topic Re: RTCS TCP window size issue in MQX Software Solutions

RTCS TCP window size issue

brieuc — Thu, 07 Aug 2014 15:07:41 GMT

Hello

I'm currently evaluating the network performances of the Cortex-M4 core in the Vybrid VF6 SoC. For that I'm running a TCP server on MQX to receive any incoming tcp packet. A client sends packets to the server and records the debit. The server is a modified version of the eth-to-serial example.

The problem is that the TCP rx buffer isn't flushed by the software (I think), as a result the tcp window size decreases until I get a "TCP WINDOW FULL" packet . Increasing the size of the buffer using the OPT_RBSIZE option isn't a solution since the error is still present but appears later. The measured debit is very low compared to what I could expect (about 10 times less).

Do you have any idea why the buffer isn't emptied fast or hint about the origin of this error. Please find attached the modified demo.c file and the wireshark capture of the packets (192.168.0.44 is the Vybrid).

Brieuc

Original Attachment has been moved to: mqx_capture.zip

Original Attachment has been moved to: demo.c.zip

Re: RTCS TCP window size issue

alejandrolozan1 — Tue, 12 Aug 2014 15:44:37 GMT

Hi,

Let me test your code, I will see if I can find the problem.

Best Regards,

Alejandro

Re: RTCS TCP window size issue

brieuc — Wed, 13 Aug 2014 06:50:15 GMT

Hello

Do you want the linux executable i'm using to inject data packets ?

Regards

Brieuc

Re: RTCS TCP window size issue

alejandrolozan1 — Wed, 13 Aug 2014 23:11:04 GMT

Sure!!, If it is possible

Re: RTCS TCP window size issue

chris-quin — Tue, 13 Oct 2015 07:24:00 GMT

Hello,

i got the same Problem. Every transmission the window size is reducing when a packages is received and after x packages it returns to normal.

Example:

I have a window size of 300Bytes and i'm sending packages with about 250bytes. After every package the window is reducing by 10Bytes.

1. -> 300

2. -> 290

....

6. -> 240

After 6 Transmission the window size is to small to receive a complete packages and Data is lost.

If i sending packages with about 100bytes the windows size is also counting down, but after about 12 packages it returns to normal.

So, are there news about this issue??

Best regards, Chris

Re: RTCS TCP window size issue

chris-quin — Tue, 20 Oct 2015 15:05:17 GMT

The Reason is, that the window size depends on the buffer size of the socket. Every single time a packet is received, the function TCP_Advertise_receive_window checks if it has to send an acknowledge with the new window size. The information about the new window size will only send, if half of the buffersize was used and only increment ist about the half of the buffer size.

So the solution is to increase the buffersize of the socket 2 times larger then the maximum expected packet size.