h.323 windows desktop video client with Stun

h.323 windows desktop video client HI I have a Polycom Gatekeeper I have it on A Public Ip well with some routes from End users are having NAT problems The problem is that the end user is sending a Ras register to the gate keeper with the local ip in the header For example Client A [login to view URL] Gatekeeper XXX.XXX.XXX.555 The invite is sending out that the reply address is [login to view URL] so the gatekeeper is replying to [login to view URL] I am looking for a developer to find an open source h.323 video client that should have the option to use a stun server and a gatekeeper