Modeling and Analysis of the Behavior of GPRS Systems

The General Packet Radio Service (GPRS) has recently become a standard to extend the services provided by the Global System for Mobile Communications (GSM). GPRS addresses packetoriented traffic, by allowing a more efficient usage of the radio resources with a consequent improvement in the QoS of subscribers. This paper focuses on a preliminary evaluation of dependability and performance figures of the GPRS, by analyzing its behavior during the contention phase where users compete for the channel reservation using a random access procedure. The presented work constitutes the first step towards the analysis of the GPRS under critical conditions, as determined by periods of outages, which significantly impact on the dependability of the GPRS itself. In fact, outages imply service unavailability, with a consequent accumulation of users actively waiting for making a service request, leading to a higher probability of collisions on requests (and therefore a degradation of the QoS perceived by the users) when the system comes back up again. Here, some analysis have been performed, using a simulation approach, to gain insights on appropriate settings for the GPRS, at varying values of internal and external system conditions (mainly, users requests, available radio channels devoted to packet traffic, outages duration).