No. 1 ESS ADF: Maintenance Plan

A communication switching system must be designed with dependability and maintainability as an integral part of the overall plan. T h e N o . 1 E S S A D F store a n d f o r w a r d message s w i t c h i n g s y s t e m i s n o exception. Continuous high quality service is of vital importance. The characteristics of high quality data service include good error performance, 24-hour service with a minimum of interruptions, fast restoral of service, and no loss of messages when interruptions do occur. The system's error performance objective for basic station-to-station messages is: on the average, no more than one error in 105 bits-- 99 percent of the time while continually transmitting. The error performance will be determined largely by the station access lines since the error rates within the switching office are much lower. The switching center hardware was designed to include optional error detection and correction features (by retransmission) to achieve even greater transmission accuracy. The reliability objective for the No. 1 ESS A D F system is to provide continuous service with system downtime not exceeding 2 hours in 40 years. The store and forward data features make it possible to preserve message information under the most severe fault conditions so messages can be retransmitted or retrieved when service resumes. Once a store and forward message office accepts incoming traffic for 2831