4. Traffic. PBX performance

4.1 Notions of telephone traffic

A telephone subscriber doesn't phone all the time. Moreover, it is obvious that, depending on the different phases of economic and social activity, telephone activity can vary considerably. Equipment sizing (connection network structure, size of the various circuit bundles, etc.) must therefore take this phenomenon into account. This introduces the notion of traffic flow quality.

For given call arrival times and call durations, we can calculate a function P = f (N, A) representing the probability of failure as a function of traffic A and the number N of circuits, traffic A being defined as the average over time of the number of busy circuits. Depending on whether the probability represents the likelihood of the beam being saturated...