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[lwip-users] Re: lwip-users Digest, Vol 49, Issue 22

From: Yang
Subject: [lwip-users] Re: lwip-users Digest, Vol 49, Issue 22
Date: Wed, 19 Sep 2007 16:38:12 +0800

 HI, Kieran 
    There's a question I didn't understand: why you said that the
retransmitting wait time in my tarce is 150ms. Is the time in ethereal
is count in seconds. I think that is is more like 15ms?  
    I still not find out why my port wait so short a time!
>On Thu, 2007-09-13 at 11:16 +0800, Yang wrote:
>> Hi Kieran!
>>   The trace is in attach file. It's a ftp server I wrote with lwip
>> socket.
>> You can see that if data is send both side, in control link, it work
>> fine.
>> but as data link send file to PC, retrans happends. 
>Hmm, I see retransmissions in both parts (both control and data
>transfer) of the connection.  Which end of the connection is lwIP, and
>which end something else?
>My guess from looking at the trace is that the receiving end is using
>delayed ACKs (it only acknowledges every other packet) and this is fine
>when the sender has enough data to send two packets.  However, if it
>only sends one packet, the receiver is supposed to time out and send an
>ACK anyway.  This isn't happening before the sender gives up waiting for
>an ACK and retransmits.  The problem is I think with the sender as it's
>not waiting long enough for the ACK, rather than with with the
>receiver's delayed ACK.  It should be waiting at least 200ms before
>retransmitting (or more like 1 second to be fully RFC compliant), but
>they're all coming out faster than that - more like 150ms.
>If lwIP is the sender, I would check that the TCP timers are being
>called with the correct intervals.


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