| Summary: | 碩士 === 國立交通大學 === 電信工程系 === 90 === Recently, the Differentiated Services (DiffServ) model has been proposed to provide different degrees of QoS guarantee. In this thesis, we aim to design scheduling mechanisms that provide proportional delay differentiation among different classes. These scheduling algorithms have two important goals need to be achieved. First one is predictability, which means the higher classes will always get better services than the lower classes (or at least no worse) even under short timescales. The second critical factor is controllability. That is, we claim that a scheduling algorithm should also provide consistent quality differentiation regardless of any system load, class load distribution, or stochastic arrival process.
First, we investigate the behavior of waiting-time priority (WTP) scheduler, which was regarded as the most effective method in achieving proportional delay differentiation. By referencing the result from its theoretical queueing analysis, we propose an algorithm, which called dynamic waiting-time priority (D-WTP). It indeed improves the system performance under both long-term and short-term situations, especially in moderate load condition.
However, D-WTP still has some drawbacks. It is only valid when two classes exist and the performance downgrades with non-Poisson traffic arrivals. So we innovate another method, which called average-delay priority (ADP) algorithm, to solve these problems. ADP differs from D-WTP in the fact that it does not use the theoretical results and avoids the error caused by prediction. The simulation results show that ADP can have a very good short-term performance as well as the precise long-term achieved ratios among classes independent of any traffic intensity or class load distribution. It is also robust for bursty traffic pattern and suitable for multiple classes.
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