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THE BELL SYSTEM TECHNICAL JOURNAL, MARCH 1953 



be used to establish the connection but without affecting any of the 

 crosspoints on the intermediary switch. The number of crosspoints for 

 this case is: 



(24) 



^ = (2--i)(^+£-£) 



where T = number of two-w^ay trunks. 



By differentiation, conditions for obtaining minimum numbers of 

 crosspoints can be determined. The arrangement can also be extended 

 to cases where extra switching stages are required, 



ONE-WAY INCOMING, ONE-WAY OUTGOING AND TWO-WAY TRUNKS 



A combination of the triangular array of Fig. 9 and of unequal in- 

 puts and outputs is shown in Fig. 10. In this figure, one-way incoming, 



INPUT AND OUTPUT 

 SWITCHES 



T = 24 

 TWO-WAY 

 TRUNKS 



-o- 

 n=3 o- 



INTERMEDIARY 

 SWITCHES 



Fig. 9 — Triangular array. 



