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

[John Hoffman]

Nice setup.

I am using a TI LM3S9B92 which has an on board PHY. That's why I don't think I 
am experiencing packet loss.


-----Original Message-----
From: address@hidden [mailto:address@hidden On Behalf Of Fabrizio Beltrandi
Sent: Wednesday, May,13, 2015 10:46 AM
To: 'Mailing list for lwIP users'
Subject: [lwip-users] R: R: problem after a packet loss event

Hi,
I use a second PC (with two separate ethernet port) between embedded board
and PC host. Traffic is redirect and filtered with a custom application, so
I can receive packets from PC host and trasnmit at board except some packets
that I want loss. With this setup I can regulate ratio of packets loss too.

What is your architecture with LwIP? Fpga Xilinx with embedded micro?



-----Messaggio originale-----
Da: address@hidden
[mailto:address@hidden Per conto di John
Hoffman
Inviato: martedì 12 maggio 2015 14.43
A: Mailing list for lwIP users
Oggetto: Re: [lwip-users] R: problem after a packet loss event

What technique are you using to prove are experiencing packet loss? 

-----Original Message-----
From: address@hidden
[mailto:address@hidden On Behalf Of
Fabrizio Beltrandi
Sent: Monday, May,11, 2015 06:43 PM
To: 'Mailing list for lwIP users'
Subject: [lwip-users] R: problem after a packet loss event

Hi,
when I receive data in my receive callback I only copy packet data in
another buffer with DMA, then I think that my firmware application doesn't
take more time than expected one. In my main instead I have a loop while
where at the maximum speed I perform a call at xemacif_input() function
continuosly. I don't know why, after packet loss, my app needs about
120 ms to get every packet. I think that during packet loss recovery happens
something that disrupt synchronism, but I don't know if this is in my app or
in lwip stack. Hardware should be ok because I am working with microZed and
carrier board that are Xilinx reference boards. Tomorrow I'll try to augment
memory parameters in LwIP, and I'll disable all possible other pieces of
software don't relevant in reception of data. Further I'll try to trace
timing and duration of receive callback and xemacif_input() calls with aid
of hardware signal flag and oscilloscope.
I'll tell you results


-----Messaggio originale-----
Da: address@hidden
[mailto:address@hidden Per conto di Sergio
R. Caprile
Inviato: lunedì 11 maggio 2015 15.12
A: address@hidden
Oggetto: Re: [lwip-users] problem after a packet loss event

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
TCP_MSS

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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