VoLTE is active but does not work

IoT Modules LTE Standard Module
1

Hi,

we have a product using the EC21-E module. We have around 2500 divices in the field. On most of the devices we use VoLTE successfully. Since a view days we see an issue regarding the VoLTE functionality. In coming an outgoing calls are not working from one day after another, but the VoLTE connection seems to be established:
at+cgpaddr response:
… +CGPADDR: 2,"42.1.5…
atqcfg=“ims” response:
+QCFG: “ims”,1,1
dialing a number by atd responses with NO CARRIER.
The module is used in 4G only mode, so 2G fallback is prohibited.
After a restart of the module everything is running well again.
Is there another way to check the VoLTE connection state? What might be the reason for this behavior? Can I reestablish the VoLTE connection wihout restarting the module?

Fimrware is EC21EFAR06A03M4G_01.003.01.003

2

What do these AT commands return?

AT+QMBNCFG="List"
AT$QCPDPIMSCFGE?
3

Hi snowgun,

thanks for your your help, The responses look normal. In general VoLTE works without issues. But sometimes a few devices get in the described error state. A restart of the LTE module solves the issue.

at+qmbncfg=“List”
+QMBNCFG: “List”,0,1,1,“ROW_Generic_3GPP”,0x05010824,201712241
+QMBNCFG: “List”,1,0,0,“Reliance_OpnMkt”,0x05011B4B,201801051
+QMBNCFG: “List”,2,0,0,“TW_Mobile_China_VoLTE”,0x05800301,201801221
+QMBNCFG: “List”,3,0,0,“Telstra-Commercial_VoLTE”,0x05800710,201710161
+QMBNCFG: “List”,4,0,0,“Commercial-Smartfren”,0x05012509,201801081
+QMBNCFG: “List”,5,0,0,“Bouygues_France_VoLTE”,0x05800101,201705111
+QMBNCFG: “List”,6,0,0,“VF_Germany_VoLTE”,0x05010415,201705111
+QMBNCFG: “List”,7,0,0,“Swis_switzerland_VoLTE_VoWiFi”,0x05010421,201712231

AT$QCPDPIMSCFGE?
$QCPDPIMSCFGE: 1 , 0 , 0 , 0
$QCPDPIMSCFGE: 2 , 1 , 0 , 0
$QCPDPIMSCFGE: 3 , 1 , 0 , 0
$QCPDPIMSCFGE: 6 , 0 , 0 , 0
$QCPDPIMSCFGE: 7 , 0 , 0 , 0
$QCPDPIMSCFGE: 8 , 0 , 0 , 0
$QCPDPIMSCFGE: 9 , 0 , 0 , 0

4

Agreed, all looks okay there.

Intermittent problems like these with no obvious cause can be a real pain.

I’d be looking to try a later modem firmware version, if available.