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European quantizing method for voice PCM in G.711.



Access Card

A coded employee card, usually the size of a credit card, recognizable to the access control system and read by a reader to allow access. It can be used for photo identification of the cardholder and for other data collection purposes. Card technologies include magnetic strips, Wiegand effect, proximity (active/passive), barium ferrite, and smart/intelligent cards.

Access Code

Any system or method which automatically controls the passage of people and vehicles into or out of an area or structure.

Additional Resources:

Access Level

The door or combination of doors and/or barriers an individual is authorized to pass through.

Access Mask

Electronic alarm masking suppresses the annunciation of an alarm condition that would have been reported in the “secure” mode of operation. Masking does not block the reporting ability of tamper or fault conditions that may not be seen when alarm shunting is used.

Access Point

Each means of entry into a controlled security area, consisting of a card reader, monitor switches and/or latches. Access points are wired to an access control panel.

Access Relay

An electrically operated switch that is activated when access is granted to unlock a door.

Access Time

The period of time during which an access point is unlocked. (Also see shunt time).


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.

Adaptive Differential Pulse Code Modulation (ADPCM)

A method of sampling and converting analog signals to digital signals. Similar to DPCM except that when a wide difference occurs between two successive samples of a signal, it uses a sophisticated algorithm to code the difference.

Address Resolution Protocol (ARP)

Internet protocol used to map an IP address to a MAC address. Defined in RFC 826.


Asymmetric Digital Subscriber Line. High bandwidth network technology that transmits at a higher rate in one direction than the other. Uses standard POTS wiring for bandwidths up to several Mbps.

AF (Autofocus)

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


Automatic Gain Control. Algorithm to normalize volume regardless of speaker's position relative to microphone.


Method for sending data down two or more parallel channels.


Method for solving a problem or performing a task.


The traditional means of sending traffic over copper wires. Analog signals are continuously variable, like a flowing line or wave, as opposed to 1/0 digital signals. Analog signals must be converted into digital signals in order for computers to be able to understand them. Used in POTS.

Analog Gateway

A means of connecting dissimilar codec's. Incoming digital signal from one type of codec is decoded by a similar codec and converted to analog. The Analog signal is then passed to the dissimilar codec, coded, and decoded at the far end. Analog gateways achieved interoperability in a nonstandard environment, but have the disadvantages of degrading video and audio quality and often reducing functionality.


The field of view, relative to a standard lens in a 35mm still camera, expressed in degrees, e.g. 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.


Automatic Number Identification (ANI) is a service that provides the receiver of a telephone call with the number of the calling phone. The method of providing this information is determined by the service provider (such as AT&T, MCI, Sprint, and so forth).

Annex D

Still-image graphics mode of H.261. Can support maximum 704x576 resolution.


An audible and/or visual signaling device.


Automatic Noise Suppression. Reduces background noise from an audio signal.


American National Standards Institute.

Anti-Passback (Anti-Tailgating)

This feature protects against more than one person using the same card or number. It defines each system card reader and card I.D. number as IN, OUT, or Other. Once a card is granted access to and IN reader, it must be presented to an OUT reader before another IN reader access is granted. Cards will continue to have access to all authorized OTHER readers.


Application Programming Interface.


Coding error found in compressed audio or video signal.

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 16:9.

Aspect Ratio

Ratio of horizontal to vertical picture size. 4:3 for the standard TV. 16:9 for the new wide screen formats.


No constant rate. Not synchronous. A method of data transmission which allows characters to be sent at irregular intervals by preceding each character with a start bit and following it with a stop bit. The timing of the transmission is not determined by the timing of a previous character. Applications include communication between most small computers and mainframes, lower speed transmissions, and less expensive computer transmission systems.


Asynchronous Transfer Mode. A connection-oriented service that transmits voice, data, and video traffic in fixed cell lengths at high speeds into the gigabit range. A high bandwidth packet-based network technology.

Audit Trail

A listing created which may be created in real time, which may be used to monitor the progress of a person through protected areas.

Autoiris (or DC-Iris)

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

Automatic Call Distribution (ACD)

ACD directs incoming calls to designated stations in a specified order of priority.

Autonomous System

Internet (TCP/IP) terminology for a collection of a gateway or router that fall under one administrative entity and cooperate using a common Interior Gateway Protocol.

AVI (Audio Video Interleave)

A video format that supports simultaneous playback of audio and video

B channel

64 kbps bearer channel used for voice, circuit, or packet switched data.


Broadband ISDN. Based on ATM. Can run up to several hundred Mbps.


A pathway or cable that joins multiple computers across small distances (within the same building) or multiple LAN's across long distances.


To use a card key in a reader to gain access to protected areas; a card key itself, especially one with a photo I.D.


The capacity or speed of a telecommunications transmission medium. example -128kbps.


Bit-rate Allocation Sequence in H.221. Capabilities exchange uses these codes.


The basic direct output signal in an intermediate frequency based obtained directly from a television camera, videoconference television receiver, or video tape recorder. Baseband signals can be viewed only on studio monitors. To display the baseband signal on a conventional television set a "modulator" is required to convert the baseband signal to one of the VHF or UHF television channels which the television set can be tuned to receive.

Baud Rate

The rate of symbols per second (not the rate of bits per second.)

Bearer service

As defined by CCITT standards, a type of telecommunication service that provides the capability for the transmission of information between user-to-network interfaces. Bearer services defined for ISDN are circuit mode and packet mode.


A system of counting that is base-2. (The decimal system that we use is base-10.) Unlike the decimal system which uses digits having possible values between 0 and 9, the binary system has digits (bits) that can only have the values 0 and 1.


Refers to readers that identify human attributes such as fingerprint, hand geometry, voice recognition or retinal analysis.


A unit of information that contains one of two states: on or off. This is the unit of counting in the binary system.

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 geometrical shapes to represent the image and can thus be quickly rescaled.


Data that is transmitted between systems carrying audio, video, data, and signaling.


Artifact found in H.261, H.263 and MPEG video coding. Picture breaks up into square sub-sections when the coder cannot produce an accurate video reproduction due to limited available channel bits and/or processing power.


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


Artifact found in video when the high frequencies (detail) of the image are not coded.

BONDING protocol

Industry standard B channel aggregation protocol. Developed by the Bandwidth on Demand Interoperability Group. Method for making several BRI lines look like one high-rate line by use of an IMUX (Inverse Multiplexer.)


Bits per second. Defining the speed of a network connection in number of bits transmitted every second.


ISDN Basic-Rate Interface consisting of 2B+D channels.

Bridge (bridging)

A data communications device that connects two or more networks of compatible protocols. Multipoint Control Unit (MCU) that can link several videoconferencing systems for multipoint calls.


