TRANSMISSION SYSTEM FOR TELETYPEWRITER 



539 



The plan permits considerable flexibility with respect to arrange- 

 ments for future expansion and changes, as growth can be taken care 

 of by the provision of additional switching points or additional direct 

 circuits with practically no change in the fundamental framework. 



Regional area A Regional area B 



Fig. 4 — Principle of application of teletypewriter switching plan. 



□ Regional center 

 O Routing outlet 

 • Teletype center 



Routes to other regional centers 



X Subscriber station 



— Basic routes 



- - Supplementary routes 



Transmission Requirements 



In the consideration of the transmission requirements the following 

 items are of importance: 



1. The over-all distortion on all connections must be low enough to permit 

 satisfactor\' service. 



2. The distortion on all of the links which will at times be part of built-up con- 

 nections must be sufficiently low to permit satisfactory transmission when forming a 

 part of such connections. 



3. The distribution of distortion between the various toll links and between those 

 links and the subscriber lines should be such as to obtain the desired transmission 

 results with a minimum cost for the plant as a whole. 



Transmission Coefficients 



The transmission requirements of the over-all connection or of the 

 individual elements are expressed in terms of a system of telegraph 

 transmission coefficients which may be compared roughly to the system 

 of net losses used in telephone transmission work. 



