Transcript
International Journal of Mobile Computing and Multimedia Communications, 4(1), 57-68, January-March 2012 57
Combined Queue Management and Scheduling Mechanism to Improve Intra-User Multi-Flow QoS in a Beyond 3,5G Network Amine Berqia, University of Algarve, Portugal Mohamed Hanini, Hassan I University, Morocco Abdelkrim Haqiq, Hassan I University, Morocco
ABSTRACT Packet scheduling and buffer management are the two important functions adopted in networks design to ensure the Quality of Service (QoS) when different types of packets with different needs of quality share the same network resources. The Packet scheduling policy determines packet service priorities at the output link, it can reduce packet delay and delay jitter for high-priority traffic. The buffer management involves packet dropping and buffer allocation. The overall goal of such schemes proposed in High Speed Downlink Packet Access (HSDPA) is to take advantage of the channel variations between users and preferably schedule transmissions to a user when the channel conditions are advantageous; it does not take in consideration the characteristics of the flows composing the transmitted traffic to the user. This paper compares two queue management mechanisms with thresholds applied for packets transmitted to an end user in HSDPA network. Those mechanisms are used to manage access packets in the queue giving priority to the Real Time (RT) packets and avoiding the Non Real Time (NRT) packets loss. The authors show that the performance parameters of RT packets are similar in the two mechanisms, where as the second mechanism improves the performance parameters of the NRT packets. Keywords:
3,5G Networks, Priority, Quality of Service (QoS), Queue Management, Scheduling
1. INTRODUCTION In recent years, the performance of mobile cellular telecommunication networks have been growing continuously by increasing the
hardware capacity, and new generation of mobile networks offer more bandwidth resources. With this development, new Mobile wireless networks have to support multimedia applications that generate traffic having diverse QoS requirements, especially, the two most important requirements: packet loss and delay
DOI: 10.4018/jmcmc.2012010105 Copyright © 2012, IGI Global. Copying or distributing in print or electronic forms without written permission of IGI Global is prohibited.
58 International Journal of Mobile Computing and Multimedia Communications, 4(1), 57-68, January-March 2012
requirement. This effect needs to be taken in consideration. We assume that we can always improve performance and guarantee the QoS by increasing microprocessor speed or even building specialized hardware to replace inefficient software components. However, for a predetermined set of available resources, it becomes important to take additional measures to effectively implement the QoS in network. In this paper, our focus is on two important internal design factors in networks: packet scheduling and buffer management (Lizambri et al., 2001). The packet scheduling policy determines packet service priorities at the output link. Priority scheduling can reduce packet delay and delay jitter for high-priority traffic (Kamal & Hassanein, 2004). The ideal packet scheduling algorithm would have properties of efficiency and fairness. Some of the simplest scheduling algorithms are first-in-first-out (FIFO), round robin (RR), and a “fixed priorities” scheme where a queue with higher priority is always served before a queue with a lower priority. Many other algorithms have been proposed in this area (Bennet & Zhang, 1997; Demers et al., 1989; Golestani, 1989; Stiliadis & Varma, 1996; Suri et al., 1997). The buffer management involves packet dropping and buffer allocation. Packet dropping is used to maintain the buffer size, in order to efficiently handle both real-time and non-real time packets. Buffer allocation focuses on managing buffers by allocating buffer volume to each class, so as to reduce packet loss due to lack of buffer space (Pillai et al., 2008). Many buffer management schemes that have been studied in literature have focused either on packet dropping (Athuraliya et al., 2001; Branden et al., 1998; Floyd & Jacobson, 1993), packet scheduling (Semeria, 2001), or both (Clark & Fang, 1998). This paper shows the effect of a combined queue management and scheduling mechanism, applied to multimedia flows transmitted to an end user in HSDPA network, this effect is shown
on the QoS requirements of real time and non real time packets. The rest of this paper is organized as follows: the next section presents the packet scheduling in the HSDPA network. In section three we briefly describe the mechanisms and give their mathematical models. The performance parameters of the two mechanisms are given in section four. In section five we present and discuss the numerical results. Finally, the section six concludes the paper.
2. PACKET SCHEDULING IN HSDPA The High Speed Downlink Packet Access (HSDPA) was introduced in release 5 of UMTS in order to support the increasing demand for the multimedia applications that require high data rates (Zigmun & Marc, 2007). HSDPA defines a new physical channel, the High Speed Downlink Shared Channel (HS-DSCH) on which data traffic is transmitted. To improve system capacity, HSDPA adopts the advanced technologies, such as Adaptive Modulation and Coding (AMC), Hybrid Automatic Request (HARQ), fast Packet Scheduling, and an advanced receiver design. These features are tightly coupled and enable the transmission parameters to be adapted to the instantaneous variations of radio channel quality as discussed in Dottling et al. (2002) and Jo et al. (2008). In addition to the physical layer features introduced in the HSDPA, another change is implemented to support fast packet transfer, the packet scheduling functionality is relocated from the Radio Network Controller (RNC) to the Medium Access Control (MAC) layer in the NodeB. This allows advanced packet scheduling techniques. The wireless packet scheduler is a key element of HSDPA that determines the overall behavior of the system. The overall goal of most schedulers proposed in HSDPA is to take advantage of the channel variations between users and prefer-
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