networks and telecommunications design and operation

Contents Summary Part 1 Fundamentals of telecommunications networks Part 2 Modern telephone networks Part 4 Multimedia networks Part 5 Running a network Part 6 Setting up networks

Net works and Telecommunications

Networks and Telecommunications

Design and Operation

Copyright 0 1991 1997 by John Wiley & Sons Ltd

Baffins Lane, Chichester West Sussex, PO19 IUD, England National 01243 779777

International (+44) 1243 779777 e-mail (for orders and customer service enquiries): cs-books@wiley.co.uk Visit our Home Page on http://www.wiley.co.uk or htpp://www.wiley.com Reprinted March 1998

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, scanning or otherwise, except under the terms of the Copyright Designs and Patents Act 1988 or under the terms of a licence issued by the Copyright Licensing Agency, 90 Tottenham Court Road, London, W1P 9HE, UK, without the permission in writing of the Publisher, with the exception of any material supplied specifically for the purpose of being entered and executed on a computer system, for exclusive use by the purchaser of this publication

Neither the author nor John Wiley & Sons Ltd accept any responsibility or liability for loss or damage occasioned to any person or property through using the material, instructions, methods or ideas contained herein, or acting or refraining from acting as a result of such use The author and Publisher expressly disclaim all implied warranties, including merchantability of fitness for any particular purpose There will be no duty

on the authors or Publisher to correct any errors or defects in the software

Designations used by companies to distinguish their products are often claimed as trademarks In all instances where John Wiley & Sons is aware of a claim, the product names appear in initial capital or capital letters Readers, however, should contact the appropriate companies for more complete information regarding trademarks and registration

Other Wiley Editorial Ofices

John Wiley & Sons, Inc., 605 Third Avenue,

New York, NY 10158-0012, USA

Wiley-VCH Verlag GmbH

Pappelallee 3, D-69469 Weinheim, Germany

Jacaranda Wiley Ltd, 33 Park Road, Milton,

Queensland 4064, Australia

John Wiley & Sons (Asia) Pte Ltd, 2 Clementi Loop #20-01,

Jin Xing Distripark, Singapore 129809

John Wiley & Sons (Canada) Ltd, 22 Worcester Road

Rexdale, Ontario, M9W 1L1, Canada

Library of Congress Cataloging-in-Publication Data

1 Telecommunication systems 2 Data transmission systems

3 Computer networks I Title

TK5102.5.C53 1997

CIP

British Library Cataloguing in Publication Data

A catalogue record for this book is available from the British Library

ISBN 0 47197346 7

Typeset in 10112 pt Times by Aarontype Ltd., Easton, Bristol

Printed and bound in Great Britain by Bookcraft (Bath) Ltd

This book is printed on acid-free paper responsibly manufactured from sustainable forestry

for which at least two trees are planted for each one used for paper production

Contents

Summary

Part 1 Fundamentals of telecommunications networks

Part 2 Modern telephone networks

Part 4 Multimedia networks

Part 5 Running a network

Part 6 Setting up networks

Part 7 Specific Businesses and networks

Preface

About the Author

Acknowledgements

1 Information and its Conveyance

1.1 Types of Information

1.2 Telecommunications Systems

1.3 A Basic Telecommunications System

1.4 Common Types of Telecommunications Systems

1.5 Networks

1.6 Connection-oriented Transport Service (COTS) and Connectionless

Network Service (CLNS)

1.7 Circuit-, Packet- and Cell-switched Networks

1.8 Considerations for Network Planners

1.9 Technical Standards for Telecommunications Systems

xxi

xiii

xv

vi CONTENTS

2 Introduction to Signal Transmission and the Basic Line Circuit

2.1 Analogue and Digital Transmission

2.2 Telegraphy

2.3 Telephony

2.4 Received Signal Strength, Sidetone and Echo

2.5 Automatic Systems: Central Battery and Exchange Calling

2.6 Real Communications Networks

3.6 Frequency Division Multiplexing (FDM)

3.7 Crosstalk and Attenuation on FDM Circuits

4 Data and the Binary Code System

4.1 The Binary Code

4.2 Electrical Representation and Storage of Binary Code Numbers

4.3 Using the Binary Code to Represent Textual Information

5.5 Time Division Multiplexing

5.6 Higher Bit Rates of Digital Line Systems

5.7 Digital Frame Formatting and 'Justification'

5.8 Interworking the 2 Mbit/s and 1.5 Mbit/s Hierarchies

5.9 Synchronous Frame Formatting

5.10 Line Coding

5.1 1 Other Line Codes and their Limitations

6 The Principles of Switching

6.1 Circuit-switched Exchanges

6.2 Call Blocking within the Switch Matrix

6.3 Full and Limited Availability

6.4 Fan-in-Fan-out Switch Architecture

6.10 Packet and Cell Switches

7 Setting up and Clearing Connections

~ l e r t i n ~ the Called customer Automatic Networks

Set Up Number Translation Unsuccessful Calls Inter-exchange and International Signalling The R2 Signalling System

R2 Line Signalling Compelled or Acknowledged Signalling R2 Inter-register, Multi-frequency Code (MFC) Signalling Digital Line Systems and Channel-associated Signalling Signalling Interworking

Advanced Signalling Applications Signalling Sequance Diagrams Call Set-up and Information Transfer in Data Networks Network Interfaces: UNI, NNI, INI, ICI, SNI

Information Transfer in Connectionless Networks

8 Transmission Systems

Audio Circuits Standard Twisted Pair Cable Types for Indoor Use Transverse Screen and Coaxial Cable Transmission Frequency Division Multiplexing (FDM)

HDSL (High Bit-rate Digital Subscriber Line) and ADSL (Asymmetric Digital Subsciber Line) Optical Fibres

Radio Radio Wave Propagation Radio Antennas

Surface-wave Radio Systems High Frequency (HF) Radio Very High Frequency (VHF) and Ultra High Frequency (UHF) Radio Microwave Radio

Tropospheric Scatter Satellite Systems 'Multiple Access' Radio and Satellite Systems Electromagnetic Interference (EMI) and Electromagnetic Compatibility (EMC)

viii CONTENTS

9 Data Network Principles and Protocols

Computer ~ e t w o r k s Basic Data Conveyance: Introducing the DTE and the DCE Modulation of Digital Information over Analogue Lines Using a Modem

