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Internet Terminology - A-L

A standard for sampling video signals. The numbers refer to the sampling frequency of, respectively, luminance and the two color difference signals calculated as a multiple of the color subcarrier’s frequency. The process is described in CCIR Rec. 601.

ADC (Analog-to-digital conversion)
an electronic process in which a continuously variable (analog) signal is changed, without altering its essential content, into a multi-level (digital) signal.

ADSL (Asymmetrical Digital Subscriber Line)
a technology for bidirectional digital transmission on standard twisted-pair copper phone lines used for consumer TV applications with "VCR-like" quality.

In sound and image generation, aliasing is the generation of a false (alias) frequency along with the correct one when doing frequency sampling. For images, this produces a jagged edge, or stair-step effect. For sound, it produces a buzz.

Analog video
A non-digital video signal used by most conventional video equipment for input or output. Video in which all the information representing images is in a continuous-scale electrical signal for both amplitude and time. Three basic analog video formats exist: NTSC, PAL, and SECAM. (See separate entries for more detailed information.)

is the smoothing of the image or sound roughness caused by aliasing. With images, approaches include adjusting pixel positions or setting pixel intensities so that there is a more gradual transition between the color of a line and the background color.

application program interface; the specific method prescribed by a computer operating system or by another application program by which a programmer writing an application program can make requests of the operating system or another application.

In video systems, something distorted or unintended observed in the reproduction of an image by the system. Flaws in a picture, such as cross-color artifacts, cross-luminance artifacts, judder, blocking, ghosts, etc.

Asymmetrical Compression
Refers to compression systems, processes or algorithms that require more processing capability to compress an image than to decompress it. Ordinarily, asymmetric processes are employed for the mass distribution of programs on media like CD-ROM. In such applications, while far higher costs can be justified for the production and compression of the program, the playback system must be low in cost. (See symmetric compression)

processes that proceed independently of each other until one process needs to "interrupt" the other process with a request. Using the client- server model, the server handles many asynchronous requests from its many clients. The client is often able to proceed with other work or must wait on the service requested from the server.

Asynchronous Transfer Mode (ATM)
High-speed, packet switched and multiplexed switching technique for the efficient transmission of voice, data, and video. Transmission format uses packets of a fixed length of 53 bytes. A peak throughput of 155 Mbps or 622 Mbps is available for OC-3 and OC-13 installations, respectively.

In a network, a backbone is a larger transmission path into which smaller lines feed. At the enterprise level, a backbone is a line or set of lines that local area networks connect to for a wide area network connection or within a local area network to span distances efficiently (for example, between buildings).

Back channel
Communications link used by the client to send video stream control commands (such as fast forward or play) to the server.

Communications capacity of a specific path or transmission line through a network, measured in bits per second (bps). Refers to the frequency range transmitted by an analog system. In video systems, specifying the highest frequency value is sufficient, since all video systems must transmit frequencies down to 30 Hz or lower.

Bandwidth characteristic of networks occupied by a single digital signal, such as Ethernet or Token Ring LANs.

the prevalent measure for data transmission speed until replaced by a more accurate term, bps (bits per second). One baud is one electronic state change per second. Since a single state change can involve more than a single bit of data, the bps unit of measurement has replaced it as a better expression of data transmission speed.

Bearer Service
Service provided by the B-channel of ISDN, including digital telephony, circuit-switched data at 64 kbit/s, packet-switched data (X.25), etc.

the smallest unit of information in a computer. A bit has a single binary value, either 0 or 1.

Bit Assignment
In video compression, the process of creating the compressed data bit stream from the raw output of the compression algorithm.

defines a display space and the color for each pixel or "bit" in the display space. A GIF and a JPEG are examples of graphic image file types that contain bitmaps.

Bits per Pixel
The number of bits used to represent the color value of each pixel in a digitized image.

An artifact of visible discontinuities between adjacent blocks in a DCT-based compression. Often seen at high compressions

An abbreviation of "Bandwidth ON Demand Interoperability Group"; a specific set of methods of inverse multiplexing.

The sharing of multiple signals over the same bandwidth, accomplished simultaneously through the use of multiplexing (splitting) of the signal.

a program that provides a way to look at, read, and even hear all the information on the World Wide Web.

a data area shared by hardware devices or program processes that operate at different speeds or with different sets of priorities. The buffer allows each device or process to operate without being held up by the other.

Bursty traffic
Data transmission with low duty cycle; data in multiple periods of short duration.

