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    SubjectRe: PPP feature request (Tx queue len + close)
    Jean Tourrilhes writes:

    > Problem : IrDA does its buffering (IrTTP is a sliding window
    > protocol). PPP does its buffering (1 packet in ppp_generic +
    > dev->tx_queue_len = 3). End result : a large number of packets queued
    > for transmissions, which result in some network performance issues.

    How much buffering does IrTTP do? How large is its window? It is
    much more critical IMO to reduce the buffering below ppp_generic than
    it is to reduce the buffering above it. The ppp_generic layer itself
    does as little buffering as possible.

    > Solution : could we allow the PPP channel to overwrite
    > dev->tx_queue_len ?
    > This is similar to the channel beeing able to set the MTUs and
    > other parameters...

    Not really, the channel can't set the bundle MTU, only its own MTU.
    It can set the header length (the desired amount of headroom) but that
    is really only an optimization.

    What would happen in the case where two channels connected to the
    same ppp unit want to set the queue length to two different values?

    In general I think it would be better to get pppd to set the transmit
    queue length than to have the channel magically influencing stuff two
    levels above it.

    Could you produce some numbers showing better throughput, fewer
    retransmissions, or whatever, with a smaller transmit queue length?

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