Sustaining TCP throughput using assured forwarding and ECN in a Differentiated Services network

This paper examines the interaction among the congestion control mechanisms built into the Transmission Control Protocol (TCP), the Assured Forwarding (AF) PHB of Differentiated Services (DiffServ) mechanism, and Explicit Congestion Notification (ECN) mechanism. We show that ECN improves the fairness in sharing excess bandwidth among different AF flows. We then propose two mechanisms: (a) an out marking scheme, and (b) throughput sustaining scheme to foster cooperation between ECN and AF mechanisms to further improve the throughput of TCP sources. Our results show that the new schemes achieve significant improvement in the TCP throughput performance.