Service-level availability estimation of GPRS

Abstract

The General Packet Radio Service (GPRS) extends the Global System Mobile Communication (GSM), by introducing a packet-switched transmission service. This paper analyses the GPRS behavior under critical conditions. In particular, we focus on outages, which significantly impact the GPRS dependability. In fact, during outage periods the cumulative number of users trying to access the service grows proportionally over time.When the system resumes its operations, the overload caused by accumulated users determines a higher probability of collisions on resources assignment and therefore a degradation of the overall QoS. This paper adopts a Stochastic Activity Network modeling approach for evaluating the dependability of a GPRS network under outage conditions. The major contribution of this study lies in the novel perspective the dependability study is (*) Corresponding author -1 -framed in. Starting from a quite classical availability analysis, the network dependability figures are incorporated into a very detailed service model that is used to analyze the overload effect GPRS has to face after outages, gaining deep insights on its impact on user's perceived QoS. The result of this modeling is an enhanced availability analysis, which takes into account not only the bare estimation of unavailability periods, but also the important congestion phenomenon following outages that contribute to service degradation for a certain period of time after operations resume.

Evaluation of the Impact of Congestion on Service Availability in GPRS Infrastructures

“…To cope with congestion events, which may affect GPRS cells, e. g. due to a temporary lack of a number of traffic channels or to failures of their architectural components (as detailed in [2]), we assume that appropriate RMTs are applied. Instead of focusing on a specific RMT, we consider the class of RMTs which operate congestion alleviation by reducing the traffic of the congested cells, which is redirected to the neighbor partially overlapping cells.…”

“…These models can be obtained as a specification of the model of Figure 4 representing an abstract view of a generic GPRS cell. The "internal GPRS cell model" was deeply described in [2], and it models the behavior of a GPRS cell during the random access procedure, when users compete to get a free channel. In fact, when a mobile station (MS) needs to transmit, it has to send a channel request to the network through the PRACH (Packet Random Access Channel), that is a channel dedicated to the uplink transmission of channel request.…”

“…An inspiring work is certainly [2], in which the authors analyze the dependability of a GPRS cell under outage conditions. Another work ( [3]) evaluates the effects of outage periods on the service provision considering two GPRS cells partially overlapping (and then possibly interacting), and accounting for outage congestion treatment and outage recovery.…”

Congestion analysis during outage, congestion treatment and outage recovery for simple GPRS networks

“…In this section, we outline the methodology that we use to construct the OVERALL model starting from the BASIC one. The model of the random access procedure that we use as BA-SIC model has been deeply described in previous works (see [2] and [3]) and it is briefly outlined in [7]. With respect to the purposes of our analysis, we can consider the BASIC model as a black-box in which there are only few visible components (see Figure 2(a) which shows the interfaces among models).…”

Secure Model for SMS Exchange over GSM

“…Additionally, the GPRS service may be not available in some portions of time and after outage it needs addition recovery time which is the period of time that it needs to return to its normal behavior. According to Porcarelli et al [9] statistics, in a GSM with approximately 150 GPRS user, if the time of outage reaches about 300 seconds, another 140 seconds are needed to recover the delayed GPRS requests and return to normal service. This means that the possible member of a system may stay about 440 seconds without connection.…”