76 



BELL SYSTEM TECHNICAL JOURNAL 



Problem III 



In practice, a modification of Problem II frequently arises. As- 

 sume an arrangement similar to that of Problem II except that the 

 number of lines is multiplied by a factor of perhaps 3 or more, each 

 line switch, however, still having access to all first selectors. The 

 required number of first selectors will also be larger but not in ex- 

 actly the same ratio because the margin of idle selectors need not be 

 relatively as great in the large system as in the small. An enlarged 

 group of trunks running from the first selectors to the second selectors 

 will now be required, and it will be assumed that there are four times 



Tb Lines & Line Switches 



+ 



10 Trunks 

 to Second 

 Selectors 



FinstSelectors 



t 



04 



Fig. 4 



as many trunks coming from each level of the first selectors as there 

 are points of contact on each level. To meet this situation, the 

 first selectors and their outgoing trunks are divided into four sub- 

 groups as shown in Fig. 4. The corresponding sub-groups of second 

 selectors are designated by d, G2, G3, G4, the number of trunks to 

 each sub-group being 10. The solution of this problem depends 

 primarily on the manner in which the line switches distribute calls 

 to the first selectors. Three cases will be considered. 



