A Simulation Study of Cross Traffic on Expedited Forwarding in Differentiated Services Networks.

Abstract

The purpose of this research was to simulate Differentiated Services enabled network topologies in order to study cross traffic impact on the Expedited Forwarding (EF) Per Hop Behaviors (PHBs). The results help us understand the extent to which packets tagged for Expedited Forwarding can be protected, and the guarantees that can be given to EF flows. Cross traffic and EF can exist and interact in many ways. This study analyzed two types of cross-traffic. In the first case a single EF micro-flow was considered, while all other EF micro-flows as well as any best effort traffic, was considered to be cross traffic that could affect this EF micro-flow. This case was analyzed under two conditions: a) a single EF micro-flow consisting of packets of small size, and b) a single EF micro-flow consisting of large packets. In the second case, the EF aggregate as a whole was considered composed of EF micro-flows of small as well as large packets, and any best effort traffic was considered cross-traffic that could affect the EF aggregate as a whole. Two schedulers, namely the Priority Queue Scheduler and the Weighted Round Robin Scheduler, were used to simulate the EF PHB and a comparison was made to determine which could provide better Quality of Service guarantees. Possible metrics for quantifying Quality of Service provided to the EF PHB were also investigated. Further, the bounds on the recent redefinition of the EF PHB by IETF were also studied. A variant of the EF PHB, called the Delay Bound (DB) PHB was defined by IETF. The DB PHB was studied, and recommended values for parameters that characterize the DB PHB were presented. Finally end-to-end Quality of Service obtained from the EF Per Domain Behavior was studied across multiple autonomous Differentiated Services domains governed by common Service Level Agreements.