Video Tele-Conferencing

Conducting a conference between two or more participants at different sites by using computer networks to transmit audio and video data. For example, a point-to-point (two-person) video conferencing system works much like a video telephone. Each participant has a video camera, microphone, and speakers mounted on his or her computer. As the two participants speak to one another, their voices are carried over the network and delivered to the other's speakers, and whatever images appear in front of the video camera appear in a window on the other participant's monitor.

Multipoint videoconferencing allows three or more participants to sit in a virtual conference room and communicate as if they were sitting right next to each other. Until the mid 90s, the hardware costs made videoconferencing prohibitively expensive for most organizations, but that situation is changing rapidly. Many analysts believe that videoconferencing will be one of the fastest-growing segments of the computer industry in the latter half of the decade.

ISDN and IP
ISDN was the traditional transport for digital videoconferencing because it provided dedicated channels end to end and allowed bandwidth to be dynamically allocated in multiples of 64 Kbps. Although still used, ISDN usage has mostly given way to networks that use the Internet protocol (IP).

In a private IP network, either deployed by the enterprise itself or by using carriers, the quality can be controlled. Carriers such as International Video Conferencing and Glowpoint, Inc. specialize in high-quality backbones for high-speed conferencing traffic.

Using the Internet as the transport provides reasonable quality without additional cost to users. Although periods of congestion are inevitable on a public network, systems can throttle down to lower frame rates to eliminate jerkiness, and users are willing to accept occasional blips. Using forward error correction, a videoconferencing system may be able to compensate for lost packets, but generally requires the same brand of equipment at both ends.

A point-to-point conference between two people is straightforward, but a conference with several people requires some moderating. A multipoint control unit (MCU) is used to mix the audio and make the video of the dominant speaker the larger window on screen (see MCU). Multipoint conferences are also achieved by connecting to a carrier's conferencing network service. A more immersive environment for group meetings is achieved with multiple monitors and loudspeakers.

Firewalls often present a problem for videoconferencing over the Internet because they are designed to block packets that have not been requested and thus stop a video caller. There are numerous ways of configuring routers and firewalls to accept videoconferencing data. Another option is to place the video system in the demilitarized zone (DMZ), which sits between the company's private network and the Internet.

Like a telephony PBX, a video PBX is used to switch calls and provide call forwarding and call transfer, features that are becoming more important as videoconferencing becomes mainstream. Video network management is also required to adjust bandwidth, provide quality of service and log calls for accounting and billing purposes.