1000 THE BELL SYSTEM TECHNICAL JOURNAL, SEPTEMBER 1956 



registering function has two parts, one to detect or receive the informa- 

 tion and the second to store it until a sufficient amount has been re- 

 ceived for processing. The processing function is usually allotted to 

 other circuits such as the markers in Crossbar systems. 



SR-D 



CONVERSATION 



SWITCHING 



NETWORK 



CONTROL 



SWITCHING 



NETWORK 



Fig. 8 — Control access. 



Since the input of information to a switching system is usually limited 

 to two conductors, a serial form of signaling is used. It would seem only 

 natural that if a detector were fast enough it could function to receive 

 the serial information in several simultaneously active inputs. Relays 

 are not fast enough to do this, but high speed time sharing electronic 

 devices have been designed to perform this information gathering func- 

 tion. Since it is a time sharing arrangement it is analogous to the time 

 division switching. A time division control access as shown in Fig. 8 and 

 9 requires memory to control the time division switching function. Time 

 sharing when applied to the gathering of information in telephone 

 switching systems has been called "scanning". The individual register 

 memories are still in parallel form because of the relatively long time 

 required for sufficient information to be received before processing may 

 start. Higher speed means for placing information into switching sys- 

 tems such as preset keysets is one way of reducing, if not eliminating, 

 this need for parallel register storage in the switching system prior to 

 processing. However, with this type of device one merely transfers the 

 location of the storage from the central office to the customer's telephone 

 set. The fundamental limitation is the rate at which a human being is 

 able to transfer information from his brain into some physical repre- 

 sentation. 



Lower cost memory is a practical means for improving this portion 