High Bit Rate Modems Modem 'Constellations' Computer-to-network Interfaces Synchronization

Bit Synchronization Character Synchronization: Synchronous and Asynchronous Data Transfer

Handshaking Protocols for Transfer of Data The Open Systems Interconnection Model Data Message Format

Implementation of Layered Protocol Networks The Use of Null Layers

Other Layered Protocols Data Network Types Point-to-point Data Networks Circuit-switched Data Networks Packet-switched Data Neworks Practical Computer Networks

10 Integrated Services Digital Network (ISDN)

10.1 The Concept of ISDN

10.2 Bearer, Supplementary and Teleservices

10.3 ISDN Interfaces and End-user Applications

10.4 Basic Rate Interface (BRI)

10.5 The SIT Interface Specification

10.6 Use of the Basic Rate Interface

10.7 ISDN Terminals

10.8 Primary Rate Interface

10.9 The Public Network and ISDN

10.10 Deployment of ISDN

10.1 1 The Marketing of ISDN and the Early User Benefits

10.12 Network Interworking

10.13 Companies' Private ISDNs (Corporate ISDN)

10.14 Broadband Services over ISDN

11 Intelligent Networks and Services

1 1.1 The Concept of Intelligent Networks

11.2 Intelligent Network Architecture

CONTENTS ix

The Service Control Point (SCP) The Service Switching Point (SSP) The Service Management System (SMS) and Service Creation Environment (SCE)

Benefits of Intelligent Networks Intelligent Network (IN) Services Calling Card

Freephone Service (or 800 Service)

900 Service Centrex Service and Virtual Private Network Line Information Database (LIBD)

Televoting Cellular Radio Telephone Service Network Intelligence and PBXs Voicemail and Voice Response Systems Considerations Before Introducing I N to a Network The Future of Intelligent Networks

12 Signalling System No 7

12.1 SS7 Signalling between Exchanges

12.2 SS7 Signalling Networks

12.3 The Structure of SS7 Signalling

12.4 The Message Transfer Part (MTP)

12.5 The User Parts of SS7

12.6 The Telephone User Part (TUP)

12.7 The Data User Part (DUP)

12.8 The Integrated Services User Parts (ISUP)

12.9 The Enhanced Telephone User Part (TUP+)

12.10 The Signalling Connection Control Part (SCCP)

12.11 Transaction Capabilities (TC)

12.12 The Mobile Application Part (MAP)

12.13 Operation and Maintenance Application Part (OMAP)

12.14 Intelligent Network Application Part (INAP)

12.15 The Use and Evolution of CCITT7 Signalling

12.16 Signalling Network Planning and Testing

12.17 Interconnection of SS7 Networks

13 Synchronous Digital Hierarchy (SDH) and Synchronous

Optical Network (SONET)

13.1 History of the Synchronous Digital Hierarchy (SDH)

13.2 The Problems of PDH Transmission

13.3 The Multiplexing Structure of SDH

13.4 The Tributaries of SDH

13.5 Path Overhead

13.6 Section Overhead (SOH)

13.7 Network Topology of SDH Networks

13.8 Optical Interfaces for SDH

x CONTENTS

13.9 Management of SDH Networks

13.10 SONET (Synchronous Optical Network)

13.1 1 SDH and ATM (Asynchronous Transfer Mode)

14 Operator Assistance and Manual Services

14.1 Manual Network Operation

14.2 Semi-automatic Telephony

14.3 Calling the Operator

14.4 Operator Privileges

14.5 Typical Assistance Services

14.6 Cooperation between International Operators: Code 1 1 and

Code 12 Services 14.7 A Modern Operator Switchroom

14.8 Operator Assistance on Telex Networks

14.9 Operator Assistance on Data Networks

15 Mobile Telephone Networks

15.1 Radio Telephone Service

15.2 Cellular Radio

15.3 Making Cellular Radio Calls

15.4 Tracing Cellular Radio Handsets

15.5 Early Cellular Radio Networks

15.6 Global System for Mobile Communications (GSM)

15.7 GSM Technology

15.8 Personal Communications Network (PCN) and DCS- 1800

15.9 Aeronautical and Maritime Mobile Communications Services

15.10 Iridium, Globalstar and the Evolution Towards the Universal Mobile

Telephone Service (UMTS)

16 Cordless Telephony and Radio in the Local Loop (RILL)

16.1 The Drive for Radio in the Local Loop

16.2 Fixed Networks Based on Radio Technology

16.3 Cordless Telephones

16.4 Telepoint or Cordless Telephone 2 (CT2)

16.5 DECT (Digital European Cordless Telephony)

16.6 DECT Handover

16.7 The Radio Relay Station Concept in DECT

16.8 The DECT Air Interface (D3-interface)

16.9 Other ISDN Wireless Local loop Systems

16.10 Shorthaul Point-to-multipoint (PMP) Microwave Radio

17 Fibre in the Loop (FITL) and Other Access Networks

17.1 Fibre Access Networks

17.2 Fibre to the Building (FTTB)

17.3 Fibre to the Curb (FTTC)

17.4 Fibre to the Home (FTTH)

17.5 Broadband Passive Optical Network

Access Network Interfaces

ETSI V5 Interfaces

V5.2 Interface

V5.1 Interface

Significance of the V5.x Interfaces

Re-use of Existing Copper Access Networks

HDSL (High Bitrate Digital Subscriber Line)

ADSL (Asymmmetric Digital Subscriber Line)

Hybrid FibreICoax (HFC) Networks

18 Packet Switching

Packet switching Basics

Transmission Delay in Packet-switched Networks

Routing in Packet-switched Networks

ITU-T Recommendation X.25

The Technical Details of X.25

X.25 Link Access Procedure (LAP and LAPB)

X.25 Packet Level Interface (Layer 3 Protocol)

Typical Parameter Default Settings Used in X.25 Networks Packet Assembler/Disassemblers (PADS)

