Improving the Performance of TCP over the ATM-UBR service

In this paper we study the design issues for improving TCP performance over the ATM UBR service. ATM-UBR switches respond to congestion by dropping cells when their bu ers become full. TCP connections running over UBR can experience low throughput and high unfairness. Intelligent switch drop policies and end-system policies can improve the performance of TCP over UBR with limited bu ers. We describe the various design options available to the network as well as to the end systems to improve TCP performance over UBR. We study the e ects of Early Packet Discard, and present a per-VC accounting based bu er management policy. We analyze the performance of the bu er management policies with various TCP end system congestion control policies including slow start and congestion avoidance, fast retransmit and recovery and selective acknowledgments. We present simulation results for various small and large latency con gurations with varying bu er sizes and number of sources.