THE INTERCONNECTION OF TELEPHONE SYSTEMS 535 



in the split group calls may be lost when as few as 10 trunks are busy 

 provided they are all in the group to which the calls at the moment are 

 being originated. Thus the splitting of the group and the consequent 

 reduction of the access may prevent a call in one subgroup, upon 

 finding its 10 trunks busy, from continuing on over the remaining 



(A) (B) 



Fig. 5^Comparison of arrangements of twenty trunks. 



trunks, one of which might have been idle. We conclude then that, 

 other things being equal, a given load may be more economically 

 carried over one large group than over two or more smaller groups. 



Switching Limitations 

 Unfortunately, "other things" are decidedly not equal. Three 

 major considerations may be pointed out which quite definitely tend 

 to limit the number of trunks to which a particular source may be 

 given access: 



1. The high cost of switches having a large number of contacts. 



2. The undesirable long hunts which occur in trunk groups of large size. 



3. The double connections which increase directly with the load 



carried. 



Of these the first two are usually the more instrumental in regulating 

 the practicable upper limits to the access or hunt. When considered 

 with the efficiency of the trunk groups in a system they comprise, in 

 general, the fundamental data for determining the appropriate arrange- 

 ment which may be economically employed to handle any given amount 

 of traffic. 



We are then faced with the problem of obtaining the maximum 



