Question About Korean Local Ringback Tone in EC25EFAR08A05M4G_KR Firmware

IoT Modules LTE Standard Module
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Dear Quectel Support Team,

We are currently using the EC25 module with the following firmware:

EC25EFAR08A05M4G_KR_01.001.01.001

While analyzing this firmware package, we found audio resources that appear to be related to local ringback tones, including a file named ringing_korea.wav.

We also noticed that the release notes for the EC25EFAR08A04M4G_KR version mention the following item:

“Supported playing local ringback tone based on the voice over USB function.”

Because of this, we would like to understand how the Korean local ringback tone function is intended to be used.

We performed some tests using AT commands through the OpenVox gateway’s module toolkit. The command below is supported by the module:

AT+QLTONE=?

The module returned:

+QLTONE: (0,1),(100-4000),(0-1000),(0-1000),(0-15300000)

We also tested:

AT+QLTONE=1,1000,200,300,3000

During a call or ringback state, we could hear an additional beep tone mixed with the GSM ringback audio. However, it did not replace the GSM network ringback tone. It only appeared to add a generated tone on top of the existing audio.

We also tested a longer cadence such as:

AT+QLTONE=1,440,1000,2000,6000

However, this caused the call to disconnect. We later noticed that the silent interval parameter seems to be limited to 0–1000 ms, so this value may have been invalid.

Our questions are:

  1. What is the correct method to enable or use the ringing_korea.wav local ringback tone included in the EC25EFAR08A05M4G_KR firmware?

  2. Is there an AT command to select or play ringing_korea.wav directly?

  3. Is the Korean local ringback tone used only through the Voice over USB function?

  4. If so, which AT commands or configuration are required to enable Voice over USB local ringback tone playback?

  5. Is AT+QLTONE only for generating simple frequency tones, or can it be used to trigger built-in ringback tone files?

  6. Is there any way to suppress or replace the GSM network early media ringback tone with the module’s local Korean ringback tone?

  7. During outbound calls, can the module send a RINGBACK URC or similar event so that the host system can know when to start or stop local ringback playback?

  8. For failed calls such as invalid number, call rejected, or user busy, can the EC25 module provide the original network release cause through AT+CEER or another URC so that the host can distinguish these cases?

Our goal is to provide a Korean-style local ringback tone instead of the GSM network ringback tone, while still correctly detecting call answer and call failure causes.

Could you please provide the recommended AT command sequence or integration guide for using the Korean local ringback tone feature in EC25EFAR08A05M4G_KR?

Best regards,