Understanding TCP dynamics in an integrated services Internet

A large number of Internet applications are sensitive to overload conditions in the network. While these applications have been designed to adapt somewhat to the varying conditions in the Internet, they can benefit greatly from an increased level of predictability in network services. We propose minor extensions to the packet queueing and discard mechanisms used in routers, coupled with simple control mechanisms at the source that enable the network to guarantee minimal levels of throughput to different network sessions while sharing the residual network capacity in a cooperative manner. The service realized by the proposed mechanisms is an interpretation of the controlled-load service being standardized by the IETF. Although controlled-load service can be used in conjunction with any transport protocol, our focus in this paper is on understanding its interaction with TCP. Specifically, we study the dynamics of TCP traffic in an integrated services network that simultaneously supports both best-effort and controlled-load sessions. In light of this study, we propose and experiment with several variations to TCP's control mechanisms with the objective of fine-tuning them for an integrated services environment. We then investigate the overheads associated with these enhancements and the benefits they provide. Finally, we show how the service mechanisms proposed here can be embedded within more elaborate packet and link scheduling frameworks in a fully-evolved integrated services Internet.