User`s manual
44
AXIS 207 - Glossary of Terms
LAN - A local area network (LAN) is a group of computers and associated devices that typically share common resources
within a limited geographical area.
Linux - A popular operating system, which is “open source” and practically free of charge.
Lux - A standard unit for the measurement of light, where 1 Lux equals the light emitted from a single candle at a distance
of one meter.
Mbit/s - Megabits per second. A unit for measuring speeds in networks. A LAN might run at 10 or 100 Mbit/s.
Motion JPEG - This format uses standard JPEG still images for the video stream. These images are then displayed and
updated at a rate sufficient to create a stream that shows constantly updated motion.
MPEG-4 - A standard video format, used for low bandwidth video streams.
Multicast - Multicast reduces bandwidth usage by delivering a single stream of information to multiple network recipients.
This is primarily used on private networks (intranets).
NTSC - National Television Standards Committee. NTSC is the standard format used for televisions in most of North and
Central America, and Japan.
NWAY - A network protocol that automatically negotiates the highest possible common transmission speed between two
devices.
PAL - Phase Altering Line. PAL is the standard format used for televisions in most of the world (other than the US, Canada,
and Japan).
PCM - Pulse Code Modulation. Analog signal converted directly to a digital.
Ping - A small utility used for sending data packets to network resources to check that they are working and that the
network is intact.
Pre/post alarm image - The images from immediately before and after an alarm.
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.
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 is often included as part of a network switch (see below).
RTP - Real-Time Transfer Protocol. A transfer protocol designed for delivery of live contents, e.g. MPEG-4, via unicast or
multicast.
RTSP - a control protocol, and a starting point for negotiating transports such as RTP, multicast and Unicast. 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.
Simplex - In simplex operation, a network cable or communications channel can only send information in one direction.
SMTP - A common e-mail protocol.
Subnet Mask - An IP address consists of two components: the network address and the host address. ‘Subnetting’ enables a
network administrator to further divide the host part of the address into two or more subnets. The subnet mask identifies the
subnet to which an IP address belongs.
Switch - Whilst a simple hub transmits all data to all devices connected to it, a switch only transmits the data to the device
it is specifically intended for.
TCP/IP - Transmission Control Protocol/Internet Protocol. A suite of network protocols that determine how data is
transmitted. TCP/IP is used on many networks, including the Internet. TCP keeps track of the individual packets of
information and IP contains the rules for how the packets are actually sent and received.
UDP - UDP is an alternative to TCP (Transmission Control Protocol). The advantage of UDP is that it is not required to
deliver all data and may drop network packets when there is e.g. network congestion. This is suitable for live video, as there
is no point in re-transmitting old information that will not be displayed anyway.
Unicast - a communication between a single sender and a single receiver over a network. This means that the video stream
goes independently to each user, and each user gets their own stream. A benefit of unicasting is that if one stream fails, it
only affects one user. See Multicasting.
UPnP - Universal Plug and Play. An ‘address’ on the network. UPnP is an architecture for pervasive peer-to-peer network