MVP Elan Shudnow wrote a thorough post on Audio/Media Negotiation.

There are several ways in which we can utilize Audio/Video streams in Office Communications Server. While this article is based off of R2, the same “should… but not verified” work the same in OCS 2007 R1. There aren’t really any places out there that describe how the media session works in different circumstances. For example, what servers and ports are utilized when doing Audio/Video through the Live Meeting 2007 client when connected to the On-Premise Web Conferencing feature in OCS 2007 R2? How about when you do a peer to peer with both users being internal to the network? How about both users being external to the environment and connecting through the Edge? How about when you do a peer to peer with one user being internal and one user being external?

Want to know? Read his post at: http://www.shudnow.net/2009/08/29/office-communications-server-2007-r2-audiomedia-negotiation/