ELECTRONICS IN TELEPHONE SWITCHING SYSTEMS 



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Fig. 9 — Time division control access with separate functional memory. 



of the switching system. Many small low cost relay registers have been 

 designed and placed into service.^" Electronics, however, offers memory 

 at one tenth, or less, of the cost per bit if used in large quantities with 

 a common memory access control. New low cost bulk electronic mem- 

 ories are now available to be used in this manner. As shown in Fig. 10 

 the memor^y for the control of the time division control access network 

 and the register memory may be combined in the bulk memory. 



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Fig. 10 — Time division control access with bulk memory. 



Memory appears in the control portion of a switching system in 

 many ways. Some are obvious and others are more subtle. Fig. 11 shows 

 a typical electromechanical switching system, much like No. 5 crossbar 

 and attempts to indicate various memory functions. First there is 

 active memory designated A such as the call information storage A2 

 whether in a register, sender or marker during processing. There is 

 also certain pertinent call information storage associated with trunk 

 circuits such as a "no charge class" on outgoing calls or the ringing 

 code used on incoming calls. Another type of active memory Ai has 

 been mentioned in connection with switching networks to remember the 

 input-output associations. In most electromechanical systems active 

 memory has been emplemented with relaj^s or switches. 



Another form of memory is also employed in all telephone switching 

 systems and much effort has been devoted to devising improved means 

 for effecting this memory. This memory is of the type that is not 

 changed with each call but is of a more permanent nature. Examples 

 of this type of memory, which may be called passive memorj^, designated 

 P, (Fig. 11), are the translations required in common control sytems to 

 obtain certain flexibility between the assignment of lines to the switch- 

 ing network and their directory listing. These translations between 



