SRVCC Handover Issue on EC25-EM Module – Call Drops When LTE Signal Lost

IoT Modules LTE Standard Module
1

Dear Quectel Support,

I am testing SRVCC (Single Radio Voice Call Continuity) on the EC25-EM module and would like to confirm the correct procedure and any prerequisites needed for it. Here is a summary of what I did:

  1. Module Initialization & Configuration
at+cfun=1,1  (Reset the module)  
at+cfun=1,1  (Repeated to ensure full initialization)  
AT+QCFG="nwscanmode"  → returned 0 (automatic network selection)
  1. SIM and Network Information
AT+cimi;+iccid;+CSQ;+QNWINFO;+cops?;+creg?;+cereg?;+cgreg?;+cgdcont?;+CGCONTRDP;+QENG="servingcell";+cgact?

Observed:

  • IMS and PDN contexts activated (+CGACT: 1,1 and +CGACT: 2,1)
  • Module registered on LTE (FDD Band 3)
  • Signal strength fluctuating around CSQ 21 → 11 → 27
  • IMS enabled: @+QCPDPIMSCFGE? shows IMS PDN activated for context 2
  1. Voice Call Test
atd+492115335775;  (Outgoing call)  
at+clcc  (Call monitoring)

Observed:

  • Call successfully established over LTE
  • When LTE signal dropped (CSQ decreased), the module attempted to attach to 0 (no service), but the call dropped instead of handing over to 2G/3G
  1. Additional Checks
AT+QVOLTEDBG, AT+QCFG="ims", AT+QMBNCFG="autosel","list"
  • Verified voice and SMS domain preference
  • IMS enabled

Issue:
The SRVCC handover does not occur when LTE signal drops; the call is dropped immediately.

Request:

  1. Could you confirm if there are any additional prerequisites or configurations needed on EC25-EM to enable SRVCC?
  2. Are there specific AT commands or settings that must be set to allow a live LTE call to hand over to 2G/3G?

Thank you for your guidance.

2

Dear Customer,

Thank you for reaching us.

Thank you for sharing the detailed test information.
SRVCC is a network-controlled feature and cannot be enabled or triggered through AT commands on the EC25-EM module. While the module supports SRVCC, the handover from LTE to 2G/3G will only occur if the mobile network and SIM subscription support SRVCC and the network initiates the handover procedure. If LTE coverage degrades rapidly or SRVCC is not enabled on the network side (especially for LTE-to-3G), the VoLTE call may be released instead of being handed over. We kindly recommend confirming SRVCC support and provisioning details with the network operator for your test environment.

Best regards,
Fazrul Redzuan

3

Thanks for the update.

Can you also confirm whether eSRVCC is supported by the EC25‑EM module, assuming everything is fine on the network side?

Do we have any documentation or past cases that clearly show SRVCC and eSRVCC support for this module?

4

Dear Customer,

According to the official datasheets and product documentation, the Quectel EC25 series (including variants such as EC25-EM and EC25-M) does not specify support for SRVCC or eSRVCC as part of the standard feature set.

Based on the publicly available specifications, SRVCC/eSRVCC functionality is not listed among the supported voice or mobility features of the EC25 series. Therefore, these capabilities are not guaranteed within the standard firmware configuration. For now, it only supported VoLTE.

Best Regards,
Fazrul Redzuan