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AXIS 243SA - Glossary
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 iris - See Autoiris.
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.
See also GOV and VOP.
GOV structure - The GOV structure describes the
composition of an MPEG-4 video stream, as regards the
type of images (I-VOPs or P-VOPs) included in the stream,
and their internal order. See also GOV and VOP.
Half-duplex - See Full-duplex.
HTML (Hypertext Markup Language) - HTML is the set
of "markup" symbols or codes inserted in a file intended
for display in web browser. The markup tells the browser
how to display the page's words and images for the user.
HTTP (Hypertext Transfer Protocol) - H
TTP is the set of
rules for exchanging files (text, graphic images, sound,
video, and other multimedia files) on the web. The HTTP
protocol runs on top of the TCP/IP suite of protocols.
HTTPS (Hypertext Transfer Protocol over SSL) - HTTPS
is a protocol used by web browsers and servers to encrypt
and decrypt user page requests and the pages returned by
the server. The encrypted exchange of information is
governed by the use of an HTTPS certificate (issued by a
Certificate Authority), which guarantees the authenticity
of the server.
Hub - A (network) hub is used to connect multiple devices
to the network. The hub transmits all data to all devices
connected to it, whereas a switch will only transmit the
data to the device it is specifically intended for.
IEEE 802.11 - A family of standards for wireless LANs.
The 802.11a standard supports 1 or 2 Mbit/s transmission
on the 5 GHz band. IEEE 802.11b supports data rates up
to11 Mbit/s on the 2.4 GHz band, while 802.11g allows up
to 54 Mbit/s on the 2.4 GHz band.
Image compression - Image compression minimizes the
file size (in bytes) of an image. Two of the most common
compressed image formats are JPEG and GIF. See also
MPEG and Motion JPEG.
Interlacing - Interlaced video is video captured at 50
pictures (known as fields) per second, of which every 2
consecutive fields (at half height) are then combined into