RATIXC TRANSMISSION PERFORMANCE 131 



tests and other similar measurements for interpolating between the 

 points established by the repetition method. In this way it is planned 

 to put the rating of transmission on a basis which indicates the effect on 

 service of changes in the various parts of the circuit. 



Conclusion 



In concluding, it may be restated that the primary purpose here has 

 been to discuss the rating of the transmission performance of telephone 

 circuits and the method which is being adopted in the Bell System for 

 determining and expressing effective transmission ratings for the design 

 of the plant. The salient features of this method which should be 

 emphasized are the following : 



1. In establishing the rating of the transmission performance of a tele- 



phone circuit, its performance is taken as that obtained when 

 the circuit forms part of the combination of talker, circuit and 

 listener, where the talker and listener represent the users of the 

 telephone system in commercial service. 



2. The ratings of the effective transmission of circuits are based on the 



rate of repetitions required. 



3. The ratings of effective transmission will eventually be referred to a 



modification of the Master Reference System arranged with 

 typical distortion, sidetone and noise. For a working reference 

 circuit, use is made of a circuit which has transmission charac- 

 teristics typical of those encountered in service. The trunk of 

 this circuit is taken as adjustable in attenuation for the purpose 

 of providing a scale for specifying different grades of overall 

 transmission performance and also for expressing ratings of the 

 effect on transmission performance of the various transmission 

 characteristics of circuits and their parts. 



