netdev - Re: the congestion window rfc2001

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Date:	Tue, 13 Aug 2013 07:29:51 -0700
From:	Yuchung Cheng <ycheng@...gle.com>
To:	Dong Fang <yp.fangdong@...il.com>
Cc:	netdev <netdev@...r.kernel.org>
Subject: Re: the congestion window rfc2001

Please ask those questions on more relevant list such as
tcpm@...f.org. This list is for discussing Linux kernel networking
development, not generic TCP protocol.

On Tue, Aug 13, 2013 at 4:35 PM, Dong Fang <yp.fangdong@...il.com> wrote:
> hi, all
>
>
> http://tools.ietf.org/html/rfc2001
>
>
>    1.  When the third duplicate ACK in a row is received, set ssthresh
>        to one-half the current congestion window, cwnd, but no less
>        than two segments.  Retransmit the missing segment.  Set cwnd =
>        ssthresh + 3 times the segment size.  This inflates the
> -- what is the meaning of '3'
>
>        congestion window by the number of segments that have left the
>        network and which the other end has cached (3).
>
>    2.  Each time another duplicate ACK arrives, increment cwnd by the
>        segment size.  This inflates the congestion window for the
>        additional segment that has left the network.
> -- why do this
>
>        Transmit a packet, if allowed by the new value of cwnd.
>
>    3.  When the next ACK arrives that acknowledges new data, set cwnd
>        to ssthresh (the value set in step 1).  This ACK should be the
>        acknowledgment of the retransmission from step 1, one round-trip
>        time after the retransmission.  Additionally, this ACK should
>        acknowledge all the intermediate segments sent between the lost
>        packet and the receipt of the first duplicate ACK.  This step is
>        congestion avoidance, since TCP is down to one-half the rate it
>        was at when the packet was lost.
> --
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