ITU-T Recommendation X.75

When X.25 Packet switching May and May Not Be Used Alternatives to X.25-based Packet Switching

IBM's 'Systems Network Architecture'

APPN (Advanced Peer-to-peer Networking)

19 Local Area Networks (LANs)

19.1 The Emergence of LANs

19.2 LAN Topologies and Standards

19.3 CSMAICD (IEEE 802.3, I S 0 8802.3): Ethernet

19.4 Token Bus (IEEE 802.4, I S 0 8802.4)

19.5 Token Ring (IEEE 802.5)

19.6 Logical Link Control for LANs

19.7 LAN Operating Software and LAN Servers

19.8 Interconnection of LANs: Bridges, Routers and Gateways

20 Frame Relay

20.1 The Throughput Limitations of X.25 Packet Switching 20.2 The Need for Faster Response Data Networks

20.3 The Emergence and use of Frame Relay

20.4 Frame Relay UNI

20.5 Frame Relay SVC Service

20.6 Congestion Control in Frame Relay networks

xii CONTENTS

20.7 Frame Relay NNI

20.8 Frame Format

20.9 Address Field Format

20.10 ITU-T Recommendations Pertinent to Frame Relay

20.1 1 FRAD (Frame Relay Access Device)

21 Campus and Metropolitan Area Networks (MANs)

21.1 Fibre Distributed Data Interface

21.2 Switched Multimegabit Digital Services (SMDS)

21.3 The Demise of MANs

22 Electronic Mail, Internet and Electronic Message Services

22.1 Videotext

22.2 Electronic Mail (e-mail)

22.3 Addressing Schemes for Electronic Mail

22.4 The Advantages and Disadvantages of e-mail

22.5 EDI: Corporate Communication with Customers and Suppliers

via e-mail 22.6 Internet

22.7 TCP/IP Protocol Stack

22.8 Common Applications Using TCP/IP

22.9 The Internet Protocol

22.10 The Internet Control Message Protocol (ICMP)

22.11 Transmission Control Protocol (TCP)

22.12 Online Database Services

23 The Message Handling System (MHS)

23.1 The Need for MHS

23.7 MHS and the OSI Directory Service

23.8 Message Conversion and Conveyance Using MHS

23.9 Setting Up a Message Handling System

23.10 File Transfer Access and Management (FTAM)

23.1 1 Summary

24 Mobile and Radio Data Networks

24.1 Radiopaging

24.2 Mobile Data Networks

24.3 TETRA (Trans-European Trunked Radio System)

24.4 Wireless LANs

24.5 Radiodetermination Satellite Services (RDSS) and the Global

Positioning System (GPS)

CONTENTS xiii

Part 4 MULTIMEDIA NETWORKS

25 Broadband, Multimedia Networks and the B-ISDN

25.1 Multimedia Applications: the Driver for Broadband Networks

25.2 Video Communication

25.3 The Emergence of the B-ISDN

25.4 The Services to be Offered by B-ISDN

25.5 The Emergence of the ATM Switching Technique as the Heart of ATM 25.6 Connection Types Supported by B-ISDN

25.7 User Device Connection to B-ISDN

25.8 Evolution to Broadband-ISDN

26 Asynchronous Transfer Mode (ATM)

A Flexible Transmission Medium Statistical Multiplexing and the Evolution of Cell Relay Switching The Problems to be Solved by Cell Relay

The Technique of Cell Relay The ATM Cell Header The Components of an ATM Network The ATM Adaption Layer (AAL) ATM Virtual Channels and Virtual Paths User, Control and Management Planes How is a Virtual Channel Connection (VCC) Set Up?

Signalling Virtual Channels and Meta-signalling Virtual Channels Virtual Channel Identifiers (VCIs) and Virtual Path Identifiers (VPIs) Information Content and Format of the ATM Cell Header

ATM Protocol Layers The ATM Transport Network Capability of the ATM Adaption Layer (AAL) Protocol Stack when Communicating via an ATM Transport Network ATM Protocol Reference Model (PRM)

ATM Forum Network Reference Model ATM Forum Network Management Model

27.4 The Q3-interface, the Common Management Information

Protocol (CIMP) and the Concept of Managed Objects (MO) 483

27.7 The Network Management Forum (NMF), OMNIpoint and SPIRIT 487

27.8 Realization of a TMN 487

27.12 Telecommunications Intelligent Network Architecture (TINA) 490

28 Network Routing, Interconnection and Interworking

28.1 The Need for a Network Routing Plan

28.2 Network Routing Objectives and Constraints

28.3 The Administration of Routing Tables

28.4 Routing Protocols Used in Modern Networks

28.5 Network Topology State and the 'Hello State Machine'

28.6 Signalling Impact upon Routing and Call Set-up Delays

28.7 Plausibility Check During Number Analysis

28.15 The Point of Interconnection and Collocation

28.16 The Interconnection Contract

28.17 Interworking

29.2 International Public Data Network Address Scheme 520

29.5 X.500: The Addressing Plan for the Message Handling Service (MHS) 524

29.8 Network Addresing Schemes Used in Support of Broadband-ISDN

30 Teletraffic Theory

30.1 Telecommunications Traffic

30.2 Traffic Intensity (Circuit-switched Networks)

30.3 Practical Traffic Intensity (Erlang) Measurement

30.4 The Busy Hour

30.5 The Formula for Traffic Intensity

30.6 The Traffic-carrying Capacity of a Single Circuit

30.7 Dimensioning Circuit-switched Networks

30.8 Example Route Dimensioning

30.9 Call Waiting Systems

30.10 Dimensioning Data Networks

CONTENTS

30.1 1 Pollaczek-Khinchine Delay Formula

30.12 Practical Dimensioning of Networks

30.13 Appendix: The Derivation of Erlang's Formula

31 Traffic Monitoring and Forecasting

3 1.1 Measuring Network Usage

3 1.2 Usage Monitoring in Circuit-Switched Networks

31.3 Traffic Intensity

3 1.4 Total Usage Monitoring

31.5 Number of Calls Attempted

31.6 Number of Calls Completed

3 1.7 Monitoring Usage of Data Networks

3 1.8 Forecasting Models for Predicting Future Network Use

3 1.9 Fitting the Forecasting Model

3 1.10 Other Forecasting Models

32 Network Traffic Control

32.1 Networks

32.2 Sizing Circuit-switched Networks

32.3 Hierarchical Network

32.4 Overflow of 'Automatic Alternative Routing' (AAR)

32.5 Wilkinson -Rapp Equivalent Random Method

32.6 Dimensioning 'Final Routes'

32.7 Trunk Reservation

32.8 'Crankback' or 'Automatic Re-routing' (ARR)

