996 THE BELL SYSTEM TECHXICAL JOURNAL, SEPTEMBER 1956 



large capacity. To set up connections at a high rate in such a network 

 requires a pluraHty of controls each capable of operating on all or part 

 of the network. In any case, the controls function in parallel on the 

 network because of the speed considerations. 



With electronics applied to space division switching networks, two 

 improvements over the operation of relay type space division networks 

 may be achieved. First, the speed of operation of the crosspoint elements 

 may be made high enough so that only one control is needed to operate 

 on networks of the size now requiring a plurality of controls. Second, 

 the properties of proposed electronic crosspoint elements are such that 

 the principle of "end-marking" may be employed. 



In contrast to the grid of testing and actuating wires required in 

 electromechanical versions of space division networks, the electronic 

 space division switching network requires only the selectors at each end 

 of a desired network connection to apply the marking potentials. (This 

 is what is meant by "end-marking"; see Fig. 6). The electronic cross- 



I o 



•C- 



-^ 



2 O- 



m 



z 



a 



-> 



-O A 



m 



A 





-O 8 



m 



b 



m 



B 



Fig. 4 — Space division switching. 



CROSSBAR 

 SWITCHING NETWORK 



Dn 



^B. 



^ 



[} 



X )( 



COMMON CONTROL 

 (MARKER) 



): )? 



NETWORK 

 CONNECTOR 



Fig. 5 — Typical common control of a crossbar switching network. 