Cable Modem
a device connected to or integrated in a PC that enables you to receive and request information from the Internet over your local cable TV line. Cable modems provide throughput of up to 27 Mbps with about 2.5 Mbps of bandwidth for interactive responses in the other direction. This bandwidth far exceeds that of the prevalent 14.4 and 28.8 Kbps modems and the up to 128 Kbps of ISDNs or even the much higher speeds (up to 8 Mbps) of ADSL telephone technology.

1. a signal that carries modulation; 2. a provider of data carrying services.

CCIR Rec. 601
The most important studio standard for digital video based on analog component 4:2:2 signals. Describes how to sample the component signal and how to structure the data.

CCIR Rec. 656
The standard describing how to interface to a CCIR Rec. 601 formatted signal (serial and parallel 4:2:2 interfaces, commonly known as D-1 interfaces).

now known as the ITU-T (for Telecommunication Standardization Sector of the International Telecommunications Union), is the primary international body for fostering cooperative standards for telecommunications equipment and systems. It is located in Geneva, Switzerland.

A fixed-size packet of data, for example that found in ATM.

The color information of a video signal, including hue and saturation, but not brightness (luminance).

Distribution of computing responsibility between front-end and back-end programs. When multiple machines are used, a client-server architecture supports reduced network traffic and increased overall performance.

Coaxial and Fibre Optic Cable
A coax can provide 100 channels each of which is effectively a 36 Mbps pipe, these can be further broken down into 12 x 3 Mbps MPEG-2 digital television channels thus giving a total of 1200 channels (plus spare capacity for control and management) as opposed to one on a twisted pair. (There are many variations on this calculation, but all indicate an enormous number of channels.) Likewise a fibre optic cable can provide up to 150,000 times the capacity of a twisted pair.

1) In communications engineering, the term codec is used in reference to integrated circuits, or chips that perform data conversion. In this context, the term is an acronym for "coder/decoder." This type of codec combines analog-to-digital conversion and digital-to-analog conversion functions in a single chip. In personal and business computing applications, the most common use for such a device is in a modem. 2) The term codec is also an acronym that stands for "compression/decompression." A codec is an algorithm, or specialized computer program, that reduces the number of bytes consumed by large files and programs.

The process of representing a varying function as a series of digital numbers.

COFDM (Coded Orthogonal Frequency Division Multiplexing)
a multi-carrier modulation technique with applications for DAB and digital TV.

Component Video
Video signals in which the chrominance and luminance are processed as separate signals (or components). Three color video signals that describe a color image. Typical component systems are RGB, YIQ, 4:2:2 or YUV.

Composite Video
A color video signal that contains all of the color information in one signal. Typical composite television standard signals are NTSC, PAL, and SECAM. The complete visual waveform of the color video signal, comprising chromatic and luminance picture information; blanking pedestal; field, line and color synchronization pulses; and field equalizing pulses.

The translation of audio, digital data, or video into a more compact form for storage and transmission. Computer algorithms and techniques such as ETSI, G.722, JPEG or MPEG enable data content compression. A digital process that allows data to be stored or transmitted using less than the normal number of bits. Video compression refers to techniques that reduce the number of bits required to store or transmit images.

Data package--found in SDH--which floats with respect to the payload area of STM frames.

any form of source material: movies, games, news, images, sounds, etc. which will appear on the user's television or PC screen.

Common phrase for the gathering of audio and/or video material, usually in high quality and often between studios.

Interference from luminance into the chrominance in composite video. The luminance information is perceived as color information by the system.

A component digital video format, which is a subset of CCIR Rec. 601. D-1 is a serial 270 Mbit/s signal used for recording CCIR Rec. 601 video).

A composite digital videotape format for recording PAL in a digital form. D-2 is a serial 177 Mbit/s signal.

Dark Fiber
A fiber optic line without terminal equipment provided by the telephone company, and without switching.

The process of converting coded data into its original format.

describes electronic technology that generates, stores, and processes data in terms of two states: positive and non-positive. Positive is expressed or represented by the number 1 and non-positive by the number 0. Thus, data transmitted or stored with digital technology is expressed as a string of 0's and 1's. Each of these state digits is referred to as a bit (and a string of bits that a computer can address individually as a group is a byte).

Digital Video
Video where all of the information representing images has been digitized, allowing it to be more flexible and rapidly manipulated or displayed by a computer.

DVB (Digital Video Broadcasting)
The European group that works on digital TV broadcasting standards based on MPEG. Numbers more than 110 members, and has issued standards for digital TV broadcasting on cable and satellite.

