Axis Communications Video Server 243Q Blade - Manual (Page 65)

65 AXIS 243Q Blade - Glossary
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
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).
Inputs/Outputs (I/Os) - 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.
For example, if 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.
ISMA (Internet Streaming Media Alliance) - ISMAs goal
is: "To accelerate the adoption and deployment of open
standards for streaming rich media content such as video,
audio, and associated data, over Internet protocols."
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.
Lux - A standard unit of illumination measurement.
MAC address (Media Access Control address) - A MAC
address is a unique identifier associated with a piece of
networking equipment, or more specifically, its interface
with the network. For example, the network card in a
computer has its own MAC address.
Manual iris - This is the opposite of 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.
Commonly used to give the "speed" of a network. A LAN
might run at 10 or 100 Mbit/s. See also Bit rate.
Monitor - A monitor is very similar to a television set, but