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.


A service or network capable of supporting a wide range of multiple transmissions (video, data or audio) at the same time.

Buffer Capacity

Refers to the amount of information the system can store, this may include the users, time of day and specific door.


8 bits to a byte.

Cardioid microphone

A directional microphone with a heart-shaped pickup pattern used for specialized audio applications.


A transmitted electromagnetic pulse or wave at a steady base frequency of alternation on which information can be imposed by increasing signal strength, varying the base frequency, varying the wave phase, or other means.


Charge-coupled device. Camera technology that captures video signals.


Studio standard format for video. 720 x 480 pixels at 30 frames per second (NTSC) or 720 x 576 at 25 fps (PAL).


Consultative Committee on International Telephony and Telegraphy. A body of the International Telegraph Union (ITU) which prepares recommendations, commonly refered to as international standards, to resolve technical telegraph and telephone problems.


(53-bytes) Unit of data used in ATM technology for carrying information.


Code Excited Linear Prediction. Compression method used in G.728.

Central Office (CO)

In telephony, the phone company switching facility or center, usually a Class 5 end office, at which subscriber's local loop terminate. Handles a specific geographic area, identified by the first three digits of the local telephone number.


Central Office based service provided to business customers that allows direct outward dialing from the organization as well as direct inward dialing to phone extensions. Provides most, if not all, PBX type features.


A separate path through which signals can flow.

Channel bank

Equipment in a telephone central office that performs multiplexing of lower speed digital channels into a higher speed composite channel. The channel bank also detects and transmits signaling information for each channel, transmitting framing information so that time slots allocated to each channel can be identified by the receiver.

Chroma (Chrominance)

Color information in a video image.


Common Intermediate Format. 352x288 pixels, 30fps clock. H.261 and H.263 optional format.

Clear channel

A channel in which all the 64 kbps are used for transmission. To achieve this bit robbing signals must be eliminated.


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 fulfils the request. Typically, multiple client programs share the services of 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.

Clock Speed

The number of pulses per second by an oscillator that sets the tempo for the processor. Clock speed is usually measured in MHz (megahertz, or millions of pulses per second).

Coaxial cable

A coaxial cable can carry great quantities of information compared to twisted pair copper wire and is typically used by cable providers to carry television signals into houses and schools.

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.


Coder-decoder. Device to compress and decompress information (video, audio, data, etc.)


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.


A component in videoconferencing solutions that translates digital signals into video pictures.


The property of a magnetic material, as on a magnetic stripe keys, which is a measure of the coercive force. It is used when describing the strength of magnetic saturation when discussing magnetic stripe card keys.

Communications closet (CC)

The CC represents the physical connection where information is received via the wiring system to the communications outlets in individual rooms. Each educational facility must construct a space to house at least one CC per floor.

Communications equipment room (CER)

The CER is the entry point for communications into the building. It houses the head-end equipment of the school's communications system and is connected via cabling to the communications closets for distribution to the end user. At least one CER is recommended per facility.

Communications outlet (CO)

The CO's, which differ from power outlets, are generally designed to receive multi-cable signals and provide access directly to the user. CO's should be installed within six to eight feet of every workstation to preclude the use of extension cords and cables.

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.


The method of taking a raw data and processing it so that it may be represented with less information (or bits in the digital world). Compression falls into two categories: lossless- the original data may be completely recovered—and lossy— the representation of the original data contains errors.

Continuous Presence

The ability to see more than one far-end site at a time in a multipoint call.

Control Logic

The computer in a switching system (either time-division, space-division, or multistage) that monitors and controls switching to properly route calls.

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 Unit: Multiplexer, Switch and Quad.

Cooled Thermal Sensors

Cooled sensors are high-end systems often found in military applications. They are expensive and are available in different subtypes. While the performance of cooled sensors is widely superior to the uncooled sensors, the price difference makes the uncooled sensor the only viable option for the regular, non-military surveillance market. Cooled sensors also have another downside: the cooler needs to be maintained with a certain interval to maintain the same performance over time. The increased total-cost-of-ownership, for thermal cameras supporting cooled sensors, typically makes them too expensive for non-military applications.


Customer premises equipment. A generic term for communications terminal gear owned by the customer, residing on customer premises.


Conjugate Structure algebraic code excited linear prediction. Compression method used in G.729.


Circuit Switched Network (for example ISDN, POTS.)


Channel service unit. A component of CPE used to terminate a digital circuit, such as DDS or T1 at the customer site. Performs certain line-conditioning functions, ensures network compliance per FCC rules, and responds to loopback commands from central office. Also ensures proper ls density in transmitted bit stream and performs bipolar violation correction.


Computer-Telephony Integration relates to the implementation of traditional telephone - based audio (and sometimes video) services over a data network. CTI may be implemented over systems that guarantee bandwidth, such as ATM, or frame-based networks like Ethernet or frame relay.


The ISDN channel that carries signaling information to control the call setup, teardown, or invocation of supplementary services. The D-channel may also be used to provide Packet Mode Data Service.


Digital to analog.

Data compression

The shrinking of digital information to achieve smaller file size. One would compress information to allow for faster upload/download times or to fit information on a certain size disk.


A collection of data used and produced by a computer program. The files created at the host of the access control system forms its database.


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


Data communications equipment. The portion of a data terminal that provides the interface to the network.


Discrete-cosine transform. Method used to encode video information in H.261, H.263, MPEG.


Dataphone digital service. AT&T private line service for transmitting data over a digital system. The digital transmission system transmits electrical signals directly, instead of translating the signals into tone of varied frequencies as with traditional analog transmission systems. Digital techniques provide more efficient use of transmission facilities, resulting in lower error rates and costs than analog systems.


A component in videoconferencing solutions that breaks down video input into digital signals.


See video decoder.

Dedicated Line

(1) A communications circuit or channel provided for the exclusive use of a particular subscriber. Dedicated lines are used for computers when large amounts of data need to be moved between points. (2) A transmission circuit installed between two sites of a private network and ""open"", or available, at all times. Synonym private line leased line.

Delta Modulation

A method of sampling and converting analog signals to digital signals. It is based on encoding the direction of signal change, indicating the direction of signal change with a single bit.


A videoconference receiver circuit which extracts or "demodulates" the "wanted" signals from the received carrier.


Data Encryption Standard.

Desktop videoconferencing

Videoconferencing on a personal computer. Most appropriate for small groups or individuals.

Device Address

Value set on an access control device to determine its unique identity.

DHCP (Dynamic Host Configuration Protocol)

DHCP is a protocol that lets network administrators automate and centrally manage the assignment of Internet Protocol (IP) 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.


