Much industry attention has recently been focused on providing differentiated levels of service to users on IP 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.
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