Glossary of Terms

The security industry is a complex and often highly technical business. Our glossary is the last word in the security terms.



ActiveX is a standard that enables software components to interact with one another in a networked environment, regardless of the language(s) used to create them. Web browsers may come into contact with ActiveX controls, ActiveX documents, and ActiveX scripts. ActiveX controls are often downloaded and installed automatically as required.

AF (Autofocus)

A system by which the camera lens automatically focuses on a selected part of the subject.


The field of view, relative to a standard lens in a 35mm still camera, expressed in degrees, i.e. 30°. For practical purposes, this is the area that a lens can cover, where the angle of view is determined by the focal length of the lens. A wide ­ angle lens has a short focal length and covers a wider angle of view than standard or telephoto lenses, which have longer focal lengths.

ARP (Address Resolution Protocol)

This protocol is used to associate an IP address to a hardware MAC (Media Access Control) address. A request is broadcast on the local network to discover the MAC address for an IP address.

ASIC (Application Specific Integrated Circuit)

A circuit designed for a specific application, as opposed to a general purpose circuit, such as a microprocessor.

Aspect ratio

A ratio of width to height in images: A common aspect ratio used for television screens and computer monitors is 4:3. High- definition television (HDTV) uses an aspect ratio of 9:16.

Auto Iris (AI)

This special type of iris is electrically controlled by the camera, to automatically regulate the amount of light allowed to pass through the lens to the image sensor of the camera.

Auto White Balance (AWB)

Auto White Balance is a color camera feature that uses a complex algorithm to set the proper balance of primary colors (red -green-blue) to reproduce accurate color images when displayed on a monitor.
The AWC circuit samples the image and tries to determine what is the neutral or gray or white area or areas of the image and then using that reference sets the RGB values accordingly. For the best results a white card is held in the camera’s view (at least 40% of scene) when AWB is selected. Many surveillance cameras do not cover static scenes therefore ATW circuits are used for constantly monitoring, re-evaluating and adjusting the color values. There are also manual color settings (R +B) that can be used if the scene that the camera is viewing has constant consistent lighting.
Many cameras have presets that reference values for lighting given in degrees of Kelvin. These reference values are typically referencing outdoor sunlight from 6200°≥10,000° and indoor lighting from 2000≥5500 depending on if the light is from tungsten(2000°-3500°) or fluorescent(4000°-5500°) bulbs.

Automatic Gain Control (AGC)

Automatic Gain Control is employed in CCTV cameras in an attempt to keep the output signal at or near the specified one volt peak to peak (written 1Vp-p). The video signal output is sampled and fed back into the video amplifier as a reference to maintain the recommended one volt output signal. The AGC circuit in most modern day CCTV cameras with auto-iris lenses only comes into play after the lens iris is fully open.  Some AGC circuits can amplify the video signal as much as 32 times but with every increase in amplification more video noise is introduced into the picture. Video noise is seen as graininess, blotchiness or distortion.  If a camera’s menu has AGC settings as an option choose the lowest amount of AGC gain to give a usable picture during the time of lowest light.

AVI (Audio Video Interleave)

A video format that supports simultaneous playback of audio and video


Bit rate

The bit rate (in Kbit/s or Mbit/s) is often referred to as speed, but actually defines the number of bits/ time unit and not distance/ time unit.


A bitmap is a data file representing a rectangular grid of pixels. It defines a display space and color for each pixel (or “bit”) in the display space. This type of image is known as a “raster graphic.” GIF’s and JPEG’s are examples of image file types that contain bitmaps.
Because a bitmap uses this fixed raster method, it cannot easily be rescaled without losing definition. Conversely, a vector graphic image uses genome trial shapes to represent the image, and can thus be quickly rescaled.


Blue tooth is an open standard for wireless transmission of voice and data between mobile devices (PCs, handheld computers, telephones and printers).


Also known as zero - configuration networking, Bonjour enables automatic discovery of computers, devices and services on IP Networks. Bonjour allows devices to automatically discover each other without the need to enter IP addresses or configure DNS servers. Bonjour is developed by Apple Computer Inc.

BOOTP (Bootstrap Protocol)

A protocol that can automatically configure a network device (give it an IP address). BOOTP is the basis for a more advanced network management protocol, the Dynamic Host Configuration Protocol (DHCP).


In network engineering terms, this describes transmission methods where two or more signals share the same carrier. In more popular terminology, broadband is taken to mean high-speed data transmission.


