A survey of the telephone transmission-rating problem

Abstract

The quality of service provided by a telephone concern is an essential factor in its financial economy. In this relation it is necessarily the overall quality as experienced by the subscribers. Division into different aspects such as traffic quality and transmission quality is arbitrary; each may be separately measured, but for economic balanced planning there is need of a combined measure of overall quality. The paper deals only with transmission quality. Planning has, in the past, been in terms of circuit attenuation and instrument efficiency, with the object of ensuring an adequate level of received speech, but this conception is no longer adequate or economical.The direct observation of the number of times a subscriber finds it necessary, in a unit time-interval, to repeat a word or a sentence is the best known indication of transmission quality in service; a complete rating system based upon such observations and other considerations has been put into operation by the American Telephone and Telegraph Co.In Europe, the repetition-rate criterion of service quality has been accepted, but application of the practice presents difficulties. Two plans are being investigated: (a) attempts are being made to find, under certain restricted conditions, a correlation between repetition rate in service and laboratory articulation tests; and (b) a provisional system of rating based on articulation tests (without reference to repetition rate) is being studied.Both plans are described, and possible correlation procedures are discussed. Reference is made to the economy aspect of rating on the broader basis of transmission quality, but the subject is too large to treat adequately in the present paper.Brief mention is made of foreign publications.Appendices include detailed descriptions of the experimental procedure to establish transmission service ratings.On account of the fluid condition of the subject of the paper, standardized terminology is not in existence and therefore definitions of the terms used are given as a final appendix.