Analogue Digital Converter; converts analogue signals into digital input.
Adaptive Delta Pulse-Code Modulation; a process which severely compresses audio data. Using this up to 19 hours of recording can be stored on a CD.
Asynchronous Digital Subscriber Line – modern system for transmitting data using traditional copper cabling. The signal does not need to be synchronised between the source and the receiver.
Automatic Gain Control – an automatic amplification control ensuring that the camera output signal voltage remains between predetermined limits.
Application Programming Interface – where the programmer has access to the operating system functions and the user interface.
In the context of video conferencing, this refers to the ability to see and edit documents and data and to exchange them online. The standard for Application Sharing is ITU Recommendation T.120 which is supported by Microsoft NetMeeting.
Automatic Send and Receive – refers to a modem's operating mode in which data are automatically exchanged between modem and the target recipient.
ISDN connection with SO interface which consists of 2 data channels (B channels) with 64Kbps and a data channel (D channel) with 16 Kbps.
Channel for transmission of ISDN user-data with a transmission speed of 64kbit/s.
Bi-directional Frame – this type of frame is produced in MPEG encoding, and can only be encoded if the previous and following frames are also known.
Binary Synchronous Communication – a transmission protocol for synchronous (binary) data transmission.
Basic Rate Interface – the international term for the basic ISDN connection.
Connection between two or more networks. Can only be networks with the same topology (e.g. Ethernet) and the same protocols.
Buffer memory which can be installed between different kinds of memory media. Intermediate storage in a cache reduces the access speed.
Common ISDN-API – the standardised interface for ISDN cards.
Comitée Consultatif International Télégraphique et Téléphonique – the international advisory body concerned with standardisation of data and telephone services.
The combining of several B-channels which together form a virtual channel with a higher data transmission rate, especially valuable for video-conferencing and video phones.
Two-pin plug connection for transmission of audio and video information.
Coding/decoding and compression/decompression of video conferencing signals according to a particular procedure. The process has been standardised by the ITU. The conversions are done using a special CODEC card which usually includes communication interfaces (ISDN/LAN).
Continuous Presence (Quarter Split)
A form of multipoint conference in which people in 5 locations can participate via picture and sound. With this each screen is split into 4, each sector showing a different location.
Internal management system through which the processor exchanges data with its environment.
A video signal including colour, picture, blanking, and synchronisation information, produced by video recorders and camcorders which operate according to the Video 8 or VHS standards and in which brightness and colour are transmitted in parallel.
A means of increasing the effective data transmission performance. Data are compressed using special mathematical processes.
Discrete Cosinus Transformation – a process for data reduction, predominantly for M-JPEG. Individual pictures are divided into blocks of 8×8 pixels and simplified colour information allocated to them.
Dynamic Data Channel – is a protocol for data communication between video conferencing systems.
Digital European Cordless Telecommunication – is the European digital transmission standard for cordless telephones.
In ISDN, a channel for the transmission of service information. All the relevant signals for connection and disconnection of the link are carried in the D channel. 1TR6 and DSS1 are different and non-compatible D channel protocols.
A safety function which is triggered when one part of the B channels used for communication fails, and this ensures that the transmission is not completely interrupted.
Digital Subscriber Signalling System No.1 – a signalling protocol used between the ISDN terminal devices and the PBX.
Digital Signal Processor or single chip microcomputer which is used in electronic systems to control independent processes and take on computational tasks.
Digital Simultaneous Voice Data – a modem which supports both data transmission and voice communication at the same time.
Dual Tone Multi Frequency – dialling and controlling signals in the form of combinations of tones.
Digital Video Interface – where video pictures are digitised in real time and saved as compressed video files.
A system for filtering the echo feedback which occurs with speech transmission. This considerably improves the quality of the voice transmission.
Encryption/decryption is used to ensure that data communications cannot be eavesdropped. The encryption systems have to be installed at both transmitter and receiver sides.
An electronic data processing network which nowadays is the most widely used system for local networks.
Fibre Distributed Data Interface – interface for data which is transmitted in light waves by fibre optic cable. High speed technology based on the Token ring principle.
A firewall seals off data networks. Any data going into or out of the network must pass through the firewall and only the data which complies with security requirements is allowed through.
Permanent active connection between two sub-networks within in the network. No other users can use this connection.
A frame is an single picture within the body of video data.
With digital video this is the picture refresh rate. To achieve a full motion video a frame rate of 25 frames per second is required. With less than 15 frames per second the video movement is jerky.
refers to the ability to send and receive data simultaneously at maximum speed.
In video conferencing these allow H.323-compatible systems to communicate with H.32x terminals. For example a gateway system can link an H.323 system with H.320 (SIDN), H.321 (ATM), H.322 (ISO Ethernet) or H.324 (PSTN). At present an H.323 to H.323 connection (LAN/LAN) is still the most used form of VC gateway.
Generator Lock – in analogue systems this is how the video signal is fed into the PC. Using Genlock the video signal can also be blended with a graphic or with another video signal and then be put on tape.
This relates to the grabbing and storage of picture data on the computer. There are various grabbing functions: screen grabbing, frame grabbing, motion grabbing. (Screenshots are individual pictures taken from the video sequence.)
Global System for Mobile Communications – international standard for the digital mobile radio telephone network.
The ITU-T (International Telecommunication Union) standard for picture and sound communication over ISDN.
High-Level Data Link Control – transmission protocol
Special peripheral circuit for smear suppression and to give full detailed picture reproduction of extremely bright areas.
Intelligent Call Management – this function dynamically distributes and manages the transmission bandwidth between video, audio and data.