Burst or Color Burst is a specific frequency (3.579545 MHz) that is generated as a part of the composite video signal and is used as a reference to encode color information generated in the camera. Some of the new camera models have the option in the menu to turn the “Burst” off when the camera shifts to B/W mode due to low light levels. This can be helpful when recording the video signal because it reduces the noise level in the signal. The only time that this may not be wanted is if the cameras are connected to a switcher and removing the burst will make the switching of the cameras roll or flip between each camera switch.


CCD (Charged Coupled Device)

This light- sensitive image device used in many digital cameras is a large integrated circuit that contains hundreds of thousands of photo sites (pixels) that convert light energy into electronic signals. Its size is measured diagonally and can be 1/4”, 1/3”, 1/2” or 2/3”.


Compact Disc - Read Only Memory. An optimal disc that is used to store text, graphics and audio data for computer applications. The contents may not be changed or rewritten.

CGI (Common Gateway Interface)

A specification for communication between a web server and other (CGI) programs: For example, a HTML page that contains a form might use a CGI program to process the form data once it is submitted.

CIF (Common Intermediate Format)

CIF refers to the analog video resolutions 352x288 pixels (PAL) and 352x240 pixels (NTSC). See also Resolution.


Client/server describes the relationship between two computer programs in which one program, the client, makes a service request from another program, the server, which fulfills the request. Typically, multiple client programs share the services o f a common server program. A web browser is a client program that requests services (the sending of web pages or files) from a web server.

CMOS (Complementary Metal Oxide Semiconductor)

A CMOS is a widely used type of semiconductor that uses both negative and positive circuits. Since only one of the circuit types is on at any given time, CMOS chips require less power than chips using just one type of transistor. CMOS image sensors also allow processing circuits to be included on the same chip, an advantage not possible with CCD sensors, which are also much more expensive to produce.

Coaxial cable

Coaxial cable is the standard means of transmitting analog video in a CCTV system. Coaxial is also used by cable companies to distribute television in residential buildings.


In communications engineering, a codec is usually a coder/decoder. Codecs are used in integrated circuits or chips that convert e.g. analog video and audio signals into a digital format for transmission. The codec also converts received digital signals back into analog format. A codec uses analog- to - digital conversion and digital- to - analog conversion in the same chip. Codec can also mean compression/decompression, in which case it is generally taken to mean an algorithm or computer program for reducing the size of large files and programs.

Composite video

A type of video signal in which the red, blue and green signals (sometimes audio signals too) are mixed together.


See Image Compression.


Defines the degree of difference between the lightest and darkest parts of an image or video stream.

Control unit

If a CCTV system has more than one camera, there must be a way to control the video signals going to recorders and monitors. There are three basic types of video control units: Multiplexer, Switch and Quad.


A cookie is a piece of text that a web site can store on your computer to enable it to recognize you when you return to the site.



This special type of iris is electrically controlled by the camera, to automatically regulate the amount of light allowed to enter.


See “Interlacing”.

Dead Pixel Cancellation (DPC)

There are times when one or more pixels within the millions of pixels in a CCD image device stops functioning. This “dead” pixel will appear as a small black or white dot in the image. The DPC circuit will detect the “dead” pixel and compensate for it by removing it from the pixel sequence and using the adjacent pixel average values to replace the output of the “dead” pixel.

DHCP (Dynamic Host Configuration Protocol)

DHCP is a protocol that lets network administrators automate and centrally manage the assignment of internet Protocol (P) addresses to network devices in a network.
DHCP uses the concept of a “lease” or amount of time that a given IP address will be valid for a computer. The lease time can vary, depending on how long a user is likely to require the network connection at a particular location.
DHCP also supports static addresses for e.g. computers running web servers, which need a permanent IP address.

Digital Image Stabilization (DIS)

Digital Image Stabilization is a method of eliminating a small amount of camera shake. This is achieved by reserving three pixels in each direction from a center pixel for the image to take up or mask the physical movement of the camera. When this feature is enabled the resolution of the image is reduced

Digital Noise Reduction (DNR)

Digital noise reduction is processed in the DSP. 2D DNR is a method of sampling one frame against another to find noise or changing bits of white and black not associated with the edge of a figure within the frame. Bits that change from frame to frame are considered noise and removed from the frame. The 3D process is said to be a refinement of the 2D system that can work in low light frames removing noise and also boosting the overall level of the image.  2D and 3D noise reducing methods differ between manufacturers; there is no set standard to measure the effectiveness of any advertised system.

