Rating the Transmission Performance of Telephone Circuits

M E T H O D of rating the transmission performance of telephone circuits is of course an essential in specifying the grades of transmission service to be furnished, in designing, constructing and maintaining 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 telephone 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 employed 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 uttering 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.