Call
Multimedia communication between two or more H.323 endpoints.

Call Signaling Channel
Reliable channel used to convey call setup messages following Q.931

Camera presets
Allows pre-defined camera angles to be programmed into a videoconferencing system.

Carrier
A term used to refer to various telephone companies that provide Local, long distance or value added services.

Centralized Multipoint Conference
A call in which all participating terminals communicate in a point-to-point fashion with an MCU.

CIF
Common Intermediate Format, an optional part of the ITU-T's H.261 and H.263 standards. CIF specifies 288 non-interlaced luminance lines, that contain 176 pixels. CIF is to be sent at frame rates of 7.5, 10, 15, or 30 per second. When operating with CIF, the number of bits that result can not exceed 256 K bits (where K equals 1024).

Codec
Coder-Decoder. Videoconferencing hardware that codes the outgoing video and audio signals and decodes the incoming signals. Prior to transmission, the codec converts analog-signals to digital signals and compresses the digital signals. Incoming audio and video must be decompressed and converted from digital back to analog.

Component video
Video system in which colour components are carried as discrete signals, either as a colour difference matrix of luma (Y) and two colour difference signals (canonically BY and RY), or as a tristimulus colour separation system (for example RGB). In current technical usage, it most commonly refers to the former.

Composite video
Video signal or interface in which the transmission of luma, chroma and synchronising pulses is combined on a single circuit.

Compressed video
When the vast amount of information in a normal tv transmission is squeezed into a fraction of its former bandwidth by a codec, the resulting compressed video can be transmitted more econmically over a smaller carrier. Some information is dacrificed in the process, which may result in diminished picture and sound quality.

CP, Continuous Presence
A multipoint videoconferencing mode where remote sites are displayed continuously rather than being switched.