DID call with unconditional forwarding?

Question

Telephony

Hello,
There is: 1 main office and 2 remote offices, each now has an analog phone connected.
I want to implement the following scheme:
Register 1 external SIP trunk from the provider on the telephony server, remove analog phones in all 3 offices and install IP phones for them, which will be registered on the server.
I will start all outgoing calls from all 3 offices through this 1 external SIP trunk.
On old analog numbers, I want to set unconditional forwarding to an External SIP number (I need to write an application to the telephony provider) and here I have a question:
What DID will come to my IP PBX - the number that I originally called (the old analog number) or my external SIP number?
Or is it always configured differently by providers and I need to talk to them?
It is impossible to resolve calls through IVR - the presented scheme is not entirely correct, in fact there are much more remote offices.
The option with an FXO gateway in each office is also not suitable.

Answer 1

If this is one provider, and everything is in order with his head, he will culturally bring these numbers into your trunk and that's it. As a DID, of course, the old number will come.
When communicating with the provider, it should not be about forwarding, but about changing the analog line to a trunk.
If the providers are different, you will most likely receive the DID of the trunk. Although you may be able to negotiate.

Answer 2

. Your commits are in the patch-4 branch. It lags behind the master branch. The author wants the commits to be in the current master. You need to do a git rebase