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Glossary of Terms
vary, depending on how long a user is likely to require the
network connection at a particular location.
DHCP also supports static addresses for e.g. computers running
web servers, which need a permanent IP address.
DNS (Domain Name System) - DNS is used to locate and
translate Internet domain names into IP (Internet Protocol)
addresses. A domain name is a meaningful and
easy-to-remember name for an Internet address. For example
the domain name www.example.com is much easier to
remember than 192.0.34.166. The translation tables for domain
names are contained in Domain name servers.
D-1 - SMPTE digital VTR video standard. It has a resolution of
720 × 486 for NTSC systems and 720 × 576 for PAL systems.
Domain Server - Domains can also be used by organizations
who wish to centralize the management of their (Windows)
computers. Each user within a domain has an account that
usually allows them to log in to and use any computer in the
domain, although restrictions may also apply. The domain
server is the server that authenticates the users on the network.
DVI - Digital Visual Interface, an interface standard that
specifies a connector and signaling methods used to transmit
video information in both analog and digital formats.
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 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.
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 VOPs is the basic unit of
an H.264 video stream. The GOV contains different types and
numbers of VOPs (I-VOPs, P-VOPs) 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 H.264 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.
H.264 - Also known as MPEG-4 Part 10. This is the new
generation compression standard for digital video. H.264 offers
higher video resolution than Motion JPEG or MPEG-4 at the
same bit rate and bandwidth, or the same quality video at a
lower bit rate.
Half-duplex - See Full-duplex.
HDCP - High Bandwidth Digital Content protection, is designed
to protect digital entertainment content that uses the DVI
interface. HDCP encrypts the transmission of digital content
between the video source or transmitter (e.g. encoder or
camera) and the digital display or receiver (e.g. a monitor,
television or projector).
HDMI - High-Definition Multimedia Interface is the first
industry-supported uncompressed, all-digital audio/video
interface. HDMI has the capacity to support existing
high-definition video formats such as 720p, 1080i, and 1080p.
It also supports enhanced definition formats like 480p, and
standard definition formats such as NTSC or PAL.
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.