Research Unit in Networking
	Abstract

A Scheduler for Relative Delay Service Differentiation G. Jennes1 , G. Leduc1 and M. Tufail1 1 Research unit in Networking, EECS department, University of Liège, Belgium 2 Research unit in Networking, EECS department, University of Liège, Belgium 3 Research unit in Networking, EECS department, University of Liège, Belgium (2002) Abstract We propose a new delay-based scheduler called as RD-VC (Relative Delay VirtualClock). Since it performs a delay-based service differentiation among flow aggregates, the quality at microflow level is the same as that at aggregate level. This is not easily achievable when the service differentiation is bandwidth-based or loss-based. Unlike the EDF (Earliest Deadline First) scheduler [1], our proposed scheduler self-regulates and adapts the delays according to load changes. This characteristic permits us to implement it in an AF-like PHB providing the relative quantification service in a DiffServ network. Finally, we compare our proposed RD-VC scheduler with two important existing propositions: WTP (Waiting Time Priority) [2, 3] and Ex-VC (Extended VirtualClock) [4]. Both these propositions are delay-based and have self-regulation property. All three schedulers RD-VC, WTP and Ex-VC) maintain the required service differentiation among aggregates and have comparable long term average performance like mean throughput per aggregate and packet loss ratio etc. However, RD-VC and WTP take an edge over Ex-VC at short-term performance like jitter. Both RD-VC and WTP have good long term and short-term performance. Our proposed RD-VC, compared to existing WTP, has two additional characteristics, i.e. unlike WTP which is limited to architectures with one queue per QoS class, it has no limitation on implementation scope (with or without separate queues per class) and it has lower complexity. This renders RD-VC an interesting proposition. Keywords differentiated services, DiffServ, proportional service quality, QoS, queuing delay, scheduling

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