The process of converting an analog signal into a digital representation. With images, it refers to the processes of scanning and analog to digital conversion.

the attempt by a computer program to approximate a color from a mixture of other colors when the required color is not available.

Dry pair
A copper line without terminal equipment provided by the telephone company, and without switching.

The process of converting analog electronic signals into digital format for storage, manipulation, and display by a computer. Audio capture boards, scanners, video frame grabbers, or a combination of these devises carry out content encoding.

the most widely-installed local area network technology. Now specified in a standard, IEEE 802.3, Ethernet was originally developed by Xerox and then developed further by Xerox, DEC, and Intel. An Ethernet LAN typically uses coaxial cable or special grades of twisted pair wires. The most commonly installed Ethernet systems are called 10BASE-T and provide transmission speeds up to 10 Mbps. Devices are connected to the cable and compete for access using a Carrier Sense Multiple Access with Collision Detection (CSMA/CD) protocol.

Fast Ethernet
also called 100BASE-T10 provides transmission speeds up to 100 megabits per second and is typically used for LAN backbone systems, supporting workstations with 10BASE-T cards. Gigabit Ethernet provides an even higher level of backbone support at 1000 megabits per second (1 gigabit or 1 billion bits per second).

FDDI (Fiber Distributed-Data Interface)
a standard for data transmission on fiber optic lines in a local area network that can extend in range up to 200 km (124 miles). The FDDI protocol is based on the token ring protocol. In addition to being large geographically, an FDDI local area network can support thousands of users.

Fibre Channel
a technology for transmitting data between computer devices at a data rate of up to 1 Gbps (one billion bits per second).

One of the two scans of a frame in interlaced scanning formats.

Relative to a part of a data rate, for instance 64 kbit/s fractions of the 1.544 Mbit/s T-1 service.

1. a single image in video or film. PAL and SECAM use 25 frames per second to create the image and simulate motion, whereas NTSC uses 30 frames per second (fps); 2. a group of data bits organized according to a specified format. Considered a logical entity with control information for use in bit-oriented protocols. 3. The result of a complete scanning of one image. In motion video, the image is scanned repeatedly, making a series of frames. Typical video frames comprise two interlaced field of either 525 lines (NTSC) or 625 lines (PAL/SECAM), and running either at 30 frames per second (fps) or 25 fps. Motion picture film runs at 24 fps.

Frame Grabber
A device that captures and stores on complete video frame.

Frame Rate
Measured in frames per second (fps), frame rate indicates the speed of frame display impressions on a monitor. Standard broadcast TV frame rates equal 30 fps in North America and 25 fps in Europe. Most Internet video streaming facilities offer a frame rate of 15 fps.

Frame Relay
Frame relay is a technology for transmitting data packets in high-speed bursts across a digital network encapsulated in a transmission unit called a frame.

Frequency Interleaving
In the NTSC or PAL television systems, the technique of choosing the color sub-carrier frequency so that the chrominance frequency components of the signal fall between the luminance frequency components of the signal.

Full motion video
Video displays shown at the broadcast frame rate of 30 fps for NTSC-original signals or 25 frames per second for PAL-original signals.

The process of synchronization to another video signal. It is required in computer capture of video to synchronize the digitizing process with the scanning parameters of the video signal.

Gbit/s (gigabet per second)
A digital transmission speed of billions of bits per second.

Gbps (gigabets per second or billions of bits)
A measure of bandwidth on a digital data transmission medium such as optical fiber.

Gigabit Ethernet
A local area network (LAN) transmission standard that provides a data rate of 1 billion bits per second (one gigabit). Gigabit Ethernet is defined in the IEEE 802.3 standard and the first product versions of it are now available. Gigabit Ethernet is used as an enterprise backbone.

Gigabit LAN
A term for the increasing of the data transmission speed of a conventional LAN to nearly 1 billion bits per second. Efforts are underway to boost Ethernet and AnyNet types of LAN to the gigabit range.

The measure of memory capacity that is "roughly" a billion bytes. A gigabyte is two to the 30th power, or 1,073,741,824 in decimal notation.

A graphical user interface to a computer

Most likely the earliest DCT-based video compression standard. It is an ITU-T standard that assumes CIF or QCIF format and is targeted at ISDN and LAN bandwidths. It has, for the most part, been superceded by the H.263 standard.

An ITU standard video codec for audiovisual services that specifies video coding for low-bit rate communication. H.263 supports high-quality, detailed images of 1408 by 1152 resolution for telemedicine and similar applications.

HAL (Hardware Abstraction Layer APIs)
The HAL separates the hardware from the OS, and makes the OS portable across any platform that supports the HAL.

