UBR+: Improving Performance of TCP over ATM-UBR Service

ATM-UBR switches respond to congestion by dropping cells when their bu ers become full. TCP connections running over UBR experience low throughput and high unfairness. For 100% TCP throughput each switch needs bu ers equal to the sum of the window sizes of all the TCP connections. Intelligent drop policies can improve the performance of TCP over UBR with limited bu ers. The UBR+ service proposes enhancements to UBR for intelligent drop. Early Packet Discard improves throughput but does not attempt to improve fairness. Selective packet drop based on per-connection bu er occupancy improves fairness. The Fair Bu er Allocation scheme further improves both throughput and fairness.