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Re: [lwip-users] TCP window update and TCP DUP ACK

From: Kieran Mansley
Subject: Re: [lwip-users] TCP window update and TCP DUP ACK
Date: Thu, 25 Nov 2010 14:12:04 +0000

On Wed, 2010-11-24 at 07:08 -0800, deepaknaik wrote:
> Hello all, 
> I am using LWIP 1.3.1 version which is ported on my board. I have a web page
> in my flash which is more then 40KByte. I have connected the board with the
> PC using Cross cable to access the webpage from board continously. But
> inbetween PC stop accessing the web page from board. I have captured the
> transaction between PC and my board using Ethereal. When I go through the
> capturing details, PC sends TCP window update request to my board. And after
> some transaction I am getting "TCP DUP ACK" and transaction stops. 

It looks like two packets from the lwIP end have been dropped.  lwIP
should wait a little while and then retransmit them but either it
doesn't or they also get dropped.  My guess would be that the lwIP
timers aren't getting called correctly as the TCP retransmission code in
lwIP is based around these timers.  Alternatively there is some problem
like lwIP has run out of packet buffers because they haven't been freed
properly.  Is this problem repeatable?  Is it always the same?


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