Telephone Traffic Time Average

OR mathematical studies of telephone traffic, like those of call loss or delay which are used in trunking engineering, the traffic is considered as a flow of probability in time. In the period of most importance, the busy hour, this flow is usually regarded as stationary; that is to say, the probability of a given number of busy trunks, or the probability of delay of an incoming call (or any other probability of the system which comes in question) is taken as independent of the particular moment in the busy hour at which the system is examined. The system is said to be in statistical equilibrium. For such theoretical studies, the statistical quantities which determine these probabilities, like the rate at which calls appear, are of course taken as given, but in the application they must be determined by observations, such as those being taken in the current extensive program of traffic measurements. Here a difficulty appears. To abridge the extensive amount of observational material, either measurements are made of traffic averages over periods small compared to the busy hour (but not small enough to be neglected) or the measurements of continuous recorders are averaged by hand. It may be noticed here that for application of the results given below the traffic averages obtained by measurements must be those of a continuous device which records all traffic changes and not, as in some measuring devices, those obtained from a number of "looks" at points within the averaging interval.