DID: what can i do that implement "DID" function i

Can I do it by write extensions.conf?

can you be more detailed, please?

Yes, of course. And thank your attention.
I have an IPPBX that connect to PSTN and VoIP Service Provider. I wish do that any caller in PSTN or Internet (Voip) can direct any extension.
How can I do?
What different do I implement DID function in PSTN and Internet (VoIP)?

:question:
If you can’t tell me more, Could you tell me whether asterisk can do DID function.

If you can’t tell me more, Could you tell me whether asterisk can do DID function.[/quote]

Yes, Asterisk can route based on DID.