NAT VPN VOIP result no audio or one way audio

[rehman1720]

Dear sir
i m using vpn for voip
the sturcture of my network is Main line of internet is connected with HUb and from hub 2 lines are passing one for my voip gateway and otherone is for my Computer where XP is installed
in XP - TCP/IP settings - Main TCP/IP i assignd 10.0.5.44 ( NATed IP ) provided my ISP and in advance settings i assignd 192.168.2.3 ( Bcoz. my VoipGatweay i.e Quintum. has 192.168.2.11 )
I m using vpn in XP.
and In XP i have installed Gatekeeper ( GNUGK Voip Gatkeeper ) it recives the voip calls and pass these calls to my voip Gateway.
Now the problem is using this Senario we got one way Audio or No Audio

Whereas, when  i take static and real ip from isp and apply rest all same above mention structure. Every thing works fine

but i cannot take static ip
issue is NAT with VPN
please try to solve this issue
waiting for your reply
regards,
rehman.phattan@hotmail.com