 Information about TCP/IP and the Internet 560 Information about OSI 564 Authors’ Electronic Mail Addresses 566 REFERENCES 567 INDEX 587 PREFACE Why This Book, Now? Open systems—in particular, Open Systems Interconnection (OSI) and TCP/IP1—are all the rage. There are plenty of books that discuss OSI and plenty more that discuss TCP/IP. However, despite the facts that the architecture and goals of OSI and TCP/IP are essentially the same, and that they are really just currently popular manifestations of the same fun- damental principles and techniques, no previous book has examined the two in parallel. This book covers both Open Systems Interconnection and the Internet architecture and protocols, commonly known as TCP/IP. There are many compelling reasons for examining these architectures in parallel, which is what this book intends to do. TCP/IP Has Strongly Influenced the Design of OSI Many of the fea- tures and functions present in OSI trace their roots back to TCP/IP; for example, OSI’s transport protocol class 4 and connectionless network protocol (CLNP) are functionally equivalent to TCP and IP. Furthermore, OSI’s application services—Message Handling System, File Transfer Access and Management, the Directory, and Virtual Terminal—are all attempts to improve upon their TCP/IP ancestors; the OSI Message Handling System, for example, is intended to improve upon the highly successful electronic-mail facilities provided in the TCP/IP protocol suite by the Simple Mail Transfer Protocol by permitting facsimile, images, and voice to accompany text in a mail envelope. The OSI Message Handling 1. Transmission control protocol (TCP) and internet protocol (IP) are the core protocols of the Internet architecture. xiii xiv OPEN SYSTEMS NETWORKING: TCP/IP AND OSI System also provides a platform for Electronic Data Interchange and Of- fice Document Interchange, and the OSI Directory will provides a power- ful, object-oriented, global information base that can be accessed by humans as well as by distributed applications such as electronic mail and network file and resource management, building on services hitherto provided by TCP/IP applications such as FINGER, WHOIS,