DNS (Domain Name System)

DNS is used to locate and translate Internet domain names into (internet Protocol) addresses. A domain name is a meaningful and easy- to -remember name for an   internet address. For example the domain name, www.example .com , is much easier to remember than The translation tables for domain names are contained in Domain name servers.

Domain server

Domains can also be used by organizations that wish to centralize the management of their (Windows) computers. Each user within a domain has an account that usually allows them to log in to and use any computer in the domain, although restrictions may also apply. The domain server is the server that authenticates the users on the network.


Digital Signal Processor: This is a circuit that is specially designed for digital signals in processor-intensive applications, such as wireless communications links and image processing. DSP circuits are often used in consumer products, such as mobile phones, faxes and digital TVs.


Digital Slow Shutter is the same as Sense-Up which has been in our camera terminology for several years. DSS allows the shutter speed of the camera to slow down giving more time for the CCD image device to gather light. The normal shutter speed for a CCTV camera is 1/60 second so slowing it down will cause it to be 1/15, 1/5, 1/1 (one second), 2/1 (two seconds) or capturing a still picture 15 times a second, 5 times a second or capturing a still picture every 1 or 2 seconds. This setting will produce a picture in very low light but it also causes smear if any movement occurs in the scene.


See “Full- duplex”.


Digital Versatile Disc: An optic disc with the same physical size as a CD but with significantly greater storage capacity.



This is a circuit in a camera that when activated will turn very white areas of the picture into black. An example of this is when an automobile’s headlights are in a scene the circuit will “eclipse” the headlights and render them black leaving only a thin halo where the extremely bright white lights were in the scene. This can be helpful by allowing the remainder of the scene to be captured within the normal range of lighting. The eclipse could be thought of as a powerful backlight compensation for specific points of extreme bright white light.


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.


Factory default settings

These are the settings that originally applied for a device when it was first delivered from the factory. I f 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.


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 iris

See Auto iris.

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.


A frame is a complete video image. In the 2:1interlaced scanning format of the S- 170 and CC R formats, a frame is made up of two separate fields of 262.5 or 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.

FTP (File Transfer Protocol)

FTP is an application protocol that uses the TCP/ P protocols, used to exchange files between computers/devices on networks.


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



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.


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

GOV length

The GOV length determines the number of images (VOP’s) 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 type of images (I- VOP’s or P - VOP’s) included in the stream, and their internal order. See also GOV and VOP.



See Full- duplex.

High Light Compensation (HLC)

High light compensation is one of the electronic exposure adjustments similar to backlight compensation and side light compensation. High light compensation limits the intensity of very bright light in the image, i.e. automobile head lights, street lights, building flood lights etc. This setting may sometimes also be called “eclipser”.

Hot swappable

Hot swappable refers to the ability to remove and replace a hard drive within a recording system without having to power down or reset the entire system. Hot swappable hard drive systems are found in RAID arrays and have the HDD installed in trays that are easily removed from the cage.

HTML (Hypertext Markup language)

HTML is the set of “markup” symbols or codes inserted in a file intended for display in web browser. The markup tells the browser how to display the page’s words and images for the user.

HTTP (Hypertext Transfer Protocol)

HTTP is the set of rules. for exchanging files (text, graphic images, sound, video, and other multimedia files)  on the web. The HTTP protocol runs on top of the TCP/ P suite of protocols.

HTTPS (Hypertext Transfer Protocol over SSL)

HTTPS is a web protocol used by browsers and web servers to encrypt and decrypt user page requests and the pages re turned by the server. The encrypted exchange of information is governed by the use of an HTTPS certificate (issued by a Certificate Authority),which guarantees the authenticity of the server.


A (network) hub is used to connect multiple devices to the network. The hubransm1ts all data to all dev1ces connected to 1t,whereas a sw1tch Will only transmit the data to the device it is specifically intended for.


IEEE 802.11

A family of standards for wireless LANs. The 802.11 standard supports 1or 2
Mbits transmission on the 2.4 GHz band. IEEE 802.11b supports data rates up to 11 Mbits on the 2.4 GHz band, while 802.11g allows up to Mbits on the 5GHz band.

Image compression

Image compression minimizes the file size (in bytes) of an image. Two of the most common compressed image formats are JPEG and G F. See also MPEG and Motion JPEG. Read more: Compression standards.

