Connect to Asterisk

I have registered two SIP extentions in an IP PBX (the IP PBX is already connected to the PSTN), and I have installed sterisk18, and now I want to connect the IP PBX to asterisk, how do I configure pjsip and dialplan?

By understanding and following the documentation or hiring a consultant. The broad outline is the same as connecting to an external provider.

(I’ve already gone beyond what I’d normally do in answering a question in connecting two Asterisk’s in a reply I made yesterday.

Note that what goes in the dialplan is a very personal thing)