Loop Test System: A New Maintenance Feature for the Distributed Integrated Digital Network

The introduction of the digital Class 5 switch offers unique solutions to the requirements of growth and demands for improved service. For example, remote subscriber switches (RSS's) and subscriber carrier terminals (SCT's) can now be located near subscribers and digitally connected to the Class 5 switch via T1 repeatered lines or radio links. The result is shorter subscriber loops, improved transmission, and deferment or elimination of feeder plant additions. Traditionally, interposing electronics between the subscriber loops and the Class 5 switch resulted in isolating these loops from the office loop testing facilities. Remote testing of RSS and SCT assigned loops is an important step toward minimizing maintenance costs. Loop testing is accomplished in TRW Vidar's ITS5 switching system by locating loop test equipment in the remote RSS and SCT cabinets. This equipment is available to the test operator for real-time testing, and to the switch for automatic line testing. Some of the requirements that the loop test equipment must meet are: low cost, no adjustments, low power consumption, small size, operation in a harsh environment, and centralized testing capability from a test console. The data returned to the office must be in a quantitative form to allow further processing by the console. It must also be compatible with the direct distance dialing (DDD) network to allow transmission not only to the Class 5 switch serving the RSS and SCT, but also to distant service centers. This paper describes a newly developed system that meets the above objectives.