32.9 Proportionate Bidding Facility (PBF)

32.10 Dynamic Routing

32.1 1 Routing and Traffic Control in Data Networks

32.12 Network Design

32.13 Appendix: The Wilkinson-Rapp Route Dimensioning Method

33 Practical Network Transmission Planning

Network Transmission Plan Send and Receive Reference Equivalents Connection Reference Points and Overall Reference Equivalent Measuring Network Loss

Correcting Signal Strength The Control of Sidetone The Problem of Echo Echo Control and Circuit Instability Signal (or 'Propagation') Delay Noise and Crosstalk

Signal Distortion Transmission Plan for Digital and 'Data' Networks International Transmission Plan

Private Network Transmission Plan Circuit and Transmission System Line-up

33.16 Network Resource Management

33.17 Circuit Provisining Planning

33.18 New Cable Planning

33.19 Local Line Planning

33.20 Trunk and International Line Planning

33.21 Radio Transmission Systems

33.22 Satellite Transmission Management

34 Quality of Service (QOS) and Network Performance (NP)

34.1 Framework for Performance Management

34.2 Quality: A Marketing View

34.3 Quality of Service (QOS) and Network Performance (NP) 34.4 Quality of Service Parameters

34.5 Generic Network Performance Parameters

34.6 Performance Monitoring Functions of Modern Networks 34.7 Network Performance Planning and Measurement

34.8 A Few Practical Tips

34.9 Summary

35 Charging and Accounting for Network Use

Recompense for Network Use

Customer Subscription Charges

Customer Usage Charges

Pulse Metering

Electronic Ticketing

Accounting

Route Destination Accounting

Charging and Accounting on Data Networks

Charging and Accounting for Manual (Operator) Assistance Charging and Accounting for Leased Circuits

Charging Payphone Calls

Customer Billing

Setting Customer Charges and Accounting Rates

Network Costs and How to Recharge Them

Future Accounting and Charging Practices

36 Maintaining the Network

36.1 The Objectives of General Maintenance

36.2 Maintenance Philosophy

36.3 Maintenance Organization

36.4 Centralized Operation and Maintenance

36.5 Lining Up Analogue and Mixed AnalogueIDigital Circuits 36.6 High Grade Data Circuit Line-up

36.7 Lining Up Digital Circuits

36.8 Performance Objectives

36.9 Maintenance 'Access Points'

36.10 Localizing Network Faults

CONTENTS xvii

36.1 1 Hardware Faults

36.12 Software Faults

36.13 Change Control Procedure for Hardware and Software

37 Containing Network Overload

37.1 The Effect of Congestion

37.2 Network Monitoring

37.3 Network Management Controls

37.4 Expansive Control Actions

37.5 Restrictive Control Actions

37.6 Network Management Systems

38 Network Economy Measures

38.1 Cost Minimization

38.2 Frequency Division Multiplexing (FDM)

38.3 Time Division Multiplexing (FDM)

38.4 Wavelength Division Multiplexing

38.5 Circuit Multiplication Equipment (CME)

38.6 Speech Interpolation and Statistical Multiplexing

38.7 Analogue Bandwidth Compression and Low Rate Encoding of PCM

38.8 Data Multiplexors

38.9 Data Compression

38.10 Practical Uses of CME

38.1 1 Constraints on the Use of CME

39 Network Security Measures

The Trade-off between Confidentiality and Interconnectivity Different Types of Protection

Encryption Network Access Control Path Protection

Destination Access Control Specific Technical Risks Carelessness

Call Records Mimicked Identity Radio Transmission, LANs and Other Broadcast-type Media EM1 (Electro-Magnetic Interference)

Message Switching Networks Other Types of Network Abuse

40 Technical Standards for Networks

40.1 The Need for Standards

40.2 Worldwide International Standards Organizations

40.3 Regional and National Standards Organizations

40.4 Regulatory Standards Organizations

xviii CONTENTS

40.5 Other Standards-promoting 'Fora'

40.6 Proprietary Standards

40.7 The Structure and Content of ITU-T Recommendations

Part 6 SETTING UP NETWORKS

41 Building, Extending and Replacing Networks

41.1 Matching Network Capacity to Forecast Demand

41.2 Other Factors Affecting the Need for New Exchanges

41.3 Factors in Determining an Exchange Provision Programme

41.4 Determining a Strategy for Network Evolution

41.5 Comparison of Strategy Options

41.6 Exchange Design and Specification

41.7 Outline Circuit-switched Design: Circuit Numbers and Traffic Balance 41.8 Outline Design of Other Types of Network

41.9 The Effect of Low Circuit Infill on Exchange and Lineplant Planning

4 1.10 Functional Requirements of Exchanges or Line Systems

4 1.1 1 Methods of Network or Exchange Modernization

42 Selecting and Procuring Equipment

42.1 Tendering for Equipment

43 Meeting Business Needs and Creating Competitive Edge

43.1 Content of an IT Strategy

43.2 The Study of Information Flows

43.3 The Tactical Development Plan

43.4 Business Applications of IT

43.5 Summary

44 Network Regulation and Deregulation

44.1 Reasons for Deregulation

44.2 The Dilemma of Deregulation

44.3 Optional Methods of Regulation

44.4 Types of Regulatory Bodies

44.5 Designation of 'Customer Premises Equipment' (CPE)

44.6 Deregulation of Value-added Services

44.7 Competition in Basic Services

44.8 The Instruments of PTO Regulation

CONTENTS xix

44.9 European Telecommunications Deregulation

44.10 Instruments of United Kingdom Regulation

44.1 1 United States Telecommunications Regulation

44.12 Other Countries

45 Corporate Networks

45.1 Telecommunications Management

45.2 Premises Cabling Schemes

45.3 Office Computer Networking

45.4 Private Networks

45.5 Architecture of Private Networks

45.6 Planning Private Networks

45.7 A Word of Warning

45.8 PTO Leased Circuit Offerings

45.9 Making Use of Mobile Radio Technology

46 Public Networks and Telecommunications Service Providers

46.1 Company 'Mission'

46.2 Identifying and Addressing the PTO's market

46.3 PTO Product Development

46.4 PTO Business Development

Preface

The second edition of this text is a much larger work than the first edition, having needed to be expanded with extensive new sections on data, broadband and multimedia networks and much extended coverage of modern transmission media, radio and network management The technology may have moved on since 1990, but the original preface is as relevant today as it was then

