Axis 0213-004 Datasheet download pdf (Page 25)

AXIS 292 - Glossary of Terms

Encoder - See video encoder.

Ethernet - Ethernet is the most widely installed local area network

technology

. An Ethernet LAN typically uses special grades of twisted pair

wires. The most commonly installed Ethernet systems are 10BASE-T and

100BASE-T10, which provide transmission speeds up to 10 Mbps and 100

Mbps respectively.

ETRAX (Ethernet Token Ring AXIS) - Axis' own microprocessor.

Factory default settings - These are the settings that originally applied

for a devic

e 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

cal 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.

Fixed iris - See aut

oiris.

Focal length - Measured in millimetres, the focal length of a camera lens

determin

es the width of the horizontal field of view, which in turn is

measured in degrees.

FTP (File Transfer Protocol) - FTP is 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

canning 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 upd

ated 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 a

udio 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

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

forma

ts 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 VOPs is the basic unit of an MPEG-4

video stream.

The GOV contains different types and numbers of VOPs

(I-VOPs, P-VOPs, etc) as determined by the GOV length and GOV

structure. See also VOP.

GOV length - The GOV length determines the number of images (VOPs)

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-VOPs or P-VOPs)

included in the stream, and their internal order. See also GOV and VOP.

Half-duplex - See Fu

ll-duplex.

HTML (Hypertext Markup Language) - HTML is the set of "markup"

ymbols 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

exchangin

g 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.

HTTPS (Hypertext Transfer Proto

col over SSL) - HTTPS is a web

protocol used by browsers and web servers to encrypt and decrypt user

page requests and the pages returned by the server.

The encrypted exchange of information is governed by the use of an

TTPS certificate (issued by a Certificate Authority), which guarantees the

authenticity 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 802.11

tandard 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

field

s) 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

de-interlaced, to produce progressive video, which consists of complete

image

s, 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 netwo

rk. 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

intende

d 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 the

m in the right

order. See also TCP.

IP Address - An IP address is simply an address on an IP network used

y 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 addre

ss 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

eparated 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.

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Axis 0213-004 Datasheet Page 25

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