Blocking Distributions for Trunk Network Administration

Blocking Distributions for Trunk Network Administration By S. R. NEAL (Manuscript received October 8, 1979) Administrative control of the Bell System telephone network requires demand-servicing procedures that maintain network service in a cost-effective manner and an administrative measurement plan that determines whether the network provisioning process is providing a proper balance between network service and network utilization. The traffic measurements available are busy-season, busy-hour, trunk-group usage and average blocking. Statistical variation of these measurements can lead to an incorrect assessment of network performance and an unstable network provisioning process, resulting in costly excess reserve capacity in the network. To minimize sensitivity to volatile measurements, administrative measurement bands have been employed to define a new demand-servicing procedure and a new trunk service measurement plan for use within the Bell System. This paper derives the probability distribution function for measured blocking, which is required to construct the measurement bands, and outlines the new Bell System administrative procedures. The distribution has a discrete component, the probability of no blocking, and a continuous component. The last function is well approximated by a two-parameter beta distribution. The resulting measurement bands are a strong function of trunk group size and a weak function of traffic characteristics. Small trunk groups (fewer than 10 circuits) are much more volatile than large groups.