Video Teleconferencing: Frequently Asked Questions

1.      What is Videoteleconferencing? (jump to explanation)

2.      What are the components of a Videoconferencing system and how does it work? (jump to explanation)

3.      Can Videoconferencing systems connect to more than one site simultaneously? (jump to explanation)

What is Videoteleconferencing?

·         Video Teleconferencing (VTC) is a technology using video and audio signals transmitted over telephone lines (most often ISDN) and computer circuits (IP).

·         VTC is fully interactive - participants at both sites see and hear each other simultaneously.

What are the components of a Videoconferencing system and how does it work?

1.      Source

2.      Translation

3.      Destination

1. Source: A video camera and microphone are usually the signal sources but any device capable of generating a video or audio signal can be routed to a starting point called the CODEC. (see definition of CODEC)

·         Video Camera: A video camera captures the visual image.  Inside a camera, a light sensitive screen coverts red, green and blue light to electricity--white only for a black and white camera. The screen is continually swept many times per second. The results of the sweeping action are sequenced according to one of several possible video standards (NTSC, PAL, SECAM or M-SECAM) and flows to the camera’s output connector. The video signal is connected to the CODEC's video input connector.  There are a variety of CODEC’s configured in various ways.

·         Microphone: A microphone captures the sound portion of your conference.  There are several types of microphones to be used with your VTC equipment, depending on the size of your group and the CODEC’s signal requirements.  Refer to your owner’s manual, or to a qualified technician if you need advice in this area.  The output of your microphone is connected to your CODEC for transmition.

·         Other Sources: Any device capable of generating a video or audio signal can be connected to a CODEC. Potential devices include: DVD players, video cassette players, CD players, audio cassette players, musical instruments (electric) document cameras and computer based audio or video. Multiple devices can simultaneously feed a CODEC if they are routed through a mixer.  For example the source from a video cassette player can be combined with the images of people watching the tape along with their commentary to form the single feed going into a CODEC.

2. Translation: CODEC’s are the beginning and end point of a Videoconferencing System. CODEC’s serve a similar function in video conferencing as MODEM’s (modulator/demodulator) do in computer communication.

·         Videoconferencing CODEC Unit: CODEC is an acronym for COmpression DECompression, COmpressor DECompressor, or COder DECoder.

·         A CODEC compresses its video and audio input using computed algorithms.  The compressed signal is adapted for transmission over either computer (IP) or digital telephone (ISDN) lines. Each ISDN line is similar to two traditional analog lines. Multiple ISDN lines may be bound together for increased bandwidth.

·         Your personal analog phone line may give you mixed and unexpected results if used in videoconferencing.  The amount of bandwidth it supports is usually inadequate for the task of meaningful video communication.  

·         We feed our CODEC a video and audio signal from our cameras and microphones through a matrix. . The CODEC compresses and transmits it over the internet or digital phone lines while simultaneously decompresses the incoming video and audio signal so that it can be viewed on a monitor or projector, locally.

·         The CODEC’s at each site verify the technical signal specifications (handshake).  Once that is done, each CODEC simultaneously transmits near-end video and audio information and receives far-end video and audio information.  The information from the far-end site is converted back to viewable and understandable information passing through the CODEC.

3. Destination: The video and audio signal from a CODEC is routed to appropriate devices for viewing and preserving (recording).

• Viewing devices: --Video monitor/receiver (TV), conventional baseband monitor, or alternate technology such as plasma display, LCD screen, projector, or computer monitor
• Preservation devices: --VCR, DVD burner, video CD burner.

Can Videoconferencing systems connect to more than one site simultaneously?

·         Videoconferencing now allows three or more sites to connect at once through the use of a video bridge called a Multi-Point Control Unit (MCU). Although this type of hardware can be expensive, certain applications, such as distance learning to multiple classrooms, can be more effective in a multi-point configuration.  Additionally, there are commercial companies who will perform this bridging service for you at a nominal cost.  (Instructional Services cannot provide this service, but we can assist you in finding an appropriate agency.)