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Glossary of Terms
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.
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-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.
Multicast - Bandwidth-conserving technology that reduces
bandwidth usage by simultaneously delivering a single stream
of information to multiple network recipients.
Network connectivity - The physical (wired or wireless) and
logical (protocol) connection of a computer network or an
individual device to a network, such as the Internet or a LAN.
NTSC (National Television System Committee) - NTSC is the
television and video standard in the United States. NTSC
delivers 525 lines at 60 half-frames/second.
NWay - A network protocol that automatically negotiates the
highest possible common transmission speed between two
devices.