An electronic signal coded in binary format as opposed to analog's continuously variable flow. All digital information is ultimately stored in 1/0 signals that computers process. ISDN is digital.

Digital loopback

Technique for testing the digital processing circuitry of a communications device. May be initiated locally or remotely via a telecommunications circuit. Device being tested will echo back a received test message after first decoding and then encoding it. The results are compared with the original message (compare with analog loopback.)

Digital Switch

A means of supporting multiway conferencing using the signals in their digital format without converting them to analog. Digital switches permit multiple users with similar codecs to conference generally with voice-activated switching.

Distance Learning

The incorporation of video and audio technologies so that students can "attend" classes and training sessions that are being presented at a remote location. Distance learning systems are usually interactive and are becoming a highly valuable tool in the delivery of training and education to widely-dispersed students or in instances where the instructor cannot travel to the student's site.

Distributed Intelligent Devices

Access control devices that make their own access decisions uploading event messages periodically to the central processing unit for storage.

DNS (Domain Name System)

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

Document sharing

A feature supported by many videoconferencing systems that allows participants of a videoconference to view and edit the same computer document.

Door Open Time

The time allowed for a controlled door to remain open after a valid entry. At the expiration of this time, the system records a transaction which may be defined as an alarm. If the alarm bypass relay is used, it would also de-energize at the end of this time.


The act of the near and far ends of a call speaking at the same time. (Good test for the effectiveness of an echo canceller.)


Differential Pulse Code Modulation. Coding technique.


High speed network line, operates at 44.73 MBPs.


Digital Subscriber Line is a technology for bringing high-bandwidth information to homes and small businesses over ordinary copper telephone lines.


Digital Signal Processor


Data service unit. A device providing interface between a data terminal or other data communications device and a digital access line.


Data terminal equipment. The portion of a data terminal that interfaces to the end-user's equipment. The main difference between DCE and DTE is that pins 2 and 3 are reversed on the RS-232.


Dual Tone Modulated Frequency. Touch-tone signals.


Electronics box (the main codec box) of a group videoconferencing system.

E&M lead signaling

Method of signaling using dual connection ports (""E"" and ""M""). When a signal reaches a switch, it enters through the E lead. Switches send signals out through the M lead.


2.048 Mbps.

Echo suppression

To reduce echoes in the audio portion of a conference, it silences all sound when on by temporarily deadening the communication link in one direction. Unfortunately, not only the echo is stopped but also the remote end's new speech, which results in clipping.


Process which attenuates or eliminates the acoustic echo effect on videoconference calls.


Exit, depart, leave (opposite of ingress).

Electric Door Strike

An electric door-locking device, usually solenoid operated, that will unlock a door when electric power is either applied, or removed, depending upon the configuration.


Pertaining to combined electric & magnetic fields associated with movements of electrons through conductors.


A box or cabinet usually constructed of metal, that houses system components, such as circuit boards and other electronic and electrochemical controls and circuitry.


The conversion of data into a form, called a cipher, that cannot be easily understood by unauthorized people.

End-to-End Digital Connectivity

Signals are in digital form during their entire path through the network.

Erasable Programmable Read-Only Memory (EPROM)

A programmed memory (often in a chip) that cannot only be read but can be repeatedly erased under high-intensity ultraviolet light and reprogrammed.


A commonly used platform for transmitting information across a local area network. Ethernet is a bus-based topology, nodes are connected to a single cable with terminators at each end. Transmits data at 10 Mbps, 100 Mbps, or gigabit over twisted pair wire or coaxial cable.


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. Read more: IP networks.

Executive Privilege

An option which allows a cardholder unlimited access to all operational access points. Access may be without the system referring to any other access parameters, or there may be a PIN-code requirement has been enabled.

Exit Switch

A push button, switch mat, proximity detector, or other device that starts a timer in the reader interface electronics when someone is leaving through a controlled entry or exit. The timer bypass (shunts) the door-open detector for a selected period of time.

Facility Code

A numeric code programmed into a card reader and encoded on the access card/token, which is unique to the one card access systems facility. In a distributed or semi-distributed intelligent card reader system, the facility code will allow access to cardholders with the proper facility code when communications are lost with the CPU.

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.

Fail - Secure

An electric lock that requires power to unlock. Also called fail-locked.

Fail Safe

On loss of power, access points will automatically unlock allowing free access, and signal the card access system of a device malfunction or loss of power.


An electric lock that automatically unlocks with any power interruption. Also called fail-safe.


Frame Alignment Signal in H.221.


Full-CIF. Another name for CIF.


Forward Error Correction. Method to prevent/fix bitstream errors.


Far-End Camera Control.

Fiber Distributed Data Interface (FDDI) Network Services (FNS)

An all fiber network service that connects subscriber's LANs at their full speeds in select metropolitan areas, via a shared 100 Mbps fiber backbone.

Fiber optic cable

A cable technology that carries light signals over thin glass fiber at unlimited speeds.


One-half of a video frame in the interlaced NTSC or PAL standards. A field contains all of the even or odd lines. In the 30 frames per second NTSC world, each field is displayed at 1/60 of a second intervals. In the PAL world, the interval is 1/50 of a second.

File Transfer Protocol (FTP)

The first and the most fundamental way to transfer files to and from remote computer sites. " Anonymous ftp " refers to being able to access public file archives without a password.

Fixed Iris

In indoor environments where light levels may be constant, a fixed iris lens can be used. With fixed iris lenses, the iris opening cannot be adjusted and is fixed at a certain f-number. The camera can compensate for changes in the level of light by adjusting the exposure time or using gain.

Fixed Point

Integer precision arithmetic. Numbers are typically represented by 16 or 32 bits.

Floating Point

Fractional precision arithmetic. Numbers are typically represented by 32 or more bits.

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.

Four-wire circuits

Telephone lines using two wires for transmitting and two wires for receiving offering much higher quality than a 2-wire circuit. All long distance circuits are 4-wire. Almost all local phone lines and analog phones are 2-wire.


Frames per second (video).

Fractional T-1 or T-3 line

A T-1 or T-3 digital phone line in the North American T-carrier system that is leased to a customer at a fraction of its data carrying capacity and at a correspondingly lower cost. A T-1 line contains 24 channels, each with a data transfer capacity of 64 Kbps.


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 262.5 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

Frequency in which video frames are displayed on a monitor, typically described in frames-per-second (fps). Higher frame rates improve the appearance of video motion.

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. Read more: Frame rate control.

Frequency Division Multiplexing (FDM)

Most common method of multiplexing analog signals.

Frame relay

A high-speed packet switching protocol used in wide area networks (WANs). Provides service up to rates of 45 Mbps and is suited for data, image, and voice transfer. Method for sending high-bandwidth data in frames (not video frames but "blocks" of data).