Infrared (IR )

Infrared radiation is radiation at a longer wavelength than visible light, which means it cannot be seen by the naked human eye. As infrared radiation can be detected as heat, this can be shown on a screen or captured by a digital camera, with hotter objects showing up brighter against colder surroundings (e.g. a human body against a colder background). As color cameras can “see” infrared radiation as well as visible light, these cameras are equipped with an IR-cut filter, to prevent distortion of the colors the human eye can see. To use the camera in very dark locations or at night, this filter can be removed, to allow infrared radiation to hit the image sensor. An infrared lamp can be used for improved illumination for night surveillance, whilst not producing any extra visible light.

Inputs/Outputs (I/O’s)

The digital /Os on, for •example, a network camera can be used to connect any device that can toggle between an open and a closed circuit. If, for example, a door switch is used as an input device, opening the door could trigger the upload of video images and the sending of notification messages. An output might, for example, be used to automatically start a siren when there is a motion detection trigger.


Interlaced video is video captured at 60 pictures (known as fields) per second, of which every 2 consecutive fields (at half height) are then combined into 1 frame. Interlacing was developed many years ago for the analog TV world and is still used widely today. It provides good results when viewing motion in standard TV pictures, although there is always some degree of distortion in the image. To view interlaced video on e.g. a computer monitor, the video must first be de ­interlaced, to produce progressive video, which consists of complete images, one after the other, at 30 frames per second. See also Progressive scan.

IP (Internet Protocol)

The Internet Protocol is a method transmitting data over a network. Data to be sent is divided into individual and completely independent “packets.” Each computer (or host) on the Internet has at least one address that uniquely identifies it from all others, and each data packet contains both the sender’s address and the receiver’s address. The Internet Protocol ensures that the data packets all arrive at the intended address. As IP is a connectionless protocol, which means that there is no established connection between the communication end-points, packets can be sent via different routes and do no t need to arrive at the destination in the correct order. Once the data packets have arrived at the correct destination, another protocol Transmission Control Protocol (TCP) - puts them in the right order. See also: TCP

IP address

An IP address is simply an address on an IP network used by a computer/device connected to that network IP addresses allow all the connected computers/devices to find each other and to pass data back and forth. To avoid conflicts, each IP address on any given network must be unique.  An IP address can be assigned as fixed, so that it does not change, or it can be assigned dynamically (and automatically) by DHCP.
An IP address consists of four groups (or quads) of decimal digits separated by periods, e.g. Different parts of the address represent different things. Some part will represent the network number or address, and some other part will represent the local machine address. See also IP (internet Protocol).

IP camera

The terms IP camera, network camera and Internet camera all refer to the same thing - a camera and computer combined in one unit. It operates as stand-alone unit and only requires a connection to the network.

ISMA (Internet Streaming Media Alliance)

ISMA’s goal is: “To accelerate the adoption and deployment of open standards for streaming rich media content such as video, audio, and associated data, over Internet protocols.”



Just a bunch of disks (JBOD) is not an official RAID configuration but most RAID controllers offer this setting as a large partition to the OS.  Some but not all RAID controllers will allow individual HDD to be hot swappable within the JBOD settings.  If the HDD are not identified as individual HDD by the OS but instead are counted as a single large partition the RAID controller will reset the recording process when one of the HDD is removed and replaced

JPEG (Joint Photographic Experts Group)

Together with the GIF file format, JPEG is an image file type commonly used on the web. A JPEG image is a bitmap, and usually has the file suffix ‘.jpg’ or “.jpeg.” When creating a JPEG image, it is possible to configure the level of compression to use. As the lowest compression (i.e. the highest quality) results in the largest file, there is a trade - off between image quality and file size.


kbit/s (kilobits per second)

A measure of the bit rate i.e. the rate at which bits are passing a given point. See also Bit rate.


LAN (Local Area Network)

A LAN is a group of computers and associated devices that typically share common resources within a limited geographical area.

Lens Shading

Lens shading is the same as “Side Light Compensation”. Lens Shading is a term used in cinematography and digital photography more than in surveillance CCTV.


Linux is an open source operating system within the UNIX family. Because of its robustness and availability, Linux has won popularity in the open source community and among commercial application developers.


A standard unit of illumination measurement


MAC address (Media Access Control address)

A MAC address is a unique identifier associated with a piece of networking equipment, or more specifically, its interface with the network. For example, the network card in a computer has its own MAC address.

