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Re: [lwip-users] Duplicate ACK problem with LWIP 1.3.2

From: address@hidden
Subject: Re: [lwip-users] Duplicate ACK problem with LWIP 1.3.2
Date: Wed, 06 Jan 2010 17:40:54 +0100
User-agent: Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10.6; de; rv: Gecko/20091204 Thunderbird/3.0

Please attach wireshark captures in wireshark's own file format, not as text export or any other format to make sure they are readable.


Hafiz Bashir wrote:

We seem to have a problem when using LWIP 1.3.2 to request a large file 
from a remote server. Our target is an ST7101 running OS21.

Our application uses the netconn API to request a large file from a 
remote server using HTTP GET

 From what I can see from Wireshark, the transfer begins OK with correct 
ACK's being sent.

However at what appear to be random points during the transfer, I start 
to see duplicate ACK's. It seems LWIP is sending the same ACK for the 
next few segmemts it receives.

I have experimented with adjusting the TCP_WND size in lwipopts.h with 
mixed results. It would appear that if TCP_WND > 8*TCP_MSS, then we 
start seeing the duplicate ACK problem. TCP_MSS is set to 1460. However 
having a lower TCP_WND size results in a lower transfer performance.

I have attached a text file containing the Wireshark export.

Any help would be greatly appricated.


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