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Glossary of Terms
PAL (Phase Alternating Line) - PAL is the dominant television
standard in Europe. PAL delivers 625 lines at 50
half-frames/second.
Ping - Ping is a basic network program used diagnostically to
check the status of a network host or device. Ping can be used
to see if a particular network address (IP address or host name)
is occupied or not, or if the host at that address is responding
normally. Ping can be run from e.g. the Windows Command
prompt or the command line in UNIX.
Pixel - A pixel is one of the many tiny dots that make up a
digital image. The color and intensity of each pixel represents a
tiny area of the complete image.
PoE (Power over Ethernet) - Power over Ethernet provides
power to a network device via the same cable as used for the
network connection. This is very useful for IP-Surveillance and
remote monitoring applications in places where it may be too
impractical or expensive to power the device from a power
outlet.
PPP (Point-to-Point Protocol) - A protocol that uses a serial
interface for communication between two network devices. For
example, a PC connected by a phone line to a server.
PPTP (Point-to-Point Tunneling Protocol) - A protocol (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 organization 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 organization’s network from the outside network
and the local firewall. It is the firewall server that protects the
network against outside intrusion.
A proxy server receives requests for Internet services (such as
web page requests) from many users. If the proxy server is also
a cache server, it looks in its local cache of previously
downloaded web pages. If it finds the page, it is returned to the
user without forwarding the request to the Internet. If the page
is not in the cache, the proxy server, acting as a client on behalf
of the user, uses one of its own IP addresses to request the page
from another server over the Internet. When the requested
page is returned, the proxy server forwards it to the user that
originally requested it.
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.
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.
RTCP 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) - RTP is 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) - RTSP is 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.
Server - In general, a server is a computer program that
provides services to other computer programs in the same or
other computers. 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 supplies the requested HTML
pages or files to the client (browser).
Sharpness - This is the control of fine detail within a picture.
This feature was originally introduced into color TV sets that
used notch filter decoders. This filter took away all high
frequency detail in the black and white region of the picture.
The sharpness control attempted to put some of that detail
back in the picture. Sharpness controls are mostly superfluous
in today's high-end TVs. The only logical requirement for it
nowadays is on a VHS machine.