4. Multipart Conferences

The basic usage of video conferences is between two parts, which both can hear and see each other on a monitor with loudspeakers. The two video conferencing systems are connected either by a telephone line (ISDN networks) or a data line (IP networks).

If there are more than two parts, we speak about a multipart video conference. To achieve this, there is a need for a MCU (Multipoint Control Unit), which can build a 'bridge' between three or more parties. The unit is, therefore, referred to as a MCU-bridge. Internal MCUs with a limited capacity may be found on expensive group systems. Otherwise you have to buy it yourself, which is very expensive, or you can get access to MCUs from commercial companies, which may be profitable if the usage is limited.

In the video clip below, four groups in different countries participate in a video lecture. All four parties can hear and see each other on the screen - a monitor view called "continuous presence".

In multipart conferences the monitor view must reflect the activities going on. Therefore, choice of suitable monitor views is essential. The main operator with access to the MCU-bridge will in normal have full control and possibilities to change monitor views.

The most common options for monitor views are:

• Continuous presence - all parties are visible on the screen. Best suited for discussions where several locations contribute.
• Voice controlled view - the recent part making sound (speech) is visible on the whole screen. Best suited for lecturing when the sound comes from one location most of the time. If there is a question from another location, this part will automatically be visible on the whole screen.
• Assign floor - the main operator can decide who is to be shown in full screen.

In the video clip below, the monitor view "assign floor" is demonstrated.