Simultaneous SMS and GPRS internet connection


I’m working with a system that needs to have an always on internet connection so it uses a GPRS modem and keeps the PPP link up the whole time. This application also needs to be able to send and receive SMS messages. I know that one solution is to use an SMS gateway to send the SMS messages (over the Internet, e.g. email to SMS gateway), but for various reasons we would like to send and receive the SMS messages from the GPRS modem. Is this possible?
We would probably have to use both UARTs (so that one UART handles the data link for the PPP/internet connection and the second UART is in AT command mode so that it can send and receive SMS) or use CMUX multiplexing.
Apparently modems that are “Class A” GPRS modems can send and receive SMS while a GPRS data connection is active - are the Q24 series modems “Class A”?
If not we would have to regularly drop the PPP connection and check for SMS (not a nice solution).


I may have found something that will handle the multiplexing.
Two options, gsmd ( which is part of the OpenMoko project apparently has a driver that does what we want (see this post )
Also gsmmux ( ).


In an Open-AT application, you can still use the SMS Service while a GPRS session is open.


That’s what I would have thought, but the local Wavecom distributor has told me that none of the Wavecom products support Class A operation so they can’t do it.
Also, unfortunately I am not using OpenAT, because I need a standard PPP connection over GPRS.
Mind you, I guess I could write an OpenAT application that didn’t use the TCP/IP stack and just forwarded the data and in the back ground handled the SMS, but if the modem is capable of this then it shouldn’t be necessary to run an OpenAT application.