NOTES ON DISTANCE DIALING AMERICAN TElEPHONE AND TElEGRAPH COMPANY DEPARTMENT OF OPERAnON AND ENGINEERING (COPYRIGHT, 1956, BY AMERICAN TELEPHONE AND TELEGRAPH COMPANY) PRINTED IN U. S. A. NOTES ON DISTANCE DIALING TABLE OF CONTENTS SECTION TITLE Foreword I General II The National Numbering Plan III Switching Plan for Distance Dialing IV Interoffice Signals V Equipment Requirements VI Transmission Considerations VII Switching Maintenance Requirements and Considerations VII Bibliography Revised September 1956 NOTES ON DISTANCE DIALING FOREWORD These Notes outline the technical requirements for nationwide operator distance and di­ rect distance dialing. They are a revised edition of "Notes on Nationwide Dialing - 1955", which superseded the Notes on "Nationwide Operator Toll Dialing" furnished to the U.S.I.T.A. in 1945 and published in Volume 130 (January-June 1946) of Telephony. In the period since the Notes were first issued, several suggestions have been made to include additional material and to expand the discussion on certain subjects. In this interval, too, there have been some changes in basic plans. Therefore, it was decided to revise and re­ issue the Notes to provide up-to-date information. The important changes covered by the revision are: 1. Elimination of National Center Concept (Section ill). 2. Change in requirements for supervision on trunks to distant point information (Section V, Part 4B). 3. Change in requirements from "full" intercept to "adequate" intercept including a definition of "adequate" intercept (Section V, Part 4A). 4. Establishment of single-channel operation as a Bell System long range object­ ive (Section V, Part 4G). In addition to these changes, this new edition brings the planning maps up to date. Also, technical requirements have been revised in a few instances and charts modified for clearness. Each new or revised page is so indicated under the page number. Specific revisions and new material are indicated by arrows and brackets in the outside margin (as shown on this page) . The Notes are confined to matters bearing directly on distance dialing. In addition to the technical data required by manufacturing and engineering personnel, discussions are included covering in some detail the National Numbering Plan, the Switching Plan, Equipment, Trans­ mission and Maintenance Considerations, etc., which should be of value to operating and main­ tenance people, generally. For those intel'ested in the over-all plan rather than the technical details, the "General" section briefly outlines the contents and scope of the other sections in non-technical terms, and also discusses some of the fundamentals that are usually considered wheY' preparing to incorporate offices into the distance dialing network. I Revised September 1956 Foreword, Continued In many instances it has been necessary to specify the particular requirements or design objectives without including a discussion of the factors underlying their selection. Also, there are many problems in th,e Accounting, Commercial, Public Relations and Traffic fields relating to distance dialing that are not covered by the Notes. Nevertheless, it is expected that the Notes will go a long way in furnishing information needed by the Telephone Industry for the successful integration of distance dialing plans. It should be emphasized that the transition from local manual and ringdown toll operation [ to operator and direct distance dialing as described by these Notes will require an orderly pro­ gram extending over a number of years. Also, it should be recognized that while the Notes des­ [ cribe the requirements as visualized today, details will necessarily change as experience is gained and new instrumentalities are developed. However, the fundamental plan is considered sound and it is believed that the minor changes which may be necessa:ty will not have any [ serious effect on plant designed to meet the requirements outlined in the Notes. [ In certain situations the requirements of the Notes need not be rigidly adhered to for operator and direct distance traffic items which will not reach the nationwide network and [ where exception to the provisions of the Notes will result in significant industry economy. It is recognized, too, that a book of such general nature as the Notes can not cover all details of every technical requirement for distance dialing. As to questions concerning technical matters [ not discussed in the Notes, direct contact at the local or state level between the Independent and Bell segments of the Telephone Industry is encouraged. [ During the next few years, planning for distance dialing will involve the entire Telephone Industry in the United States and Canada. Accordingly, all Telephone Companies participating [ in