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AXIS 207MW - Glossary of Terms
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
type of images (I-VOP's or P-VOP's) 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) - 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.
802.11b supports a data rate of 11 Mbit/s on the 2.4 GHz
band, 802.11a allows up to 54 Mbit/s on the 5 GHz band,
and 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.
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
for 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.
Internet Protocol version 6 - IPv6 follows IPv4 (see IP
(Internet Protocol) above) as the second version of the
protocol to be formally adopted for general use. IPv6 is
intended to provide further IP addresses for the increasing
number of networked devices. IPv6 supports 3.4x10
38
IP
addresses.
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).
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
the Unix family. Because of its robustness and availability,
Linux has won popularity in the open source community
and among commercial application developers.
MAC address (Media Access Control address) - A MAC
address is a unique identifier associated with a piece of
networking equipment, or more specifically, with its
interface with the network. For example, the network card
in a computer has its own MAC address.
Manual iris - This is the opposite to an autoiris, i.e. the
camera iris must be adjusted manually to regulate the
amount of light allowed to reach the image sensor.
Mbit/s (Megabits per second) - A measure of the bit rate,
i.e. the rate at which bits are passing a given point.