CSD call not working on EHS5-E | Telit Cinterion IoT Developer Community

Hi,

I'm working wih the following scenario:

1) a desktop GSM modem based on TC65i engine, conntected to a PC

2) a device manufacured by our company, based on a EHS5-E engine

The test we are doing is the following:

- the GSM modem make a CSD call to the EHS5-E based device, using AT command (e.g.: ATD number)

- a Java midlet on the EHS5-E engine should receive the "RING" URC and answer the call (ATA)

This test is not working, because teh EHS5-E engine NEVER receives the RING.

But I've found a trick that makes it working: if I set the RAT (Radio Access Tecnhnology) as follows:

AT^SXRAT=0,0

that means Access Technology = GSM and preferred RAT = GSM

it works!

But, this could not be the solution for us, because in other use cases we would like to have 3G packet data connections to send/receive data to remote servers.

So the question is: is it necessary to set EHS5-E engine in GSM only mode to receive CSD calls ? 

Could the problem be related to something regarding SIM type (we have a 4G SIM) or operator issues ?

Thank you very much for your help.

Best regards

Marco