[Serusers] Proxy sending ACK on port 5060 instead of on contact port

[mahesh]

Hi all,

I am using the following configuration to test SJPhone through IPTEL proxy 
server(publicly
available:195.37.77.99).

HOST1(win2K)---FW1---Internet---FW2---HOST2(winXP)

Host1 and Host2 are hosts with private IPs having SJPhone application. FW1 
and FW2 are
firewall/NAT devices with SIP-ALG implementation. This means all the SIP 
messages are modified to include the public IPs in them. Also the 
via,contact ports are modified. Now both host1 and host2
register with the iptel proxy server. A call is initiated from host1. Host2 
sends 200 OK response
to the HOST1. After this the ACK sent by Host1 is sent to port 5060 on 
HOst2,instead of the
contact port advertised in 200 OK. This is observed from ethereal captures 
on Host2. All these
messages are going through the proxy server(195.37.77.99).

Can someone please tell me why the proxy server is behaving this way, i.e. 
sending ACK on 5060
instead of the contact. Is there anything that i am missing here or doing 
wrong.

Thanks
Mahesh