Datasheet

27
AXIS 292 - Glossary of Terms
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.
Quad view - A Quad view displays images from up to four cameras on a
single screen;
where the images from each camera take up approximately
a quarter of the display area.
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 pixel
s (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 - RS-232 is 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-422 - RS-422 is a serial data communication protocol that specifies
4-w
ire, full-duplex, differential line, multi-drop communications. It
provides balanced data transmission with unidirectional/non-reversible,
terminated or non-terminated transmission lines. RS-422 does not allow
multiple drivers, only multiple receivers. Maximum recommended range
is 4,000 feet (1200 meters). Maximum recommended baud rate is
10Mbit/s.
RS-485 - RS-485 is an upgraded version of RS-422 that supports up to
32 devic
es 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 metres).
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.
RTCP offers quality-of-service feedback from rece
ivers 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 negotia
ting 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 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
w
as 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 communications
c
hannel can only send information in one direction.
SMTP (Simple Mail Transfer Protocol) - SMTP is used for sending and
re
ceiving 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 extension of SMTP, whereby the client is
re
quired 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
p
rogram 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/Transport Laye
r Security)
These two protocols (SSL is succeeded by TSL) are cryptographic protocols
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 part of an
o
rganization's network. Typically, a subnet may represent all the
machines at one geographic location, in one building, or on the same
local area network (LAN). Having an organization's network divided into
subnets allows it to be connected to the Internet with a single shared
network address.
The subnet mask is the part of the IP address that tells a network router
how
to find the subnet that the data packet should be delivered to. Using
a subnet mask saves the router having to handle the entire 32-bit IP
address; it simply looks at the bits selected by the mask.
Switch - A switch is a network device that connects network segments
tog
ether, and which selects a path for sending a unit of data to its next
destination. In general, a switch is a simpler and faster mechanism than a
router, which requires knowledge about the network and how to
determine the route. Some switches include the router function. See also
router.
TCP (Transmission Control Protocol) - TCP is used along with the
Interne
t Protocol (IP) to transmit data as packets between computers over
the network. While IP takes care of the actual packet delivery, TCP keeps
track of the individual packets that the communication (e.g. requested a
web page file) is divided into, and, when all packets have arrived at their
destination, it reassembles them to re-form the complete file.
TCP is a connection-oriented protocol, which means that a connection is
e
stablished between the two end-points and is maintained until the data
has been successfully exchanged between the communicating
applications.
Telnet - Telnet is a simple method with which to access another network
d
evice, e.g. a computer. The HTTP protocol and the FTP protocols allow
you to request specific files from remote computers, but do not allow you
logon as a user of that computer. With Telnet, you log on as a regular