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Early-demultiplexing techniques for quality of service in serving GPRS support nodes Lefebvre, Geoffrey

Abstract

The General Packet Radio Service(GPRS) is a wireless data service that sits on top of the existing GSM infrastructure. It provides access to the Internet and packet based billing. It is often referred as a 2.5G system and is designed to evolve to UMTS(3G). The Serving GPRS Support Node(SGSN) is one of two new nodes added to the GSM infrastructure to support GPRS. Its role is to route data to users in its geographical area and provide user mobility, access control and security. We have studied a SGSN from a system point of view, looking at how it interacts with the operating system. We have found that a SGSN implemented as a user level process will not be able to properly support Quality of Service(QoS). We have looked at three QoS parameters: throughput, delay and precedence and have found that a SGSN will not be able to maintain guaranteed services based on those parameters when heavily loaded. This behavior is due to the fact that operating systems are unaware of the QoS requirements of incoming traffic and are therefore unable to properly queue incoming packets. We have designed and built a SGSN where the incoming traffic flow is demultiplexed on arrival. The QoS requirements of incoming packets are identified before they are queued. Packets can now be classified and queued properly. Our results show that our Early Demultiplexing SGSN(ED-SGSN) provides large improvements. The ED-SGSN is able to maintain service guarantees in terms of throughput, delay and precedence even under serious loads.

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