High-definition TV; the idea of improved spatial resolution with an improved temporal resolution, improved color rendition, fewer artifacts, a wider aspect ratio, and multi-channel sound. Common name for several proposed standards for improved image quality.

HFC (Hybrid Fiber Coax)
A type of network that contains both fiber-optic cables and copper coaxial cables. The fiber-optic cables carry TV signals from the head-end office to the neighborhood; the signals are then converted to electrical signals and then go to houses on coaxial cables.

High Bit Rate
Data streams of 1.5 Mbps or greater, providing 30 frames per second of full-motion video delivery (comparable to broadcast television quality).

An area of the computer screen display that is sensitive to a mouse click or other user input. Hotspots are typically revealed to the user by a cursor change, and when clicked will trigger another action.

The four unique hues, or colors, are red, blue, green, and yellow. Hue usually refers to a color’s comparison with these unique hues, for example, its relative redness, blueness, greenness, yellowness. Technically, the dimension of color that is referred to a scale of perceptions ranging from red through yellow, green and blue, and circularly back to red.

Hz (Hertz)
A unit of electromagnetic frequency (of change in state or cycle in alternating current) of one cycle per second. Hertz (Hz) replaces the earlier term of "cycle per second (cps)." One kilohertz (kHz) is equal to 1,000 cycles per second.

The MPEG compressed video frame where redundancy between adjacent frames is not taken into account, only the information I a single frame is compressed. It is used in conjunction with the B (bi-directional) and P (predictive) frame encoding. If frames are lost during MPEG decoding, the decoder cannot fully recover until the next I frame comes along. The frequency of I-frames in a sequence determines how long it takes to get a reasonable picture after a random access or loss of data.

IEC (International Electrotechnical Commission)
International standards and conformity assessment body for all fields of electrotechnology.

IETF (Internet Engineering Task Force)
A group supervised by the Internet Society's Internet Architecture Board and is responsible for developing the TCP/IP protocols.

A still picture, or one frame of a motion sequence.

Image File
A file of data which represents an image.

Image Plane
In digital video display hardware which has more than one video memory array contributing to the displayed image in real time, each memory array is called an image plane. See also bit plane.

Image Processing
Techniques which manipulate the pixel values of an image for some particular purpose. Examples are: brightness or contract correction, color correction, changing size (scaling), or changing shape of the image (warping).

Interactive TV
Enables viewers to interact with the television set in ways other than simply controlling the channel and the volume and handling videotapes. Typical interactive TV uses are selecting a video film to view from a central bank of films, playing games, voting or providing other immediate feedback through the television connection, banking from home, and shopping from home.

Interactive Video
The fusion of video and computer technology. It denotes a video program and a computer jointly operated under the user’s control. The interactive choices he makes influence the manner in which the program unfolds.

Interactive Video Module (IVM)
the combination of a CPU card and NICs.

The ability of a user (or a computer) to control the presentation by a multimedia system, not only for material selection, but for the way in which material is presented.

Interframe Coding
Video coding that examines differences between frames.

Interlaced Scanning
The concept of splitting a TV picture into two fields of odd and even lines.

Intraframe Coding
Video coding within a frame of a video signal.

An intranet is a network that is contained within an enterprise. It may consist of many interlinked local area networks and also use leased-lines in the wide-area network. It may or may not include connections through one or more gateways to the outside Internet. The main purpose of an intranet is usually to share company information and computing resources among employees. An intranet can also be used to facilitate working in groups and for teleconferences.

Inverse Multiplexing
The splitting of one (broadband) data stream into a number of independent data streams with lower bit rates and the subsequent combination of these separate circuits into one data stream.

IP Multicast
Transmission of an IP datagram to a host group, identified by a single IP destination address. All members of a destination host group receive the multicast datagram, making this technique well-suited for multiparty conferencing applications. Host groups may be a permanent or transient.

ISDN (Integrated Services Digital Network)
A CCITT digital telecommunications standard developed to transmit high-bandwidth digital data, voice, and video signals. Bearer channel (ISDN B) provides circuit-switched bandwidth in multiplex of 64 Kbps, while a 16 Kbps packet-switched data channel (ISDN d) is also available. Common interface packages include Basic Rate Interface (BRI), consisting of two 64 Kbps B channels an done D channel, and Primary Rate Interface (PRI), consisting of 24 channels, usually composed of 23 B channels and a single D channel.

ISO (International Organization for Standardization)
Founded in 1946, the leading international standards organization. Among its developed standards is Open Systems Interconnection (OSI), a suite of communication protocols used widely in Europe.

