A Transmission System for Teletypewriter Exchange 



Service * 



By R. E. PIERCE and E. W. BEMIS 



A nationwide transmission system has been established in the United 

 States for teletypewriter exchange service by means of which 2-way com- 

 munication between teletypewriter subscribers can bo established in a time 

 comparable to that required for long distance telephone service. A brief 

 description of the principle of operation of teletypewriters is included in this 

 paper as an introduction to the discussion of the transmission requirements 

 and the plan of the present system. 



TO MEET the growing needs of business organizations, par- 

 ticularly those operating on a nationwide basis with branches at 

 widely separated locations, there has developed in the United States an 

 extensive use of private line telegraph service. This trend has been 

 accelerated by the perfection of the teletypewriter, which makes it 

 possible for regular office employees to transmit and receive com- 

 munications without a large amount of special training. Some of these 

 private line teletypewriter networks have been provided with switching 

 facilities to permit the customer to set up connections between his 

 various offices or groups of offices as desired. As these arrangements 

 were perfected and as the public gained experience with the teletype- 

 writer method of communication, a demand developed for a tele- 

 typewriter service in which all connections would be set up on a 

 switched basis similar to that provided for spoken conversation by 

 the telephone system. To meet this demand teletypewriter exchange 

 service or as it is usually called, TWX service, was inaugurated by the 

 Bell System in November 1931. 



Briefly described, teletypewriter exchange service makes available 

 to subscribers a complete communication system for the written word, 

 consisting of: 



(a) Teletypewriters for sending and receiving, installed on the customers' premises 



with a connection to a nearby switching center. 



(b) Transmission channels interconnecting all of the switching centers. 



(c) Teletypewriter switchboards for connecting the subscribers' stations and loops 



to each other or to the inter-city transmission channels and for making through 

 connections between inter-city circuits. 



This system provides for direct teletypewriter connections between 

 the customers or their employees at the sending point and at the 

 receiving points. The connection is two-way so that questions can 



* Published in Electrical Engineering, September, 1936. Presented at A.I.E.E. 

 Southwest District meeting, Dallas, Texas, October 26-28, l<)36. 



529 



