On the effects of outages on the QoS of GPRS networks under different user characterizations

Standard network QoS analysis usually accounts for the infrastructure performance/availability only, with scarce consideration of the user perspective. With reference to the General Packet Radio Service (GPRS), this paper addresses the problem of how to evaluate the impact of system unavailability periods on QoS measures, explicitly accounting for user characteristics. In fact, the ultimate goal of a service provider is user satisfaction, therefore it is extremely important to introduce the peculiarities of the user population when performing system analysis in such critical system conditions as during outages. The lack of service during outages is aggravated by the collision phenomenon determined by accumulated users requests, which (negatively) impacts on the QoS provided by the system for some time after its restart. Then, depending on the specific behavior exhibited by the variety of users, such QoS degradation due to outages may be perceived differently by different user categories. We follow a compositional modeling approach, based on the GPRS and user models; the focus is on the GPRS random access procedure on one side, and different classes of users behavior on the other side. Quantitative analysis, performed using a simulation approach, is carried out, showing the impact of outages on a relevant QoS indicator, in relation with the considered user characteristics and network load.