Engineering Transmission

Tel ecommunicati ons Transmission

Engineering

Telecommunications Transmission

Engineering

Volume 3 - Networks and Services

Technical Personnel

American Telephone and

Company, Bell Telephone Companies,

and

Bell Telephone Laboratories

Bell System Center for Technical Education

Prepared for Publication by Western Electric Company, Inc.

Technical Publications Winston-Salem, North Carolina

This book has been written and printed for use in the Bell System only. Its distribution, use, or other disclosure outside the Bell System is not authorized.

Printed in the United States of America, 1975

Transmission Engineering

Introduction

Communication Engineering is concerned with the planning, de- sign, implementation, and operation of the network of channels, switching machines, and user terminals required to provide communi- cation between distant points. Transmission Engineering is the part of Communication Engineering which deals with the channels, the transmission systems which carry the channels, and the combinations of the many types of channels and systems which form the networks of facilities. It is a discipline which combines many skills from science and technology with an understanding of economics, human factors, and system operations.

This three-volume book is written for the practicing Transmission Engineer and for the student of transmission engineering in an undergraduate curriculum. The material was planned and organized to make it useful to anyone concerned with the many facets of Communication Engineering.

Volume 1, Principles, covers the transmission engineering prin- ciples that apply to communication systems. It defines the charac- teristics of various types of signals, describes signal impairments arising in practical channels, provides the basis for understanding the relationships between a communication network and. its com- ponents, and provides an appreciation of how transmission objectives and achievable performance are interrelated.

In Volume 2, Facilities, the emphasis is on describing how the principles of Volume 1 are applied to the design, implementation, and operation of transmission systems and facilities which form telecom- munication networks. The descriptions are illustrated by examples taken from the most modern types of facilities.

iii

Volume 3, Networks and Services, shows how the principles of Volume 1 are applied to the facilities described in Volume 2 to pro- vide a variety of public and private telecommunication services. This volume reflects a strong Bell System operations viewpoint in its con- sideration of the problems of providing suitable facilities to meet customer needs and expectations at reasonable cost.

The material has been prepared and reviewed by a large number of technical personnel of the American Telephone and Telegraph Company, Bell Telephone Companies, and Bell Telephone Labora- tories. Editorial support has been provided by the Technical Publica- tions Organization of the Western Electric Company. Thus, the book represents the cooperative efforts of many people in every major organization of the Bell System, and it is difficult to recognize indi- vidual contributions. One exception must be made, however. The material in Volume 1 has been prepared in its entirety by Mr. Robert H. Klie of the Bell Telephone Laboratories, who was associated in this endeavor with the Bell System Center for Technical Education.

Mr. Klie is also coordinating the preparation of Volumes 2 and 3.

C. H. Elmendorf, III Assistant Vice President - Transmission Division.

American Telephone and Telegraphy Company

Preface

Overall Bell System objectives are to provide high-quality, low-cost communications services as needed with a fair return on investment;

this volume presents transmission-related technical and administra- tive information to help achieve these objectives.

Service quality is provided by meeting established transmission ob- jectives and by ensuring adequate reliability. Networks and services must be engineered to meet design objectives; facilities· and circuits must ^be constructed to meet the design objectives. Facilities and cir- cuits must also be maintained so that deviations from the engineered objectives are not excessive; the effects of failures are thus minimized.

Transmission, maintenance, and reliability objectives are discussed throughout this volume as they relate to various kinds of networks and services.

The provision of a service when it is needed often requires meeting near-immediate initial service dates with short intervals available for procurement of material and installation of facilities and equip- ment. To establish satisfactory minimum intervals requires that functions directly associated with the process of filling specific service requests be clearly defined and efficjently configured. These functions are discussed separately for designed special services and for services provided by the switched message network.

