ELECTRONICS IN TELEPHONE SWITCHING SYSTEMS 



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than speed. Even in the telephone switching field, this property of 

 electronics has made its inroads to provide us with better signaling and 

 more accurate timing. 



It was not, however, until World War II that the speed advantages 

 of electronics were exploited. This exploitation came primarily in the 

 quantizing of information, both in transmission and information proc- 

 essing equipment. In the latter field new digital computers made their 

 appearance. These machines brought forth the development of new 

 forms of electronic devices, most important of which are those classified 

 as "bulk memory" devices.^ Later in this paper the characteristics of 

 many of these devices will be discussed in more detail. 



In the post-war period the exploitation of another phase of electronics 

 developed from research in semiconductor devices. The transistor is 

 perhaps the best known invention to emerge from these investigations. 

 The impact of the application of semiconductor devices is yet to be 

 felt in the electronics industry and it will most likely find greatest 

 application in the information processing field and in communications 

 generally. 



Before one may understand and appreciate the impact electronics 

 will have on the design of new telephone switching systems it is nec- 

 essary to consider the question: "What is a Telephone Switching Sys- 

 tem?" By evolution it is now^ generally recognized that the central 

 office portion of a telephone switching system consists of two prin- 

 cipal parts and certain physical and operational characteristics of these 

 parts. These parts, as illustrated in Figure 2, are the interconnecting 

 network, or conversation channel, and its control. 



In some switching systems, particularly those of the progressive 



LINES- 



SWITCHING NETWORK 



CONC 



N I 

 T I 



GATHERING 



DIST 



EXP 



CONTROL 



INFORMATION 



PROCESSINGS 



INTERPRETING 



-TRUNKS 



EFFECTING 



Fig. 2 — Principal parts of common control telephone switching system. 



