Emergency - Caller ID

[contoured]

I understand that I need to use a dedicated SIP trunk for Emergency dialing but how can I ensure that the default caller ID on such a trunk is not overwritten by the caller ID defined in an extension's settings?

 

[dan_tx]

Depending on your SIP trunk provider, whichever field they look to for the Caller ID, set that to Variable "Custom Field" and put whatever number you want it to be.
For example,in this SIP trunk the provider displays the caller ID referencing the "From: Display Name" field. Set it to Custom and put whatever you want.

Now be warned, some SIP trunk providers don't let you put whatever you want. Or you have to get the number you put "verified" before they will transmit it in the required field.

Obviously, test whatever you do. Once I have a Emergency Trunk setup, I do some outbound calls on it to make sure the proper caller ID shows up.

 

[leejor]

Here is an article on the outbound trunk field variables...

https://www.3cx.com/docs/sip-trunk-outbound-calls/

Since this trunk is for emergency calls (only?), you could choose a, less expensive provider that does not allow caller Id spoofing. One that provides basic, measured service, with a low, or no monthly fee, as there should not be many outgoing calls (hopefully).

You may even consider (for reliability, in the event of a DSL failure), a single PSTN trunk with a gateway. perhaps an existing one, currently used for a fax machine..

 

[YiannisH_3CX]

If this is a dedicated trunk you could also set the outbound parameters to only send the main trunk number. Similar to what @dan_tx suggested you need to know the SIP field the provider uses to read the number from and change that to "LineNumber" External number of line.