2B+D – Configuration of a Basic Rate Interface (BRI) line. A single ISDN circuit divided into two 64 kbps digital channels for voice or data and one 16 kbps channel for low speed data ( up to 9,600 baud ) and signaling. 2B+D is carried on one or two pairs of wires depending on the interface, same wire pairs that today bring a single voice curcuit into your home or office.

10baseT – 10 Mbps Ethernet LAN technology.

100baseT – 100 Mbps Ethernet LAN technology.

16CIF – 16 times Common Intermediate Format: 1408×1172 pixels. H.263 optional format.

4CIF – 4 times Common Intermediate Format: 704×576 pixels. H.263 optional format.

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AAL – ATM Adaptation Layer. Format for sending packets on a ATM network.

Access Device – A gateway to the ATM network. It provides entry between various hardware and applications to the device.

Accunet – Trademark name for high speed switched digital service provided by AT&T.

A/D – Analog-to-digital.

ADPCM – Adaptive Differential Pulse-Code Modulation. Coding technique used in G.728.

ADSL – 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.

AGC – Automatic Gain Control. Algorithm to normalize volume regardless of speaker’s position relative to microphone.

Aggregation – Method for sending data down two or more parallel channels.

A-law – European quantizing method for voice PCM in G.711.

Algorithm – Method for solving a problem or performing a task.

Analog – 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.

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

Annex D – Still-image graphics mode of H.261. Can support maximum 704×576 resolution.

ANSI – American National Standards Institute.

API – Application Programming Interface.

Artifact – Coding error found in compressed audio or video signal.

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

Asynchronous – 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.

ATM – 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.

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

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

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

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

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.

Binary – 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.

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

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

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

Blocking – 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.

Blurring – Artifact found in video when the high frequencies ( detail ) of the image are notcoded.

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. )

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

BRI – 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.

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

Byte – 8 bits to a byte.

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

CCIR-601 – Studio standard format for video. 720 x 480 pixels at 30 frames per second (NTSC ) or 720 x 576 at 25 fps ( PAL .)

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

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

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

Central Office ( CO ) – In telephony, the phone company switching facility or center, usually a Class 5 end office, at which subcriber’s local loop terminate. Handles a specific geographic area, identified by the first three digits of the local telephone number.

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.

CIF – Common Intermediate Format. 352×288 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.

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.

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

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

Communications closet ( CC ) – The CC represents the physical connection where information is recieved 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 recieve 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.

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.

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

CS-ACELP – Conjugate Structure algebraic code excited linear prediction. Compression method used in G.729.

CSN – Curcuit Switched Network ( for example ISDN, POTS. )

CSU – 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.

CTI – 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.

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D-channel – 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.

D/A – 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.

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

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

DDS – 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.

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

DES – Data Encryption Standard.

Digital – 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. )

Doubletalk – 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. )

DPCM – Differential Pulse Code Modulation. Coding technique.

DS-3 – High speed network line, operates at 44.73 MBPs.

DSP – Digital Signal Processor.

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

DTE – 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.

DTMF – Dual Tone Modulated Frequency. Touch-tone signals.

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E1 – 2.048 Mbps.

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

Ethernet – 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.

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FAS – Frame Alignment Signal in H.221.

FCIF – Full-CIF. Another name for CIF.

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

FECC – 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.

Field – 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 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.

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.

Fps – Frames per second ( video ).

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.

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GCC – Generic Conference Control in the T.120 standard.

GSTN – General Switched Telephone Network. Also known as POTS.

G.711 – 3.4 kHz bandwidth audio transmitted at 56 or 64 kbps. Uses A-law or u-Law PCM.

G.722 – 7 kHz bandwidth audio transmitted at 48, 56 or 64 kbps. Uses ADPCM.

G.723.1 – 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.

G.728 – 3.4 kHz bandwidth audio transmitted at 16 kbps. Uses CELP processing.

G.729 – 3.4 kHz bandwidth audio transmitted at 8 kbps. Uses CS-ACELP processing.

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H.221 – Multiplex standard used in H.320. Combines audio, video, data in one bitstream.

H.223 – Multiplex standard for H.324.

H.224 – Standard for data transfer in H.320.

H.225.0 – Multiplex standard for H.323.

H.230 – Standard for control and indication signaling within H.320.

H.231 – Standard for specifying MCU requirements in H.320.

H.233 – The ITU-T’s data-encryption standard for real-time multimedia.

H.234 – specifies how encryption keys are handled.

H.242 – Standard for establishing communication in H.320.

H.243 – Standard for multipoint communication in H.320.

H.245 – Standard for multimedia system control in H.323, H.324 and H.310. Includes features such as capability exchange and signaling.

H.261 – Required video compression standard in the H.320, H.323 and H.324 standards.

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

H.263 – Video compression standard created and required for H.324. Is also an optional mode of the other H-series standards.

H.281 – Standard for Far End Camera Control.

H.310 – Standard for multimedia conferencing and one-way video applications on B-ISDN. Not based on H.320.