The networks that I have personally had to develop and operate have bridged not onIy

the classical subdivisions of voice and data, but also national boundaries, technological

standards and regulations As a result, I have found it necessary to become familiar with

a broad range of technology, telecommunications practices and worldwide regulations

I have needed to know how things work and interwork, and the practical problems to be overcome I have needed to understand the basic electrical engineering detail underlying telecommunications, but experience has also given me two equally valuable resources: an armoury of practical techniques and a knowledge of both technical and regulatory constraints

In my time I have used plenty of books, each addressing one of the many individual technologies that I have had to deal with However, to date I have not discovered a book aimed at technical managers who need a broad range of knowledge about how to develop and operate a number of different types of network in a pragmatic way This

seems perverse, since many of today's professional telecommunications managers are

expected to know about all the various types of network making up their trade It is also perverse given the fact that, in my experience, network problems cannot be neatly categorized by technology I have rarely needed to know all the technical details of a particular technology and cannot remember having been able to use any network to its full capability Seldom have I had the opportunity, because seldom have I had a prob- lem where one technology alone will suffice, and never have I had the option anyway to scrap the established network with its constraints and start entirely afresh

Surprisingly perhaps, my major problems have arisen not from technical incompat- ibility of different international networks; such problems are soluble with time and money Rather the difficulty has been in gaining a basic understanding of how different types of network operate, and therefore how they could be made to co-exist, interwork

or cooperate to serve a given user's need It is from this background that I decided to write this book, a day-to-day encyclopaedia for practical folk like me, people faced with

xxii PREFACE

voice, data and a whole compendium of other networks to be responsible for Here in 46 chapters we have a picture of an evolving jungle of techniques and administrative controls, all about telecommunications to-day and how they got that way

The book provides an insight for all telecommunications-affected parties: end users, engineers, private companies, public telecommunications operators, regulators and governments The sort of people that I hope will read it and use it, the interested parties, are students and academics, telecommunications and computer practitioners, and technical managers Through our greater common awareness and understanding, I hope that we in turn can help extend familiarity with telecommunications and their effective use to a much wider audience: business managers, directors, and consultants; specialist press and publicity people; chairmen and board members of companies, politicians and everyday folk

How to read a book of this kind with advantage depends on what one hopes to get out of it: the student may plough through it from cover to cover, while the academic toys fastidiously with the bibliography, glossary and index The chairman only reads what his advisers put in front of him However, it will take more than that if we are to harness telecommunications for their full potential; expanding systems of linked computers, international and mobile communications are turning business and society upside down, whether we like it or not

In all quarters more know-how is needed, more shared knowledge, more mutual awareness of what is actually going on, not only here and now under our noses, but in other minds and in other countries as well To meet this need, this book sets out at length the raw facts and the jargon; and although the picture presented is strictly contemporary, I hope the book will give its readers the suggestion and confidence to carry things forward into the future among themselves This, in its way, is the most hopeful and important part of the book

I have chosen not to remove any technical coverage from the first edition You, the reader, might be confronted by an older technology and need to deal with it Beyond this, many old ideas find new lease of life in 'modern technologies'

For those using the book to unravel an outside world full of jargon and opportunity, the bibliography, glossaries and index will be invaluable, but the acronyms abound, beyond the possibilities of a single book A number of excellent dictionaries will help

the reader who finds himself at a loss

MARTIN CLARK Eppstein, Germany 30th November 1996

About the Author

Martin Clark spent eight years in the international network planning department of

British Telecom, where he gained knowledge and experience of the fundamentals and practicality of telecommunications He also developed a good understanding of the tech-

nical, regulatory and other problems associated with international networks In 1989

he became Group Telecommunications Manager with Grand Metropolitan, where his experience gave him an insight into global corporate network management and the

business opportunities offered by telecommunications In 1991 he moved to Germany,

where he has worked on setting up a pan-European managed data network for Cable & Wireless, in managing the Deutsche Bank's corporate network and also helped Mannes-

mann in the establishment of a new public telecommunications carrier (ARCOR) to rival Deutsche Telekom Recently he has been active with the wireless ATM company, Netro, and he also works as a freelance consultant

Martin Clark is a Chartered European Engineer and a member of the IEE

Acknowledgements

When reviewing the list of sources, reference bodies and helpers who have contributed

to this work, I come to think of myself more as a coordinator than a sole author, and

my special thanks are due to the many who have encouraged me, contributed material

or reviewed sections of text

The material that appears in the chapters on PCM, network traffic control, network

overload and ISDN is derived from articles first published in the African Technical

Review and African Review Two of these articles (on ISDN and PCM) were co- authored by Felix Redmill, my colleague at British Telecom, and it is to him that I owe the initial idea and the encouragement to pursue this work at all

British Telecom supplied many of the photographic illustrations, and also an education in telecommunications spanning eight years My particular thanks are due

to John Kelly of the customer communications photographic library and David Hay, the BT Group Archivist The pictures represent only a glimpse of the rich history of telecommunications, and I hope they will encourage others to use the