Full-duplex audio

Two-way audio may be captured and reproduced simultaneously. With full-duplex audio, the microphone may capture local audio for transmission while the far end audio may be heard clearly. Interruptions and doubletalk are possible.


In compressed video, picture quality that is generally acceptable to users although not of broadcast quality; typically, from 10 - 30 frames per second depending on the bandwidth allocated.


3.4 kHz bandwidth audio transmitted at 56 or 64 kbps. Uses A-law or u-Law PCM.


7 kHz bandwidth audio transmitted at 48, 56 or 64 kbps. Uses ADPCM.


3.4 kHz bandwidth audio at 5.3 or 6.4 kbps. Developed for H.324 POTS standard. Being considered for other uses. Uses CELP processing.


3.4 kHz bandwidth audio transmitted at 16 kbps. Uses CELP processing.


3.4 kHz bandwidth audio transmitted at 8 kbps. Uses CS-ACELP processing.


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.


Generic Conference Control in the T.120 standard.

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.

Global Linking

An input at one Access Control panel effecting the output at another.

GOV (Group of VOPs)

A group of VOP’s is the basic unit of an H.264 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.


Transmission of still images, usually from a video source, but in some cases PC-generated.

Ground Start

Method of supervisory signaling, primarily for analog in-band networks. Customer Premise Equipment (CPE) transmits offhook condition by creating a zero-voltage condition. See loop start and wink start for other similar techniques.


General Switched Telephone Network. Also known as POTS.

Guard Tour

A defined route of a security guard.


Multiplex standard used in H.320. Combines audio, video, data in one bitstream.


Multiplex standard for H.324.


Standard for data transfer in H.320.


Multiplex standard for H.323.


Standard for control and indication signaling within H.320.


Standard for specifying MCU requirements in H.320.


The ITU-T's data-encryption standard for real-time multimedia.


specifies how encryption keys are handled.


Standard for establishing communication in H.320.


Standard for multipoint communication in H.320.


Standard for multimedia system control in H.323, H.324 and H.310. Includes features such as capability exchange and signaling.


Required video compression standard in the H.320, H.323 and H.324 standards.


ITU-T name for MPEG-2. H.262 is used within H.310, and is an optional mode of H.320.


Video compression standard created and required for H.324. Is also an optional mode of the other H-series standards.


Also known as MPEG-4 Part 10. This is the new generation compression standard for digital video. H.264 offers higher video resolution than Motion JPEG or MPEG-4 at the same bit rate and bandwidth, or the same quality video at a lower bit rate.


Standard for Far End Camera Control.


Standard for multimedia conferencing and one-way video applications on B-ISDN. Not based on H.320.


Standard for multimedia conferencing on narrowband switched digital networks. Can be used from 56 kbps to 2 Mbps.


Standard which specifies how H.320 terminals can be used on broadband switched digital networks (B-ISDN).


Standard which specifies how H.320 terminals can be used on isochronous ethernet LANs (guaranteed bandwidth and quality of service.)


Standard for multimedia conferencing on traditional packet-switched LANs.


Standard for multimedia conferencing on analog phone lines (POTS).


Standard which specifies how H.320 terminals can be used in a one-way broadcast mode.


Switched 384 kbps service.

Half duplex

Method to either transmit or receive without the ability to do both simultaneously.

Half-duplex audio

Audio that permits only one site to speak at a time.

HDTV (High-definition television)

HDTV provides up to five times higher resolution than standard analog TV. HDTV has better color fidelity and a 16:9 format. The two most important HDTV standards today are SMPTE 296M and SMPTE 274M, which are defined by the Society of Motion Picture and Television Engineers, SMPTE. Read more: HDTV.


A log of system activity that can be recalled by utilizing the report command. Most systems offer a feature that notifies the console operator of the amount of available storage for history information preventing information from being written over. The message will usually alert the operator to archive the information onto a removable magnetic tape.

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/IP suite of protocols.


A (network) hub is used to connect multiple devices to the network. The hub transmits all data to all devices connected to it, whereas a switch will only transmit the data to the device it is specifically intended for.


A device used to concentrate incoming data from multiple nodes onto a common network medium. Also commonly referred to as a concentrator or repeater.


A device that converts a 4-wire voice communication circuit into a 2-wire circuit.

Hyper Cardioid Microphone

A super directional microphone with a narrow heart-shaped pick up pattern used for specialized audio applications.

Image Compression

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

In-band signaling

Signaling made up of tones which pass within the voice frequency band and are carried along the same circuit as the talk path being established by the signals. Virtually all signaling (request for service, dialing, disconnect, etc.) in the U.S. is inband signaling. Most of that signaling is MF (multi-frequency) dialing. The more modern form of signaling is out-of-band.

Information element

The name for the data fields within an ISDN Layer 3 message.

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 and thus produce images. An infrared lamp can be used for improved illumination for night surveillance, whilst not producing any extra visible light.


Enter (opposite of egress).

Inputs/Outputs (I/O’s)

The digital I/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.

Interexchange carrier (IXC)

A common carrier that provides services to local exchanges on an intra or interLATA basis in compliance with local or Federal regulatory requirements. Traditionally IXCs have been long distance carriers.


A common boundary between two systems over which the inter-system communication occurs.


Interlaced video is video captured at 50 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 25 frames per second. See also Progressive scan. Read more: Progressive scan vs. interlaced.

International Telecommunications Union-Telecommunications Standards

(the new name for CCITT). An international standards body which is a committee of the ITU, a UN treaty organization.

Inverse Multiplexing

Speeds up data transmission by dividing a data stream into multiple concurrent streams that are transmitted at the same time across separate channels (such as T-1 or E-1 lines) and are then reconstructed at the other end back into the original data stream.


The Internet Protocol (IP) is the method or protocol by which data is sent from one computer to another on the Internet.

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 not 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

A 32-bit number that identifies each sender or receiver of information that is sent in packets across the Internet.

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).


Integrated services digital network. A digital transmission technology that allows large quantities of data to be transmitted over copper or fiber at speeds from 64 kbps to 128 kbps. ISDN comes in two forms: BRI and PRI, depending on your needs. BRI, Basic Rate Interface, is designed for desktop applications. PRI, Primary Rate Interface, is designed primarily for telephone switches, computer telephony, and processing systems.


Information Technology is a term that encompasses all forms of technology used to create, store, exchange, and use information in its various forms (business date, voice conversations, still images, motion picture, multimedia presentations, and other forms, including those not yet conceived).


International Telecommunications Union Telecommunications Standardization Sector.


