Routing calls between trunks

I would like to route one trunk over to another trunk.

How would you do this

so I have an incoming call on box1 and I want it to forward to box2

and in the future have box1 forward to a box3

so that box1 route between systems and each box after box one is independent of each other.

any help on this would be more than awesome thank you!

right now an out bound call from box2 goes out box1

but inbound calls to box1 do not and I cannot see how you would forward them to box2

box1 (incoming)
Asterisk (Ver.

box2 (extension)
Asterisk (Ver.