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    SubjectRe: TCP, congestion window & retransmission
       Date: Wed, 11 Nov 1998 17:31:37 +0100 (CET)
    From: Andrea Arcangeli <>

    According to the RFC2001 in case of duplicate acks or timeout TCP
    has to do slow-start until TCP has not the congestion window open
    to the value of sstresh (set to max(cwnd/2,1) before -> at timeout
    time). When the congestion window is >= sstrash, TCP must go in
    congestion avoidance incrementing cwnd of segsize*segsize/cwnd and
    at most incrementing of 1 unit every RTT (this way cwnd increase
    liner and not exponential).

    rfc2001.bis draft clarifies the issue here, and states that our
    current behavior is in spec. The idea is that if you don't increase
    the congestion windows at all during timeout based retransmissions,
    this is being concervative and is OK. A copy of this draft is
    available from:

    In any event, it's bad for performance not to do the congestion window
    increases, so I've made the "fix" in tcp_input.c which I'll send to
    Linus shortly.

    David S. Miller

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