The control of costs is an integral part of the process of deciding how to provide and maintain any network. The process is one of com- promise, i.e., of striking the best balance between customer satisfac- tion, plant performance capability, and cost.

v

Volume 3 builds on the principles and facilities discussed in Volumes 1 and 2, respectively. For instance, the definition andcharac- terization of impairments, their effect on voice services as measured by grade of service, the methods of setting objectives, and the physical plant used to provide services are necessary to an understanding of the specific objectives and maintenance methods covered in this volume. In essence, the provision of networks and services represents the attainment of a basic Bell System objective.

Section 1 discusses the overall structure and features of the message network which consists of loops, trunks, and switching machines con- figured into a hierarchy planned for the efficient handling of tele- phone calls. Local and toll portions of the network are discussed as are the transmission plans for each.

Loops are the circuits which connect telephone station sets to local central offices and thus to the rest of the message network. Their performance characteristics are important because each connection generally involves at least two loops. Section 2 discusses the charac- teristics, range limits, and design considerations for the provision of loops.

Trunks provide transmission paths to interconnect switching machines. Section 3 defines the various trunk types and then discusses traffic engineering concepts which establish the methods used to de- termine the required number of trunks. Design criteria are different for local trunks, toll trunks, and auxiliary service trunks and are treated in separate chapters. Consideration of through and terminal balance techniques, used in the control of echo and singing impair- ments, is also included.

The many types of special services are introduced and defined in Section 4. Design criteria for the principal switched and private line special ,services types are included. Visual communications over a common user network has long been a desired service. The technology required to accomplish this now exists and is also discussed in Section 4.

Transmission performance must be monitored to ensure that quality standards are met, to detect trends, and to develop plans for improve- ment. Section 5 covers the measurement plans, both internal and external to the telephone company, and the maintenance, planning, engineering, and management functions required in operating the complex facilities n~twork used for the provision of telecommunica- tions services.

Contents

Introduction iii

Preface v

SECTION 1 THE MESSAGE NETWORK 1

Chapter 1. The Network Plan for Distance Dialing 1-1 The Toll Switching Plan

The Hierarchical Plan Call Routing ... .

3 3 4 8

1-2 Transmission Plan . . . 12

Network Transmission Design ... " 14 Transmission Requirements for a Control Switching Point ... 20

Maintenance Considerations .. . . . . . .. 20

Chapter 2. Metropolitan Network Plans 21 2-1 Metropolitan Tandem Networks . . . .. 22

Single Tandem Sector-Originating Network. . . .. 23

Single Tandem Sector-Terminating Network ... 24

Central Tandem System . . . .. 25

Double Tandem Network . . . . .. 26

2-2 Transmission Considerations .. . . . .. 28

General Network Requirements . . . .. 29

Local Networks ... . . . .. 31

Combined Local and Toll Connecting Networks ... 31

Mixed Local and Toll Connecting Networks ... 32

Expected Network Performance . . . .. 33

SECTION 2 CUSTOMER LOOPS ... . 38

Chapter 3. Loop Plant Characteristics ... . 40

3-1 Outside Plant Engineering ... 41

Changing Patterns of Telephone Usage . . . .. 41

Evolution of Designs ... 42

Outside Plant Engineering Functions ... 46

vii

3-2 Physical CharacterIstics of Loops ^{0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0} 47 3-3 Loop Transmission Characteristics ^{0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0} 49 Insertion Loss ^{0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0} 49 Loop Resistance ^{0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0} 51 Return Loss ^{0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0} 52 Noise 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 53

3-4 The Outside Plant Plan ^{0 0 0 0 0 0} 63

64 69 71 Development of the Plan ^{0 0 0 0}

Evaluation of the Alternatives Other Planning Considerations

Chapter 4. Range Limits 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 73 4-1 Loop Resistance Limits ^{0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0} 73 Direct Current ^{0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0} 73 Supervisory and Dial Signalling Limits ^{0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0} 74 Ringing and Ring Tripping Ranges ^{0 0 0 to 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0} 74 Overall Central Office Range Limits ^{0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0} 78 4-2 PBX Trunk and Station Line Resistance Limits 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 80 Limiting Factors ^{0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0} 80 Range Charts ^{0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0} 82

