User Guide

55
AXIS Q1755/-E - Glossary of Terms
prompt or the command line in UNIX.
Pixel - A pixel is one of the many tiny dots that make up a
digit
al 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
an
d 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 t
hem 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
wil
l 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 digit
al 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 pix
els (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 Cont
rol 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
mult
icast group as well as support for the synchronization of
different media streams.
RTP (Real-Time Transport Protocol) - RTP is an Internet
proto
col 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
proto
col, 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 stre
am 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 c
omputer 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.
Simplex - In Simplex operation, a network cable or
comm
unications channel can only send information in one
direction.
SMTP (Simple Mail Transfer Protocol) - SMTP is used for
sending
and receiving e-mail. However, as it is ‘simple,’ it is
limited in its ability to queue messages at the receiving end,
and is usually used with one of two other protocols, POP3 or