PBX to PBX dialing

I was wondering if it was possible to set up two asterisk PBXs…both with different extensions…and have one PBX dial an extension of a user on another PBX and ring the extension on the other PBX. Here is what I tried so far:

I set up one PBX to register to another PBX using an extension on that PBX. I then tried inputing the desired extension I want into the outbound routing’s dial pattern. I made sure I was registered on the other PBX and then I made the call…hoping it would ring that extension…but call I get is a busy tone. Is there a way I can make it so that I have two pbx’s with their own extensions…but the ability to directly dial each other’s extensions…to make it seem like everyone is using one PBX…or give the impression that that is what’s happening? Thanks in advance.

use IAX, see here: voip-info.org/wiki/view/Aste … al+servers