Fundamentals of Digital Switching

425 Pages·1983·7.252 MB·English

by  A. E. Joel Jr. (auth.), John C. McDonald (eds.)

Fundamentals
of Digital Switching
Applications of Communications Theory
Series Editor: R. W. Lucky,
Bell Laboratories
INTRODUCTION TO COMMUNICATION SCIENCE AND SYSTEMS
John R. Pierce and Edward C. Posner
OPTICAL FIBER TRANSMISSION SYSTEMS
Stewart D. Personick
TELECOMMUNICATIONS SWITCHING
J. Gordon Pearce
ERROR-CORRECTION CODING FOR DIGIT AL COMMUNICATIONS
George C. Clark, Jr., and J. Bibb Cain
COMPUTER NETWORK ARCHITECTURES AND PROTOCOLS
Edited by Paul E. Green, Jr.
FUNDAMENT ALS OF DIGITAL SWITCHING
Edited by John C. McDonald
A Continuation Order Plan is available for this series. A continuation order will bring
delivery of each new volume immediately upon publication. Volumes are billed only upon
actual shipment. For further information please contact the publisher.
Fundamentals
of Digital Switching
Edited by
John C. McDonald
Continental Telecom Inc.
New York, New York
PLENUM PRESS • NEW YORK AND LONDON
Library of Congress Cataloging in Publication Data
Main entry under title:
Fundamentals of digital switching.
(Applications of communications theory)
Includes bibliographical references and index.
I. Telephone switching systems, Electronic. 2. Digital electronics. I. McDonald,
John c., 1936- . II. Series.
TK6397.F86 1983 621.3815137 83-2143
ISBN 978-1-4684-4441-4 ISBN 978-1-4684-4439-1 (eBook)
001 10.1007/978-1-4684-4439-1
© 1983 Plenum Press, New York
Softcover reprint of the hardcover 1s t edition 1983
A Division of Plenum Publishing Corporation
233 Spring Street, New York, N.Y. 10013
All rights reserved
No part of this book may be reproduced, stored in a retrieval system, or transmitted,
in any form or by any means, electronic, mechanical, photocopying, microfilming,
recording, or otherwise, without written permission from the Publisher
Contributors
D. H. Carbaugh. Western Electric, Lisle, Illinois
A. E. Joel, Jr. • Bell Telephone Laboratories, Holmdel, New Jersey
John C. McDonald • MBX Inc., New Canaan, Connecticut
N. L. Marselos • Western Electric, Lisle, Illinois
David G. Messerschmitt • University of California, Berkeley, California
Sushil G. Munshi • United Telecommunications Inc., Kansas City, Miss-
OUfl
Myron J. Ross • GTE Products Corporation, Sylvania Systems Group,
Needham Heights, Massachusetts
Matthew F. Slana. Bell Telephone Laboratories, Naperville, Illinois
Preface
The development of low-cost digital integrated circuits has brought digital
switching from a concept to an economic reality. Digital switching systems
have now found worldwide acceptance and there are very few new switch
ing systems being considered either for design or application which are not
digital. Digital technology has created new opportunities for innovation
including the integration of digital transmission and switching, the combi
nation of voice and data services in one switching entity, and the design of
switching systems which are economical over a broad range of sizes.
In the strict sense, the term "digital switching" refers to a system
which establishes a message channel between two terminations where infor
mation is represented in digital form. In more common usage, a digital
switch usually contains a time-divided network composed of logic gates and
digital memory to accomplish the switching function.
The intent of this book is to provide an introductory level explanation
of the principles of digital switching. These principles apply to both public
and PABX switching. The book is aimed at those who apply, design, main
tain, or simply wish to understand digital switching techniques. An electri
cal engineering degree is definitely not required for comprehension. We
have concentrated on explaining digital switching techniques without the
use of detailed mathematics. However, each chapter contains a comprehen
sive list of references which will lead the reader to sources for a more
in-depth study of the many subjects covered. Also, a glossary of digital
switching terms is located at the end of the book for easy reference. Since
digital switching is international in scope, the impact of international stan
dards is referenced throughout the book.
There are many technologies involved in digital switching and one
individual can rarely master them all. Therefore, this book has many au
thors who are experts in various digital switching specialties. A sincere
attempt has been made to minimize any subject overlap in the various
vii
viii Preface
chapters without detracting from the benefits a reader might derive from
multiauthor views.
Material for the book comes from a course on digital switching which
has been presented over the past four years at the University of California
at Los Angeles and at the University of Maryland. The authors have all
lectured in this course and have received valuable suggestions from the
students regarding organization and presentation of the material.
The book is organized as follows. Chapters 1 through 4 contain ma
terial on circuit switching fundamentals, traffic theory, stored program con
trol, and software. These subjects are not unique to digital switching and
apply equally to analog switching. The balance of the book is unique to
digital switching. Chapters 5 and 6 discuss the time-divided network for
both circuit switching and packet switching. Analog and digital information
interfaces to a digital switch are discussed in Chapters 7 and 8. Digital
switching architectures are presented in Chapter 9, and the book concludes
with a discussion of networks containing digital switches in Chapter 10.
This book is organized around a historical approach to the subject
with Chapter 1 covering the basics of circuit switching and subsequent
chapters proceeding more deeply into digital switching. However, each
chapter stands alone and it is not necessary for the reader to begin at
Chapter 1 and proceed to Chapter 10. Each author has referenced other
chapters in his text so readers can begin with their favorite subject and
proceed on. The "meat" of digital switching begins in Chapter 5.
Finally, on behalf of the authors, I wish to acknowledge the support
and assistance of their companies. In alphabetical order they are:
Bell Laboratories, Inc.
Continental Telecom, Inc.
General Telephone and Electronics, Inc.
MBX, Inc.
TRW, Inc.
United Telecommunications, Inc.
University of California
Western Electric, Inc.
A final acknowledgment goes to the hundreds of students who have
stimulated us to write this book and who have helped us to more com
pletely understand this powerful technology.
New Canaan, Connecticut Jack McDonald
Contents
1. Circuit-Switching Fundamentals
A. E. Joel, Jr.
1. Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
2. Circuit-Switched Networks. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
2.1. Relations between Transmission and Switching....................... 2
2.2. Networking............................................................... 9
2.3. Signaling. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
2.4. Signal Networking....................................................... 16
3. Circuit-Switching Systems..................................................... 19
3.1. Switching System Design. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
3.2. Switching System Functions ............................................ 23
3.3. Switching Networks ..................................................... 24
4. Introduction to Digital Switching. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
4.1. Digital What? ............................................................ 32
4.2. Need For Digital Switching............................................. 32
4.3. Basic Building Blocks. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
