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UBC Theses and Dissertations

Active queue management techniques to improve Quality of Service for real-time flows in third generation wireless networks Chen, Jian

Abstract

In this thesis, we analyze the behavior of real-time flows with hard time deadline using link layer retransmission to overcome wireless errors, and propose two new mechanisms to improve these flows' end-to-end Quality-of-Service (QoS) over a wireless network. Wireless channels have the characteristic that link quality varies according to propagation conditions. For real-time flows with hard time deadlines, link layer retransmissions over a wireless network, necessitated by fluctuations in link quality, may result in a high number of packets being dropped, as deadlines expire. The expired packets waste network resources and lead to long queuing delays for subsequent packets. After analyzing the characteristics of the Radio Link Control (RLC) layer of the General Packet Radio Service (GPRS)/Universal Mobile Telecommunication Services (UMTS) network, we have developed a new set of mechanisms to minimize expiration packet drops in favour of overflowlike packet drops. We propose to use active queue management to limit transmission queue length, hence queuing delay, thus eliminating expiration packet drops. This allows the buffer and wireless bandwidth, otherwise be wasted by expiring packets, to be released earlier for other packets. We apply this mechanism to the radio link control layer in the GPRS/ UMTS wireless networks. The effectiveness of the proposed mechanism is verified by simulations. Furthermore, we extend the similar idea from the radio link control layer to the whole GPRS/UMTS domain. We adapt the Early Regulation of Unresponsive Flows (ERUF) to the characteristics of wireless channels employing link layer retransmissions. We propose to regulate those congested flows at the DiffServ domain ingress edge nodes of the GPRS/UMTS core network, and drop undeliverable packets earlier to release some shared network resources for other flows. We also present simulation results to show that this new Wireless Early Regulation of Unresponsive Flows (WERUF) scheme can significantly improve the overall end-to-end quality-of-service.

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