Manual iris

This is the opposite of an auto iris, i.e. the camera iris must be adjusted manually to regulate the amount of light allowed to reach the image sensor.


See Pixel.


A monitor is very similar to a standard television set, but lacks the electronics to pick up regular television signals.

Motion JPEG

Motion JPEG is a simple compression/decompression technique for network video. Latency is low and image quality is guaranteed, regardless of movement or complexity of the image. Image quality is controlled by adjusting the compression level, which in turn provides control over the file size, and thereby the bit rate.
High- quality individual images from the Motion JPEG stream are easily extracted. See also JPEG and GIF. Read more: Compression standards.

MPEG (Moving Picture Experts group)

The Moving Picture Experts Group develops standards for digital video and audio compression. It operates under the auspices of the International Organization for Standardization (SO). The MPEG standards are an evolving series, each designed for a different purpose. Read more: Compression standards.


MPEG- 2 is the designation for a group of audio and video coding standards, and is typically used to encode audio and video for broadcast signals, including digital satellite and Cable TV. MPEG-2, with some modifications, is also the coding format used by standard commercial DVD movies. Read more: Compression standards.


MPEG- 4 is a group of audio and video coding standards and related technology. The primary uses for the MPEG- 4 standard are web (streaming media) and CD distribution, conversational (videophone), and broadcast television. Most of the features included in MPEG- 4 are le ft to individual developers to decide whether to implement them or not. This means that there are probably no complete implementations of the entire MPEG- 4 se t of standards. To deal with this, the standard includes the concept of “profiles” and “levels”, allowing a specific se t of capabilities to be de fined in a manner appropriate for a subset of applications. Read more: Compression standards.


Bandwidth conserving technology that reduces bandwidth usage by simultaneously delivering a single stream of information to multiple network recipients
See also Unicast.


A multiplexer is a high- speed switch that provides full- screen images from up to 16 analog cameras. Multiplexers can playback everything that happened on any one camera with no interference from the other cameras on the system.


Network connectivity

The physical (wired or wireless) and logical (protocol) connection of a computer network or an individual device to a network, such as the Internet or a LAN

NTSC (National Television System Committee)

NTSC is an analog color encoding system used in television systems in Japan, the United States and other parts of the Americas. NTSC de fines the video signal using 525 TV lines per frame, at a re fresh rate equal to 30 frames per second. See also PAL.


OEM (Original Equipment Manufacturer)

This is a designation for companies that manufacture equipment that is then marketed and sold to other companies under their own names.


PAL (Phase Alternating line)

PAL is an analog color encoding system used in television systems in Europe and in many other parts of the world. PAL defines the video signal using 625 TV lines per frame, at a re fresh rate equal to 25 frames per second. See also NTSC.

PEM (Privacy Enhanced Mail)

An early standard for securing electronic mail: The PEM- format is often used for representing an HTTPS certificate or certificate request.


Ping is a basic network program used diagnostically to check the status of a
network host or device. Ping can be used to see if a particular network address (P address or host name) is occupied or not, or if the host at that address is responding normally. Ping can be run from e.g. the Windows Command prompt or the command line in UNIX.

Pixel (Picture Element)

A pixel is one of the many tiny dots that make up a digital image. The color and intensity of each pixel represents a tiny area of the complete image.

PIXIM® Seawolf

CMOS image sensor and a “Digital Pixel System” technology DSP, which empower hundreds of thousands of pixels to act like individual cameras that constantly self-adjust to any lighting condition or application. Pixim measures the resolution of the chipset as “690 HTVL effective resolution” which, according to company literature, is the true representation of the actual resolution of the camera’s picture image.

PoE (Power over Ethernet)

Power over Ethernet t 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 (se t 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 and 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 them 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 de tail 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.


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.

Proxy server

In an enterprise 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 severer effectively separates the enterprise network from the outside network and the local firewall. It is the firewall server that protects the enterprise network from 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.


(QoS) Quality of Service

QoS provides the means to guarantee a certain level of a specified resource to selected traffic on a network. Quality can be de fined as e.g. a maintained level of bandwidth, low latency, no packet losses etc. The QoS in Axis network video products marks the data packets for various types of network traffic originating from the product. This makes it possible for network routers and switches to reserve a fixed amount of bandwidth for these types of traffic.

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.



