EG25 in ECM mode and voice call at the same time

IoT Modules LTE Standard Module
1

I’m using EG25 LTE module in ECM mode on a Linux embedded box. The data connection works, I can communicate over Internet.

Now I need to make a voice call at the same time, keeping data connection on (VoLTE). I called sudo minicom -D /dev/ttyUSB3 and send the command ATD<phone>;.

After some seconds, minicom reports an error on the serial port /dev/ttyUSB3 and I see the modem disconnects from USB and reconnect again after some time.

What could be the problem?

2

hi，
Do you have a specific error code?
Please use /dev/ttyUSB2 to test it, because /dev/ttyUSB2 is an AT port.
thanks.

3

Ok I open /dev/ttyUSB2 with sudo minicom -d /dev/ttyUSB2.

However the first strange thing is that I see a few AT commands at the output of /dev/ttyUSB2, even if I don’t type anything on the keyboard. For example:

AT+CIND?
+CIND: 0,5,1,0,1,0,1,0

OK
AT+CSQ
+CSQ: 28,0

OK

I see these “internal commands” continuously, about every 20-30 seconds. It seems there is something internal that sends these AT commands that are echoed to /dev/ttyUSB2.

I sometimes received URC +CIEV too, but I couldn’t find any info about it on the manuals.

In this situation is difficult to send my AT commands, because what I type is intermixed with these “internal commands”.

Anyway, I tried again to send ATD<num>; and I receive NO CARRIER.

ATD0039....;
OK

+CIEV: 1,3

+CREG: 5,"A064","3427",0

+CGREG: 5,"A064","3427",0

+CIEV: 7,3
AT+CIND?
+CIND: 0,3,1,0,1,0,1,3

OK
AT+CSQ
+CSQ: 16,0

OK

+CIEV: 3,0

+CIEV: 7,0

NO CARRIER

+CIEV: 1,5

+CREG: 5,"A44B","1363B0B",7

+CGREG: 5,"A44B","1363B0B",7

I noticed the +CREG URC after ATD. It seems the modem goes in fallback to GSM (2G). Why doesn’t it use VoLTE, staying in 4G mode?

ATI
Quectel
EG25
Revision: EG25GGBR07A08M2G

OK
4

hi，
Because the 2G network cannot make calls and surf the Internet at the same time, volte can only make calls and surf the Internet at the same time. When connecting to this interface, there will be some output when registering the network, which is normal. Please use the following command to query the current configuration:
AT+QCFG=“ims”