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AXIS 243SA - Glossary
network by using a video server.
CGI (Common Gateway Interface) - A specification for
communication between a web server and other (CGI)
programs. For example, a HTML page that contains a form
might use a CGI program to process the form data once it
is submitted.
CIF (Common Intermediate Format) - CIF refers to the
analog video resolutions 352x288 pixels (PAL) and
352x240 pixels (NTSC). See also Resolution.
Client-server - Client-server describes the relationship
between two computer programs in which one program,
the client, makes a service request from another program,
the server, which fulfils the request. Typically, multiple
client programs share the services of a common server
program. A web browser is a client program that requests
services (the sending of web pages or files) from a web
server.
CMOS (Complementary Metal Oxide Semiconductor) - A
CMOS is a widely used type of semiconductor that uses
both negative and positive circuits. Since only one of the
circuit types is on at any given time, CMOS chips require
less power than chips using just one type of transistor.
CMOS image sensors also allow processing circuits to be
included on the same chip, an advantage not possible
with CCD sensors, which are also much more expensive to
produce.
Coaxial cable - Coaxial cable is the standard means of
transmitting analog video in a CCTV system. Coaxial is
also used by cable companies to distribute television in
residential buildings.
Codec - In communications engineering, a codec is
usually a coder/decoder. Codecs are used in integrated
circuits or chips that convert e.g. analog video and audio
signals into a digital format for transmission. The codec
also converts received digital signals back into analog
format. A codec uses analog-to-digital conversion and
digital-to-analog conversion in the same chip.
Codec can also mean compression/decompression, in
which case it is generally taken to mean an algorithm or
computer program for reducing the size of large files and
programs.
Composite video - A type of video signal in which the
red, blue and green signals (sometimes audio signals too)
are mixed together.
Compression - See Image Compression.
Contrast - Defines the degree of difference between the
lightest and darkest parts of an image or video stream.
Control unit - If a CCTV system has more than one
camera, there must be a way to control the video signals
going to recorders and monitors. There are three basic
types of Video Control Unit: Multiplexer, Switch and
Quad.
dB (Decibels) - A unit to measure sound level changes. A
3dB change is the smallest level change we can hear. A
3dB change is actually twice or half the audio power
level. A gain of 0dB will leave the signal level unchanged.
DC-Iris - This special type of iris is electrically controlled
by the camera, to automatically regulate the amount of
light allowed to enter.
Decoder - See Video decoder.
De-interlacing - See Interlacing.
DHCP (Dynamic Host Configuration Protocol) - DHCP is
a protocol that lets network administrators automate and
centrally manage the assignment of Internet Protocol (IP)
addresses to network devices in a network.
DHCP uses the concept of a "lease" or amount of time that
a given IP address will be valid for a computer. The lease
time can vary, depending on how long a user is likely to
require the network connection at a particular location.
DHCP also supports static addresses for e.g. computers
running web servers, which need a permanent IP address.
DIP switch - A DIP switch is an electric switch that is
packaged in a group in a standard dual in-line package
(DIP).
DNS (Domain Name System) - DNS is used to locate and
translate Internet domain names into IP (Internet
Protocol) addresses. A domain name is a meaningful and
easy-to-remember name for an Internet address. For
example the domain name www.example.com is much
easier to remember than 192.0.34.166. The translation
tables for domain names are contained in Domain name
servers.
Domain server - Domains can also be used by
organizations that wish to centralize the management of
their (Windows) computers. Each user within a domain
has
an account that usually allows them to log in to and
use any computer in the domain, although restrictions
may also apply. The domain server is the server that
authenticates the users on the network.
Duplex - See Full-duplex.
DVR (Digital Video Recorder) - A DVR records analog
video to a hard disk in digital format. Most DVRs use the
MPEG-2 format for encoding analog video signals.
Encoder - See Video encoder.
Ethernet - Ethernet is the most widely installed local area
network technology. An Ethernet LAN typically uses
special grades of twisted pair wires. The most commonly
installed Ethernet systems are 10BASE-T and
100BASE-T10, which provide transmission speeds up to
10 Mbps and 100 Mbps respectively.
ETRAX (Ethernet Token Ring AXIS) - The ETRAX chip is
the cornerstone of Axis technology and the 'brain' in
nearly all Axis products. A multipurpose Linux chip with