Inverse Multiplexer – a device for managing transmission when using several ISDN channels for video or data communication
Interfaces allow the communication between different kinds of hardware and software, and between users and programs.
A process for compressing digital videos in which only the changes between sequential pictures are saved. – Whereas with intra-frame compression only the data within the frame is reduced.
Integrated Services Digital Network.
Local Area Network – the networking of computers within a limited area.
Local Application Control BUS System – interface for controlling video recorders and camcorders.
A special program for data exchange between two PCs via serial or parallel ports or an ISDN card.
Low Frequency Signal Level
Low frequency signal level (linein/lineout).
Multipoint Control Unit – a system which enables and controls a conference with more than two participants.
Music Instruments Digital Interface – software interface for the exchange of data between a musical instrument (keyboard etc.) and a computer.
Motion Joint Photographic Experts Group – a digital editing compression procedure for the storage of video sequences. Whereas with MPEG (Moving Pictures Experts Group) only the differences between individual pictures are saved, here each picture is retained.
Multiple Subscriber Number – number with many devices connected.
Device for recording signals from up to 16 cameras using only one video recorder. Can provide full-screen replay of individual chosen cameras as well as multi-screen displays.
Network Driver Interface Specification – definition of interface between the local network operating system and the network adapter.
Microsoft NetMeeting 2.0 enables users all to benefit from audio, video, data and applications in real time over various kinds of link. The functions available vary according to the kind of connection. For connections between two modems, data and applications are supported but audio and video are not. The same is true for connections in local networks (IPX/SPX-LANs). A TCP/IP connection or a local area network (LAN) is needed to support audio and video.
Network Terminal Base Connection, the connecting element between the ISDN circuit and the user connection.
National Television System Committee – the American TV standard (power supply frequency 50 Hz, 525 lines, 30 pictures/s). PAL, the European standard and SECAM, the French standard, have 625 lines and 25 pictures/s.
Open Database Application Programming Interface – software interface controlling the data exchange between databases and other applications.
OSI- Layer Model
Open Systems Interconnection (OSI) – is an ISO working group which lays down general standards. The Open Systems layer model specifies the handling and management of data transmission in a network which is divided in to different levels or layers.
Phase Alternation Line – the European video standard (50 Hz power supply).
Private Branch Exchange; private telecommunications exchange.
Peripheral Component Interconnect – bus format for computer cards.
Pulse Code Modulation – a process for converting analogue signals into digital information, e.g. for digitising audio data.
Public Data Network.
Point to Point Protocol – serial transmission protocol for point to point connections, for example for access to the internet using a modem.
Plain Old Telephone Service – analogue telephone network, using for example twisted pair cabling for modulated voice signals.
Public Switched Telephone Network – (fixed) analogue telephone network.
For simultaneous display of four camera pictures on one monitor.
Quality of Service
This ensures an application is allocated specific necessary network resources in the form of a guaranteed bandwidth – an important consideration with video conferencing and voice over IP (VoIP).
Rewriteable Consumer Timecode – for linear cutting in video editing.
Remote control of devices.
Réseau IP Européens – the TCP/IP network in Europe which is supervised by the EUnet European Unix Network.
Radio Manufacturer Association Testcard – test card or slide for testing camera quality.
Remote Network Access.
A special device for forwarding data packages to the appropriate junctions and intersections in the network and thus linking the network together. The network topologies can be different (e.g. Token Ring and Ethernet).
This is the computer connection where the mouse and the modem are plugged in. Only 9 and 25 pin connections conforming to the V.24 standard can be made with this kind of interface .
A device for converting data (usually audio) into digital data. These data can then be processed in a PC. Sampling refers to the digitisation of graphics (using a graphics card) and notes, speech and sounds (using a sound card).
The standard socket used in TV and video.
Small Computer System Interface – standardised interface for small computer systems to which peripherals (e.g. a CD drive) is connected.
A digital audio interface which is connected to a digital audio device (e.g. DAT recorder) and enables copies to be made without any losses.
The internationally standardised interface for ISDN end-user applications. It consists of two data channels (B channels) and a signal channel (D channel). Up to eight devices with 12 ISDN sockets can be linked to the SO interface.
Basic ISDN connection (also primary multiplex connection) consisting of 30 user channels (B channels), one control channel (D channel) and a synch channel. Of the 32 channels, 30 are available for telephone use. (Interesting for larger firms).
Transmission Control Protocol/Internet Protocol – TCP is responsible for the correct delivery of the data packets, IP for the transportation.
Thin Film Technology – the term used to describe flat screens with active internal illumination.
In the video editing program this is the first frame which is used to represent the video clip.
Time Multiplex Process
controls the transmission of different sources via a single transmission medium (serial circuit). A multiplexer allocates each source a time window in which digital data transmission is possible.
A special data packet which is passed from station to station in a Token Ring Network. The packet can only be forwarded by the current station so that there are no collisions in the transfer of information.
is a control protocol for serial data transfer between a DTE (a piece of Data Terminal Equipment) and a DCE (a Distributed Computing Environment) – as between a computer and a modem. The term V.24 is often used to refer to an R232C interface.
The name for a video signal produced by a black & white camera.
Video Graphics Array – the graphic standard used by all modern graphics cards (resolution up to 640×480 pixels).
Wide Area Network – the networking of PCs or local networks over public or private telecommunication networks.
Wide Angle View Camera – camera with a particularly wide field of view (wide angle lens + camera panning radius).
White Value Limit
Protection system for avoiding video signals levels above >1.1 Vpp.
A transmission protocol, defining an interface in the physical layer. X.21 is used for X.25 networks.