Bandwidth assurance issues for TCP flows in a differentiated services network

Much industry attention has recently been focused on providing differentiated levels of service to users on JP networks. One such proposal is the RIO scheme proposed by Clark [4]. RIO is an extension of the RED algorithm that relies on a differentiated drop treatment during congestion to cause different levels of service. The end result of differentiated dropping of packets during congestion is differentiated throughput rates for end-users. The IETF's Diffserv Working Group has recently standardized a PHB (Per Hop Behaviour) that is based on a differentiated drop scheme - Assured Forwarding (AF). This paper raises issues with providing bandwidth assurance for TCP flows in a RIO-enabled Differentiated Services network. The main contribution is a detailed experimental study of five different factors that impact throughput assurances for TCP and UDP flows in such a network. Our study demonstrates that these factors can cause different throughput rates for end-users in spite of having contracted identical service agreements.