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Friday, April 20th 2007, 5:29pm

UDP communication

Q: Type of module? A: GM862-GPRS - GSM900/1800 voice/data/fax module
Q: Firmware version? A: 1.05.000 GM862-GPRS
Q: Type of starter kit you have? S2

We are trying to communicate with UDP but are running into problems when trying to receive data. We set up the connection with


And on the other end (a UNIX workstation running netcat at the moment) we receive data. However, when sending data from the UNIX workstation and back to the module, it does not show up on our terminal. How come?

By monitoring the transactions with tcpdump on the UNIX end, we know that all port numbers are correct, in both directions. Also, by running netcat against other workstations using other technology, we know that our commands using netcat are correct for both receiving and sending data.

Another issue is that we don't seem to be able to terminate the data transfer mode once established. UDP is of course connectionless, but we would like to be able to stop sending packets and continue with AT-commands as before opening the UDP socket. The lack of escape sequence for UDP hints that it might not be possible, but this does sound very odd. Why wouldn't we be able to stop sending UDP packets? Of what use is the UDP functionality without this option?

We have successfully sent data back and forth using TCP connections, although no data is displayed in the test software terminal until the connection is terminated on the other end. Sending +++ to terminate the connection from the terminal side seems to do nothing. (AT#SKIPESC returns 0).

Since we are stuck with an old module and this is not subject to change, switching module is not a viable solution to our problem.

We have read this other thread but to no avail.

Cosmin Buhu



Monday, April 23rd 2007, 3:23pm

Please update your User Profile including your Round Solutions customer number, link on top of page, thank you.


Tuesday, April 24th 2007, 10:53am

The project is educational, and unfortunately we do not currently have access to the customer number used by the university's purchasing department.

Cosmin Buhu



Tuesday, April 24th 2007, 11:34am

OK, then you have teachers conducting and helping with your project right? We would like to help you through your professor, please tell him to address the question (and have the Round Solution customer number handy).

I think you agree we cannot support thousand of students on one kit purchase. Thank you for understanding.


Tuesday, April 24th 2007, 3:53pm

This is a part of our bachelor thesis, and there are no other students using the kit. There are no thousands of students here, we are three students, one board (and other materials ordered from RoundSolutions for a couple of houndred Euros), and one project. Our instructor has never used the board in question so the documentation and online resources are our only sources for specific technical details. However, we will try to communicate with you through our instructor if you see fit.

Meanwhile, our question remains: Is it possible to communicate in dual directions with UDP using this module?

By the way, we've upgraded the firmware to 1.05.002 GM862-GPRS.

Edit: We have supplied the customer ID in our user profile.

This post has been edited 1 times, last edit by "rov" (Apr 24th 2007, 4:05pm)


Tuesday, April 24th 2007, 4:54pm

Hi rov,

I know from anlaog modems that you have to take care about the timing of sendig +++. I think in front of it, there must be a silent time space and the "+" must not sent to fast to the next "+". Maybe this helps? But I also don't know if this helps during UDP communication ?(.



Tuesday, April 24th 2007, 5:48pm

Thanks Norbert, we had read about the silence requirement, but we hadn't seen anything about timing between "+" and "+"... We'll look into it!


Sunday, April 29th 2007, 4:48pm

We have now looked into it and managed to get birectional UDP communication going. Leaving the bundled TelitTest.exe behind and using a proper terminal application helped for getting the UDP part working, and the timing between the pluses solved the problem with aborting a "connection".

Thank you for your help!

Cosmin Buhu


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