SWITCHING PLAN FOR TELEPHONE TOLL SERVICE 439 



great an amplification into the circuit. As an extreme case, this 

 might result in a sustained oscillation or singing on the circuit. Other 

 effects which may be important are those of crosstalk between tele- 

 phone circuits, or of noise induced in the telephone circuits from 

 outside sources, both of which are increased by increasing repeater 

 gains. On the longer connections, echoes are almost always the 

 controlling factor, whereas on the shorter connections, such effects as 

 crosstalk, singing and noise generally are limiting. A reduction in 

 any of these effects generally involves more expensive types of con- 

 struction. 



The difference between the attenuation loss of the circuit and the 

 total transmission gain introduced into the circuit by repeaters is 

 spoken of as the net equivalent. For long telephone circuits it is 

 generally economical to provide sufficient repeater gain so that the 

 circuit can be operated at the minimum net equivalent permissible, 

 this minimum equivalent being determined by the transmission 

 factors just mentioned. Therefore, in establishing satisfactory trans- 

 mission efficiencies for the overall toll connections in accordance with 

 the toll switching plan, each link must be designed on the basis of 

 the minimum working net equivalent which it will contribute to an 

 overall connection made up of several circuits switched together. 



The establishment of satisfactory and economical transmission 

 requirements for the toll circuits laid out in accordance with the plan 

 involves the following steps: 



a. The establishment of satisfactory overall net transmission equiva- 

 lents. 



h. The coordinated design of all classes of toll circuits, and of the 

 subscribers' circuits, toll switching trunks and tributary trunks 

 connected to them, in such a way that the desired overall 

 transmission standards will be given at a minimum total cost 

 when suitable transmission gains are provided by repeaters 

 in the toll circuits and at toll switching points. 



c. The economical and satisfactory distribution of transmission gain, 

 permitting all toll circuits to be operated at their minimum 

 net equivalents when this is desirable. 



The overall transmission equivalents to be given under the plan 

 are based on standards which have heretofore been used for a large 

 part of the toll business but which it has been impracticable to meet 

 in many cases between widely separated points. With the means 

 now available for operating circuits at their minimum working net 

 equivalents, it was found that satisfactory overall transmission 

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