T1 Carrier Characterization-Field-Measurement Results

Abstract

We undertook a field-measurement program for T1 carrier to gain an understanding of crosstalk performance in the outside plant and office environments. This would help us to use the existing plant more efficiently and to predict the performance of future systems. Repeater-section lines were measured in the trunk plant of three Bell System operating companies during 1977 and 1978. Results given here include the distributions of repeater section crosstalk margin, noise, and various system and cable properties. We describe a T1 crosstalk engineering model which explains the significant contributions to section margin. The measurements and analysis show that repeater apparatus-case crosstalk dominates intermediate repeater-section performance, while the performance of sections adjacent to central offices (end sections) is limited by cable crosstalk with evidence of impulse noise present on some lines. Maximum use of cable and equipment for T1 and future digital transmission systems has been made much easier with the knowledge gained from these field measurements. For instance, the results of this program have already been used to redefine engineering rules for bidirectional cable operation, allowing more wire pairs in the cable to be used for T1 operation.