videoconferencing (redirected from Videotalk)

A real time video session between two or more users or between two or more locations. Although the first videoconferencing was done with traditional analog TV and satellites, inhouse room systems became popular in the early 1980s after Compression Labs pioneered digitized video systems that were highly compressed. While videoconferencing may comprise any number of end points communicating, the term "video chat" typically means between two end points only. Some of the major players in the field are Polycom (www.polycom.com), TANDBERG (www.tandbergusa.com), VCON (www.vcon.com), RADVISION (www.radvision.com) and VTEL (www.vtel.com).

ISDN - The Traditional Transport
Video frames are typically delivered in CIF format (352 x 288 resolution) over digital lines from 128 Kbps to 784 Kbps. ISDN has been the traditional transport for digital videoconferencing because it provides dedicated channels from end to end and allows bandwidth to be dynamically allocated in multiples of 64 Kbps.

Over IP
Videoconferencing over internal IP LANs and private lines has become very popular because the quality can be controlled. Using the public Internet as the transport also provides reasonable quality. During periods of congestion, systems can throttle down from 30 fps to a lower number of frames per second to eliminate jerkiness. However, the Internet is a cost-free transport, and users accept occasional blips. Some IP carriers, such as International Video Conferencing (www.ivci.com) and Glowpoint, Inc. (www.glowpoint.com), provide high quality IP service similar to dedicated ISDN circuits.

Firewalls
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 (see DMZ).

Multipoint Conferences and MCUs
A point-to-point conference between two people is straightforward, but a videoconference with three or more parties requires human moderation. A multipoint control unit (MCU) is used to mix the audio and send the video of the predominant speaker to every screen (see MCU). Multipoint conferences are also achieved by connecting to a conferencing network service from a common carrier.

Video PBXs
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.

Summary
For years, the explosion of videoconferencing has long been forecast to be right around the corner, but that corner has been farther down the road than expected. However, it is gaining significant ground within the enterprise. As cable modems and DSL lines become ubiquitous, it will begin to accelerate for the consumer as well (see Metcalfe's Law). See videoconferencing standards and telepresence.

Room Systems - The Beginning

Videoconferencing got its start with room systems, and they are still commonly used for small and large business groups. (Image courtesy of TANDBERG, www.tandbergusa.com)

Video on the Desktop

Desktop videoconferencing has become more widely used since the universal adoption of IP protocols in the late 1990s. (Image courtesy of Polycom, Inc., www.polycom.com)