Modelling differentiated services in conservative PDES

This paper explains how DiffServ has been implemented in an IP network simulator using an asynchronous conservative parallel discrete event simulation (PDES) kernel. DiffServ provides quality of service (QoS) functionality for IP networks and is designed to provide greater scalability and lower overhead than previous IP based QoS schemes. The paper explains the DiffServ components that have been implemented, focusing on the implementation of the preemptive network buffers required to provide DiffServ functionality. Certain optimisations possible for non-preemptive network buffers are not possible here. The paper explores which will work in the preemptive case. In particular, exploiting lookahead is more difficult leading to reduced performance in some cases. Optimisation schemes are described for two different preemptive buffering strategies and performance results demonstrating the costs of using these buffers are presented.