NON-BLOCKIXG SWITCHING SYSTEMS 



423 



one-way outgoing and two-way trunks can be freely interconnected 

 without blocking. The number of crosspoints for this case is: 





-1 



(25) 



The comments concerning the triangular array also apply for this case. 



COMPARISON WITH EXISTING NETAVORKS 



Few existing crossnet arrays are non-blocking. An example is the four- 

 wire intertol] trunk concentrating system. In one of its standard sizes 

 4,000 crosspoints are required for 100 incoming trunks and 40 outgoing 

 intertoll trunks. From Fig. 8, for A^ = 100 and M = 40 it may be noted 

 that the nearest integral value for n is 5. By substituting this value in 

 equation (22), a non-blocking three-stage switching array of 2,700 cross- 



INTERMEDIARY 

 SWITCHES 



ONE-WAY 

 OUTGOING TRUNKS 



Fig. 10 — One-way incoming, one-way outgoing and two-way trunks. 