H.320 – Standard for multimedia conferencing on narrowband switched digital networks. Can be used from 56 kbps to 2 Mbps.

H.321 – Standard which specifies how H.320 terminals can be used on broadband switched digital networks ( B-ISDN ).

H.322 – Standard which specifies how H.320 terminals can be used on isochronous ethernet LANs ( guaranteed bandwidth and quality of service. )

H.323 – Standard for multimedia conferencing on traditional packet-switched LANs.

H.324 – Standard for multimedia conferencing on analog phone lines ( POTS ).

H.331 – Standard which specifies how H.320 terminals can be used in a one-way broadcast mode.

H0 – Switched 384 kbps service.

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

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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.

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.

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

ISDN – 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.

ITU-T – International Telecommunications Union Telecommunications Standardization Sector.

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

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

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

kHz – Kilohertz.

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

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

LATA – 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.

LD-CELP – 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.

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.

Loopback – 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 recieve leads. A signal is then sent around the loop. Measuring differences between the sent and recieved signal is the essence of a loopback test.

LSD – Low speed data channel of H.320.

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

Luminance – Brightness ( black and white ) information in a video image. Often called luma.

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

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

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

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

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

MIPS – Million Instructions Per Second (fixed-point).

MLP – 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.

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

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

MPEG – Motion Picture Experts Group of ISO. Responsible for MPEG-1 and MPEG-2 standards.

MPEG1 – Video Standard targeted at 1.5 Mbps playback on multimedia PCs.

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

Multiplexing – 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).

Multipoint – A call involving three or more parties.

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

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Narrowband – Bandwidths from 64kbps to 2Mbps.

NIC – Network Interface Card. Connects a PC to a LAN.

N-ISDN – Narrowband ISDN (The ISDN currently used).

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

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.

NT1 – 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.

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

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OC-3 – connection capable of carrying data at 155.52 MBPs.

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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.

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

PBX – Private branch exchange.

PCI – Peripheral Component Interface. Bus interface technology for PC cards.

PCM – Pulse-code modulation. Sample-based coding technique.

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

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).

POTS – 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.

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

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

Protocol – 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.

PSN – Packet Switched Network (Internet, LAN).

PTZ – Pan-Tilt-Zoom. Camera functionality

Px64 – 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.

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

QOS – 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.

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

RGB – Red-Green-Blue picture display format.

RJ-11 – The plastic four-wire jack on a phone wire.

RJ-45 – The plastic eight-wire ISDN jack.

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

RS-232 – 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-366 – Generic dialing interface ( An EIA interface standard for autodialing).

RS-449 – Generic 37-pin fast differential data interface.

RS-530 – Interface using DB-25 connector, but for higher speeds than RS-232. Has balanced signals (like EIA-422) except for three maintance signals which are EIA-423.

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

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

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

SG3 – 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.

SG4 – PictureTel’s proprietary software generation 4. Based on SG3; improvements include: transmission over standard H.221 multiplex, better motion coding, and contrast enhancement.

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

S/T-interface – 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.

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

SPID – Service Profile Identifier.

SQCIF – Sub-QCIF 128X96 pixels.

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

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

TCP/IP – 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.

TDM – Time Division Multiplex.

TDMA – Time Division Multiple Access.

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.

Trunk – 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 – 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.

T1 – 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).

T3 – A connection capable of carrying data at 45,000,000 bits-per-second or 45MBPs.

T.RES – T.120 conference reservation protocol.

T.Share – Now T.128.

T.120 – Standard for data conferencing and conference control for interactive multimedia communication both multipoint and point-to-point.

T.121 – Specifies T.120 general application protocols.

T.122 – Specifies T.120 service interface for multipoint operation.

T.123 – 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.

T.124 – Generic Conference Control (GCC) for T.120. Provides control of a conference (joining, locating, scheduling, ect.) and supports application protocols.

T.125 – Specifies T.120 protocol for multipoint operation.

T.126 – T.120 still image transfer and annotation protocol.

T.127 – T.120 binary file tranfer protocol.

T.128 – T.120 application sharing protocol.

T.133 – Audio and video control protocol within T.120.

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UI – User Interface.

U-interface – 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.

UL – Underwriters Laboratory-U.S. Safety standards body.

u-Law – Quantization for voice PCM used in North America.

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

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

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VBR – Variable Bit Rate.

VC – Virtual Channel.

VCS – Video Conferencing System.

VGA – Video Graphics Adapter. Standard PC video format.

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

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

Videoconferencing – 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.

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.

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

V.24 – Same as RS-232

V.34 – Modem standard for 33.6 kbps operation.

V.35 – 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.

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

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XDSL – 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.

XMODEM – An error -correcting file transfer, data transmision 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.

X.21 – Same as RS-449 with in-band dialing capability.

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Y/C – Video format with separate signals for Y (luminance) and combined C (Chrominance) signals. S-Video uses Y/C.

YUV – Video format with separate signals for Y (luminance) and separated U and V Chrominance signals.