5. Summary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . 36
Questions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
References....................................................................... 37
2. Random Nature of Service Demands
Sushil G. Munshi
1. Introduction.................................................................... 41
2. Nature of Demand ............................................................. 41
2.1. Elements of Demand ..................................................... 42
2.2. Origination of Calls. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
2.3. Service Time. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
3. Important Probability Distribution Functions ............................... 54
3.1. Binomial Distribution................................................... 54
3.2. Negative Exponential Distribution ..................................... 55
3.3. Poisson Distribution. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
ix
x Contents
4. Digital Switching Systems ..................................................... 58
4.1. Class-5 Configuration................................................... 58
4.2. Traffic Considerations ................................................... 60
4.2.1. Line Stage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
4.2.2. Switching Matrix................................................ 61
4.2.3. Processors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
4.2.4. Remote Units.................................................... 63
4.2.5. Service Circuits .................................................. 64
5. Traffic Engineering............................................................. 65
6. Conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
Questions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
3. Switching System Controls
A. E. Joel, Jr.
1. Introduction................ .................................................... 69
2. Switching Center Network Controls .......................................... 70
2.1. Progressive versus Common Control................................... 70
2.2. Network Control Access ................................................ 73
3. Call Information Processing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
3.1. Traffic versus Functional Division. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
3.2. Controller Access ........................................................ 79
3.3. Distributed Control. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
3.4. Scheduling. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
3.5. Stored Program Control and the Software Dimension ................ 86
3.6. Redundancy. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
4. Operations Support. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
5. Summary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
Questions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
4. Switching System Software
D. H. Carbaugh and N. L. Marselos
1. Introduction.................................................................... 101
2. Historical Introduction to Switching System Software ...................... 101
2.1. Early Development of Stored Program Control for
Telecommunications. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
2.2. Early Software Design to Accommodate Commercial Electronic
Telecommunications. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
3. Central Office Design Criteria. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
3.1. Telephone Company Criteria........................................... 104
3.1.1. Cost.............................................................. 104
3.1.2. Reliability and Performance.................................... 105
3.2. Customer Criteria. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105
3.3. System Cost Considerations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106
3.3.1. Processor Speed ................................................. 106
3.3.2. Memory Usage.................................................. 107
3.3.3. Program Design ................................................. 108
Contents xi
4. Basic Electronic Switching Software .......................................... 109
4.1. Generic Program. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
4.1.1. Functional Model of Call Processing .......................... 110
4.1.2. System Maintenance............................................ 115
4.1.3. Administrative Functions....................................... 116
4.2. Office Data Base ......................................................... 117
4.2.1. Office Data Base Contents ...................................... 117
4.2.2. Office Data Base Architecture .................................. 117
4.3. Current Design of Switching Software. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118
4.3.1. Architectural Structure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119
4.3.2. Program Scheduling............................................. 120
4.3.3. Limitations in Prior Software Designs ......................... 122
5. New Model for Switching System Software .................................. 123
5.1. Architectural Objectives. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123
5.1.1. Software Engineering Concepts .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124
5.1.2. Considerations for Distributed Processing.. . . . . . . . . . . . . . . . . . . . 127
5.2. An Ideal Software Architecture Model................................. 127
5.2.1. Structural Overview............................................. 128
5.2.2. Operating System. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131
5.2.3. Benefits of the Model. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132
6. Conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133
Questions....................................................................... 134
References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134
5. Time-Division Networks
Matthew F. Slana
1. Introduction.................................................................... 137
2. Sampling and Modulation..................................................... 137
3. The Time-Division Switching Concept ....................................... 139
4. Lossless Analog Time-Division Switching.................................... 142
5. Lossy Analog Time-Division Switching....................................... 145
6. Digital Encoding and Multiplexing........................................... 147
7. Time-Division Switching....................................................... ISO
7.1. Time-Slot Interchanging................................................. ISO
7.2. Time-Shared Space-Division Switching ................................ 153
7.3. Network Functions...................................................... 158
7.4. Network Architectures................................................... 162
7.4.1. TOnly ........................................................... 163
7.4.2. SOnly ............................................................ 163
7.4.3. T -S ............................................................... 164
7.4.4. S-T . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165
7.4.5. T-S-T............................................................ 166
7.4.6. S-T -S ............................................................ 167
7.4.7. More Complex Arrangements.................................. 168
8. No.4 ESS ....................................................................... 168
9. Conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173
Questions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173
References....................................................................... 175