Rating the Transmission Performance of Telephone 



Circuits 



By W. H. MARTIN 



This paper discusses the rating of the transmission performance of 

 telephone circuits on the basis of the rate of repetitions in telephone conver- 

 sations and presents the rating method set up on this basis, which is being 

 adopted in the Bell System for determining and expressing the data for 

 the transmission design of the telephone plant. 



A METHOD of rating the transmission performance of telephone 

 circuits is of course an essential in specifying the grades of trans- 

 mission service to be furnished, in designing, constructing and main- 

 taining telephone systems to provide the desired grades of service 

 economically and in the development of the various elements of the 

 telephone system which affect its transmission. As the art of tele- 

 phone transmission has developed and greater refinements have become 

 possible and desirable, changes have naturally been made in the 

 methods of specifying and rating transmission performance. Since 

 many such changes have been made in recent years, it seems opportune 

 to discuss the rating of transmission performance and to set forth the 

 rating method which is now being adopted in the Bell System for 

 determining and expressing the data for the transmission design of the 

 plant. In this connection, various methods which have been em- 

 ployed for measuring the transmission performance of telephone circuits 

 will be discussed to indicate their application and also their relation to 

 the new rating method. It is the purpose here to discuss this rating 

 matter primarily from the qualitative standpoint rather than to present 

 in quantitative detail the various relations involved in rating telephone 

 transmission. Obviously, the determination of many of these relations 

 presents sufficient material for separate treatment. 



In carrying on a telephone conversation three major functionings are 

 involved, namely, that of the talker in formulating his ideas and utter- 

 ing words to convey these ideas, that of the telephone circuit in taking 

 the sounds of these words and reproducing them at another point, and, 

 lastly, that of the listener in hearing and recognizing these reproduced 

 sounds and in comprehending the ideas which they are intended to 

 convey. It is evident that all three of these functionings affect the 

 success of the telephone conversation. Since, however, the function- 

 ings of the talker and listener are common to both direct and telephone 

 conversations it might seem that the consideration of the transmission 



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