This is copied straight from the TechNet article posted here, http://technet.microsoft.com/en-gb/library/dd441209(office.13).aspx.
The A/V Edge service requires the port range from 50,000 through 59,999 to be open outbound for TCP for federation.
- Additionally, if you will be federating with organizations that run Office Communications Server 2007 and earlier, you must open this 50,000 to 59,999 port range for both RTP/TCP and RTP/UDP, and for both inbound and outbound connections.
- If you will be federating only with organizations that run Office Communications Server 2007 R2, you need only to open this port range for RTP/TCP, only for outbound connections.
- Otherwise, if you will not be sharing audio/video over a federated relationship, you can close this port range.
So remember, when taking a look at what ports you need open for your Edge server deployments, just because you're running R2, it doesn't necessarily mean that you don't need ports 50,000-59,999 open.