M22: How to keep the GPRS connection alive

[techie]

telit socket dial problem

Using the M22 in M2M with built in TCP/IP stack, if I need to communicate with 2 servers (1 for HTTP and one for SMTP). But when the connection to one server is disconnected, the M22 also drops the GPRS connection and thus a packet is charged.

Is there a way to keep the GPRS connection alive and switch TCP connections.

 

[pisoiu]

gprs connection example socket mode

If you have separate AT commands for attaching to the GPRS context (and get an IP address from the network) and for "dialing" a TCP socket, you can do this. Otherwise it's imposible, dialing a TCP socket means attach to GPRS context then establishing TCP connection, and closing the TCP connection means also detaching from GPRS context. Simcom and Telit has this feature, I don't know about M22. Older implementation of TCP/IP stacks inside of GpRS modems have this problem.

/pisoiu

 

[techie]

attaching gprs

Then I can practically not use the M23 to download a web page. Downloading a web page (with images etc) means that the TCP socket is broken after each file. It would be impossible to do it with this scheme.

 

[pisoiu]

Basically yes. I had the same problem with Telit. They have not offered this feature in their implementation for the first firmware versions, and for each socket opened I had to pay for a one whole packet. This was particulary annoying because the transfers were very small in size, few tens of bytes. Later updates in their firmware included the posibillity to attach to the GPRS context then dial TCP sockets at will, in separate steps. Check if for your modem are some firmware updates available, maybe you'll have some luck.

/pisoiu

 

[techie]

M22 is very poorly supported. There is no website in English and it is practically impossible to get to talk to the support service.

What command do you use for the GPRS connection and for TCP dialing. Maybe I can try these on M22 and see if these are already implemented on M22. They could well be.

 

[pisoiu]

No chance. TCP/IP stack implementations in GSM/GPRS modems is no standardised at all, and chosing AT commands for this is at free will of the designer. For example, at telit you have to configure APN, user name and password for access with three diffrent AT commands instead of just one command for Simcom. Also, attaching to the GPRS context means one command for telit, two for simcom, and then for dialing TCP socket just one command for both. Buth the syntax is completely diffrent for each modem. If you really want to try, check the documentation of both modem. For telit, go to www.telit.co.it , then browse the GM862 model, you will find a download link. For simcom, look here , there are some datasheets.

/pisoiu