Direct Routing PSTN call closed from SBC on Mute

Frequent Contributor

I am now facing issue with my setup of Direct Routing and AudioCodes SBC.

Simply when user put himself on mute the SBC does not recognize any RTP stream and close the call with reason code 400 as RTP connection broken.

I can see that Teams does not send any re-INVITE informing SBC that there will be no audio.

Not sure on which side to handle this. How can I for example force Teams send empty RTP packets?

On AudioCodes SBC I tried to change some settings on IP Profile in order to support Remote re-Invites, RTCP mode as Generate Always etc. 

Not sure what else to try. 

Putting on Hold is working fine. No issue that the call would be dropped. Just Mute function is making this issue. 

10 Replies

Thanks @DaveChomi 


@Linus Cansby @Chris Webb @adam deltinger    - you ever come across muting closing off the call in a direct routing scenario with a SBC?


Best, Chris

Nope, not seen that problem. Had to test it with my Audiocodes setup and no problem with mute. Does your call disconnect directly or is it after a couple of seconds/minutes? 

I believe that the timer for that is set for 10 seconds.
Once I mute myself the SBC recognize no RTP and then populate error. 

15:08:14 1 RTP packets lost: CID=33 [Code:0x600b] [CID:33] [Time:29-01@15:08:14

15:08:14 PL:1 [Code:0x5004] [CID:33] [Time:29-01@15:08:14

15:08:16 !!! Repeated 10 times : Validate Stun Message - got unknown attribute type:32880 [Time:29-01@15:08:16

15:08:24 ( lgr_psbrdex)( 304680) recv <-- EV_BROKEN_CONNECTION Ch:33 [Time:29-01@15:08:24

And then sends BYE on both sides of connection. 



In addition I tested mute from the opposite side (SIP phone registered to our on-prem PBX) and it's working fine. There is also no re-Invite send from PBX to SBC but obviously it's still generating RTP traffic so the SBC does not recognize any loss of RTP stream. 


I have pointed out from my tests that issue appeared only if I made the connection from our PBX environment to Teams user. It made me believe that issue is related to chosen codec. Additionally only if the connection is established with G711 the problem on mute appeared. If I make the session with the only preference and it's G729 then the Mute can be also used and the issue does not appear :) 

I also play around with Suppressed Silence feature in Coder Groups but this had not any effect on the issue. 

Any input why only G711 might be the case for the root cause would be appreciated :\ 

I will definitely check with Aduiocodes for any known error or ceveat...  



Hi Dave,


Did you find solution for G711?

Hi @Damian Kozlowski 
at the end I have chosen the workaround in my eyes not the best one but working best :) 

I have set the SBC to ignore "no media" so as it is not considered as error. So far it didn't bring any other odd behavior. 


For Audiocodes devices, try setting "Disconnect on Broken Connection" to "No".  You can find this parameter in the IP Profile that you are using for the external SIP trunk with Office365.  You are also likely using a separate IP Profile with your internal IP-PBX in which case you would also need to set it there.  That setting will likely fix up your issues.


There are also settings that allow you to manipulate how the SBC handles MUTE scenarios, but try above first.

@Trevor Miller Hi Trevor, thanks. That's exactly what I started to do but didn't upload this post. I can confirm that this was the solution for me.  

Hi I have the same issue and tried this and t does not work for me. Could you share you other options for this mute drop issue.