Peak-Load Traffic Administration of a Rural Multiplexer with Concentration

The SLM (Subscriber Loop Multiplexer) system is a digital carrier and switching system that was developed to provide economically for main-station growth and upgraded service on long rural cable routes. It is capable of serving 80 lines, all sharing 24 channels. Each of the 80 lines can be used for single- or multi-party service. (For a detailed description of the SLM system see Ref. 1.) For the purposes of this paper, which is concerned with traffic, the SLM system may be viewed as a remote line-concentrator serving 80 lines on 24 full-access channels. The quality of service given to SLM subscribers should be kept well above levels that might lead to complaints, and to the need for hasty rearrangements that would interfere with the orderly growth of subscriber plant. Hence, service for these subscribers should not be noticeably different from that for customers served by physical pairs to the central office. This service objective will be met if blocking exceeds one-half percent in no more than a few hours per year. (It is possible to imagine a distinct service, for sparsely populated rural areas, in which a less stringent service objective would be appropriate.) The Rural Line Study, 2 3 a study of subscriber line usage in rural areas, has confirmed that rural residential subscribers like those studied in the territory of South Central Bell can almost always be served on one SLM system with essentially no blocking in groups of 80 main stations or more. (In fact, as shown below, most rural systems should be able to serve many more than 80 main stations.) However, the load per main station does vary greatly from place to place and from customer to customer.