TCP-aware packet marking in networks with DiffServ support

Abstract

In the context of Differentiated Service, the Assured Forwarding class recently proposed by the IETF offers the capabilities of distinguishing two or more classes of packets, based on bit marking in packet headers. Originally, packet marking was intended to be performed according to the aggregate user-profile in the DiffServ model. In this paper we show the benefit of an alternative strategy in which packet-marking is based on the states of individual TCP flows. The marking scheme can be implemented either in end systems or ingress routers, where the number of concurrent flows is limited, thus allowing per-flow management of packets. In addition, it can be integrated with a marking scheme that is based on the user-profile. Through extensive simulations, we show that the proposed scheme can improve the throughput of long lived TCP flows by up to 20%, and reduce by half the completion time of short lived TCP flows, such Web traffic is. These gains are consistent over different TCP variants, such as TCP-RENO and TCP-SACK, and even in the presence of ECN.