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    SubjectRe: Excessive TCP retransmits over lossless, high latency link
    > I don't see what is broken about the remote end in this case.

    The remote end is probably not broken, at least in this
    case. This looks like an artifact of a disgustingly
    large queue, and a very slow link. When the time to
    transmit tiny packets in the initial handshake is much
    smaller than the time to transmit a full size frame,
    retransmission timers can get confused. A complete trace
    would settle this.

    I strongly recommend setting the mtu of your ppp0 interface
    down to 576 (or smaller) to reduce the time it takes to
    transfer a full size frame, decrease the likelihood that
    frames suffer corruption, and allow acknowledgements more
    often than every 5 seconds. This is a setting in your ppp
    configuration, don't do this using ifconfig.

    Don't take my word for it, see RFC1144, section 5.2: a
    good MTU is chosen so that a full size frame is transferred
    in 200ms.

    RFC1144, written by Van Jacobson:

    To illustrate, note that for a 9600 bps line with
    header compression there is essentially no benefit
    in increasing the MTU beyond 200 bytes: If the MTU is
    increased to 576, the average delay increases by 188%
    while throughput only improves by 3% (from 96 to 99%).

    Besides, if you do what you propose (not ack old data with the
    next byte expected) you risk stalling the connection entirely.


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      Last update: 2005-03-22 13:17    [W:2.984 / U:0.048 seconds]
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