BT Archives

The American Telephone and Telegraph Corporation (AT&T) also provided a large number of photographs, as well as making available some of their world-respected Bell Laboratories staff to review portions of the text I am sincerely grateful to Tim Granger

of the National Accounts staff for arranging these contributions

No book on telecommunications as they are today could fail to recognize the contribution to world standards made by the International Telecommunications Union and its subordinate entities ITU-R and ITU-T You will find references littered throughout the text Particular copyright extracts (chosen by the author, but reproduced with the prior authorization of the ITU) are labelled accordingly The full texts of all ITU copyright material may be obtained from the ITU Sales and Marketing Service, Place des Nations, CH-1211 Geneva 20, Switzerland, Telephone: $41 22 730 6141 or Internet: Sales@itu.int

The cartoons that bring humour and parody to the chapters on quality and technical standards are by Patrick Wright of Fernhurst, Sussex, England, but the copyright is that of the author

In this second edition I am also indebted for photographs to the international satellite organisation INTELSAT, to Siemens AG and to Netro Corporation Further

xxvi ACKNOWLEDGEMENTS

thanks are also due to ATM Forum for their kind permission to reproduce the ATM network reference model and network management model from their standards Let me thank all those personal friends who helped especially with the first edition - without it there would have been no second edition! Those few I have the space to mention are: Pettrel Adams, who toiled unfailingly with the typing; Elizabeth Bathurst, the editing assistant at John Wiley; Richard Cawdell (formerly of the European Commission); Colin Clark, my father and critic; Ann-Marie Halligan, John Wiley's editor; John Goatly, father-in-law, critic and adviser; John Green of GrandMet, for his advice on IBM networks; Martin Pigott, former CCITT rapporteur for number seven signalling; Peter Walker, formerly of British Telecom network planning department and now with Oftel; and Arthur Watson, my first telecom boss and part-time golfing friend

Special thanks go to my close family, for enduring the months of aspiration and toil

Martin Clark

PART 1

FUNDAMENTALS OF TELECOMMUNICATIONS

NETWORKS

Information and its Conveyance

The world about us brims with information All the time our ears, eyes, fingers, mouths and noses sense the environment around us, continually increasing our 'awareness', 'intelligence' and 'instructive knowledge' Indeed these last two phrases are at the heart of the Oxford Dictionary's definition of the word information Communication, on the other hand, is defined as 'the imparting, conveyance or exchange of ideas, knowledge or information' It might be done by word, image, instruction, motion, smell - or maybe just a wink! Telecommunication is com- munication by electrical, radio or optical (e.g laser) means We introduce the basic capabilities and terminology of telecommunications and networking in this chapter

As hybrid words go, 'telecommunications' wins no prizes, but it is all we have to work with The greek 'tele' prefix means distant, and nothing else; communication, in the sense

of information passed to and fro between human beings, and animals, is an activity that goes back beyond recorded times With a broad view, long distance communications brings to mind Armada beacons, heliographs flashing between Frontier posts, empires held together by relays of post-houses, whales singing to one another in the deep, and the family dog which conducts its social life by laying and following scent trails For the narrower purposes of this book telecommunications is going to mean the transfer of information by electromagnetic means, (and with this will go a certain amount of accepted jargon) All systems have much in c o q n o n , whatever their age In principle each requires a transmitter, a carrying device or transmission medium, a receiver, and a supply of information which will be equally comprehensible at both ends For lessons in technique nothing should be disregarded, however ancient: for a cheap, speedy and comprehensive message, what is there to beat a human wink?

In the science and business of telecommunications, a structured framework has been created for conveying certain types of information across long distances, with little respect for the barriers of geography In this book we study this framework; first we understand how the forces of electricity, light and radiowaves may be tamed to provide

a basis for such communication; then we focus on the pragmatic operation of networks and the quest for solutions to the business needs of information flow

4 INFORMATION AND ITS CONVEYANCE

Figure 1.1 illustrates a simple but powerful model for understanding and categorizing

various different means of communication The model illustrates a number of different

ways in which a business may communicate either within itself, or with its external

environment of suppliers and customers Thus we introduce the concept of an

'information environment', across which information flows in one of a number of

different forms

The simplest form of information flow (illustrated by Figure 1.1) might be directly

from one person to another, by word of mouth or by a visual signal Alternatively the

information could have been conveyed on paper or electrically The advantage of either

of the latter two methods is that the information in paper or electronic form may also

be readily stored for future reference

In this book we shall use the model of Figure 1 I twice Here we use it to illustrate

how different methods of communication may be categorized into one of the three

broad types, and as a basis for explaining the prerequisite components of a telecom-

munications system In Chapter 43 it is used to illustrate the analysis, simplification and

planning of business information flows This double theme runs throughout the book:

understanding telecommunications technology, and explaining its exploitation in a

pragmatic business-oriented manner Well-known examples of communications met-

hods that fall into the three categories of paper, person-to-person and electronic are

given in Figure 1.2

Some types of communication are hybrids of the three basic methods Modern fac-

simile machines, for example, are capable of relaying images of paper documents over

the telephone network and recreating them at a distant location This would appear as

quite a complex information path on our model of Figure 1 I, as Figure 1.3 shows

First a person must record the relevant information on paper (shown as (a) on

Figure 1.3), then he must feed it into the facsimile machine which converts it into

INFORMATION AND ITS CONVEYANCE 5

Talking Winking

Acting Television Radio

Figure 1.2 Categorizing simple communication methods

electronic format (b) Next the telephone network conveys the electronic information (c), before the distant facsimile machine reconverts the information to paper (d) and the receiver reads it (e)

The example we have chosen is rather convoluted, requiring several successive conversions to take place, changing the format of the information from 'personal' to 'paper' to 'electronic' and back again All these conversions make the process inefficient, and as we shall find out later, companies who have recognized this fact have already set about converting all their key business information into electronic (computer) format, not only for conveyance, but also for storage and processing purposes

Paper ( a ) Information process

typed

Person

( sender )

(b) Paper fed into facsimile machine

process

I h ; ; ; r i s ( d l Receiving

facsimile machine

6 INFORMATION AND ITS CONVEYANCE

Put specifically in the context of telecommunications, information might be a page of

written text, a conversation or a television picture The information usually requires conversion into an electrical signal in order to be conveyed by telecommunication

means However, there are many different types of information, so can they all be treated identically? The answer to this is 'no', because each type of information makes slightly different demands on the telecommunication system

