3CX v20 Update 9 - IVR, Voicemail & Music on Hold Have No Audio (DTMF Works, RTP Stops After 8 Packets)

[Rohit Subhedar]

Hello 3CX Team,

We are experiencing an issue with one of our 3CX systems and would appreciate your guidance.

Environment​

• 3CX Version: Version 20 Update 9 (Build 995 Release - AI 1.4.48)
• Deployment: AWS
• SIP Trunk: Custom SIP Provider

Issue Description​

Incoming and outgoing calls are connecting successfully, and normal conversations work without any audio issues.

However, all announcement-based media is completely silent, including:

• Digital Receptionist (IVR)
• Voicemail Greeting
• Music on Hold (MOH)

Current Behavior​

• Incoming calls connect successfully.
• DTMF input is detected correctly in the IVR.
• The IVR executes the correct destination based on the key pressed.
• No IVR greeting is audible.
• No voicemail greeting is audible.
• No Music on Hold is audible.
• Once the call is connected to an extension, two-way audio works normally.

Troubleshooting Performed​

• Created a new Digital Receptionist.
• Tested with the default 3CX greeting.
• Uploaded a new custom greeting.
• Tested voicemail using the default greeting.
• Tested Music on Hold.
• Restarted 3CX services.
• Verified firewall configuration.
• Verified codec negotiation (G.711 μ-law).
• Confirmed DTMF is detected correctly.

Packet Capture Analysis​

We captured traffic using Wireshark.

Observations:

• SIP signaling is successful.
• Codec negotiated: G.711 μ-law (PCMU).
• RTP stream is established.
• However, only 8 RTP packets are transmitted from the 3CX server toward the SIP provider.

RTP Analysis:

• RTP Packets: 8
• Duration: 0.14 seconds
• Packet Loss: 0%
• Jitter: Normal

For a normal IVR announcement, we would expect several hundred RTP packets over multiple seconds, but the RTP transmission stops almost immediately.

Additionally, the RTP payload appears to contain only silence (FF FF FF...) rather than actual audio.

Event Logs​

We observed the following events previously:
The following service(s) were interrupted:
- 3CXIVR01
- 3CXCallFlow01
- 3CXQueueManager01
After restarting the services, they are running normally, but the issue persists.

Questions​

1. Has anyone experienced a similar issue on 3CX v20 Update 9?
2. Is there any known issue where the media engine stops transmitting RTP after only a few packets?
3. Are there any logs related to the IVR/media subsystem that should be collected for further diagnosis?
4. Could this indicate an issue with the 3CX media engine despite normal SIP signaling and successful two-way audio after the call is answered?

Any suggestions or guidance would be greatly appreciated.

 

[NikosT_3CX]

@Rohit Subhedar if you call the internal IVR number directly from an extension, do you have the same issue ?
Also, does your Trunk have Re-Invite and Replaces enabled ? Check on the template.

 

[Rohit Subhedar]

@Rohit Subhedar if you call the internal IVR number directly from an extension, do you have the same issue ?
Also, does your Trunk have Re-Invite and Replaces enabled ? Check on the template.

Hello @NikosT_3CX ,

yes same issue for internal IVR number directly from an extension and after enabling Re-Invite and Replaces as well.

 

[NikosT_3CX]

@Rohit Subhedar please open a ticket so we can check this further.
Also the Re-Invite and Replaced on the Trunk must be disabled, I just asked to see how the setup on the Trunk is.