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AXIS M3014 - Glossary of Terms
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 VO
P.
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 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
prot
ocol 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.
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
IMAP. These other protocols allow the user to save messages in
a server mailbox and download them periodically from the
server.
SMTP authentication is an extensi
on of SMTP, whereby the
client is required to log into the mail server before or during the
sending of email. It can be used to allow legitimate users to
send email while denying the service to unauthorized users,
such as spammers.
SNMP (Simple Network Management Protocol) - SNMP
forms part
of the Internet Protocol suite, as defined by the
Internet Engineering Task Force. The protocol can support
monitoring of network-attached devices for any conditions
that warrant administrative attention.
Sockets - Sockets are a method for communication between a
client program and a server program
over a network. A socket is
defined as ‘the endpoint in a connection.’ Sockets are created
and used with a set of programming requests or ‘function calls’
sometimes called the sockets application programming
interface (API).
SSL/TSL (Secure Socket Layer/Tran
sport Layer Security)
These two protocols (SSL is succeeded by TSL) are cryptographic
proto
cols that provide secure communication on a network. SSL
is commonly used over HTTP to form HTTPS, as used e.g. on the
Internet for electronic financial transactions. SSL uses public
key certificates to verify the identity of the server.
Subnet/subnet mask - A subnet is an identifiably separate
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