Working with 2 Asterisk boxes

Dear The Expert,

I have 2 AsteriskNow 1.6.2.11 + FreePBX 2.7.0.10 boxes that located in different locations,

Asterisk 1 had 2 FXO ports connected to PSTN lines and also had ext no. 100 - 110

Asterisk 2 also had 2 FXO ports connected to PSTN lines… and also had ext no. 200 - 210

from Asterisk 2… how do I get the trunk line of the Asterisk 1?

I need tips

Thanks & Regards
Winanjaya