Video Server User's Manual

67
AXIS 243Q Blade - Glossary
(set of communication rules) that allows corporations to
extend their own corporate network through private
"tunnels" over the public Internet. In this way a
corporation can effectively use a WAN (Wide Area
Network) as a large single LAN (Local Area Network). This
kind of interconnection is known as a virtual private
network (VPN).
Pre/post alarm images - The images from immediately
before and after an alarm. These images are stored in a
buffer for later retrieval.
Progressive scan - Progressive scan, as opposed to
interlaced video, scans the entire picture, line by line
every sixteenth of a second. In other words, captured
images are not split into separate fields as in interlaced
scanning.
Computer monitors do not need interlace to show the
picture on the screen, but instead show them
progressively, on one line at a time in perfect order i.e. 1,
2, 3, 4, 5, 6, 7 etc., so there is virtually no "flickering"
effect. In a surveillance application, this can be critical
when viewing detail within a moving image, such as a
person running. A high-quality monitor is required to get
the best from progressive scan. See also Interlacing.
Protocol - A special set of rules governing how two
entities will communicate. Protocols are found at many
levels of communication, and there are hardware
protocols and software protocols.
Proxy server - In an enterprise that uses the Internet, a
proxy server acts as an intermediary between a
workstation user and the Internet. This provides security,
administrative control, and a caching service. Any proxy
server associated with a gateway server, or part of a
gateway server, effectively separates the enterprise
network from the outside network and the local firewall.
It is the firewall server that protects the enterprise
network from outside intrusion.
PTZ (Pan Tilt Zoom) - A PTZ-enabled camera can be
remotely controlled so as to change the view from the
camera. Panning is the movement of the camera along its
horizontal axis, tilting is the movement of the camera
along its vertical axis, and zooming is the adjustment of
the zoom lens to magnify the view.
P-VOP - See VOP.
Resolution - Image resolution is a measure of how much
detail a digital image can hold: the greater the resolution,
the greater the level of detail. Resolution can be specified
as the number of pixel-columns (width) by the number of
pixel-rows (height), e.g. 320x240.
Alternatively, the total number of pixels (usually in
megapixels) in the image can be used. In analog systems
it is also common to use other format designations, such
as CIF, QCIF, 4CIF, etc.
RS-232 - A long-established standard that describes the
physical interface and protocol for low-speed serial data
communication between devices. This is the interface that
e.g. a computer uses to talk to and exchange data with a
modem and other serial devices.
RS-485 - An upgraded version of RS-422 that supports
up to 32 devices on the same connection. RS-485 is an
electrical specification of a two-wire, half-duplex,
multipoint serial connection. It enables the configuration
of inexpensive local networks and multidrop
communications links. It offers high data transmission
speeds (up to 10Mbit/s), and as it uses a differential
balanced line over twisted pair (like RS-422), it can span
relatively large distances (4000 feet or 1200 meters).
RS-485 only specifies the electrical characteristics of the
driver and the receiver. It does not specify or recommend
any data protocol.
RTCP (Real-Time Control Protocol) - RTCP provides
support for real-time conferencing of groups of any size
within an intranet. This support includes source
identification and support for gateways like audio and
video bridges as well as multicast-to-unicast translators.
It offers quality-of-service feedback from receivers to the
multicast group as well as support for the synchronization
of different media streams.
RTP (Real-Time Transport Protocol) - An Internet
protocol for the transport of real-time data, e.g. audio and
video. It can be used for media-on-demand as well as
interactive services such as Internet telephony.
RTSP (Real Time Streaming Protocol) - A control
protocol, and a starting point for negotiating transports
such as RTP, multicast and Unicast, and for negotiating
codecs. RTSP can be considered a "remote control" for
controlling the media stream delivered by a media server.
RTSP servers typically use RTP as the protocol for the
actual transport of audio/video data.
Router - A device that determines the next network point
to which a packet should be forwarded on its way to its
final destination. A router creates and/or maintains a
special routing table that stores information on how best
to reach certain destinations. A router is sometimes
included as part of a network switch. See also Switch.
Security surveillance - Network video's advanced
functionality makes it highly suited to the applications
involved in security surveillance. The flexibility of digital
technology enhances security personnel's ability to
protect people, property and assets. Such systems are
therefore an especially attractive option for companies
currently using CCTV.
Server - In general, a server is a computer program that
provides services to other computer programs in the same
or other comp
uters. A computer running a server program
is also frequently referred to as a server. In practice, the
server may contain any number of server and client
programs. A web server is the computer program that