Axis Communications AXIS 241SA user manual Encoder See Video encoder, Fixed iris See Autoiris

74AXIS 241QA/AXIS 241SA - Glossary

Dome network camera - A remotely controllable camera mounted in a special housing, characterized by the dome shaped glass or plastic covering behind which the camera resides. Usually mounted on a ceiling and looking downwards, a dome camera can often rotate up to 360 degrees, thus providing excellent coverage of large areas.

Duplex - See Full-duplex.

DVD (Digital Versatile Disc) - An optic disc with the same physical size as a CD, but with significantly greater storage capacity.

DVR (Digital Video Recorder) - A DVR records analog video to a hard disk in digital format. Most DVRs use the MPEG-2 format for encoding analog video signals.

Encoder - See Video encoder.

Ethernet - Ethernet is the most widely installed local area network technology. An Ethernet LAN typically uses special grades of twisted pair wires. The most commonly installed Ethernet systems are 10BASE-T and 100BASE-T10, which provide transmission speeds up to 10 Mbps and 100 Mbps respectively.

ETRAX (Ethernet Token Ring AXIS) - The ETRAX chip is the cornerstone of Axis technology and the 'brain' in nearly all Axis products. A multipurpose Linux chip with integrated Ethernet networking and extremely flexible I/O options.

Factory default settings - These are the settings that originally applied for a device when it was first delivered from the factory. If it should become necessary to reset a device to its factory default settings, this will, for many devices, completely reset any settings that were changed by the user.

Firewall - A firewall works as a barrier between networks, e.g. between a Local Area Network and the Internet. The firewall ensures that only authorized users are allowed to access the one network from the other. A firewall can be software running on a computer, or it can be a standalone hardware device.

Fixed dome network camera - This type of camera cannot be remotely controlled as regards movement, but is mounted in the same type of dome as a controllable network dome camera. This camera must be positioned manually to provide the required coverage.

Fixed network camera - This type of camera cannot be remotely controlled as regards movement. It must be positioned manually to provide the required coverage.

Fixed iris - See Autoiris.

Focal length - Measured in millimeters, the focal length of a camera lens determines the width of the horizontal field of view, which in turn is measured in degrees.

FTP (File Transfer Protocol) - FTP is an application protocol that uses the TCP/IP protocols, used to exchange files between computers/devices on networks.

Frame - A frame is a complete video image. In the 2:1 interlaced scanning format of the RS-170 and CCIR formats, a frame is made up of two separate fields of

262.5or 312.5 lines interlaced at 60 or 50 Hz to form a complete frame, which appears at 30 or 25 Hz. In video cameras with a progressive scan, each frame is scanned line-by-line and not interlaced; most are also displayed at 30 and 25 Hz.

Frame rate - The frame rate used to describe the frequency at which a video stream is updated is measured in frames per second (fps). A higher frame rate is advantageous when there is movement in the video stream, as it maintains image quality throughout.

Full-duplex- Transmission of data in two directions simultaneously. In an audio system this would describe e.g. a telephone systems. Half-duplex also provides bi-directional communication, but only in one direction at a time, as in a walkie-talkie system. See also Simplex.

G.711 - The international standard for encoding telephone audio on a 64 kbps channel. It is a pulse code modulation (PCM) scheme operating at 8 kHz sample rate.

G.726 - A frequently used speech-compression algorithm in telecommunications due to its high perceived speech quality and low resource requirements.

Gain - Gain is the amplification factor and the extent to which an analog amplifier boosts the strength of a signal. Amplification factors are usually expressed in terms of power. The decibel (dB) is the most common way of quantifying the gain of an amplifier.

Gateway - A gateway is a point in a network that acts as an entry point to another network. In a corporate network for example, a computer server acting as a gateway often also acts as a proxy server and a firewall server. A gateway is often associated with both a router, which knows where to direct a given packet of data that arrives at the gateway, and a switch, which furnishes the actual path in and out of the gateway for a given packet.

GIF (Graphics Interchange Format) - GIF is one of the most common file formats used for images in web pages. There are two versions of the format, 87a and 89a. Version 89a supports animations, i.e. a short sequence of images within a single GIF file. A GIF89a can also be specified for interlaced presentation.

GOV (Group Of VOPs) - A group of VOPs is the basic unit of an MPEG-4 video stream. The GOV contains different types and numbers of VOPs (I-VOPs, P-VOPs) as determined by the GOV length and GOV structure. See also VOP.

GOV length - The GOV length determines the number of images (VOPs) in the GOV structure.

See also GOV and VOP.

GOV structure - The GOV structure describes the composition of an MPEG-4 video stream, as regards the