Abstract :
Transmission planning of a switched telephone network consists largely of allocating losses, and other degradations of conversation, to the various elements that will be associated to form tandem connections. Even a given number of trunk circuits linked in tandem will yield a distribution of overall reference equivalent for different calls owing to unavoidable random variations and to the distribution of subscribers´ lines. Clearly, a statistical approach is needed. One problem that arises and is the subject of the paper is to determine, for a given allocation of losses and impairments, the percentage of calls that are likely to be of acceptable quality. This is to enable the relative merits of different allocations to be compared. Basic subjective data must be assembled, and a method devised, for estimating the degree of satisfaction for any required combination of factors. These are already available in respect of overall loss, circuit noise and certain types of bandwidth limitation and attenuation/frequency distortion. Yet to be completed is the treatment of nonlinear distortions and mutilation due to voice-operated equipment. Some results are also available for echo and propagation time.
