Observations of Errors and Error Rates on T1 Digital Repeatered Lines

The T1 repeatered line is a short-haul digital transmission system using cable pairs to transmit binary information at a rate of 1.544 X 106 bits per second. 1 T1 lines have been in use since 1962, primarily in conjunction with D1 channel banks to provide a carrier system for voice channels. In the design of the T1 line, the distribution of error rates was an essential design parameter. 2 However, since the field trial of an experimental prototype system, in which the error performance of one worst-case repeatered line was briefly reported,* it has become clear that more knowledge is needed on the subject of the error performance of working T1 lines. Measurements of timing jitter and errors on Tl lines were made at five Bell System offices during 1973-74. The error measurements were of two types: a survey of error rates and error-free seconds; and detailed recordings of the error process, normally for 24 hours duration, on selected Tl lines. The jitter measurements will be reported elsewhere.4 The survey consisted of error rate measurements (determined by * See pp. 95-96, Ref. 3. 711