On our OCS 2007 R2 setup users connect to OCS externally. Users can initiate video sessions successfully and can see each other. About the audio, something strange is going on. If they call each other from the same LAN the audio works. But if one of them is at a different location and on a separate LAN they both can't hear any audio. I think there is something wrong about IP configurations but I don't know where to start. Can someone help me? Thanks.