High-performance scheduler to achieve proportional delay differentiation

The proportional delay differentiation model provides a consistent packet delay differentiation between various classes of service. The waiting time priority (WTP) scheduler is a priority scheduler in which the priority of a packet increases in proportion to its waiting time, and it is known to be the best scheduler to achieve the proportional delay differentiation model. The author proposes an advanced WTP (AWTP) scheduler, modified from WTP, that accounts for the packet transmission time. Simulation results reveal that when the link utilisation is moderate (60%-90%), this scheduler not only obtains a more accurate delay proportion than the WTP scheduler, no matter whether in short or long timescales, but also reduces the average queueing delay (waiting time). The effects of traffic load distribution, and the mean packet size and its coefficient of variation on both schedulers´ performance are also examined. AWTP always outperforms WTP in these cases. However, AWTP may not maintain stable delay ratios under some traffic load distributions. A modification named AWTP⁺ is proposed and proved to overcome this problem.