Joint Bi-Level Image Experts Group of ISO. Produced text compression standard used in T.120.


Joint Photographics Experts Group of ISO. Produced still-image compression standard used in T.120.

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 extension ‘.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.


Kilobits per second. A measurement for the speed of data transmission.

Key Switch

A switch, which must be operated with a key.

Key System

CPE that provides line sharing capabilities to the user. Typical key systems share a few lines among many phones.


A flat device, which has buttons that may be pressed in a sequence to send data to a controller, and which differs (said to be “non-QUERTY”) from a typewriter-like computer board.




One thousand bits.


A measure of computer memory or storage.


Local Area Network. A network that connects computers, modems, and printers within a limited area such as a school or office.

LAN (Local Area Network)

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


Local Area Network Emulation. ATM devices communicate by emulating a LAN.

Last-Mile Technology

Any telecommunications technology, such as wireless radio, that carries signals from the broad telecommunication infrastructure along the relatively short distance (hence, the "last mile") to and from the home or business.


Local Access and Transport Area. A local geographical area that was originally established to define the area in which a local telephone company may offer telecommunications services.


The delay between the time a device receives a frame and the frame is forwarded out of the destination port.


An acronym for Liquid Crystal Display.


Low-Delay Code Excited Linear Prediction.

Leased line

A telecommunication facility or link reserved for the exclusive use of one customer. Also called a dedicated line.

Leased service

The exclusive use of any channel or combination of channels designated to a subscriber.


An acronym for Light-Emitting Diode.


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.


Any device that converts the computer system’s digital information into analog information and transmits it over a telephone line. Another modem must be used when the information back from analog to digital.

Loading coil

Equipment used to increase resistance to electrical current and balance attenuation of high and low frequency signals in the voiceband.

Local loop

In telephony the wire pair that connects a subscriber to a phone company end office, typically containing two wires. Four-wire local loops are common, however, especially with leased voice grade circuits.


A diagnostic procedure where data is sent to the device being tested, and the output of the device is fed directly back to its input, looped around, and the returning data is checked against that which was sent.

Loopback test

A test typically run on a 4-wire circuit. Two transmit leads are joined to the two receive leads. A signal is then sent around the loop. Measuring differences between the sent and received signal is the essence of a loopback test.


Low speed data channel of H.320.


Brightness (black and white) information in a video image. Short for luminance.


Brightness (black and white) information in a video image. Often called “luma”.


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.

Magnetic Stripe

A band of ferrous material that is sealed onto or into a card key or credit card.

Manual Iris

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

Master clock

The source of timing signals, or the signals themselves, which all network stations use for synchronization.

Mbit/s (Megabits per second)

A measure of the bit rate, i.e. the rate at which bits are passing a given point. Commonly used to give the “speed” of a network. A LAN might run at 10 or 100 Mbit/s. See also Bit rate.


Megabits per second (Million bits per second). A measurement for the speed of data transmission. One megabit equals approximately 1,000,000 bits.


Multipoint Control Unit that can link several videoconferencing systems for multipoint calls.


The Layer 3 information that is passed between CPE and SPCS for signaling.

Metropolitan Statistical Area (MSA)

A term used by government agencies and other organizations. The MSA divides the United States into 306 areas according to population density. Cellular contracts are awarded by MSA.


Management Information Base. Specifications which contain the format definitions of data fields for remote management by SNMP.


Million Instructions Per Second (fixed-point).


Multi-layer protocol for data (in H.221). MLP data and audio can only be placed in the first 64 kbps channel of a connection. T.120 must use the MLP or HMLP channel.

Mobile Telephone Switching Offices (MTSO)

A cellular CO, for use only within the cellular network. Interacts with cell sites.


Device that converts the computer system’s digital information into analog information and transmits it over a telephone line. Another modem must be used when the information is received to convert the information back from analog to digital.


Modulator-demodulator. Converts digital signals to and from analog.


The process of manipulating the frequency or amplitude of a carrier in relation to an incoming video, voice or data signal.


A device which modulates a carrier. Modulators are found as components in broadcasting transmitters and in videoconference transponders.

Momentary Switch

A switch that, after being activated, automatically returns to its original position; a spring-loaded contact that, when pressed, closes two contacts, and when pressure is removed, opens the contact.


Artifacts found around edges when the coder cannot keep up with the detailed video content. Resemble speckles.

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.


Motion Picture Experts Group of ISO. Responsible for MPEG-1 and MPEG-2 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 (ISO). The MPEG standards are an evolving series, each designed for a different purpose. Read more: Compression standards.


Video Standard targeted at 1.5 Mbps playback on multimedia PCs.


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.


Video Standard targeted at 2-10 Mbps broadcast television. Will also be used for higher bandwidth HDTV.


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 left 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 set of standards. To deal with this, the standard includes the concept of "profiles" and "levels", allowing a specific set of capabilities to be defined in a manner appropriate for a subset of applications. Read more: Compression standards.


Communication between a single sender and multiple receivers on a network.

Multimode Fiber

Optical fiber that is designed to carry multiple light rays or modes concurrently, each at a slightly different reflection angle within the optical fiber core.


The combining of multiple data channels onto a single transmission medium. Any process through which a circuit normally dedicated to a single user can be shared by multiple users. Typically, user data streams are interleaved on a bit or byte basis (time division) or separated by different carrier frequencies (frequency division).


A call involving three or more parties.

Multipoint circuit

A circuit consisting of three or more stations connected directly electrically.


An abbreviation for multiplexer, a device that sends multiple signals on a carrier channel at the same time in the form of a single, complex signal to another device that recovers the separate signals at the receiving end.


Narrowband ISDN (The ISDN currently used).


Bandwidths from 64kbps to 2Mbps.


A group of stations (computers, telephones, or other devices) connected by communications facilities for exchanging information. Connection can be permanent, via cable, or temporary, through telephone or other communications links. The transmission medium can be physical (i.e. fiber optic cable) or wireless (i.e. satellite).

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.


Network Interface Card. Connects a PC to a LAN.


A point of interconnection to a network, such as computers, printers, routers, faxes, or bridges.


Caused by random electrical signals, which act to corrupt the bits being transmitted. Noise can come from outside electrical sources.

Non-ISDN line

Any connection from a CPE to a SPCS that is not served by D-Channel signaling.

Non-ISDN trunk

Any trunk not served by either SS7 or D-Channel signaling.


Network Termination 1. Network termination equipment for ISDN BRI. A unit that provides physical and electromagnetic termination of the U-interface 2-wire transmission line, converts between Layer 1 formats used at the U- and T- reference points, and performs some maintenance functions. Turns a U interface into an S/T interface. Not needed when connecting to most digital PBXs.


