Industry standards - Glossary

In last month's issue of NETWORK Solutions we kicked off our glossary part two - looking at the minefield that is industry standards. This month we move on to letters C and D ...

Caesium standard - This is a standard for defining frequency, basedry part two - looking at the minefield that is industry standards. This month we move on to letters C and D ... on the microwave spectral line of caesium-133 atoms. The frequency involved is that of the energy absorbed from photons which hit a caesium-133 atom and excite the outermost electron in the atom and cause it to jump from lower to a higher electron shell. A caesium clock, which measures time according to this definition, is the most accurate clock possible with today's technology.

CCIR - Comite Consultatif International des Radiocommunications. This French organisation is responsible for setting international standards for European television.

CCIR 601 - CCIR's standard, internationally agreed-upon, which covers the digital encoding of colour television, derived from the earlier SMPTE RP125 and EBU 324E standards. It specifies the luminance and chrominance of the transmission, using frequencies which are suitable for both NTSC and PAL/SECAM broadcasts.

CCIR 656 - Another CCIR standard, this one defines the electrical and mechanical interfaces for digital TV. This includes the serial and parallel interfaces.

CCITT - The Comite Consultatif Internationale de Telegraphique et Telephonique (the Consultative Committee on International Telegraphy and Telephony) is part of the International Telecommunications Union (ITU), a UN body based in Geneva. Originally set up for telegraphy and telephony, it had to expand to include cutting edge technologies such as ISDN and ATM, and sets many of the European-agreed standards on these matters, although it doesn't actually have any power to enforce these standards - they are 'recommendations'.

CCITT V.24 - This set of standards specifies interfaces, such as a description of each of the pins. It is comparable although not exactly the same as the American RS-232-C. There are lots of these V standards - collect the whole set when we reach V in a few months.

Centronics printer standard - A narrower definition than either the RS-232-C or V.24 standards, the Centronics standard for 36-pin parallel connectors has been adopted by a number of companies, including IBM.

CIF - This is a CCITT standard for ISDN, specifically for video-conferencing, and part of the larger CCITT H.261/Px64 standard. It defines the number of luminance lines (288), the number of pixels per line (352) and the rate (30 frames/s). It uses two ISDN B channels, with 32Kbps for voice and the rest for the video image.

Continuity check zone - Part of CCITT recommendation 271, it is defined as a single frequency of 2,000Hz, continually transmitted by the sending exchange and looped back by the receiving exchange; the completed loop shows that the channel is available.

De facto standard - A de facto standard is one which is in current, widespread use, but has no official approval. Often, they become de jure standards due to their ubiquity. For example, the de jure standard IEEE 802.3 for Ethernet, which was approved after the standard was already in use.

De jure standard - A de jure standard is one which has been approved by an official body. Often, a widely used de facto standard will become a de jure standard.

DES - The data encryption standard is the algorithm for encrypting data as defined by the National Bureau of Standards; data coded in this way can only be decoded using the decryption key. However, since it is over 20 years old, there are more advanced and more secure proprietary systems available.