Information conveyed over telecommunications systems is usually classed as either

an analogue signal information or as data (digital information) An analogue signal is

an electrical waveform which has a shape directly analogous to the information it

represents (e.g speech or a television picture) Data, on the other hand, is the word

given to describe information in the form of text, numbers or coded computer or video information

Different forms of data and analogue signal information require different treatment For example, when conversing with someone we expect their reply to follow shortly after our own speech, but when we send a letter we do not expect a reply for some days The analogy runs directly into telecommunications Thus, an electrical representation

of conversation must allow the listener to respond instantly However, in the case of data communication, slightly more leeway exists, as a computer is prepared to accept response times of several seconds A human would find this length of delay intolerable

in everyday speech Another difference between electrical representations designed for different applications will be the speed with which information can be transferred This

is normally referred to as the information rate, the bandwidth or the bitrate A speech circuit requires more bandwidth to carry the different voice tones than a telegraph wire needs simply to carry the same information as text Later chapters in this book discuss the various methods of electrical representation and the technical standards used

a the fourth requirement is that the conveyed information is coded in such a way as to

be compatible with, and comprehensible to, the receiver

All four components together form a telecommunications system

In the example of a communication system consisting of two people talking to one another, the transmitting device is the mouth, the transport mechanism is the sound through the air, and the receiving device is the other person's ear Provided that both people talk the same language, then the fourth requirement has also been met, and

A BASIC TELECOMMUNICATIONS SYSTEM 7

conversation can continue However, if the talker speaks English, and the listener only understands French, then, despite the availability of the 'physical components' of the system (i.e mouth, ear and air), communication is ineffective due to the incompatibility

of the information

The coding and method of transfer of the information over the transport mechanism

is to said to be the protocol In our example the protocol would be either the English

or the French language: the fact that the talker is English and the listener French is

an example of protocol incompatibility Protocol also defines the procedure to be used

An example of the procedural part of protocol is the use of the word 'over' to signify the end of radio messages (for example 'Come in Foxtrot, Over') The protocol in this case prompts a reply and prevents both parties speaking at once The hardest part of telecommunications system design is often the need to ensure the compatibility of the

protocol In some cases, this necessitates the provision of interworking devices In our

example, the interworking device might be a human EnglishIFrench interpreter

1.3 A BASIC TELECOMMUNICATIONS SYSTEM

Figure 1.4 illustrates the physical elements of a simple telecommunications system including the transmitter, the receiver and the transport mechanism

As already discussed, the physical element shown in Figure 1.1 must be comple-

mented by the use of a compatible protocol between transmitter and receiver Together

with such a protocol, we have all the means for communication from point A to point B

in Figure 1.4 We do not, however, have the wherewithal for communication in reverse (i.e from B to A) Such single direction communication, or simplex operation as it is

called, may suffice for some purposes For many more examples of communication, two

way, or duplex operation is normally required For duplex operation, a transmitter

and a receiver must be provided at both ends of the connection, as shown in Figure 1.5

A telephone handset, for example, contains both a microphone and an earphone Duplex operation allows both parties to talk at once and both to be able to (and have to) listen This allows the human listener to interrupt, or two computers to send information to one another in both directions at the same time Not all devices are capable of talking and listening at the same time as required for duplex operation

8 INFORMATION AND ITS CONVEYANCE

Figure 1.5 A basic duplex telecommunications system

Information flow

4 b

There is also half-duplex operation, in which communication is possible in both directions, but not at the same time, as only one communications path is available First the talker must stop speaking, then the listener can reply

The transport mechanism can be one of a range of different media, ranging from sound waves passing through air to laser light pulses passing down the latest tech- nology, optical fibre Furthermore the transport mechanism may or may not comprise

an element of switching, as we describe later in the chapter

Most transport mechanisms demand an encoding of the information or data into a signal form suitable for conveyance over electrical transmission media Chapters 2 to 5 describe how many of the common forms of information (e.g speech, TV, telex, computer data, facsimile, etc.) are converted into a transmittable signal carried in either 'analogue' or 'digital' form In Chapters 6 and 9 we discuss various methods of switch- ing and in Chapter 8 we discuss a range of different transmission media (cables, radio systems, etc.), describing how different ones provide the optimum balance of low cost and good transmission performance for individual cases of application

-

In order to meet differing communications needs, a number of different types of telecommunications equipment have been developed over time These include, in chronological order:

Let us now consider the ideal properties of the various components of the telecommunications system illustrated in Figure 1.5 If both stations A and B are provided with telephones, then the transport mechanism need be no more than a single transmission line, as illustrated in Figure 1.6

The system can also be extended to include further parties For example, if a third station C wishes to be interconnected for private interconnection with either or both of the other two stations (A and B) then this can be achieved by duplication of the simple

layout In this way a triangular network between A, B and C is created, as shown in Figure 1.7

Figure 1.6 A simple two station telephone system

Telephone

-

Telephone

10 INFORMATION AND ITS CONVEYANCE

The configuration of Figure 1.7 is used today by some companies in their private networks, where a dedicated 'private line telephone' may operate over a special telephone line, leased from a telecommunications administration, to connect different premises However, for a network interconnecting a large number of stations, the configuration is uneconomical in equipment In the three-station (A, B, C) case illustrated, six telephones and three lines are needed to interconnect the stations, but only two telephones and one line can ever be used at any one time (unless one of the people is superhuman and can talk and listen on more than one telephone at a time)

As even more stations are introduced to the configuration, the relative inefficiency grows In a system of N stations in which each has a direct link to each other, a total of

~ N ( N - 1) telephone lines will be needed, together with N(N - 1) telephone sets If configured in the manner shown in Figure 1.7, the linking of 100 stations would need

5000 links (and 10 000 telephones) and a 10 000 station system would need 50 million lines and 100 million telephones We need to find a more efficient configuration! Let us limit each station in Figure 1.7 to one telephone only To make this possible

we install a switching device at each station to enable appropriate line selection, so that connection to the desired destination may be achieved on demand This is now a simple switched network, as Figure 1.8 shows Now the transport mechanism (stylised in Figure 1.5) is no longer just a single 'line', but is a more complex 'switch' and line arrangement