Chapter 5. Design Considerations 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 85 5-1 Resistance Design ^{0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0} 86 Basic Procedures ^{0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0} 87 Transmission Considerations ^{0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0} 92 Supplementary Design Considerations for Special Services ^{0 0 0 0 0 0 0 0 0} 96 5-2 Unigauge Design 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 . 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 99 Application ^{0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0} 99 Design Ranges ^{0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 • 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0} 101 Expected Range of Losses ^{0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0} 106 5-3 Long Route Applications ^{0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0} 107 Long Route Design 0 0 0 0 0 0 0 0 0 . 0 . 0 . 0 0 0 0 0 0 0 • • 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 108 Subscriber Loop Multiplexer .. ^{0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0} o. 116 Multichannel Subscriber Carrier Systems . ^{0 0 0 0 0 0 0 0 0 0 • • 0 0 0 0 0 0 0 0 0 0 0 0} 117

5-4 Centrex Station Line Design 118

SECTION 3 TRUNKS ^{0 0 0 0 0 0 0 0 0 • 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 • 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0} 120 Chapter 6. Trunk Types and Uses 0 0 0 0 0 . 0 . 0 . 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 122 6-1 Transmission Design Categories 0 0 0 0 0 0 • • 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 • • • • • • • • 123

6-2 Operational Categories ... . 126

126 130 6-3 6-4 Traffic Class and Traffic Use ... . . . ... . Functional or Popular Names ... . ... . Common Language Trunk Designations ... . Auxiliary Services and Miscellaneous Trunks 132 135 Chapter 7.' Traffic Engineering Concepts 139 139 142 142 143 7-1 7-2 7-3 7-4 Principles of Trunk Group Engineering Basic Traffic Distributions ... . . . ... . The Traffic Load ... . ... . Load Distribution Assumptions Trunk Network Design ... Trunk Group Efficiency and Size Service Criteria Alternate Routing ... . Load Separation ... . Adjustment for N onrandomness '" ... . Traffic Measurements ... . 152 152 155 156 158 164 164 7-5 Trunk Estimating ... 167

7-6 Trunk Administration ... . 168

Chapter 8. Local Trunk Design 171 8-1 Relationships of Trunks and Loops ... 171·

8-2 Loss Relationships ... 174

Inserted Connection Loss ... 174

Expected Measured Loss ... 175

Actual Measured Loss ... 176

8-3 Loss Objectives ... 177

8-4 Transmission Design Considerations ... 178

Loss ... 178

Signalling and Supervision ... 182

Stability ... 184

Crosstalk ... 189

Chapter 9. Toll Trunk Design ... . 191

9-1 Transmission Objectives ... 192

Loss Evaluation ... 192

Administration of Loss Objectives ... 193

Transmission Level Points ... 195

Noise Limits ... 196

Return Loss and Balance ... 196

Facility Selection ... 205

9-2 Echo Suppressors ... 205

Types of Echo Suppressors .., _ . . . .. 206

Application of Echo Suppressors ... 207

9-3 Toll Connecting Trunk Design 209 209 213 214 Loss Components ... . Trunk Length Considerations .- Impedance Matching ... - ... - 9-4 Intertoll Trunk Design 217 218 219 219 Loss Components . - ... . Intertoll Trunk Layout .... - Secondary Intertoll Trunks ... - ... . 9-5 Impact of Digital Switching on Toll Trunk Design .. . . .. 220

Loss Plan For All Digital Network .... . . .. 220

Combination Analog-Digital Network _ ... - 223

Chapter 10. Through and Terminal Balance ... . 228

10-1 Impedance Relationships .. , __ 10-2 Control of Echo and Singing " . 228 232 232 233 Via Net Loss Design _ . Return Loss ... _ ... _ 10-3 Balance Objectives _ ... _ ... _ ... 234

