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AXIS COMMUNICATIONS
<Product Name> Quick User’s Guide
AXIS 211M - Glossary of Terms
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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.
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) - An application protocol that uses the
TCP/IP protocols. It is 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.
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 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. 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).
I-VOP - See VOP.
IPv6 (Internet Protocol version 6) - A set of specifications designed as
improvements to the current IP Version 4. Network hosts and
intermediate nodes with either IPv4 or IPv6 can handle packets for
either level of the Internet Protocol.
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.