Let us develop Figure 1.8 further, by permitting more stations (telephones in this case) to be connected to each of the three switches Three more stations, A', B' and C' are shown in Figure 1.9 The new configuration allows the idle lines of Figure 1.8 (A-C and B-C) to be put to use

Telephone C

0

Figure 1.8 A simple three station switched network

CONNECTION-ORIENTED TRANSPORT SERVICE AND CONNECTIONLESS NETWORK SERVICE 11

6 Switchpoint ( a p e n 1

+ Switchpoint ( a c t i v e )

Figure 1.9 A simple telephone network

Figure 1.9 illustrates simultaneous calls involving A and B, B' and C', A' and C' In

this example each of the switches (which are now labelled as exchanges) is shared by a number of stations, each of which is switched and connected to the exchange by a local

line or local loop Our example now resembles a public switched telephone network ( P S T N ) Because the lines between exchanges are correctly referred to as junctions or trunks, they have been labelled accordingly

In a real telephone network the numbers of exchanges and their locations are governed by the overall number and geographical density of stations (telephone users)

requiring interconnection Similarly, the number of junctions or trunks provided

between the various exchanges will be made sufficient to cater for the normal telephone call demand In this way, far fewer junctions than stations need to be provided This affords a significant cost saving over the configuration of Figure 1.6

Before leaving Figure 1.9, note how each of the exchanges has been drawn as an array of individual switch points This allows either of the telephones connected to the

exchange to access either of the junctions, and this is a so-called full availability switch

as any one of the incoming lines may be connected to any one of the available junctions

We shall come back to circuit theory of switching and availability in Chapter 6

1.6 CONNECTION-ORIENTED TRANSPORT SERVICE (COTS) AND CONNECTIONLESS NETWORK SERVICE (CLNS)

In the example of the last section we justified on economic grounds alone the use of

switched as opposed to 'transmission line only' networks The particular case that we

12 INFORMATION AND ITS CONVEYANCE

have developed is an example of a circuit-switched network Other important switched

network types, especially used for data transmission, are those of packet switching, message switching and cell switching

Circuit-switched and most packet-switched and cell-switched networks are examples

of connection-oriented switching or connection-oriented transport service (COTS) In a connection-oriented switching technique a circuit, virtual circuit, connection or virtual connection (VC) is established between sender and receiver before information is

conveyed Thus a telephone connection is first established by dialling, before the con- versation takes place This ensures the readiness of the receiver to receive information before it is sent (There is no point in talking if nobody is listening) In contrast,

connectionless switching techniques or connectionless-network service (CONS) allow

messages to be despatched, maybe even without checking the validity of the address Thus, for example, the postal service is analogous to a connectionless service The sender

posts the entire message (envelope and contents) into the post box and forgets about it Sometime later, the receiver receives the message, either delivered directly through his letter box or by picking it up from his local post office Electronic mail, today's com-

puterized version of the postal service, is also a connectionless network service for

sending letters directly between computers

The advantage of connectionless service is that the sender need not wait for the

receiver to be ready and the network need not be encumbered with the extra effort of setting-up a connection Thus neither sender nor network need bother to keep redialling when either the receiver is already busy on another call, asleep on the other side of the world, disconnected, switched-off or otherwise unable to answer the call Instead the message is lodged in a temporary store or 'post office'-like device The disadvantage is that the sender has no clear guarantee or confirmation of message delivery He is left in doubt: did the receiver not get the message or was he simply too lazy to reply?

Message switching networks are networks which deliver the message (e.g letter or

document) in one go Most message switching networks (including perhaps the best

known, Internet) are based on connectionless network service

As an aside, sometimes the end-to-end communication is connectionless even though

each of the individual links in the physical communication chain is a connection-oriented

connection Thus both sender and receiver might telephone an electronic mail post ofice to send and receive their mail The connection between the two post offices may

be a permanent connection and both telephone calls (to deliver and pick up the message) are connection-oriented, but because the sender and receiver d o not both need to connect to their respective post offices at the same time, the end-to-end com- munication is connectionless

1.7 CIRCUIT-, PACKET- AND CELL-SWITCHED NETWORKS

The distinguishing property of a circuit-switched connection is the existence throughout

the communication phase of the call, of an unbroken physical and electrical path

between origin and destination points The path is established at call set-up and cleared

after the call The path may offer either one direction (simplex) or two direction (duplex) use Telephone networks are circuit-switched networks

CIRCUIT-, PACKET- AND CELL-SWITCHED NETWORKS 13

Conversely, although packet-switched networks are also connection-oriented, an entire

physical path from origin to destination will not generally be established at any time during communication Instead, the total information to be transmitted is broken down into a number of elemental 'packets', each of which is sent in turn An analogy might be sending the text of a large book through the post in a large number of envelopes In each individual envelope might be just a single page The envelopes can either be sent sequentially (say one each day), or numbered so that the receiver can reassemble the pages

in order Figure 1.10 illustrates this simple packet-switched communication system Should the receiver in Figure 1.10 not receive any given numbered envelope, he may write back over the reverse connection and re-request it In this way, very accurate and reliable communication may be established

Packet-switched networks are usually connection-oriented A connection set-up phase

confirms the readiness of the receiver to receive information and it determines the route

through the network which will be used to carry the packets The connection which results is actually termed a virtual connection, because though it appears to the two

end-users as though a dedicated path exists, the physical connection is actually shared

with other users By breaking the information into packets, statistical multiplexing may

be used to increase the network throughput Statistical multiplexing is the technique

of sending packets from different users' virtual connections over the same physical

connection (Figure 10) This is made possible by labelling each packet (pages of Figure 1.10) with the identity of the virtual connection to which it belongs (separate books could be sent simultaneously in Figure 1.10) The labelling allows packets to be sent from any of the virtual connections, provided that the line is at that moment idle

If the line is already busy, it may be that the new packets must wait a fraction of a second before transmission is possible This possibility of slight delay leads to another

description of packet-switching as a store-and-forward technique Packet-switching is the

technique behind X.25, frame relay and many other computer network techniques

Circuit-switched networks are generally necessary when very rapid o r instantan-

eous interaction is required (as is the case with speech) Conversely, packet-switched