Firmware request for EC20CEHCLGR — need VoLTE support for Viettel (Vietnam)

IoT Modules LTE Standard Module
1

Hi,

We have EC20 modules currently running firmware EC20CEHCLGR06A14M1G_AUD (queried via AT+CGMR/AT+GMR; module reports AT+CGMM = EC20F, manufacturer = Quectel).

We are unable to establish voice calls on Viettel (Vietnam) SIMs. Testing shows:

  • ATD<number>; returns OK.
  • AT+CLCC shows the call in state 2 (DIALING) for a few seconds, then either the entry disappears or NO CARRIER is returned. The call never reaches state 3 (ALERTING) or 0 (ACTIVE).
  • AT+QCFG="volte",1 returns ERROR (command not supported on this firmware).
  • AT+QCFG="ims",1,1 (2-param) returns ERROR. Only AT+QCFG="ims",1 (1-param) returns OK and persists after AT+CFUN=1,1 reboot (+QCFG: "ims",1,0), but this alone does not fix call establishment.
  • Data (2G/3G/4G) works fine; only voice calls fail.

Questions:

  1. Does our current firmware build (EC20CEHCLGR06A14M1G_AUD) support VoLTE at all, or is it a data-only / CSFB-only build?
  2. Is there a firmware version for the EC20/EC20CE series that is certified for VoLTE on Viettel (Vietnam), similar to region-specific builds like EC20CEFAG?
  3. If such a firmware exists, could you please share the download link or send it to us, along with the QFlash upgrade procedure?

We have ~32 units of this module in production and would like to confirm whether a firmware upgrade can resolve this before pursuing other troubleshooting paths.

Current version details:

  • AT+CGMI: Quectel
  • AT+CGMM: EC20F
  • AT+GMR / AT+CGMR: EC20CEHCLGR06A14M1G_AUD

Thank you!

2

Hi @HydraByte ,

The latest firmware EC20CEHCLGR06A15M1G_AUD includes a Voice Call fix for certain scenarios where the call session fails.

A15 can be recommended for testing as an improvement over A14, but am still in the process of confirming if it includes support for Viettel VoLTE compatibility.

Since the current firmware is A14 and the latest release is A15, we recommend upgrading one unit to A15 and testing the call on the Viettel network. If the issue persists, we would need the relevant network/IMS logs to further investigate.

Please check your email. Thank you.

3

Hi, I am also using EC20CEHCLGR06A14M1G_AUD and experiencing VoLTE call issues. Could you please send me the latest EC20CEHCLGR06A15M1G_AUD firmware by email for testing? Thank you.

4

Hi, I also have an EC20CEHDLGR06A09M1G module and would like to request the latest compatible firmware for this model.

I am using it with China Mobile (CMCC). VoLTE calls and MO SMS work normally, but MT SMS cannot be received. There is no +CMT or +CMTI URC, and both AT+CMGL=4 and AT+QSMSL=4 return no received messages. I have also reproduced the issue by testing directly through the AT port without Asterisk or any other application in between.

Could you please send me the latest official EC20CEHDLG firmware and, if available, the corresponding release notes/changelog for testing?

Thank you.