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To use the glossary, simply click on the first letter of the term of interest below:

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C

C-band

A microwave frequency band. When used for satellite links, the frequencies assigned are:

• uplink (to the satellite): 5.925-6.425 GHz
• downlink (from the satellite): 3.700-4.200 GHz

C-band signals are only slightly attenuated by rainfall, making its use advantageous over Ku-band for some applications.

CATV

Community Antenna TeleVision (system), commonly known as "cable-TV".

CCIR (now ITU-R)

From the French for the International Radio Consultative Committee, an International Telecommunications Union (ITU) (United Nations) body that mainly sets international standards for radio and satellite telecommunications.

CCIR 601

A CCIR recommendation regarding various standardized image resolutions for coding high quality video images, primarily for broadcasting. It provides the foundation for MPEG1 and MPEG2 resolutions and coding.

CCIS

Common Channel Inter-office Signaling. A technique where signaling for a number of channels is carried on a single common channel, in contrast to each channel carrying its own signaling information.

CCITT (now ITU-T)

From the French for the International Telegraph and Telephone Consultative Committee. An International Telecommunications Union (United Nations) body that sets international standards for telecommunications.

CCR

Comparison Category Rating. An ITU-T P.800 subjective test where the signal from a device under test is compared to a known-quality signal and may be rated from better to worse. See also DCR. This is a test performed by HEI.

CCTV

Closed Circuit TeleVision. Non-broadcast television, intended for limited user access, often used for security and monitoring.

CDMA

Code Division Multiple Access, a spread-spectrum technique used with Ku-band satellites to provide mobile data, to truckers for example. CDMA provides benefits under multipath conditions. Also, the IS-95 digital PCS cellular standard in the USA.

Center Clipper

In an Acoustic Echo Canceller (AEC) or a Telephony Echo Canceller (TEC), a clipper that only operates at very low signal levels, to remove residual echo and artifacts.

CEPT

Conference of European Post and Telecom administrations.

CFS

Communications Frame Structure.

CGI

Common Gateway Interface, a method of extending web server functionality using scripts or programs in response to Web browser requests.

Checksum

The information produced by a mathematical technique used to determine whether or not errors have been introduced into a data stream. Usually used for low-bit-rate data transmission. A checksum does not include forward error correction capabilities. Compare with syndrome.

Chrominance

That portion of a composite video signal containing the color information (amplitude and phase information representing color-hue and saturation) in the image.

CIF

(Full) Common Intermediate Format.

When used with ITU-T Rec. H.261, H.263 and other coding methods, the CIF describes the type of coded video frame transmitted.

The CIF is 352H x 288V pixels at video frame rates of 7.5, 10, 15 and 30 fps. Note that a codec providing no more than 7.5 fps is compliant with the recommendation. If better motion handling is needed, look for a numerically greater video frame rate specification.

The following table provides the range of resolutions possible under H.320 and H.323:

 

Picture Format	Luminance Pixels	Video Mode
		H.261	H.263
SQCIF	128H x 96V	O	R
QCIF	176H x 144V	R	R
CIF	352H x 288V	O	O
4CIF	704H x 576V	-	O
16CIF	1408H x 1152V	-	O

where:
S = Sub, Q = Quarter, H = Horizontal pixels, V = Vertical pixels,
R = Required, O = Optional and, - = Not Defined.

CLEC

Competitive Local Exchange Carrier.

CMOS

Subjective testing case: Comparison Mean Opinion Score, ITU-T P.800 subjective listening tests where test subjects compare samples of signals passing through a device under test with a known reference signal.

Semiconductor case: Complimentary Metal Oxide Semiconductor, a high speed technology used for integrated circuits and as CCDs, used for imaging in cameras, for example.

CNI

Calling Number Identification, in telephony.

C.O.

Telco Central Office, where telecommunications equipment is located.

Codec

COder - DECoder. A digital device for the encoding and decoding of video and/or audio signals, usually to permit their transmission in a compressed and/or encrypted form.

Color Burst

The part of an NTSC or PAL composite video signal which provides a frequency and phase reference for the demodulation of the color information in codecs and video monitors.

Common Carrier

A telephone company or similar supplier of non-private telecommunications services (telecommunications usage).

Compander

COMPresser/expANDER. Both A-law and μ-law companders are used in telephony to improve the subjective signal-to-(quantizing)-noise ratio for audio communications and telephony.

Component Video Signal

A video signal where the red (R), green (G) and blue (B) picture components are present as individual signals. Synchronization information may be included with the G signal or may be a separate signal. Less commonly (for videoconferencing, s-video), luminance and chrominance signals (YIQ or YUV) may be provided as separate signals, also referred to as component signals.

Composite Video Signal

A video signal incorporating luminance, chrominance and synchronizing information.

Compression, data

The process of reducing the quantity of data necessary to transmit or store. See below:

Compression, lossless

A process allowing data compression and its subsequent restoration to its original form without any loss of information. PKZip, ZOO, RAR and ARC are common examples. See also Huffman Coding.

Compression, lossy

A data compression process that makes subsequent complete recovery of the original data impossible. This approach is commonly used for still- or motion-images where the recovered image must only be subjectively acceptable. Algorithm examples include JPEG, MPEG1, MPEG2, MPEG4, H.261 and H.263. Note that lossy compression can provide significantly greater compression than lossless compression techniques. See also Cosine Transform.

Conditional Replenishment

In motion video compression, referrs to the conditional transmission of information from blocks of pixels in adjacent video frames only if the content has changed materially or after a certain period of time has elapsed since the last refresh.

Continuous Presence

A videoconferencing technique, allowing all participants to see all other perticipants, all the time. It makes use of a video processing, transmission and display technique generally implemented by extracting the horizontal center half of video images from two cameras, and electronically stacking the two center halves into a single video signal or data stream for transmission. At the receive location(s), the images may be displayed one above the other on a single video monitor or alternatively, viewed on two side-by-side video monitors. Continuous presence can be used with video codecs.

Cosine Transform

The two-dimensional discrete cosine transform (DCT) developed in 1981 by Wen-hsiung Chen (then Chief Scientist, Compression Labs, Inc., San Jose, CA). DCT is the basis of most lossy still-image and motion video compression algorithms including JPEG, MPEG1, MPEG2, MPEG4, H.261 and H.263 standards. The DCT converts blocks of picture elements from the vertical and horizontal spatial domains to the transform domain. Put another way, blocks of pixels in rows and columns are converted to the frequency domain. Depending on a number of factors, the coefficients produced may be truncated by varying degrees prior to storage or transmission without subjectively affecting the recovered images.

CPE

Customer-Premise Equipment.

CRC

Cyclic Redundancy Code. An error checking method for digital signals.

Cryptography

Originally, the study of secret writing, including codes and ciphers. Nowadays, the science of mathematical techniques called encryption (which see) allowing distribution or transmission of information or data so that it can only be read or used by the intended recipients.

CSDN

Circuit Switched Digital Network.

CSU

Channel Service Unit. Usually a customer-owned CPE device that provides an interface between digital equipment (like codecs) and transmission facilities that comply with FCC or other regulatory requirements. A CSU often includes network switching and control and/or line-conditioning capabilities.

CTI

Computer Telephony Integration, computer applications which augment telephony.

CVSDM

Continuously Variable Slope Delta Modulation. A digital audio coding technique providing good quality audio, especially robust under high bit error rate conditions.

To use the glossary, click on the first letter of the term of interest:

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

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