RAID (redundant array of independent disks) is a technology that provides increased storage functions and reliability through redundancy.  Different schemas using multiple Hard Disk Drives (HDD) are designated as “levels 0 through 5”.  It takes a minimum of two (2) disks to support RAID 0 and 1 while it takes at least three (3) HDD to support RAID 2 through 5.  The multiple disk arrays are looked at by the operating system as a single disk.  RAID 5 is a method of recording data across all drives in a stripe fashion and adding a parity bit for error checking. The advantage to recording data in this manner is to prevent data loss due to a hard drive failure. If one hard drive of the RAID array fails the RAID system will continue to function and when the failed HDD is replaced the OS will rebuild the new HDD with the data that was on the original HDD that failed.

RAID 0 – A block level stripe recording requiring at least two HDD without parity or mirroring. It improves performance by increasing bandwidth but has no fault tolerance. If either of the HDDs fail the entire storage is lost.

RAID 1 – Mirroring without parity or striping, data is written identically to a “mirrored set” of HDD. The fault tolerance for this configuration is -1HDD. If one HDD of the set fails the other HDD continues to function.  The fault tolerance of RAID 1 is equal to RAID 5 but takes more HDDs to accomplish the same amount of storage space with equal tolerance.

RAID 2- Bit level striping with dedicated parity requires at least three HDD with one being dedicated as the parity disk. Each sequential bit is stored on a different drive.  Bit level striping is good for small data files such as text documents.  RAID 2 can recover from one HDD failure or repair corrupt data or parity when a corrupted bit’s corresponding data and parity are good i.e. the parity disk is not fault tolerant.

RAID 3 – Byte level striping with dedicated parity requires at least three HDD with one being dedicated as the parity disk. Each sequential byte is stored on a different drive.  Byte level striping is also good for small to medium file sizes. Fault tolerance and recovery are the same as RAID 2

RAID 4 – Block level striping with dedicated parity requires at least three HDD with one being dedicated as the parity disk. Each sequential file is stored on a different disk drive. Each drive operates independently allowing parallel I/O requests but transfer speeds can suffer due to single disk parity.  Fault tolerance and recovery are the same as RAID 2

RAID 5 – Block level striping with distributed parity requires at least three HDD. Each sequential file is distributed to a different disk drive as well as the parity bit. The RAID array is not destroyed by a single drive failure and requests for data can be supported by calculating from the distributed parity until the failed HDD can be replaced and rebuilt. This configuration has be best fault tolerance between all others in these examples.


To understand different factors and features of the different RAID levels some understanding of terminology is necessary so the following terms are defined here:

Bit level - A bit is the basic unit of information, a single variable (on/off)
Byte level - A byte is comprised of eight (8) bits
Block level - A block in this instance refers to 1024 bytes
Parity bit - A bit added to a number of bits for error checking. Parity can be even or odd and is calculated by the number of “1”s in a string of bits. The parity bit will add a “1” or a “0” to make the number of “1”s in the bit string even or odd.


Image resolution is a measure of how much detail a digital image can hold: the greater the resolution, the greater the level of de tail. 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 pixels (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.


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.

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 is a serial data communication protocol that specifies 4- wire, full- duplex, differential line, multi-drop communications. I t 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 fee t (1200 meters). Maximum recommended baud rate is 10Mbitjs.


RS- 485 is an upgraded version of RS- 422 that supports up to 32 devices 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 multi-drop communications links. It offers high data transmission speeds (up to 10Mbitjs), and as it uses a differential balanced line over twisted pair (like RS- 422),it can span relatively large distances (4000 fee t or 1200 meters). 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.
I t 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 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 negotiating transports such as RTP, multicast and Unicast, and for negotiating codecs.
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.


Selectable Scanning

This feature is provided in the cameras using PIXIM technology and allows the selection of either 60ips for interlaced scanning or 30ips for progressive scanning. In addition to this area of section in the menu the system setup section offers the NTSC format or PAL format with the selection of either 60i/30p for NTSC or 50i/25p for PAL.


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).


This is the control of fine de tail 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.

Side Light Compensation (SLC)

Side light compensation is one of the electronic exposure adjustments similar to back light compensation. Side light compensation will boost the brightness of the corners of the image to try to make the overall picture equally bright.


In simplex operation, a network cable or communications channel can only send information in one direction. See also full- duplex.

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 extension 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 de fined by the Internet Engineering Task Force. The protocol can support monitoring of network­ attached devices for any conditions that warrant administrative attention.


