Specifies the ranges of dynamically-allocated ports that Microsoft Office Communicator can use to transmit audio and video ...

Specifies the ranges of dynamically-allocated ports that Microsoft Office Communicator can use to transmit audio and video data using RTP. If you open specific ranges of ports on a firewall between two clients to allow the clients to communicate, this policy forces the clients to use ports in those ranges.  Note: If you enable this policy setting, avoid creating RTP port ranges that overlap.  If you enable this policy setting, both ranges must fall between 1024 and 65535 inclusive, in each range the minimum must be less than the maximum, and the RTP range must contain at least four ports (if the lowest port number in the range is even) or five ports (if the lowest port number in the range is odd). If you specify a range that violates one of these rules, Microsoft Office Communicator cannot use the SIP Communications Service.  If you disable or do not configure this policy setting, Microsoft Office Communicator attempts to send and receive RTP data using ports selected at random throughout the range of 1024 to 65535 inclusive.