Digital Data System: Testing and Maintenance

The service objectives for the Digital Data System described in the preceding article 1 represent substantial improvements over the performance and availability of existing data services. Since the DDS exists in the present telephone plant environment, it is subjected to the same kinds of random interruptions and failures that occur in that environment. Hence, special arrangements and procedures are provided to meet the more stringent service requirements. To meet the desired service objectives, DDS equipment at the DS-1 (1.544 Mb/s) and higher levels monitors system performance fulltime, with manual or automatic switching to standby equipment in the event of a failure.* Alarms on DDS equipment alert craft personnel to system failures. Many new features in the system permit rapid sectionalization of troubles on a one-man basis and rapid identification and replacement of defective units. Since the DDS utilizes existing carrier systems for both exchangearea and long-haul transmission, maintenance planning is compatible with present and planned carrier maintenance and restoration procedures. The reliability estimates cited in the preceding paper have, therefore, included allowances for carrier system failures and restoration. * The subrate data multiplexer (SRDM), which operates at the ns-O (64-kb/s) level, also provides performance monitoring and protection switching (Ref. 2). 845