Performance analysis of a priority queue: Expedited Forwarding PHB in DiffServ

This paper studies a two-class priority queue in order to model a DiffServ router with Expedited Forwarding Per-Hop Behavior for high-priority traffic. Normally, queueing models assume infinite queue capacity but in a DiffServ router the capacity for high-priority traffic is often small to prevent this traffic from monopolizing the output link and hence causing starvation of other traffic. The presented model takes the exact (finite) high-priority queue capacity into account and introduces a framework for queue management algorithms, enabling determination of high-priority packet loss and its influence on the performance of the system. Analytical formulas for system content and packet delay of each traffic class are determined. Numerical examples indicate the necessity of modelling the high-priority queue as finite in order to accurately capture performance in a DiffServ environment.