distance dialing will be interested in the Notes. The importance of early and continuous joint planning by Independent and Bell Companies can not be overemphasized since the plans of one [ are bound to effect the plans of others. In this connection, the technical discussion in the minutes of the meetings of the U.S.l.T.A. Technical Subcommittee of the Subscriber and Opera­ tor Toll Dialing Committee heldwith representatives of the American Telephone and Telegraph Company on October 7, 1953 and on April 6 and 7, 1954 are of interest and will serve as a worthwhile supplement to the Notes. Quite recently a proposalwas made to eliminate flashing signals on the intertoll network. If adopted, this would permit the elimination of separate toll switching trains in new step-by­ step offices. Advantages which would be realized if these steps are taken are: 1. Reduced central office equipment costs. 2. More economical provision of inward dialing to P.B.X. stations. 3. More rapid integration of offices not arranged for flashing signals into the dis­ tance dialing network. 2 September 1956 Foreword, Continued Originally the Bell System and many Independents provided separate toll switching trains in the larger step-by-step offices for transmission reasons. SUbsequently, three other features, flashing signals, controlled start of ringing, and prepaid coin control, were added to the toll train. With improved station instruments, the transmission requirement for toll grade battery has been eliminated. Flashing signals could be eliminated by employing tones in their place. This means that the operator would remain on the connection a little longer on some station­ to-station sent-paid calls until she heard audible ringing, answer, or busy. Preliminary study indicates that this operating penalty would not be great and would tend to decrease as customer dialing of these calls is extended. With elimination of controlled start of ringing, relatively few calls would experience a slight service penalty. As to the prepaid coin control feature now pro­ vided by the toll train, study is under way to determine other means of handling this. Since this proposal is still in the formative stage and requires further analysis and study, no changes have been made in this revision of the text concerning the features that might be af­ fected. Should the proposal be adopted, several years would be required to complete the pro­ gram. Until that time, the Notes will continue to reflect the present features. 3 September 1956 NOTES ON DISTANCE DIALING SECTION I GENERAL CONTENTS PAGE 1. INTRODUCTION 1 2. DESCRIPTION OF SECTIONS . 2 (A) The National Numbering Plan - Section II 2 (B) Switching Plan for Distance Dialing - Section III . 3 ..- (C) Interoffice Signals - Section IV. 3 (D) Equipment Requirements - Section V 4 (E) Transmission Considerations - Section VI 4 (F) Switching Maintenance Requirements and Considerations - Section VTI 5 (G) Bibliography - Section VITI 5 3. FUNDAMENTAL PLANS 5 1. INTRODUCTION 1.01 Distance dialing (nationwide dialing) as used in these Notes, and as commonly understood within the telephone industry, means the maximum completion of dialable calls (both local and long distance) by customers, with operators dialing as much as possible of the re­ maining traffic which cannot be customer dialed.. To designate calls dialed by customers to points outside their local or extended service area, the phrase "Direct Distance Dialing" has been adopted; and when such calls are dialed by operators, the designating phrase t1 Operator ] Distance Dialing" is used. Distance dialing has been generally accepted as an ultimate indus­ trywide objective since this method of operation will usually provide the fastest, most accurate, and most dependable telephone service and at the same time should result in over-all operating economies. The distance dialing plan is also frequently referred to as "Continentwide" rather than "Nationwide" since it provides for the handling of long distance traffic both within and be­ tween the United States and Canada. 1 Revised September 1956 SECTION I L Introduction, Continued [ 1.02 The Notes are intended to serve as a general reference for the Telephone Industry on the subject. They describe the minimum requirements which need to be met. Since the basic [ plan is designed for both operator and customer dialing, no distinction has been made between the two except in instances where the requirements are not common. Detailed description of circuit operation has been avoided and the requirements for local and toll switching systems [ have not been covered except where they affect distance dialing. [ 1.03 Generally, the Notes describe the requirements that will apply when distance (nationwide) dialing has been realized and