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Re: [lwip-users] Receive window problem

From: Kieran Mansley
Subject: Re: [lwip-users] Receive window problem
Date: Mon, 22 Jun 2009 09:13:54 +0100

On Fri, 2009-06-19 at 18:21 +0200, address@hidden wrote:
> I encountered the following problem:
> With the start of transfer the receive window is 6144.
> The transmitter sends the first two segments, each 1460 Byte. After
> the second segment lwIP acknowledged the second segment with receive
> window 3224. Then the transmitter sends the next two segments (1460
> Byte) and lwip acknowledged the last segment with receive window 304.
> Then lwIP sends a window Update with window 3224.
> Here seams to be a problem, because the new window should be 6144. For
> what I've seen is that the window update message is generated after
> the data is given to the application.
> In all next transfers the receive window never reaches the initial
> value of 6144 again, so that buffer is vasted and newer used again.

Can you let us know which version of lwIP you're using?  The window
update code was completely re-written a few months ago, so there's a
good chance any problem you were seeing has been fixed.

If you can't upgrade, then to debug your problem I'd try setting the
window to a multiple of 1460 (it's currently a multiple of 1536), and
then experiment with making it larger and see how the behaviour changes.
I remember that the old code wouldn't always advertise an increased
window unless it could offer a lot more than it already had, which might
have been set to 50% of the total.


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