The simplest form of videoconferencing is a point-to-point call, one person contacting another person via the Internet. This basic level of videoconferencing is similar to making a phone call with a picture phone. Multipoint videoconferencing occurs when three or more locations connect simultaneously, much like a three-way phone conversation only the logistics are much more complex.



To begin understanding the complexity of multipoint conferencing one must enter the domain of technology and begin with ISDN. ISDN means simply Standards for Integrated Services Digital Network, a high quality, switched digital communications service that gives your standard phone line the ability to transmit voice and data simultaneously.

You can use the same line for regular telephone service, faxing, computer communication, or even live videoconferences. Each of these applications requires suitably equipped customer-provided equipment. ISDN transmissions are significantly faster than using a modem. Think of ISDN as a high-tech phone line.

The next essential ingredient in a multipoint conference is the bridge. This is a multipoint control unit known as MCU, the component that manages the videoconferences when of three or more participants are involved.

An MCU can support some or all of the following: audio-only calls, video calls at various video bandwidths, video calls, data sharing, continuous presence, cascaded calls, a conference call web page and component stacking. Component stacking can remain in the technicians domain but continuous presence deserves attention by anyone who would understand multipoint videoconferencing.

Continuous presence, also know as the CP Mode is when all sites in the videoconference can be seen at the same time on the far end monitors. Those involved in the videoconference will see themselves (or any data that they present) on their right hand monitor while at the same time they can see themselves and everyone else on the screen.

Continuous presence is often used when presentation is required. As you can see, multipoint videoconferencing with continuous presence activated can be very effective for business or hospital transmission. Another way of looking at CP is seeing each site in a split screen format on the display monitor at all times, much like the television show Hollywood Squares.

Interesting as Continuous Presence is, it is not the default mode for multipoint videoconferencing. The default mode is Voice-Activated Switching, or VAS. In VAS a multitude of sites are connected and the person all views speaking. This should bring to mind the image of a newscaster or spokesperson on standard television.

An important point in the VAS mode is that although the transmission focus will be on the one who is speaking, anyone and everyone connected to the videoconference can change the view. Remember the term is voice-activated. If someone coughs or sneezes, the camera recognizes them. In VAS multipoint videoconferencing it is very important to mute your microphone until it is your turn to speak.

There are yet other modes of transmission for a multipoint videoconference. These are Chair Control, Lecture Mode, and Broadcast with Autoscan. In Chair Control and Lecture Mode the presenter is seen full-screen by all sites at all times, even if a speaker at another site speaks. This mode is used primarily with distance learning, when the situation requires that students always see the presenter rather than speakers at other remote sites.

Broadcast with Autoscan means only the director or presenter is able to view all the remote sites while the remote sites can see the video that is being broadcast. This becomes even closer to a television broadcast via the Internet. This mode is preferred for videoconference presentations and seminars, when audience response is not anticipated or required and unlike a television broadcast, a multipoint videoconference in broadcast with Autoscan mode allows the director or presenter to view the audience and watch for response.

In todays computer world most multipoint videoconferencing systems have built-in bridges which allow you to connect to multiple sites just as you would in a point-to-point call Even more advantageous is the rise in technology to include built-in gateways. A gateway is a network point acting as an entrance to another network. This allows communication across any set of interconnected networks.

This means the World-Wide-Web is now available for anyone interested in a multipoint videoconference.