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AXIS 231D+/232D+ - Glossary of Terms
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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) - HTTP 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.
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
802.11 standard supports 1 or 2 Mbit/s transmission on the
2.4 GHz band. IEEE 802.11b specifies an 11 Mbit/s data rate
on the 2.4 GHz band, while 802.11a allows up to 54 Mbit/s
on the 5 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.
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 1
frame. Interlacing was developed many years ago for the
analog TV world and is still used widely today. It provides
good results when viewing motion in standard TV pictures,
although there is always some degree of distortion in the
image.
To view interlaced video on e.g. a computer monitor, the
video must first be de-interlaced, to produce progressive
video, which consists of complete images, one after the
other, at 25 frames per second. See also Progressive scan.
IP (Internet Protocol) - The Internet Protocol is a method
transmitting data over a network. Data to be sent is divided
into individual and completely independent "packets." Each
computer (or host) on the Internet has at least one address
that uniquely identifies it from all others, and each data
packet contains both the sender's address and the receiver's
address.
The Internet Protocol ensures that the data packets all arrive
at the intended address. As IP is a connectionless protocol,
which means that there is no established connection
between the communication end-points, packets can be sent
via different routes and do not need to arrive at the
destination in the correct order.
Once the data packets have arrived at the correct
destination, another protocol - Transmission Control
Protocol (TCP) - puts them in the right order. See also TCP.
IP Address - An IP address is simply an address on an IP
network used by a computer/device connected to that
network. IP addresses allow all the connected
computers/devices to find each other and to pass data back
and forth.
To avoid conflicts, each IP address on any given network
must be unique. An IP address can be assigned as fixed, so
that it does not change, or it can be assigned dynamically
(and automatically) by DHCP.
An IP address consists of four groups (or quads) of decimal
digits separated by periods, e.g. 130.5.5.25. Different parts
of the address represent different things. Some part will
represent the network number or address, and some other
part will represent the local machine address.
See also IP (Internet Protocol).
Infrared (IR) - Infrared radiation is radiation at a longer
wavelength than visible light, which means it cannot be
seen by the naked human eye. As infrared radiation can be
detected as heat, this can be shown on a screen or captured
by a digital camera, with hotter objects showing up brighter
against colder surroundings (e.g. a human body against a
colder background).
As color cameras can "see" infrared radiation as well as
visible light, these cameras are equipped with an IR-cut
filter, to prevent distortion of the colors the human eye can
see. To use the camera in very dark locations or at night,
this filter can be removed, to allow infrared radiation to hit
the image sensor and thus produce images.
An infrared lamp can be used for improved illumination for
night surveillance, whilst not producing any extra visible
light.
Inputs/Outputs (I/O's) - The digital I/Os on, for example, a
network camera can be used to connect any device that can
toggle between an open and a closed circuit.
If, for example, a door switch is used as an input device,
opening the door could trigger the upload of video images
and the sending of notification messages.
An output might, for example, be used to automatically
start a siren when there is a motion detection trigger.
I-VOP - See VOP.
JPEG (Joint Photographic Experts Group) - Together with
the GIF file format, JPEG is an image file type commonly
used on the web. A JPEG image is a bitmap, and usually has
the file suffix '.jpg' or ".jpeg." When creating a JPEG image,
it is possible to configure the level of compression to use. As
the lowest compression (i.e. the highest quality) results in
the largest file, there is a trade-off between image quality
and file size.
kbit/s (kilobits per second) - A measure of the bit rate, i.e.
the rate at which bits are passing a given point. See also Bit
rate.
LAN (Local Area Network) - A LAN is a group of
computers and associated devices that typically share
common resources within a limited geographical area.
Linux - Linux is an open source operating system within
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