SIP Packet dropped

Hi

am facing problem on sip configuration as Big-IP dropping the packets. Packets flows as following

MyClient: 10.1.1.1.23023 ===> 80.100.x.1.sip ( Sip Proxy )

Then my sip proxy forward the packet to one of my backeend servers so server reply

[Back end sip ] 80.100.x.2.SIP ==> 10.1.1.23023

this packet get dropped because the destination IP changed on the reply. How can i configure the Bigip to avoid this drop. Can ALG Profile avoid this