Thursday, May 21, 2009

Video Conferencing

A videoconference (also known as a videoteleconference or “VTC”) is a set of interactive telecommunication technologies which allow two or more locations to interact via two-way video and audio transmissions simultaneously. It has also been called visual collaboration and is a type of groupware. It differs from the standard videophone in that it is designed to serve a conference rather than just individuals.

The basic technology used in a video conference / videoteleconference (VTC) system is digital compression of audio and video (A/V) streams in real time. The hardware or software that performs compression is called a codec (coder/decoder). Compression rates of up to 1:500 can be easily achieved (at least today). The resulting digital stream of 1s and 0s is subdivided into labeled packets, which are then transmitted through a internet pipe of some kind (usually ISDN or IP). The use of audio modems in the transmission line allow for the use of POTS, or the Plain Old Telephone System, in some low-speed applications, such as videotelephony, because they convert the digital pulses to/from analog waves in the audio spectrum range.

The other components required for a VTC system include:

  1. Video input : video camera or webcam

  2. Video output: computer monitor , television or projector

  3. Audio input: microphones

  4. Audio output: usually loudspeakers associated with the display device or telephone

  5. Data transfer: analog or digital telephone network, LAN or Internet

Simultaneous videoconferencing among three or more remote points is possible by means of a Multipoint Control Unit (MCU). This is a bridge that interconnects calls from several sources (in a similar way to the audio conference call). All parties call the MCU unit, or the MCU unit can also call the parties which are going to participate, in sequence. There are MCU bridges for IP and ISDN-based videoconferencing. There are MCUs which are pure software, and others which are a combination of hardware and software. An MCU is characterized according to the number of simultaneous calls it can handle, its ability to conduct transposing of data rates and protocols, and features such as Continuous Presence, in which multiple parties can be seen onscreen at once.

MCUs can be stand-alone hardware devices, or they can be embedded right into the dedicated VTC units.

Some systems are capable of multipoint conferencing with no MCU, stand-alone, embedded or otherwise. These use a standards-based H.323 technique known as "decentralized multipoint", where each station in a multipoint call exchanges video and audio directly with the other stations with no central "manager" or other bottleneck. The advantages of this technique are that the video and audio will generally be of higher quality because they don't have to be relayed through a central point. Also, users can make ad-hoc multipoint calls without any concern whatsoever for the availability or control of an MCU. This added convenience and quality comes at the expense of some increased network bandwidth, because every station must transmit to every other station directly.

There are basically two kinds of VTC systems; Dedicated systems, and Desktop systems:

Dedicated systems have all required components packaged into a single piece of equipment, usually a console with a high quality remote controlled video camera. These cameras can be controlled at a distance to pan left and right, tilt up and down, and zoom. They became known as PTZ cameras. The console contains all electrical interfaces, the control computer, and the software or hardware-based codec. Omnidirectional microphones are connected to the console, as well as a TV monitor with loudspeakers and/or a video projector. Along with this solution comes a huge financial investment that tends to scare of most enthusiasts. There is also the risk of fast outdated technologies, which become inferior quickly as newer models come out. (This is not as prevalent in desktop systems with updating software and inexpensive hardware).

There are several types of dedicated VTC devices:


  1. Large group VTC are non-portable, large, more expensive devices used for large rooms and auditoriums.

  2. Small group VTC are non-portable or portable, smaller, less expensive devices used for small meeting rooms.

  3. Individual VTC are usually portable devices, meant for single users, have fixed cameras, microphones and loudspeakers integrated into the console.

Desktop systems are add-ons (hardware boards, usually) to normal PCs, transforming them into VTC devices. A range of different cameras and microphones can be used with the board, which contains the necessary codec and transmission interfaces. Most of the desktops systems work with the H.323 standard. Videoconferences carried out via dispersed PCs are also known as e-meetings, online meetings, virtual meetings, or web conferencing.

Desktop solutions are more flexible than dedicated systems, and are only a fraction of the cost. To try a desktop solution today, visit http://www.viack.com/ and download a free trial of VIA3 today, risk free.