National Television Standards Committee. Standard for broadcast television in US and Japan. Theoretical resolution of 720X480, 30 interlaced frames per second.


Connection capable of carrying data at 155.52 MBPs.


"The active condition of switched access or a telephone exchange service line. One digit of the dialed number. Stages work independently of each other, making the switch slow and inefficient. "

Offhook signaling state

A request from the telephone station set for access to the network. A set goes offhook when a caller picks up the handset.


"An inactive phone ready to send or receive calls. Represented by having the phone on the cradle or the ""hang up"" position. "

ONVIF (Open Network Video Interface Forum)

ONVIF is an open industry forum for the development of a global standard for the interface of network video products. Read more: ONVIF.

Optical Fiber

(or "fiber optic") refers to the medium and the technology associated with the transmission of information as light pulses along a glass or plastic wire or fiber.

Out of band

Transmission taking place external to allocated bandwidth. A video call with out-of-band audio requires a separate phone line for the audio.

Out-of-band signaling

Using a separate signaling channel for controlling a call.

Output Relays

The auxiliary relays found in access control panels or NODES that control external devices.


P-Iris is an automatic, precise iris control developed by Axis Communications of Sweden and Kowa Company of Japan. It involves a P-Iris lens and specialized software that optimize image quality. Read more: Types of iris control.


The unit of data that is routed between an origin and a destination on the Internet or any other packet-switched network.

Packet mode

Refers to switching of packets of information for different users by statistically multiplexing them over the same transmission facilities. ISDN packet mode capabilities are based on CCITT recommendation X.25 procedures.


The type of network in which relatively small units of data called packets are routed through a network based on the destination address contained within each packet.


Phase Alternating Line. European television format. 720X576, 25 interlaced frames per second.

Panic Bar

A device, usually a small electrical switch in a mounting plate, used for unlocking a door in an emergency.

Parking Gate

A barrier that can be opened or closed to control vehicular access.

Passive Infrared (PIR) Detector

A sensor that detects the changes in the infrared light radiating from.


Private branch exchange.


Peripheral Component Interface. Bus interface technology for PC cards.


Pulse-code modulation. Sample-based coding technique.


Picture-in-picture (a second smaller window inside the main screen).

PoE (Power over Ethernet)

Power over Ethernet 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. Read more: Power over Ethernet.

Point of Presence (POP)

The IXC equivalent of a local phone company's central office. The POP is your long distance carrier's office inside your community. It is the place where the long distance lines and connects to the local phone company's lines.

Point to Point

Describing a circuit connecting two points directly with no intermediate nodes or computers (although switching facilities could exists). A type of connection that links two logical entities (i.e., phone-line circuit).


Plain Old Telephone System. Ordinary telephone lines that transmit information over twisted pair copper wires. Analog phone system that can carry frequencies from 300Hz - 3.4 kHz.


Point-to-point protocol. Allows for more efficient connections between ISPs and clients over modems.


Primary Rate Interface. 23X64 kbps (T1--US, Japan,etc.), 30X64 kbps (E1--Europe,China, etc.).

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 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. Read more: Progressive scan vs. interlaced.


A procedure for adding order to the exchange of data. A protocol is a specific set of rules, procedures, or conventions relating to the format and timing of data transmission between two devices.


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.


Packet Switched Network (Internet, LAN).


Pan-Tilt-Zoom. Camera functionality.


(Permanent Virtual Circuit) is a software-defined logical connection in a frame relay network.


Alternative term used to refer to H.320 standard. Often used to specifically describe the video portion of H.320 (H.261). Px64 refers to an integer p times 64 kbps B channels.


Quarter-CIF picture resolution. 176X144 pixels. H.261 and H.263 mandatory format.


Quality of Service is a catchphrase for a network that can transport data without losing cells, with predictable end-to-end delay, with real-time delivery of data once the connection is completed. High-quality multimedia over a network, whether in real-time or merely playing audio or video files from a server, requires a network that can deliver QOS. Protocals such as ATM (Asynchronous Transfer Mode) are designed to deliver multiple levels of QOS. Attempting to deliver QOS using IP requires additional services such as RSVP (Resource Reservation Protocol), which allows bandwidth to be reserved and to be supported on intermediate devices such as routers.

Network transmission using radio technology, such as microwave or infrared technology.


(regional Bell operating company) is a term describing one of the U.S. regional telephone companies (or their successors) that were created as a result of the breakup of American Telephone and Telegraph Company (AT&T, known also as the Bell System or "Ma Bell") by a U.S. Federal Court consent decree on December 31, 1983.


Refers to the “front end” that a user must interact with to allow access. Readers can be keypads, card readers, and proximity readers.

Refractive index

Numerical value that describes the refraction of light when it passes through the boundary of two different materials.


Device that restores a degraded digital signal for continued transmission; also called a repeater.

Registered Jack

RJ (registered jacks, sometimes described as RJ-XX) is a series of telephone connection interfaces (receptacle and plug) that are registered with the U.S. Federal Communications Commission (FCC).


A device used in electromechanical switches that uses a current to close a mechanical switch.

Remote access

The ability to access a network from a location not directly connected to the network site.


Device that restores a degraded digital signal for continued transmission; also called a regenerator.


A measure of sharpness or clarity on a monitor.


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 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. Read more: Resolution.

Reverse battery signaling

Method of DC signaling based on the signal's changing polarity of the voltage in the circuit.


Red-Green-Blue picture display format.


A point of electrical contact in a manual switchboard plug. It connects to one of the two wires in a two-wire transmission. The other point of contact is termed the tip. Although the manually switched line is obsolete, the terms are still used for line assignment purposes. Routed on a trunk-by-trunk basis through a matrix of incoming and outgoing trunks.


The plastic four-wire jack on a phone wire.


The plastic eight-wire ISDN jack.

Room based videoconferencing

Videoconferencing using a sophisticated system. Appropriate for large groups.


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.


A protocol-dependent device that connects similar and dissimilar LANs and also WANs.


Generic 25-pin data interface used for serial byte data communication (same as V.24). An EIA-specified physical interface with associated electrical signaling between DCE and DTE. The most commonly employed interface between computer devices and modems.


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.


Generic dialing interface (An EIA interface standard for autodialing).


RS-422 is a serial data communication protocol that specifies 4-wire, 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.


Generic 37-pin fast differential data interface.


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 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 meters). RS-485 only specifies the electrical characteristics of the driver and the receiver. It does not specify or recommend any data protocol.


Interface using DB-25 connector, but for higher speeds than RS-232. Has balanced signals (like EIA-422) except for three maintenance signals which are EIA-423.


Real-Time Protocol/Real-Time Control Protocol. Protocols that provides real-time data delivery characteristics over IP.


