Issue: Media not established between Flashphoner and 3CX v20 (SRTP compatibility)

[Sebastián Acosta]

Hello,

I’m integrating a web application with my 3CX v20 PBX using Flashphoner WCS.
Registration works correctly and calls are created, but media never establishes.
The call immediately drops after the initial INVITE.

What I found:

• Flashphoner is negotiating DTLS-SRTP by default.
• 3CX v20 does not support DTLS-SRTP for SIP extensions, only SDES-SRTP.
• In 3CX v18 there was a per-extension option to disable re-INVITE / ICE, which made Flashphoner work.
  In v20 this setting was removed.
• On Flashphoner, I tried forcing SRTP modes (SDES, AVP, etc.), but media still does not connect.

It seems WCS continues offering DTLS-SRTP or mixed profiles, which 3CX rejects.
I need to know:

How to force Flashphoner WCS to use SDES-SRTP only, without DTLS?
Or if there's an updated configuration specifically for 3CX v20?

My goal is simply to connect Flashphoner WebRTC clients to 3CX extensions with working audio.

Any guidance would be greatly appreciated.

Thank you!

 

[Max]

Good day.
Please provide SSH access to WCS instance and two SIP accounts to test a call via your PBX using this private form. Or, if this is nt possible, please collect a report including traffic dump and send using this form. We will check and give a recommendations.

 

[Sebastián Acosta]

Hi Max, good morning.
Thank you for your response. I’ve already completed the form with the access details and the SIP accounts. I appreciate your help and will remain attentive.
Thank you very much

 

[Max]

We checked the server and tested a SIP call. The problem is between browser and WCS, not between WCS and 3CX:

This occurs at callee side when incoming call is initiating between WCS and Chrome 140 and above. See this thread.
The issue was fixed in WCS build 5.3.165. Please update and check.
Note that WCS 5.3 branch supports JDK 17 and above only, JDK 21 is recommended. So you should update JDK to 21 before WCS updating.

 

[Sebastián Acosta]

Hi Max,

Thank you very much for your help.
I updated WCS to build 5.3.165 as you suggested, and everything is now working correctly.

I really appreciate your support and guidance.

Best regards,