Switchboards and Signaling Facilities of the Teletypewriter 

 Exchange System * 



By A. D. KNOWLTON, G. A. LOCKE and F. J. SINGER 



The development of a nationwide teletypewriter exchange system in 

 the United States required the design of switchboards and signaling facilities 

 adapted to this special service. The two types of switchboard now in use 

 are described in this paper, and the operation of the circuits by means of 

 which connections between the various subscribers are established and super- 

 vised by the operators is explained. 



A NATIONWIDE teletypewriter service giving direct connection 

 between subscribers for the exchange of written messages by 

 means of the teletypewriter in a manner similar to the service offered 

 by the telephone system for the exchange of spoken messages was 

 offered to the public as a new aid to business by the Bell System on 

 November 21, 1931. This service, known as the teletypewriter 

 exchange (TWX) service, introduced a switching technique which, 

 although familiar in the telephone art, involved many new technical 

 problems when applied to the telegraph art. 



Records show that during the nineteenth century some telegraph 

 exchanges were established at which connections could be made on a 

 message basis for to and fro telegraph communications between sub- 

 scribers. These earlier exchanges had a commercial appeal although 

 the various forms of subscriber instruments then used were slow and 

 required considerable skill for operation. Later, when the telephone 

 was introduced, these exchanges gradually disappeared because the 

 public naturally preferred the more convenient instrument. With the 

 introduction of the modern teletypewriter the telegraph exchange idea 

 was again revived because the teletypewTiter, being very similar to 

 an ordinary typewriter and permitting an accurate written record of a 

 to and fro communication, has, from a subscriber standpoint, over- 

 come the objectional features of the early telegraph instruments. 



The private line telegraph and teletypewriter service furnished by 

 the Bell System has formed a very important background for the new 

 teletypewriter exchange service. The older service, which provides 

 relatively permanent networks interconnecting various stations in a 

 predetermined manner for a predetermined time, has been available 

 to the public since about 1890. During the earlier period it was used 



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

 Southwest District meeting, Dallas, Texas, October 26-28, 1936. 



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