No Busy Signal Via SIP Trunk


I believe this is a tried and true topic, but I wanted to find out if there is an answer to it.

When I dial out via a SIP trunk and the called party is busy, I get silence. If I call the same number from a cell phone or an analog phone then I get either a busy or Forward on Busy to voice mail. I believe the SIP trunk is reacting this way because of the messaging (or lack there of coming back) from the carrier.

Is there a tip or trick that I can employ that will allow the SIP trunk to work the same way as the cell or analog phone? I did a quick search of this topic (in the forums) but didn’t come across anything definitive.

Thanks for taking the time to respond.


In "Settings -> Advanced Settings"
remove the “r” from Asterisk Outbound Trunk Dial Options
i.e. Ttr should be Tt or empty if you don’t want to allow transfers.

… this will remove fake ringback.
Then, if the problem persists - check your sip debug to make sure your provider is returning to you 486 Busy message.

I did some reading and changed the following value: Connectivity > Trunks > My SIP Trunk > Asterisk Trunk Dial Options > Override.

When I call an unreachable cell phone, instead of a long period of silence followed by a VM, I now get a much shorter period of silence followed by the VM.

Is this a recommended way of handling the “Busy Signal Via SIP Trunk”?

Thanks in advance for any suggestions or recommendations.


This issue is not specific for FreePBX. It’s all about Asterisk.
Recommendations and explanations are available here:
Better to change in Advanced settings once for all as suggested by @dcitelecom