An ISDN NT-1 drives an S/T-bus which is usually 4 wires, but in some cases it may be 6 or 8 wires. In these optional cases, the extra wires are used to provide power to operate telephones when normal power fails (In North America there is no provision for emergency mode operation). Point T refers to the connection between the NT1 device and customer supplied equipment. Terminals can connect directly to NT1 at point T. When a PBX is present, point S refers to the connection between the PBX and the terminal.


Synchronous data link control. A data communications line protocol associated with the IBM system network architecture. SDLC is a bit-oriented protocol (not a character-oriented protocol) that includes multiple block error checking and full duplex line operation.


Sequential Colour Avec Memoire. Television format for countries such as France, Russia and Madagascar.


PictureTel's proprietary software generation 3. Audio and video compression and transmission format, provides encryption. Uses proprietary packet protocol, and provides better than standards video quality.


PictureTel's proprietary software generation 4. Based on SG3; improvements include: transmission over standard H.221 multiplex, better motion coding, and contrast enhancement.


To bypass. When an alarm is bypassed so that it doesn’t activate, it is said to be shunted.

Shunt Time

The time in seconds that a door-open alarm is suppressed after the door has been opened.


The frequencies the modulated carrier wave occupies. Upper sideband transmissions occupy the relevant frequencies above the carrier.


The transmission of the speaker's input into the microphone section of the headset into the speaker's receiver.

Signal transfer point (STP)

Node in the interoffice (CCS7) network that communicates with central offices to assist in routing.


Method of communication between network components to provide control management and performance monitoring.

Signaling point (SP)

Processor designed for handling the signaling function of a switch in a common channel signaling network.


Switched Multimegabit Data Service. A connectionless high-speed data transmission service that transmits information in fixed cell lengths at speeds from 56kbps to 34Mbps.

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.


Simple Network Management Protocol. Standard for retrieving and transmitting management information (configuration, control, performance monitoring, etc.) Information is formatted according to MIBs.


Service Profile Identifier.


Sub-QCIF 128X96 pixels.


An access control system that makes its own access decisions without communicating with a central controller

Streaming Video

A sequence of "moving images" that are sent in compressed form over the Internet and displayed by the viewer as they arrive.


A plate mortised into or mounted on the doorjamb to accept and restrain a bolt when the door is closed. In some metal installations or with a deadlock, the strike may simply be an opening cut into the jamb. (Synonym - keeper)

Strike Plate

A plate, usually of metal, mortised into or mounted on the doorjamb to accept and restrain a bolt when the door is closed.

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 IP 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.


AT&T network providing connections at multiples of 56 kbps.


In serial data transmission, a method of ensuring that the receiving end can recognize characters in the order in which the transmitting end sent them, and can know where one character ends and the next begins. Without synchronization, the receiving end would perceive data simply as a series of binary digits with no relation to one another. Synchronous communication relies on a clocking mechanism to synchronize the signals between the sending and receiving machines.


Standard for data conferencing and conference control for interactive multimedia communication both multipoint and point-to-point.


Specifies T.120 general application protocols.


Specifies T.120 service interface for multipoint operation.


Transport stack of T.120. Carries out functions such as specifying connection protocols between devices and providing network-independent interface for rest of T.120.


Generic Conference Control (GCC) for T.120. Provides control of a conference (joining, locating, scheduling, etc.) and supports application protocols.


Specifies T.120 protocol for multipoint operation.


T.120 still image transfer and annotation protocol.


T.120 binary file transfer protocol.


T.120 application sharing protocol.


Audio and video control protocol within T.120.


T.120 conference reservation protocol.


Now T.128.


A digital transmission link with a capacity of 1.544 Mbps. T1 uses two pairs of normal twisted wires. T1 normally can handle 24 voice conversations with each conversation being digitized at 64 kbps. With more advanced digital voice encoding techniques, it can handle more voice channels. T1 is a standard for digital transmission in North America (1.536 kbps).


A connection capable of carrying data at 45,000,000 bits-per-second or 45MBPs.


Terminal adapter. A DCE that connects to the ISDN S-interface and enables non-ISDN terminal equipment to communicate over the ISDN.

TCP (Transmission Control Protocol)

TCP is used along with the Internet 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 established between the two end-points and is maintained until the data has been successfully exchanged between the communicating applications.


Transmission Control Protocol/Internet Protocol. A set of protocols developed by the Department of Defense to link dissimilar computers across networks. TCP/IP is the standard upon which the Internet is based. Protocol layer that guarantees delivery of information across IP.


(Time Division Multiplex) is a scheme in which numerous signals are combined for transmission on a single communications line or channel. Each signal is broken up into many segments, each having very short duration.


Time Division Multiple Access.


A work-at-home computer user who connects to the corporate backbone using remote access technologies.


Thermography (or thermal imaging) is a method where infrared radiation is converted to, and presented as, an image. Thermography is a very powerful tool for seeing heat differences in objects. If the thermal camera is calibrated, the thermal image can provide information on the object’s surface temperature. When measuring the temperature of a specific surface, the camera is influenced by many other parameters‒such as the absorption, the emission, the reflection, the transmission and how the surrounding objects radiate the heat.

Time and Attendance

The ability to utilize the time in and time out information per user, for the purpose of keeping track of employee’s hours at a facility. Many time and attendance packages work as stand-alone systems, and interface with most payroll software.

Time Schedules

Allows for Access based on time of day, date and user. Also allows for holidays, etc.

Token ring

A platform for transmitting information across a LAN. Token ring networks are configured so that data flows in one direction over twisted pair wires at speeds from 4 Mbps to 16 Mbps.


A record created that contains pertinent information about an occurrence in the access control and monitoring system.

Transient Suppressor

A device that protects data lines from high transient such as lighting and inductive loads. They are recommended where there are data communications lines between the reader and its electronics that are subject to high-transient situations. Two are required - one at each end of the exposed communications lines.


A single transmission path connecting two switching system. Trunks can be shared by many users but serve only one call at a time.

Twisted Pair

A cable composed of two small substantially insulated conductors, twisted together with or without a common covering. Bleden 8720 cable, for instance, contains two twisted shielded pairs of stranded wire.

Twisted pair

Traditional copper wiring well suited for short distance transmission of information. It consists of two insulated copper conducters twisted around each other and surrounded by a plastic coating.

Two-wire circuit

A transmission circuit composed of two wires, signal and ground, used to both send and receive information. In contrast, a 4-wire circuit consists of two pairs. One pair is used to send. One pair is used to receive. All trunk circuits (long distance) are 4-wire. A 4-wire circuit delivers better reception, but also cost more. All local loop circuits (those coming from class 5 central office to the subscriber's phone system) are 2-wire, unless a 4-wire circuit is requested.


