User`s manual

33
AXIS 206 - Glossary
(pixels) that convert light energy into electronic signals. Its
size is measured diagonally and can be 1/4", 1/3", 1/2" or
2/3".
CCTV (Closed Circuit Television) - A CCTV system is a
closed/private video system, usually constructed with
coaxial cabling, and used within a single building/group of
buildings. It is used to visually monitor the location for
security or industrial purposes. Video from the CCTV system
can be recorded and viewed on-site or remotely.
CCTV video camera - A traditional CCTV video camera is
an analog camera, available in both monochrome (black and
white) and color. Cameras can be set in fixed positions or
placed on "Pan/Tilt/Zoom" devices, which allow the camera
to be maneuvered. Using a zoom lens provides a closer view
of the object being viewed. CCTV analog video cameras can
be viewed over a computer 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.
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.
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.
Dome network camera - A remotely controllable camera
mounted in a special housing, characterized by the dome
shaped glass or plastic covering behind which the camera
resides. Usually mounted on a ceiling and looking
downwards, a dome camera can often rotate up to 360
degrees, thus providing excellent coverage of large areas.
Duplex - See Full-duplex.
DVD (Digital Versatile Disc) - An optic disc with the same
physical size as a CD, but with significantly greater storage
capacity.
DVR (Digital Video Recorder) - A DVR records analog
video to a hard disk in digital format. Most DVR's use the