Modeling and Evaluation of the Effects of Outages on the Quality of Service of GPRS Network Systems

F. Tataranni*, S. Porcarelli**, F. Di Giandomenico*** and A. Bondavalli****

* CNUCE-CNR, Area della Ricerca di Pisa, Via G. Moruzzi 1, I-56100 Pisa, Italy

** University of Pisa, Computing Engineering Dep., via Diotisalvi 2, I-56126, Pisa, Italy

*** IEI-CNR, Area della Ricerca di Pisa, Via G. Moruzzi 1, I-56100 Pisa, Italy

**** University of Firenze, Dip. Sistemi e Informatica, Via Lombroso 6/17, I-50134 Firenze, Italy

Technical Report: CNUCE-B4-2000-028

Abstract

The General Packet Radio Service (GPRS) has been introduced to extend the GSM, by addressing packet-oriented traffic. Availability is the most important dependability requirement for such Communication Systems as GPRS. Focusing on the contention phase, where users compete for channel reservation, this paper analyses the GPRS with the objective to understand its behavior under critical conditions, as determined by periods of outages, which significantly impact on the resulting dependability. In fact, during outages (service unavailability), users trying to access the service accumulate, leading to an overload of the system. When the system resumes its operations, the accumulated users determine a higher probability of collisions on resources assignment (and therefore a degradation of the QoS perceived by the users). Our analysis, performed using a simulation approach, allowed to gain insights on the impact of outages on the QoS and of the overload that GPRS systems have to face after outages.

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