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UBC Theses and Dissertations

End-to-end application behavior in general packet radio service (GPRS) networks Pandey, Aparna

Abstract

This thesis is a part of the joint project undertaken by UBC and Motorola, Richmond. The aim of this thesis was to develop an end-to-end General Packet Radio Service (GPRS) network simulator and to investigate the end-to-end performance behavior at the application level. GPRS is a packet-switched service, which offers packet-data services like support of internet applications over wireless cellular networks. TCP (Transmission Control Protocol) is a widely used transport protocol for internet applications. TCP is a connection-oriented protocol that uses ARQ (Automatic Repeat Request) to ensure reliability. TCP has its own mechanisms for dealing with congestion in the network. However, TCP was not made with wireless networks like GPRS in mind. GPRS has RLC (Radio Link Control) layer, which may work in ACK mode and deal with the errors encountered by the data frames in the wireless medium by the means of ARQ or RLC may operate in UNACK mode and not be responsible for any error-recovery. It is an open question whether the RLC operating in ACK mode with TCP, complements TCP's effort of errorrecovery or is it more desirable for RLC to operate in UNACK mode. It has been shown in literature that for a single Mobile Station in the network, the RLC layer retransmissions (in ACK mode) do counteract the error encountered in the wireless media and TCP adjusts its behavior such that there is no unnecessary retransmission. In this thesis an end-to-end General Packet Radio Service (GPRS) network simulator was modeled using a network simulation tool, OPNET. Some of the issues examined were: • Whether RLC should operate in ACK mode or UNACK mode. • The maximum number of retransmissions at the RLC layer for optimal performance. • The limitation imposed on maximum offered load to optimize the performance. • If TCP allows support of multiple Mobile Stations without unacceptable performance degradation. It was noted that for optimal performance RLC should operate in ACK mode and maximum number of RLC retransmissions can be limited. It was also observed that for best results, the number of users for the same maximum offered load should be reduced and that TCP does not flood the network with unnecessary retransmissions.

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