Can two GSM modules communicate directly?
It depends on your network provider
That means if certain specifications are met, they can, right? Can you give me an example?
for example, if both of your modules can get a public IP address, then they can communicate to each other directly.
Did you mean can two units connect directly to each other without sending traffic via a network such as with Bluetooth? If so then the answer is no, all traffic has to go via a PLMN.
When connected to a network the units will obviously be able to call and SMS each other.
For IP based traffic its a bit more complicated.
- If they are on different networks then one of them would need to have a public IP address assigned to it to enable the the second unit to connect to but for any unit to connect to any other unit they would all need public IP addresses. Operators do not give these out at all as they are very valuable.
- Potentially if they are on the same network and APN then depending on the operator they might be allowed to connect to each other, it is all down to the routing and rules within the network. As an example when using Sierra SIM’s we do not allow inter unit communication at all.
Thanks @mlw, that really cleared things out for me. Does this also apply to the GSM modules which we connect to microcontrollers ?
To keep it in simple, if you are talking about a GSM modem like the HL6528 (2G), HL8548 (2G/3G), WP7607 (2G/3G/4G) which you would connect to a micro through it its UART, USB, etc, then yes the above applies, all data has to go through a PLMN.
I’m talking about modems like SIM900A.
So that would be a SIMCOM module and this being the Sierra forum, I am afraid I cannot comment on their units.