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The Main Components of a Videoconferencing System
Videoconferencing Codec Unit
This is the heart of the system. This box takes the video and audio from the camera and microphone and compresses it down, transmits it over your network/digital phone line and expands the incoming video and audio signal so that you can output to your TV monitor.
Camera
Most conferencing systems include a video camera with zoom lens, pan/tilt and remote control capabilities. The camera captures your video image and sends the picture to the codec.
Microphone
Typical videoconferencing systems include a standard conference table-type microphone. This captures your audio and sends the information to the codec.
TV Video Monitor, XGA Computer Monitor, Plasma Display, LCD/DLP Projector…
These display devices show the images received from the videoconferencing codec. Videoconferencing systems can have multiple display devices.
NT-1 (for use with ISDN systems)
These little electronic devices are called terminal adapters and convert ISDN into a format your conferencing system can use. You need one for each ISDN line that you bring into your system. The NT-1 for example, terminates 1 ISDN line while the NT-3 will terminate 3 lines.
Stands and Equipment Carts
Your room aesthetics are usually improved by having all your equipment neatly organized in one spot. Typically, you would place your TV monitor, codec and camera on top of the stand and below you have a cabinet to hold other equipment, like a computer or VCR, etc.
Network Connection
The pipe that carries data between your video-systems. The size of the pipe and your ability to access it in a consistent manner will determine both your video performance and quality of service. The pipe can be almost any type of network connection from an ISDN phone line to a dedicated PRI/T-1 connection.
Glossary
Bandwidth
A measure of spectrum (frequency) use or capacity. For instance, a voice transmission via phone requires a bandwidth of 3KHz. A television channel occupies 6MHz of bandwidth. In a videoconference based system, a larger bandwidth of 17.5-72 MHz is used to spread the TV signal in order to prevent interference.
Codec
This is the heart of your videoconferencing system. It stands for compression and decompression device.
ISDN (Integrated Services Digital Network)
The use of digital line circuits to provide end-to-end digital service. ISDN may consist of BRI or PRI service.
TCP/IP (Transmission Control Protocol/Internet Protocol)
The suite of networking protocols that let different types of equipment communicate over the internet or other packet based networks.
h.323
The audio and video standards used to specify voice and video communications over an IP network.
h.320
The audio and video standards used to specify voice & video over ISDN lines.
h.324
The standards used to specify voice and video transmission over traditional analog phone lines.
T-1
Typically a fiber optic based network that connects your office through a local loop to a point of presence for a major network carrier (AT&T, Sprint, World.com, etc.). A T-1 provides 1.54Mb bandwidth and can be fractionalized into 64kb or greater channels.
PRI (Primary Rate Interface)
ISDN equivalent of a T-1 circuit. It provides 23 B plus D (in North America) or 30B plus D (in Europe) running at 1.54Mbps and 2.048Mbps respectively. Each channel is 64Kbps. One channel is reserved as the D channel, the balance are bearer channels
DSL (Digital Subscriber Line)
A local-loop cable pair that is handling a digital signal using 2B1Q line coding. Maximum distance is 1800 feet away from the pop. Signal quality degrades over distance. Three types are available:
ADSL- asymmetric DSL - The bandwidth in and out are different.
SDSL-symmetric DSL - The bandwidth in and out are the same.
IDSL-ISDN based DSL - This is a residential format that can be used at further distances away. This is not as robust as ADSL & SDSL.
BRI
Provides two 64Kbps B ("bearer") channels to carry voice, video, and data. Separate D channel is used for setup and signaling. (2B+D)
ATM (Asynchronous Transfer Mode)
High speed, high bandwidth, low delay, transport technology, integrating multiple data types (voice, video, data).
Cable Modem
A hook up to your cable TV system that allows you to transmit computer information and access the internet through your cable company.
Broadband
A generic term applied to networks having bandwidth significantly greater than traditional telephone networks. Broadband systems are capable of carrying a vast quantity of data simultaneously.
T.120
International teleconferencing standard for data sharing and collaborative computing.
POTS (Plain Old Telephone System)
This is the traditional analog system for voice we use at home.
TV Frame Rate
The measure of video frames per second on a standard television. TV refreshes at a frame rate of 30 frames per second.
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