(from the Greek "equal" and "time"; pronounced "eye-SAH-krun-us") Signal delivery capability at a specified rate, suitable for continuous data such as full-motion video and voice.

Pertains to processes that require timing coordination to be successful, such as voice and digital video transmission. A sound or picture going from a peripheral computer device or across a network into a computer or television set needs to arrive at close to the same rate of data flow as the source. In feeding digital image data from a peripheral device (such as a video camera) to a display mechanism within a computer, isochronous data transfer ensures that data flows continously and at a steady rate in close timing with the ability of the display mechanism to receive and display the image data.

International Telecommunication Union; The ITU is the parent organ for ITU-T (formerly CCITT) and ITU-R (formerly CCIR).

The J.52 standard describes inverse multiplexing of B-channels in Layer II codecs.

Unwanted frequency or phase variations, such as rate variations of a data stream or phase noise of a carrier signal.

Joint stereo
A specific coding mode in Layer II audio coding. In the joint stereo mode, the upper frequencies of a stereo signal are joined and coded as intensity stereo in order to conserve valuable bits and improve overall quality.

Abbreviation for “Joint Photographic Experts Group,” a working party of the ISO-IEC Joint Technical Committee 1, working on algorithm standardization for compression of still images.

K (Kilo)
Informally, 1,000. Technically, 1,024, so 64K is actually 65,536.

Kb (Kilobit)
1,024 bits. Also kb.

KB (kilobyte)
1,024 bytes. Approximately equivalent to half a sheet of paper’s worth of typing, double-spaced.

Kbit/s (kilobit per second)
A digital transmission speed of thousands of bits per second.

Kbps (kilobits per second)
In the U.S., Kbps stands for thousands of bits per second and is a measure of bandwidth (the amount of information that can flow in a given time) on a data transmission medium such as twisted-pair copper cable or coaxial cable.

the essential center of a computer operating system, the core that provides basic services for all other parts of the operating system. Typically, a kernel (or any comparable center of an operating system) includes an interrupt handler that handles all requests or completed I/O operations that compete for the kernel's services, a scheduler that determines which programs share the kernel's processing time in what order, and a supervisor that actually gives use of the computer to each process when it is scheduled. A kernel may also include a manager of the operating system's address spaces in memory or storage, sharing these among all components and other users of the kernel's services. A kernel's services are requested by other parts of the operating system or by applications through a specified set of program interfaces known as system calls.

In a video system, the process of inserting one picture into another picture under spatial control of another signal, called keying the signal.

A network of interconnected workstations sharing the resources of a single processor or server within a relatively small geographic area. Typically, this might be within the area of a small office building. However, FDDI extends a local area network over a much wider area. Usually, the server has applications and data storage that are shared in common by multiple workstation users. A local area network may serve as few as four or five users or, in the case of FDDI, may serve several thousand.

LAN Server
A program (and by implication usually the computer it runs in) that "serves" the resources (files, storage, application programs, printers, and other devices) for a number of attached workstations.

Layered embedded encoding
The process of compressing data in layers such that successive layers provide more information and thus higher quality reconstruction of the original. That is, a single stream of data can supply a range of compression and thus, in the case of video, a scalable range of video resolution and picture quality.

Layer II
A specific subset of the audio part of the MPEG-1 and MPEG-2 standards. The Layer II specification features 32 to 384 kbit/s data rate, compression in 32 subbands with adaptive bit allocation determined by a psychoacoustic model, sampling rates from 16 to 48 kHz, and various coding modes.

Leased Line
A dedicated communications circuit for continual data transmission. Also referred to as "private line" or "dedicated line."

Live Streaming
Streaming media that is broadcast to many people at a set time.

(local) Loop
The physical wires that run between the telephone company’s central office and the customer’s telephone system.

Lossless Compression
A data compression technique that makes it possible to recover the original data exactly, with no loss in image quality as a result.

Lossy Compression
A type of compression that deliberately sacrifices some of the original data in return for much higher compression ratios than those achievable with lossless techniques.

Low Bit Rate
Data streaming at a rate of no more than a couple hundred Kbps. Modems that access the Internet at speeds of 28.8 Kbps or 56 Kbps, as well as some ISDN connections, fall into the LBR category. LBR supports full motion video at rates of 7.5 fps and resolution of 160x120.

Longitudinal Time Code; the time code that is either recorded on one of the two audio tracks or on a special address track on videotape.

The brightness information of a video signal (denoted Y).

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