In order to make a video conference between more than two participants (also called point-to-point or P2P conference) you obviously need one central machine or service, who collects all incoming video and audio data, makes up a common video and audio signal and sends it back to all participants. This machine is called a Multipoint Control Unit
or MCU. EVO, Vidyo or Skype use by default their own, dynamic MCU system in a completely transparent way for the user.
In some cases and for certain reasons (confidentiality, billing, availability of service), it may be preferrable to use a well defined MCU for video conferencing. For example IN2P3/CNRS offers MCU services in its framework of Remote Meeting System (RMS). See documentation on their website for other advantages (like recording, file hosting, streaming, ISDN bridge) which provides this service.
Clients for MCU: H.323 standard
Most modern MCU systems use the H.323 standard for data (video and audio) transmission. Typical clients are video conference room equipment. In order to transmit also screen copies or other multi-video channels, the equipment must in addition be compatible with the H.329 standard
EVO uses its own MCUs and protocols for video conferences by default. In order to control EVO connection over H.323 to a specific MCU, follow these instructions. (Cf. screenshot at the right, click to enlarge.)