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Making a Delay based Protocol Adaptive to Heterogeneous Environments Kiran Kotla and A L Narasimha Reddy Texas A M University kiran cs reddy ece tamu edu Abstract This paper investigates the issues in making a delaybased protocol adaptive to heterogeneous environments We address how a delay based protocol can compete with a lossbased 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 Keywords Congestion protocol delay based ns 2 simulations emulations incremental deployment high speed links I INTRODUCTION Multimedia applications have low delay and low loss requirements Currently applications either use UDP or TCP as transport protocols UDP does not provide congestion control and applications employing UDP have to incorporate congestion control TCP s in order reliable delivery may not be necessary for multimedia applications A number of congestion control approaches have been proposed to replace TCP to move networks towards higher multimedia

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