54
AXIS P3301/AXIS P3304 - Glossary of Terms
NWay -
A network protocol that automatically negotiates
the highest possible common transmission speed between
two devices.
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,
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.
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
