Measurements on an experimental ATM switch in a local area network have demonstrated significant performance gains for TCP traffic with ATM-level flow control. Without flow control, buffer overruns at ATM switches feeding into bottlenecks can prevent TCP from using more than a few percent of the potential bandwidth. A detailed analysis of the cell loss patterns that foil TCP's loss recovery strategy is presented. With flow control, efficiency is nearly perfect. ATM flow control prevents cell loss due to congestion, and as a result TCP can avoid retransmit time-out delays and maintain a high transmission rate.

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