Calls not going to alternate SIP Trunk when 486 Busy Here received

[SwaggerRO19]

Hello,

We have the following setup:

1. SIP Trunk where we have unlimited inbound calls but only 1 outbound call (one channel for outgoing calls).
2. SIP Trunk where we have unlimited inbound calls but only 1 outbound call (one channel for outgoing calls).
3. SIP Trunk where we have unlimited inbound calls and outbound calls.

The issue appears when we want to use the following scenario:

Outgoing call it's placed via first SIP Trunk, established without any issues but the second outgoing call will try to go on the first SIP Trunk again, where we will receive 486 Busy from Carrier because of no more available outgoing channels. Instead of switching to the second available Carrier (SIP Trunk) on Outbound Route, the call will remain stuck on the first SIP Trunk dropping the call with 486 Busy Here coming from the Carrier side and not going to the second route available.

I tried setting up only 1 concurrent call on the first SIP Trunk, but this will affect the incoming calls and it's not an option. Running with this setup will only allow the first outbound call to be established but the next outgoing/incoming call will be dropped with 486 Busy Here or had no available outgoing trunk(s) for Call error message.

My concern & question come here, shouldn't the 3CX PBX switch to the next available route on the Outbound Route if 486 Busy Here it's received from the main SIP Trunk/route?

Is there any way that we can force the PBX to switch to the next route without affecting the number of incoming calls also? It kind of sucks, in a normal way, it should overpass the first SIP Trunk when 486 Busy Here it's returned from Carrier side and go to the next available route but it's not doing this.

PBX it's running on version 18.0 (Build 314), license it's Enterprise Annual. Attaching a screenshot after Outbound Rules (in the screenshot there's no Route 3 because we were testing something that needed the third SIP Trunk to be out of equation).

Thanks,
Razvan

 

[NickD_3CX]

Hi Razvan,

Your logic is correct, when an Outbound Rule in 3CX has multiple routes, if the first route returns an error from the provider, it will try the second route, third, etc... With error "486 Busy Here" though it's a bit different.

This error implies that the destination number is busy. Logic dictates that regardless if you call the same number via Trunk A, Trunk B or Trunk C, the destination number will still be busy.
For this reason, for error 486 the call does not fail over to route 2.

Can't you ask your provider to return a different Error Code, like "603 Declined" or "488 Not Acceptable Here"?

 

[SwaggerRO19]

Hi @NickD_3CX

Thank you for your fast reply.

Yes, I know that my Carrier should return the 603 Declined or 488 Not Acceptable or a 503 Service Unavailable for route advance but they are working very slowly and they are hardly understanding the issue in my case, I've already opened a support ticket with their VoIP Administrator and they can't guarantee that they can introduce this type of response coming from their end of the adapter, that's the reason why I opened this topic in case there is an alternative for this kind of sittuation.

I know it's odd to return 486 Busy Here if there are no outgoing channels and I was hoping there might be an workaround for this.

Thanks,
Razvan

 

[NickD_3CX]

I see... I'm afraid this is hard-coded, so I don't think there is a way to override this behavior.