65
AXIS 242S IV - 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 DVR's 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 VOP's is the basic
unit of an MPEG-4 video stream. The GOV contains
different types and numbers of VOP's (I-VOP's, P-VOP's,
etc) as determined by the GOV length and GOV structure.
See also
VOP
.
GOV length
- The GOV length determines the number of
images (VOP's) in the GOV structure.
See also
GOV
and
VOP
.
GOV structure
- The GOV structure describes the
composition of an MPEG-4 video stream, as regards the
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