Statistical evaluation and modelling of Internet dial-up traffic

In times of Internet access being a popular consumer application even for "normal" residential users, some telephone exchanges are congested by customers using modem or ISDN dial-up connections to their Internet Service Providers (ISPs). In order to estimate the number of additional lines and switching capacity required in an exchange or a trunk group, Internet access traffic must be characterized in terms of holding time and call interarrival time distributions. In this paper, we analyse log files tracing the usage of the central ISDN access line pool at University of Stuttgart for a period of six months. Mathematical distributions are fitted to the measured data and the fit quality is evaluated with respect to the blocking probability caused by the synthetic traffic in a multiple server loss system. We show how the synthetic traffic model scales with the number of subscribers and how the model could be applied to compute economy of scale results for Internet access trunks or access servers.