Re: [lwip-users] Issues receiving streaming data

[JM]

Thank you for the quick reply Kieran.  After looking at these settings again, and finding an old post where you give a rough estimate for MEMP_NUM_TCP_SEG, I believe I have this set way too low.  I will try your suggestions later and see what happens.  Some of the defaults, such as PBUF_POOL_SIZE = 16, is so high it will consume too much RAM.  My guess is I can get by with much less. 

Oops....for the TCP_WND discrepancy, that's easy to explain.  I changed it after taking the capture, but it the Wireshark results were basically the same.

I will enable Stats and I can view them with my debugger after it runs for awhile.  That is something I haven't thought of before and should give good information.  I'll set these numbers high, and try shrinking them until things stop working.



--- On Thu, 7/30/09, Kieran Mansley <address@hidden> wrote:

From: Kieran Mansley <address@hidden>
Subject: Re: [lwip-users] Issues receiving streaming data
To: "Mailing list for lwIP users" <address@hidden>
Date: Thursday, July 30, 2009, 10:05 AM

On Thu, 2009-07-30 at 05:26 -0700, JM wrote:
>
> I've included two Wireshark captures in an attached .zip file (please
> add .zip to filename).  The one labeled "lan" is when the server was
> my computer on my LAN, and the one labeled "wan" is a streaming audio
> server on the Internet.  I've verified these both work fine when a
> computer is is playing the stream.  On the "lan" trace, there is a
> perfectly repeated Dup ACK and retransmission that should not be
> happening.  On the "wan" trace, the connection just seems to break
> down before I close it.  This is similar behavior to all other
> Internet streaming audio servers, so it's not just this one. 

The retransmissions are happening because there are packets being
dropped.  They are repetitive because after packet loss the sender is
very cautious about the sending rate.  As soon as the sending rate
increases, you see packet loss.  This suggests strongly that your lwIP
device can't handle > 1 packet arriving at a time, and so you're likely
running out of buffers.  You could confirm this by using the lwIP stats,
and seeing which of the buffer types are reporting errors (if you can
get a print out of these somehow).

Looking at your settings, I think it would be good to change:

MEMP_NUM_PBUF: you'll need more than one of these, I'm pretty sure.
PBUF_POOL_SIZE: 3 seems rather small.  What's the default here - see
src/include/lwip/opt.h
MEMP_NUM_TCP_SEG: only having 2 TCP segments is going to cause you
problems
LWIP_UDPLITE: you can probably set this to zero
TCP_SNDBUF: you could set this larger (smallest sane size is two MSS)
without using any extra memory, but probably not the source of your
problems as you're not sending much.

Something that looks odd to me is that you're setting TCP_WND to 2920,
but in the packet captures lwIP is giving out a larger receive window of
4380. 

Kieran



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