ATM-UBR switches respond to congestion by dropping cells when their buffersbecome full. TCP connections running over UBR experience low throughput andhigh unfairness. For 100% TCP throughput each switch needs buffers equal to thesum of the window sizes of all the TCP connections. Intelligent drop policiescan improve the performance of TCP over UBR with limited buffers. The UBR+service proposes enhancements to UBR for intelligent drop. Early Packet Discardimproves throughput but does not attempt to improve fairness. Selective packetdrop based on per-connection buffer occupancy improves fairness. The FairBuffer Allocation scheme further improves both throughput and fairness.
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