RTP problems

Hello,

My network is:
Client_SS7_1–
-----------asterisk1------asterisk2
Client_SS7_2–

• I receive a fax from Client_SS7_1
• Asterisk1 forward the call to asterisk2
• Asterisk2 forward the call to asterisk1
• Then, asterisk2 forward the fax to Client_SS7_2

I want that the SIP signaling go to asterisk2,
But, I need that the RTP don’t go more than asterisk1.

Have you an idea?

Thank you

FRANCOIS