If the Media Server needs to allocate a port for media transmission, and cannot bind, it will generate a log message such as:

MediaServerReporting:InitEndPoint [MS003003] C:179.1: RTCP socket 10.0.0.173:7023 binding failed with error code 10048

This is due to some other application already binding to some ports in the 7000-7499 range. Typically it is the Microsoft DNS server doing this. To check which ports are bound at any point in time, you can run the following command from the DOS prompt:

netstat -ano -p UDP

Microsoft Windows allows you to define which port ranges will NOT be returned to any application/service that requests a random port number, via the following registry entry:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\ReservedPorts

To ensure correct functionality, you should add the following ranges, without removing whatever the value already contains:

• 3478-3478  – STUN / Firewall Checker
• 5000-5000 – MyPhone Interface
• 5060-5090 – SIP Port for 3CX PhoneSystem and Tunnel Ports
• 5480-5490 – Management Console, FAX Server, Other 3CX Components
• 7000-7499 – range of RTP ports for Local Connections
• 9000-9049 – range of RTP ports for External Connections
• 10000-10500 – range of RTP ports for Fax (10000-10001) and Tunnel Connections
• 40000-41000 – Conference, IVR, Parking Orbits

If the value already contained “1433-1434”, the end result would look something like this (click on image to enlarge):

For more specific instructions regarding this registry entry, refer to: http://support.microsoft.com/kb/812873/