Axis Communications 241SA

74 AXIS 241QA/AXIS 241SA - Glossary

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 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

integrated Ethernet networking and extremely flexible I/O

options.

Factory default settings - These are the settings that

originally applied for a device when it was first delivered

from the factory. If it should become necessary to reset a

device to its factory default settings, this will, for many

devices, completely reset any settings that were changed

by the user.

Firewall - A firewall works as a barrier between networks,

e.g. between a Local Area Network and the Internet. The

firewall ensures that only authorized users are allowed to

access the one network from the other. A firewall can be

software running on a computer, or it can be a standalone

hardware device.

Fixed dome network camera - This type of camera

cannot be remotely controlled as regards movement, but

is mounted in the same type of dome as a controllable

network dome camera. This camera must be positioned

manually to provide the required coverage.

Fixed network camera - This type of camera cannot be

remotely controlled as regards movement. It must be

positioned manually to provide the required coverage.

Fixed iris - See Autoiris.

Focal length - Measured in millimeters, the focal length

of a camera lens determines the width of the horizontal

field of view, which in turn is measured in degrees.

FTP (File Transfer Protocol) - FTP is an application

protocol that uses the TCP/IP protocols, used to exchange

files between computers/devices on networks.

Frame - A frame is a complete video image. In the 2:1

interlaced scanning format of the RS-170 and CCIR

formats, a frame is made up of two separate fields of

262.5 or 312.5 lines interlaced at 60 or 50 Hz to form a

complete frame, which appears at 30 or 25 Hz. In video

cameras with a progressive scan, each frame is scanned

line-by-line and not interlaced; most are also displayed at

30 and 25 Hz.

Frame rate - The frame rate used to describe the

frequency at which a video stream is updated is measured

in frames per second (fps). A higher frame rate is

advantageous when there is movement in the video

stream, as it maintains image quality throughout.

Full-duplex - Transmission of data in two directions

simultaneously. In an audio system this would describe

e.g. a telephone systems. Half-duplex also provides

bi-directional communication, but only in one direction

at a time, as in a walkie-talkie system. See also Simplex.

G.711 - The international standard for encoding

telephone audio on a 64 kbps channel. It is a pulse code

modulation (PCM) scheme operating at 8 kHz sample rate.

G.726 - A frequently used speech-compression algorithm

in telecommunications due to its high perceived speech

quality and low resource requirements.

Gain - Gain is the amplification factor and the extent to

which an analog amplifier boosts the strength of a signal.

Amplification factors are usually expressed in terms of

power. The decibel (dB) is the most common way of

quantifying the gain of an amplifier.

Gateway - A gateway is a point in a network that acts as

an entry point to another network. In a corporate network

for example, a computer server acting as a gateway often

also acts as a proxy server and a firewall server. A

gateway is often associated with both a router, which

knows where to direct a given packet of data that arrives

at the gateway, and a switch, which furnishes the actual

path in and out of the gateway for a given packet.

GIF (Graphics Interchange Format) - GIF is one of the

most common file formats used for images in web pages.

There are two versions of the format, 87a and 89a.

Version 89a supports animations, i.e. a short sequence of

images within a single GIF file. A GIF89a can also be

specified for interlaced presentation.

GOV (Group Of VOPs) - A group of VOPs is the basic unit

of an MPEG-4 video stream. The GOV contains different

types and numbers of VOPs (I-VOPs, P-VOPs) as

determined by the GOV length and GOV structure. See

also VOP.

GOV length - The GOV length determines the number of

images (VOPs) in the GOV structure.