The development plan of the No. 4 ESS included provisions for measuring the effectiveness of the design, operation, maintenance, and administration of the total system. This paper reviews system performance from 1976 to 1980, describes principal factors affecting system performance, and presents the service experience measured for the No. 4 ESS. Steady improvement has been measured in the number of service‐affecting incidents experienced per office each month. This improvement is also reflected in the rate of cutoff and denied calls, as well as in system “no call processing” time. We discuss some of the factors influencing this performance record, e.g., a sound initial design, reliable hardware, effective maintenance and repair tools, continuing analysis and resolution of causes of service‐affecting incidents, and continuing development of new features for performance improvement.
Common‐channel interoffice signaling (ccis) represents a major advance in interoffice signaling speed and capability over current inband signaling systems. The introduction of ccis between Stored Program Control (spc) switching offices is reducing ineffective machine attempts (imas) caused by transmission and switching irregularities associated with inband signaling. Because signaling between ccis‐equipped switching offices is concentrated in a relatively small number of signaling links and signal transfer points (stps), a high standard of performance for the signaling network is essential. Therefore, the design of the signaling network incorporates many features to assure a high degree of availability. Cumulative data on stps and studies of signaling links are the principal measures of signaling network performance. Data on their performance are presented that confirm the high availability of the signaling network.
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