Packet schedulers to provide proportional delay differentiation and reduce packet queueing delay simultaneously

The proportional delay differentiation model provides controllable and predictable delay differentiation, that is, the packet delay proportion between two classes of services is consistent on any measured timescale. Previous studies have focused on improving the accuracy of the achieved delay proportion-between classes, and have not considered reducing the packet queueing delay since these proposed scheduling algorithms are independent of the packet service time, such that the mean queueing delay is invariant, as specified by the conservation law. This paper proposes maximum WTP (MWTP), variance WTP (VWTP), and counting WTP (CWTP) schedulers, modified from the waiting-time priority (WTP) algorithm which is an excellent scheduler for performing proportional delay differentiation. All of the proposed schedulers account for the packet transmission time. Simulation results indicate that when the link utilization is moderate, the three schedulers not only yield a more accurate delay proportions than the WTP scheduler, regardless of whether the timescale is long or short, but also reduces the mean queueing delay.