Sockets are a method for communication between a client program and a server program over a network. A socket is de fined 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 Security Layer)

These two protocols (SSL is succeeded by TSL) are cryptographic protocols that provide secure communication on a network. SS   is commonly used over HTTP to form HTTPS, as used e.g. on the Interne t for electronic financial transactions. SS   uses public key certificates to verify the identity of the server.

Subnet & subnet mask

A subnet is an identifiably separate part of an organization’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 P address; it simply looks at the bits selected by the mask.


A switch is a network device that connects network segments together, 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.

System on a chip (SOC)

An ASIC that is specially developed to meet the requirements o f a given application in which the objective is to integrate most functionality on a single chip, thereby realizing benefits in terms of price, performance and reliability. Examples of functions that are often integrated in an SOC are microprocessors, memory and interfaces.


TCP (Transmission Control Protocol)

TCP is used along with the Internet Protocol (P) to transmit data as packets between computers over the network. While II P 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 established between the two end-points and is maintained until the data has been successfully exchanged between the communicating applications.

TVL (TV lines)

A method of de fining resolutions in analog video



Communication between a single sender and a single receiver over a network: A new connection is established for each new user. See also Multicast.


A se t of computer network protocols that allows the automatic peer- to -peer detection of devices on the network. UPnP is promo ted by the UPnP Forum.

URL (Uniform Resource Locator)

An address on the network


(Universal Serial Bus) A plug- and-play interface between a computer and peripheral devices (scanners, printers etc.)


Varifocal lens

A varifocal lens provides a wide range of focal lengths, as opposed to a lens with a fixed focal length, which only provides one.

VOP (Video Object Plane)

A VOP is an image frame in an MPEG- 4 video stream. There are several types of VOP: An “I-VOP” is complete image frame.  A “P-VOP” codes the differences between images, as long as it is more efficient to do so. Otherwise it codes the whole image, which may also be a completely new image.

VPN (Virtual Private Network)

This creates a secure “tunnel” between the points within the VPN. Only de vices with the correct t “key” will be able to work within the VPN. The VPN network can be within a company LAN (Local Area Network), but different sites can also be connected over the Internet in a secure way. One common use for VPN is for connecting a remote computer to the corporate network, via e.g. a direct phone line or via the Internet. Read more: Network security


W-LAN (Wireless LAN)

A wireless LAN is a wireless local area network that uses radio waves as its carrier: where the network connections for end-users are wireless. The main network structure usually uses cables.

WAN (Wide-Area-Network)

Similar to a LAN, but on a larger geographical scale.

Web server

A Web server is a program, which allows Web browsers to retrieve files from computers connected to the Internet. The Web server listens for requests from Web browsers and upon receiving a request for a file sends it back to the browser.
The primary function of a Web server is to serve pages to other remote computers; consequently, it needs to be installed on a computer that is permanently connected to the Internet. It also controls access to the server whilst monitoring and logging server access statistics.

WEP (Wired Equivalent Privacy)

A wireless security protocol, specified in the IEEE 802.11 standard, which is designed to provide a wireless local area network (WLAN) with a level of security and privacy comparable· to that usually expected of a wired LAN. Security is at two different levels; 40-bit and 128-bit encryption. The higher the bit number, the more secure the encryption

Wide Dynamic Range (WDR)

High contrast in a scene has always been problematic for electronic cameras using a CCD imager due to the limitations of the CCD light capture process. Sony was one of the first manufacturers of low cost video cameras to introduce a WDR CCD by doubling the scan rate of the image chip or in other words the CCD produced two images in the same amount of time as a normal CCD would produce one. This allowed the two images to have different shutter speeds, one for bright light and one for low light and then blend the two images into one. D-WDR or Digital WDR is a method of correcting high light and low light in a scene using a digital algorithm in the DSP (Digital Signal Processor) of the camera. The CCD produces a normal scan rate and shutter speed for each frame and passes it to the DSP for processing.

WINS (Windows Internet Naming Service)

Part of the Microsoft Windows NT Server, WINS manages the association of workstation names and locations with IP addresses, without the user or administrator having to be involved in each configuration change.

WPA-PSK (Wi-Fi Protected Access- Pre-Shared Key)

This wireless encryption method uses a pre - shared key (PSK) for key management. Keys can usually be entered as manual hex values, as hexadecimal characters, or as a Passphrase. WPA-PSK provides a greater degree of security than WEP.


Zoom lens

A zoom lens can be moved (zoomed) to enlarge the view of an object t to show more de tail.