Transmission Aspects of Data Transmission Service Using Private Line Voice Telephone Channels

The Bell System has been approached on a number of occasions in regard to the transmission of computing machine and similar data over its telephone circuits. This has reached the point where specific possibilities for private line data transmission have been given serious consideration. The telephone network was developed for speech transmission, and its characteristics were designed to fit that objective. Hence, it is recognized that the use of it for a distinctly different purpose, such as data transmission, may impose compromises both in the medium and in the special service contemplated. A short time ago the authors were assigned the problem of examining possibilities for such an adaptation aimed at high speed, and exploring 1451 J 484 THE BELL SYSTEM TECHNICAL JOURNAL, NOVEMBER 1957 the nature of the transmission compromises that might be needed. As a result, a variety of data transmission systems in different stages of development have been investigated including some telegraph systems. Certain conclusions have been reached regarding their suitability for use over private line telephone facilities. (By "private line" facilities are meant facilities leased to the subscriber on a more or less permanent private basis, and that are not set up by operators at a telephone central office switchboard.) These conclusions are summarized below. In the later text there is included the background material for the conclusions which includes a brief characterization of the facilities.