Routing an Incoming DID Call from One SIP Trunk to Another SIP Trunk

[ITUser]

I have two SIP trunks configured on 3CX.

• SIP Trunk 1 receives incoming PSTN calls.
• SIP Trunk 2 connects to an external SIP-based voice platform.

I have a specific DID configured on SIP Trunk 1.

My requirement is:

When an external caller calls this specific DID, the call should be received by 3CX through SIP Trunk 1 and then forwarded/routed to SIP Trunk 2.

The external SIP platform connected through SIP Trunk 2 will handle the call from that point onward.

The desired call flow is:

External Caller → SIP Trunk 1 → 3CX → SIP Trunk 2 → External SIP Platform

There is no 3CX extension, queue, ring group, or IVR involved in the desired call flow.

I am essentially looking for a way to use 3CX as an intermediary between the two SIP trunks for this particular DID.

I would appreciate advice on the recommended/supported way to configure this in 3CX V20.

Specifically, I would like to know:

1. Can an inbound call received on a specific DID on SIP Trunk 1 be routed directly to SIP Trunk 2?
2. If not, what is the recommended 3CX configuration to achieve this?
3. Are there any required Outbound Rules, SIP trunk parameters, or SIP header/number transformations?

I am using IP-based SIP trunks.

 

[YiannisH_3CX]

The easiest way is to use a call script so when the specific DID is called the call is routed to an external number. You will need an outbound rule that matches the call but you can create a very specific one just for this call flow that matches the number you are forwarding the call to.
The SIP trunk parameters depend on the use case. If you want to preserve the original callers ID then you will need to customize the template and adjust the header your Voice platform reads the caller ID from.