Multipoint Control Unit (MCU)
Multipoint control unit is a device that allows to organize group video conferences between videoconferencing endpoints. To perform that, a MCU-server connects endpoint devices that can work with different protocols, most often via H.323.
During a multipoint conference session, MCU-server manages multiple endpoints at once, coordinates their functions on the video data processing, and forwards the flow of media streams between them.
Unlike software video conferencing servers, MCU-server conducts group video conferences under the principle of mixing media streams, i.e. mixing and re-encoding participants' video conferencing streams in real time. For example to create a picture-in-picture effect, which imposes very strict requirements on the computing capacity of MCU-server. While software servers often implement multiplexing pattern of the data streams, which implies no transcoding. A server just redirects the media streams of the video conference participants. Compression/decompression and media streams mixing undergoes in endpoint devices.
MCU-server is a hardware/software device that consists of a MC controller (Multipoint Controller) and MP processors (Multipoint Processors). Multipoint Controller deals with coordination of the media stream processing parameters between endpoints. In addition, the controller supports the H.245 protocol. The functions of Multipoint processors are processing, mixing and switching of multimedia streams.
There are several types of configurations that use MCU-server.
Centralized Conference. A MCU-server is necessary to perform centralized group video conferences. During such conference, all endpoint devices communicate only through the MCU-server.
Decentralized Conference. During such conference, all endpoint devices can communicate with each other without the MCU-server, using Multicast technology only. Although in this case, the MCU-server is not an interface between the endpoints, its role is not less important because it controls the exchange of media streams.
Hybrid Conference. In this case, endpoint devices which participate in a video conference can perform simultaneous transmission of only audio or only video streams to other endpoints without sending them to the MCU-server. All other media streams can be transmitted only through the multipoint control unit.
Mixed Conference. Such video conferences are conducted under the control of MCU-server, which performs the function of a "bridge" for connections of all types (centralized, decentralized or hybrid conference) between endpoints.
Author: TrueConf Team