SWITCHING PLAN FOR TELEPHONE TOLL SERVICE 441 



Provision of Transmission Gain at Intermediate 

 Switching Points 



The third step mentioned previously is the determination of the 

 best distribution of repeater gains to permit the individual circuit to 

 be operated by itself or in conjunction with other toll circuits at 

 approximately the minimum net equivalent as determined by the 

 several effects mentioned previously. In so far as the gain of repeaters 

 permanently inserted at intermediate points in a toll circuit is con- 

 cerned, this is a matter of economical design of the circuit and has 

 been adequately covered in other papers. We are interested here, 

 however, in considering the provision of gain at the intermediate 

 switching points when two toll circuits are connected together. 



As indicated previously, echo effects are usually controlling on the 

 longer connections, whereas crosstalk, singing and noise will usually 

 control on the shorter connections. This is due to the fact that for 

 the great majority of toll circuits the echo effects on individual circuits 

 increase more rapidly with length than do crosstalk and noise. Singing 

 tendencies also increase at a rapid rate with increase in length on 

 two-wire circuits but tend to be independent of length on four-wire 

 cable and carrier telephone circuits which are used to a large extent 

 to provide the circuits between the primary outlets and regional 

 centers and between the regional centers. Furthermore, when two or 

 more toll circuits are connected together, the echo effects of the indi- 

 vidual circuits add together almost directly, whereas the effects of 

 crosstalk, singing and noise increase at a much less rapid rate. The 

 result of these general considerations is that when a toll circuit is 

 switched to another toll circuit, the overall combination can, in 

 general, be operated at a lower net equivalent as determined by 

 echo effects than the sum of the two circuits when operated individually 

 in which case the minimum equivalent is determined by the crosstalk, 

 singing and noise effects. Therefore, it is necessary in the case of 

 connections built up by connecting together a number of toll circuits 

 to introduce repeater gain at the intermediate switching points. 

 If gain were not introduced at intermediate points, it would be neces- 

 sary in order to obtain the same overall results on connections involving 

 more than one toll circuit to design and build a considerably more 

 expensive type of toll circuit plant in which the crosstalk, singing 

 and noise effects would be greatly reduced. 



In the past, gain was inserted at intermediate switching points by 

 the use of cord circuit repeaters. These familiar devices consisted 

 of telephone repeaters inserted in the cord circuits and associated by 

 means of double plugs with the toll circuits and with individual 



