Making a Delay-Based Protocol Adaptive to Heterogeneous Environments

This paper investigates the issues in making a delay-based protocol adaptive to heterogeneous environments. We address how a delay-based protocol can compete with a loss- based protocol such as TCP. We investigate if potential noise and variability in delay measurements in environments such as cable and ADSL access networks impact the protocol behavior significantly. We investigate these issues in the context of incremental deployment of a new delay-based protocol, PERT. We propose design modifications to PERT to compete with SACK. We show that PERT experiences lower drop rates than SACK and leads to lower overall drop rates with different mixes of PERT and SACK protocols. Second, we show that a single PERT flow can fully utilize a high-speed, high-delay link. The results from ns-2 simulations indicate that PERT can adapt to heterogeneous networks and can operate well in an environment of heterogeneous protocols. We also show that proposed changes retain the desirable properties of PERT such as low loss rates and fairness, when operating alone. The protocol has also been implemented in the Linux kernel and tested through experiments on live networks, by measuring the throughput and losses between nodes in our lab at TAMU and different machines on the planet-lab.