Re: [tcpm] taking RFC 2861 (Congestion Window Validation) to Proposed Standard?

John Heffner <> Mon, 18 June 2007 22:24 UTC

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Date: Mon, 18 Jun 2007 18:15:46 -0400
From: John Heffner <>
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To: Sally Floyd <>
Subject: Re: [tcpm] taking RFC 2861 (Congestion Window Validation) to Proposed Standard?
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Sally Floyd wrote:
> This email is to ask the working group if RFC 2861 on Congestion
> Window Validation (CWV) should be left at Experimental, or whether
> it is time to start the process of moving it to Proposed Standard.
> RFC 2861, from June 2000, "describes a simple modification to TCP's
> congestion control algorithms to decay the congestion window cwnd
> after the transition from a sufficiently-long application-limited
> period, while using the slow-start threshold ssthresh to save
> information about the previous value of the congestion window.
> RFC 2861 also recommends that "the TCP sender should not increase
> the congestion window when the TCP sender has been application-limited
> (and therefore has not fully used the current congestion window)".
> My understanding is that CWV has been included in Linux since
> Linux 2.4, but that it is not included in Microsoft.
> Are there any experience reports about CWV (positive or negative),
> or experience reports of problems (or the absence of problems) for
> TCP connections without CWV?  Or are there other opinions about
> whether it is time to start the process of moving RFC 2861 to
> Proposed Standard?  Any feedback would be welcome.

There have been enough reports of performance problems with 
intrinsically bursty applications that an option was added to Linux to 
disable cwnd decay.  (It is still enabled by default.)  I'm not aware of 
any issues with the "not raising cwnd when application-limited" part.


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