Balance Requirements _ ... _ . . . .. 235

Office Cabling Resistance Limit .... _ ... " 237 Office Cabling Capacitance Limit . _ ... " 239 10-4 Measurements ... _ Hybrid Transmission Loss . _ _ ... . Echo Return Loss ... _ .. _ . _ ... . Singing Point and Singing Return Loss ... _ ... . Two-Wire Switching Path Capacitance ... . 239 240 240 240 241 10-5 Apparatus Considerations _ ... " 242 Built-in Four-Wire Terminating Circuits ... 243

Repeating Coils ... _ . . . .. 243

Signalling Lead Capacitors _ ... " 245 Trunk Relay Equipment . _ ... _ . . . .. 246

Impedance Compensators ... 247

10-6 Balancing Procedures ... _ .... _ ... 248

Through Balance . . . .. 249

Terminal Balance ... _ . . . .. 252

Balance Verification Tests . _ . . . ... _. . . . .. 260

No. 1 ESS Offices ... _ . . . .. 260

Engineering Responsibilities ... 261

Certification of Balance ... 262

Chapter 11. Auxiliary Services 263

11-1 Operator Functions ... 263

Call Assistance ... 263

Number Services ... ~64

11-2 Transmission Considerations ... 265

Operator Completed Connections ... 265

Customer-Operator Connections ... 270

11-3 TSPS No.1 Services ... 276

Transmission Design of Primary Paths ... 278

Transmission Design of Secondary Paths . . . .. 284

11-4 Automatic Intercept Services . .. . ... 285

Principles of Operation ... 286

Transmission Considerations ... 288

11-5 Automatic Call Distributor Services 294 11-6 Other Auxiliary Services ... 297

Conferencing Services ... 298

CAMA Operator Number Identification ... 299

SECTION 4 SPECIAL SERVICES . . . .. 300

Chapter 12. Introduction To Special Services ... 302

12-1 Characteristics of Special Services 302 12-2 Transmission Classifications and Service Features ... 304

Class 1 Special Services ... 304

Class 2 Special Services ... 309

Class 3 Special Services ... 310

Class 4 Special Services ... 311

Universal Service ... 316

12-3 Coordination and Administration of Special Services ... 316

Intercompany Services Coordination Plan ... 317

Administration of Design Services ... 318

Interrelationship of ISC and ADS ... 322

Tariffs ... 323

Chapter 13. Switched Special Services ... 324

13-1 Circuit Design ... 324

Iliustrativi Design ... 325

Design and Analysis Aids ... 325

13-2 Signalling and Supervision ... . . .. 329

Primary Functions . . . .. 329·

Features and Options ... 330

Signalling Systems ... 331

Signalling Requirements for PBX Stations ... 333

Satellite and Nontandem PBX Tie Trunk Signalling ... 334

13-3 Voice Transmission Considerations ... 335

Loss ... . ... , 335

Return Loss ... 338

Noise ... . ... , 340

Telephone Set Current ... 341

Bridge Lifters ... 341

13-4 Data Transmission Considerations ... 342

Transmission Objectives ... 342

Design Considerations ... , 346

Cable Facility Treatment .. , . . . .. 349

PBX Considerations ... 352

Chapter 14. Centrex ... 354

14-1 Centrex Features and Arrangements ... . Service Features ... . Equipment Arrangements ... . 14-2 Centrex-CO Transmission Considerations ... . Station Lines ... . Attendant Facilities ... . Tie Trunks ... " ... , ... '" ..

FX and W ATS Trunks ... . Conferencing ... . 14-3 Centrex-CU Transmission Considerations 354 354 356 357 357 357 362 363 364 364 Chapter 15. Private Switched Networks ... . 366

15-1 Tandem Tie Trunk Networks .. . . .. 366

Network Layout ... 367

Service Features ... . . . .. 369

Transmission Design ... 369

Facilities ... 376

15-2 Hierarchical Switched Services Network . . . .. 377

Network Plan ... 377

Service Features ... 378

Switching ... 380

Transmission Performance Requirements . . . .. 381

Trunk Design ... 385

Access Lines ... 387

PBX Tie Trunks ... 390

Station Lines ... ....•... 391

Universal Service ... . . . .. 392

Data Transmission ... 393

15-3 Polygrid Switched Services Network ... . 393

394 397 398 Network Plan ... . Service Features ... . Transmission ... . ... . 15-4 Maintenance Considerations ... . 399

