Datasheet

35
AXIS Camera Station - Glossary of Terms
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.
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, 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. 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 standard television set, but lacks the
electronics to pick up regular television signals.
Motion JPEG - Motion JPEG is a simple compression/decompression
technique for networked video. Latency is low and image quality is
guaranteed, regardless of movement or complexity of the image. Image
quality is controlled by adjusting the compression level, which in turn
provides control over the file size, and thereby the bit rate.
High-quality individual images from the Motion JPEG stream are easily
extracted. See also JPEG.
Megapixel - See Pixel.
MPEG (Moving Picture Experts Group) - The Moving Picture Experts Group
develops standards for digital video and audio compression. It operates under
the auspices of the International Organization for Standardization (ISO). The
MPEG standards are an evolving series, each designed for a different purpose.
MPEG-2 - MPEG-2 is the designation for a group of audio and video coding
standards, and is typically used to encode audio and video for broadcast
signals, including digital satellite and Cable TV. MPEG-2, with some
modifications, is also the coding format used by standard commercial DVD
movies.
MPEG-4 - MPEG-4 is a group of audio and video coding standards and