Performance of IP-based services over GPRS

We examine the traffic-handling capabilities of general packet radio service (GPRS) with respect to supporting IP-based Internet services. We begin with an overview of GPRS in which we discuss its general characteristics, connection set-up procedures, and data transfer procedures, both for the reverse link and the forward link. We then present an analytical model to assess throughput of the reverse link as a function of the number of users connected and the distribution of user message lengths. Next, we investigate the capability of GPRS to support World Wide Web access using the analytical model. Specifically, we present a realistic scenario for user sessions operating under the Hypertext Transfer Protocol (HTTP) and we assess the transaction-handling capabilities as a function of the number of user sessions, taking into account network delays, forward link transmission, random access delay, and other factors. The results obtained by using the analytical model in both cases are verified by simulation. We also consider, via simulation, a scenario where both continuously backlogged users and users operating HTTP sessions are present. We find that, in the case of continuously backlogged users, an increase in the number of contention slots does not always translate to an increase in throughput, while, in the case of users operating HTTP sessions, the downlink serves as the main bottleneck in the system. We conclude with a discussion of some open issues in the design of GPRS-based Internet access.