Chapter 16. Private Line Channels ^{0 0} 401 402 402 403 16-1

16-2

16-3

16-4

16-5

16-6

Private Line Service Categories Service Elements

Service Descriptions Voice Transmission

Selection of Facilities Transmission Plan Bridging Arrangements Talk-Back Features

Switching Arrangements ^{0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0} Station Features ^{0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0} Signalling Systems and Associated Arrangements ^{0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0} Voiceband Data Transmission ^{0 0 0 0} 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

Bridging Arrangements for Multipoint Circuits ^{0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0} Data Termination Arrangements ^{0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0} Transmission Plan ^{0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0} Impairments ^{0 0 0} 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

Wideband Data Transmission Wideband Facilities Transmission Requirements Circuit Testing ^{0 0 0}

Telegraph Data Transmission Transmission Requirements Selective Calling Systems Telephotograph Transmission

The Telephotograph Signal Transmission Considerations

407 407 408 409 415 417 418 419 422 422 424 424 427 434 434 436 436 438 441 441 442 443 443 Chapter 17. Program and Video Channels 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 • • • • • • • • • • 446 17-1 Audio Program Channels ^{0 0 0 0 0 0 0 0 0 0 0 0 0 0 • 0 • • • 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0}

Types of Circuits ^{0 0 0 0 0 0 0} Overall Transmission Design Terminal Arrangements Central Office Installations Stereophonic Studio-Transmitter Program Channel Noise

Links

446 446 448 456 456 458 459 17-2 Baseband Video Channels 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 460

17-3

Line Facilities ^{0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 • 0 0 0 0 0 0 0 0 0 0 0 0 0 • 0 0 0 0 0 • 0 0 0 0 0 0 • 0 0 • • •} 461 Office Cable ^{0 0 0 0 0 0 0 0 0 • • 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 • 0 • 0 • • • • • • • • • •} 462 A2-Type Video System ^{o . 0 0 0 0 • • • 0 0} • • • • 0 • • 0 • • • • • • • • • • • • • • • • • • • • • • 462 A4 Video System ^{0 · 0 0 • • 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0} 466 Television Operating Center ^{0 0 0 0 0 0 0 0 0 0 0 0 • 0 0 0 0 0 0 0 0 0 0 0} 467 Cable RF Video Channels

Transmission Objectives Frequency Assignments

468 470 474

Chapter 18. The Digital Data System 13-1 System Description

Service Objectives Signal Formats Network Configuration

Transmission Line and Terminal Facilities 18-2 De,sign Requirements ..

Network Synchronization

Network Maintenance and Restoration Local Loops

Other Design Considerations 18-3 Future Development Plans

Multipoint Service Switched Data Service

Chapter 19. PICTUREPHONE Service 19-1

19-2

19-3

19-4

Station Equipment ..

Display and Control Units Service Unit

Display Data Set Transmission

Transmission Objectives Video Facilities ...

Switching ... .

Central Office Switching Customer Premises Switching Maintenance Considerations

Manual Test Features Semiautomatic Test Lines Continuing Quality Checks 19-5 Future Plans ... .

SECTION 5 TRANSMISSION MANAGEMENT ... . Chapter 20. Measurements and Indices

20-1 External Measurements

Service Attitude Measurement

Trouble Reports and Requests for Credit

Customer Trouble Report Analysis Plan ... . Network Trouble Analysis B~eau ... .