2-wire BRI interface. A twisted pair subscriber loop that connects the NT1 reference point to the ISDN network, as defined in the I.411 recommendation. This interface provides Basic Rate Access with an operating frequency of 160 kbps and an information rate144 kbps. Under U.S. regulations, this also marks the line of demarcation between customer-owned equipment and the public network.


Quantization for voice PCM used in North America.


User Interface.


Underwriters Laboratory-U.S. Safety standards body.

Underwriters Laboratories Inc. (UL)

An independent, not-for-profit organization that tests products in the interests of public safety.

Uncooled Thermal Sensors

Uncooled sensors also come in different types but the most common type is the microbolometer thermal sensor. A microbolometer is basically a tiny resistor that changes resistance with temperature. By letting the incoming signal heat the microbolometer and then read out the resistance change compared to a “blind” microbolometer, a value for the incoming infrared radiation can be created. An image is created in an array of microbolometers pixels.


User-Network Interface. Customized device that provides entry for equipment over ATM networks.


An immensely powerful and complex operating system for computers for running data processing and telephone systems. UNIX provides multitasking or multi-user capabilities that allow multiple programs to run simultaneously and multiple users to operate a single computer.

The station used to transmit signals for a satellite videoconference.


Same as RS-232.


Modem standard for 33.6 kbps operation.


High-speed 15-pin data interface. CCITT standard for trunk interface between a network access device and a packet network that defines signaling for data rates greater than 19.2 kbps.


(Value-added reseller) is a company that takes an existing product, adds its own "value" usually in the form of a specific application for the product (for example, a special computer application), and resells it as a new product or "package".

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.


Variable Bit Rate.


Virtual Channel.


Video Conferencing System.


Video Graphics Adapter. Standard PC video format.

Video Encoder

Video server. Read more: What is a video server?

Video On Demand (VOD)

The ability to access video on the network. Can be used for applications such as web documents, video clips, PowerPoint and Word documents. Users can simply "point and click" to access and begin a video.


Device which stores video in digital form with formats such as MPEG-1, MPEG-2 and is accessible over all types of networks. Can store video content in customizable amounts with the able to have multiple users access to the same files.


Transmitting of digital video to multiple users on the network at the same time, on one or more channels.


The real-time, usually two-way, transmission of digitized video images between two or more locations. Teleconferencing requires a wideband transmission facility. Transmitted images may be freeze-frame (where television screen is repainted every few seconds to every 20 seconds) or full motion. Bandwidth requirements for two-way videoconferencing range from 6 MHz for analog, full-motion, full-color, commercial grade TV to 56 kbps for digitally encoded freeze-frame to 1.544 kbps for very good quality, full-color, full-motion TV.

Voice activated switching

In multiway videoconferencing, used so that all participating sites automatically see the site which is currently speaking.

Voice over internet protocol

The transmission of voice signals over the IP based Internet.


camera automatically tracks the voice of the person speaking.

VPN (Virtual Private Network)

This creates a secure “tunnel” between the points within the VPN. Only devices with the correct "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.


Very Small Aperture Terminal. Terminal used as the interface to a satellite-based network.

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.


Wide Area Network. A data network that interconnects multiple LANs across great distances through telecommunications links.

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.


A video camera, usually attached directly to a computer, whose current or latest image is requestable from a Web site.


(push technology) is the prearranged updating of news, weather, or other selected information on a computer user's desktop interface through periodic and generally unobtrusive transmission over the World Wide Web (including the use of the Web protocol on intranets).


A medium-capacity communications circuit/path. It usually implies a speed from 64Kbps to 1.544Mbps.

Wiegand Card Key

A plastic card, approximately the shape of a credit card, which has an embedded module of inert, specially treated ferromagnetic wires which generate a voltage pulse that can be sensed by a coil within the card reader.

Wink start signaling

Method of supervisory signaling. CPE signals offhook condition by sending a momentary pulse to the CO. Contrast ground start and loop start.

Wire center

Any point in a telecommunications network where the network's wiring is exposed to provide access.


Same as RS-449 with in-band dialing capability.


An umbrella term used to describe an emerging family of "digital subscriber line" technologies. These technologies enable existing twisted pair telco lines to become the transport mechanism for multimedia and high-speed data transmission technologies without impacting the Public Switched Telephone Network or central office switch.


An error -correcting file transfer, data transmission protocol used to transmit files between PCs. The XMODEM protocol sends information in 128-byte blocks of data. Some sums (check sums) are done on each block and the result is sent along with the block. If the result does not check out at the other end, the computer at the other end sends a request (a NAK - negative acknowledgment) to retransmit that block once again. If the block checks out, the computer sends ACK (an acknowledgment). In this way, relatively error-free transmission can be accomplished.

Zoom Lens

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


Closed Circuit Television: This refers to a system of cameras and monitors used for video surveillance and security purposes.


Digital Video Recorder: This is a device that records video footage from CCTV cameras for later viewing.


Network Video Recorder: This is a digital recording device that stores video footage from IP cameras.


Internet Protocol: This refers to a type of digital camera that transmits video footage over an internet network.


Passive Infrared: This refers to a type of motion sensor that detects changes in infrared radiation and is commonly used in security systems.


Radio Frequency Identification: This is a technology used to identify and track objects using radio waves.


Local Area Network: This refers to a network of computers and devices that are connected to each other within a limited geographical area, such as an office building.


Wide Area Network: This refers to a network of computers and devices that are connected to each other over a larger geographical area, such as the internet.


Virtual Private Network: This is a secure way to connect to a network over the internet, often used by remote workers or for secure communication between different locations.


Personal Protective Equipment: This refers to equipment worn to protect individuals from hazards in the workplace, such as helmets, gloves, and safety glasses.


Distributed Denial of Service: This is a type of cyber attack that involves overwhelming a network or website with traffic, making it unavailable to users.


dvanced Encryption Standard: This is a type of encryption used to secure data transmission and protect against cyber attacks.


Secure Sockets Layer: This is a protocol used to secure data transmission over the internet, commonly used for secure transactions on e-commerce websites.


Intrusion Detection System: This is a system that monitors a network for signs of unauthorized access or malicious activity.


Intrusion Prevention System: This is a system that actively blocks unauthorized access or malicious activity on a network.


Access Control Systems. An Access Control System is a security system that manages and regulates access to a physical space, device, or resource by controlling who is allowed to enter, exit, or access it. An Access Control System can be as simple as a lock and key or as complex as a multi-layered security system that uses advanced technology such as biometric identification, smart cards, and proximity sensors.

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