Traffic Models and Associated Parameters in GSM/(E)GPRS Networks Georgeta Budura, Cornel Balint, Adrian Budura, Eugen Marza Communication Department “Politehnica” University of Timisoara Bd. V. Parvan. No. 2 ROMANIA georgeta.budura@etc.upt.ro , cornel.balint@etc.upt.ro Abstract: - GSM/(E)GPRS networks support a mixture of traffic consisting of voice and data. A key concept of dimensioning radio resources in such networks is represented by sharing resources between different users and different services. In this paper we address the problem of voice and data traffic models according to different resources allocations strategies: CP (Complete Partitioning) and PP( Partial Partitioning) and define specific parameters in each case. The proposed traffic model depend in each case on the resources allocation strategy: for voice traffic it is based on both cases, CP and PP, on Erlang law meanwhile for data traffic we build different models depending the scheme used for resources allocation. For CP scheme we propose two models: the model based on Erlang law and those based on modified Engset law. For PP scheme we also proposed two models: one is based on the bi-dimensional Markov chain and the other on the modified Engset law. Both consider voice-data interaction according to the PP scheme. In all cases we define specific performance parameters. We also implement the studied models and evaluate the proposed performance parameters. Finally we compare the results in order to find the adequate model to use for dimensioning purposes. Key-Words: - GSM/(E)GPRS, blocking and preemption probability, Erlang-B law, Engset law, average throughput, cell utilization 1 Introduction Initially, GSM (Global System for Mobile Application standard) cellular networks were developed to offer, mainly telephonic services. GSM combines time division multiple access (TDMA) and frequency division multiple access (FDMA) for radio channel allocation. With this approach a frequency carrier is divided into eight time-slots per frame which are used to support speech and data transmission. Only a basic circuit oriented service at low transfer rate was provided to data access. Named CSD (Circuit Switched Data) this can achieves transfer rate up to 9.6 kbps per time slot. The integration of the General Packet Radio Service(GPRS) and the Enhanced (E)GPRS into GSM system world wide raises many problems. Analysis and study of data services in a cellular network require new models since traditional ones (like Erlang’s formulas) are not applicable to this kind of traffic. At the same time, the particularities of each GSM/(E)GPRS mainly on the resources allocation require an adaptation of the general model depending on the needs of each provider. For networks operators, equipment vendors and system integrators dimensioning rules have to be developed to plan and estimate the radio capacity that is needed for the predicted amount of data users when the radio resources are shared between circuit and packet switched services. GSM operators have been dimensioning their networks for voice service in terms of offered voice traffic and blocking probability. The reference performance parameter for this system model is the Erlang-B formula [1], [2]. This formula gives the proportion of calls that are blocked as a simple function of system capacity and traffic intensity. The (E)GPRS network is designed for supporting several types of data traffic such as Wap, Web, E-Mail, etc. Therefore (E)GPRS traffic process characterization is very demanding. Usually the data traffic is characterized by bursts and is application dependent. A communication session may last for an extended period of time with intermittent packet transmissions. On the other hand the (E)GPRS service allows dynamic allocation of bandwidth resources. Wireless channels are allocated to a mobile terminal based on its traffic demands which results in a better resource utilization. This traffic behavior coupled with flexible bandwidth allocation in a (E)GPRS network represent the starting point for constructing an appropriate model in order to evaluate the WSEAS TRANSACTIONS on COMMUNICATIONS Georgeta Budura, Cornel Balint, Adrian Budura, Eugen Marza ISSN: 1109-2742 833 Issue 8, Volume 8, August 2009