475 476 476 477 480 483 496 496 499 503 505 507 507 509 511 511 512 514 514 515 516 520 525 525 526 526 527 527 527 528 531 533 534 534 536 538 539

20-2 Internal Measurements ... 641

Subscriber Plant Transmission Tests ... 542

Trunk Transmission Maintenance Measurements . . . .. 544

Connection Appraisal Tests ... 548

20-3 Measurement-Derived Transmission Indices Derivation of Transmission Indices Connection Appraisal Index

Trunk Transmission Maintenance Index Subscriber Plant Transmission Index Proposed Index Components

Chapter 21. Maintenance and Reliability

555 558 561 563 567 568

571 21-1 Maintenance Principles ... . ... 571 Transmission and Signalling Measurements .... ... 572 Transmission Parameter Variations . . . .. 573

Costs and Revenues .... 576

A Comprehensive Maintenance Program 577

21-2 Facility Maintenance

Initial and Routine Testing

Surveillance ... . Demand Schedule Maintenance 21-3 Circuit Maintenance

Loops ... . Network Trunks Special Services ...

21-4 Reliability ... . Protection Facilities Emergency Restoration

Network Management Considerations

Chapter 22. Transmission Facility Planning 22-1

22-2

22-3

22-4

Elements of Current Planning Planning Studies ...

Selection of Alternatives The Planning Model

Circuit Group Routing Circuit Group Design Design Allocation .. . Facility Routing ... . Evaluation of Specific Studies

Data Summaries ... . Use of the Planning Model

Documentation and Coordination ... . Construction Project Documentation ... . Circuit Layout and Assignment ... . Coordination Information

577 577 578 580 581 581 582 587 590 591 593 596

598 599 600 605 607 609 611 611 613 613 614 614 618 618 619 619

22-5 Fundamental Planning ... . ... . 620

621 622 622 Objectives and Evaluation . . .. . Procedures ... . The Changing Network Environment Chapter 23. Engineering and Management 624 23-1 Current Engineering ... . . . 624

Economic Factors ... 624

Transmission Quality Control ... 625

23-2 The Response to Change .. . . . . . .. 627

Environmental Changes . . . .. 628

Innovations ... 628

Planning ... 630

Education and Training . . . .. 631

Index 632

Transmission Engineering

Section 1

The Message Network

Section 1 is devoted to a review of the purposes and functions of the message network as an entity because of its fundamental im- portance and central role in meeting many of today's telecommunica- tions needs. Furthermore, it provides an understanding of the overall functions and transmission objectives which is prerequisite to con- sideration of the loop and trunk components of the network.

Chapter 1 discusses the hierarchical structure, principles, and objectives which are fundamental to the operation of the entire message network. Chapter 2 discusses further service considerations that result in the formation of supplementary hierarchical structures for metropolitan areas within the overall message network. These structures have been designed to serve the unique population densities of the metropolitan areas most economically while still fulfilling the broader message network objectives intended to provide overall service performance which meets the most modern communication standards. These two chapters also provide an overview of the rela- tionships between the various trunk networks that have evolved and the switching systems necessary for efficient interconnection and utilization of the complex network of transmission paths.

Chapter 1

The Network Plan for Distance Dialing

The toll portion of the switched network, commonly known as the direct distance dialing (DDD) network, provides long distance telephone connections among virtually all of the 125 million or more telephones in the United States, Canada, and some Caribbean islands.

This network, which is operated jointly by the Bell System, inde- pendent telephone companies, and other administrations, handles about 25 million long distance calls each day. Over two-thirds of these calls are dialed directly by the customers; most of the remainder are dialed by operators. About 2000 toll switching offices are inter- connected by over 700,000 intertoll trunks.

This chapter provides an overview of the switching and trans- mission plans for the toll portion of the message network. Discussion of the switching plan includes the network hierarchy, the various classes of switching offices, the types of trunks used, and the features required for the routing of calls through the network. The discussion of the transmission plan describes the network transmission require- ments. The via net loss plan is briefly reviewed, and trunk loss and through and terminal balance requirements are given.

1-1 THE· TOLL SWITCHING PLAN

Large amounts of traffic between any two central offices are gen- erally routed most economically over direct trunks; however, when the volume of traffic between offices is small, use of direct trunks may not be economical. In these cases, traffic originating from several wire centers destined for one office may be concentrated at inter- mediate switching machines which connect together two or more trunks to build up the required connections. Conversely, where con- centrating networks have been established, the amount of traffic between· any two offices may become large enough to economically

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