外文翻译--拥塞控制中的算法.docxVIP

译文2 The Algorithm of Congestion Control1．Tahoe TCP Modern TCP implementations contain a number of algorithms aimed at controlling network congestion while maintaining good user throughput. Early TCP implementations followed a go-back-n. model using cumulative positive acknowledgment and requiring a retransmit timer expiration to re-send data lost during transport. These TCPs did little to minimize network congestion. The Tahoe TCP implementation added a number of new algorithms and refinements to earlier implementations. The new algorithms include Slow-Start, Congestion Avoidance, and Fast Retransmit. The refinements include a modification to the round-trip time estimator used to set retransmission timeout values. All modifications have been described elsewhere.The Fast Retransmit algorithm is of special interest in this paper because it is modified subsequent versions of TCP. With Fast Retransmit, after receiving a small number of duplicate acknowledgments for the same TCP segment (dup ACKs), the data sender infers that a packet has been lost and retransmits the packet without waiting for a retransmission timer to expire, leading to higher channel utilization and connection throughput.2．Reno TCPThe Reno TCP implementation retained the enhancements incorporated into Tahoe, but modified the Fast Retransmit operation to include Fast Recovery. The new algorithm prevents the communication path (“pipe”) from going empty after Fast Retransmit, thereby avoiding the need to Slow-Start to refill it after a single packet loss. Fast Recovery operates by assuming each dup ACK received represents a single packet having left the pipe. Thus, during Fast Recovery the TCP sender is able to make intelligent estimates of the amount of outstanding data.In Reno, the senders usable window becomes other gateways that fail to monitor the average queue size) until the number of dup ACKs reaches tcprexmtthresh, and thereafter tracks the number of duplicate ACKs. Thus, during Fast Recovery t