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Re: [lwip-users] problem after a packet loss event

From: Sergio R. Caprile
Subject: Re: [lwip-users] problem after a packet loss event
Date: Mon, 11 May 2015 10:11:52 -0300
User-agent: Mozilla/5.0 (Windows NT 5.1; rv:31.0) Gecko/20100101 Thunderbird/31.6.0

My 2 cents:

frame 644 gets lost
frame 651 says "send 624651"
frame 652 repeats, why ? possible software problem here, short timeout ?
frame 653 is the retransmission
frame 654 ACKs it for good
frame 655 says "send 624651" which in this context means "resume sending
after frame 650". Your device buffered content in 645+647+648+650 = 4 x

There is a 125ms delay between 654 and 655. Looks like something went
out of sync inside your device. What are you exactly doing with that
much data you are receiving ? Is it possible that you store it somewhere
and that somewhere takes more than expected and a timer times out and
then is improperly reset and immediately times out again and the system
goes nuts ?
Why did 644 get lost ? This is between your PC -> your device. Hardware
? Driver ? Looks like a driver not attend in due time problem.
My best guess on the window is that lwIP reduces its size based on the
ACK delay between frames 650 and 655, which is the time it took for your
app to tell the stack to resume sending.
I can't guess why the PC doesn't fill that window, that depends on the
app in your PC afaik, but I can tell you that 2352 is not a multiple of
TCP_MSS, so only 1 fits in there. Nagle ?

Good report, btw


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