Click on a letter to view terms beginning with that letter, or scroll down through the entire glossary.

A  |  B  |   C  |   D  |   E  |   F  |   G  |   H  |   I  |   J  |   K  |   L  | M  |   N  |   O  |   P  |   Q  |   R  |   S  |   T  |   U  |   V  |   W  |   X

2-Line Mode – A term referring to a mode of operation where codecs [generally MPEG] are connected together utilizing both B-channels of the ISDN circuit for transmitting audio with the codec internally combining the channels. This increases the connection bandwidth to 112Kbps (2 *56) or 128Kbps (2 * 64).

2-Wire – 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 and one to receive. All trunk circuits (long distance) are 4-wire. A 4-wire circuit delivers better reception, but also costs more. All local loop circuits are 2-wire, unless a 4-wire is requested

2B+D – Two Bearer channels and one Data channel. The basic rate interface (BRI) in ISDN. A single ISDN circuit divided into two 64Kbps digital channels for voice data and one 16Kbps 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, the same wire pairs that today bring a single voice circuit into your home or office.

2B1Q – Two Binary, One Quaternary. An ISDN line encoding technique, which uses two bits to represent four variations in amplitude and polarity.

4-Wire – 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.


AAC – A new standardized algorithm for compressing audio (often called MPEG4 audio) licensed by MPEG including the intellectual property of several companies comprising Dolby Labs and others . (See also, algorithm, MPEG2, MPEG3, apt-X, AC-3). AC-2 operates at a sample frequency of 48KHz.

AC-2 – A proprietary algorithm for compressing audio used exclusively with Dolby codecs. (See also, algorithm, MPEG2, MPEG3, apt-X, AC-3). AC-2 operates at a sample frequency of 48KHz. Uses a combination of predictive and perceptive coding techniques.

AC-3 – A proprietary algorithm for compressing audio used exclusive with Dolby codecs. (See also, algorithm, MPEG2, MPEG3, apt-X, AC-2). AC-3 allows for variation in sample frequencies. Uses a combination of predictive and perceptive coding techniques.

ADR – Automated Dialogue Replacement. Technique where unusable location dialog in a film / TV show is replaced in the studio by ‘looping’ the video and having the actor(s) read to picture.

ADSL — Asymmetrical Digital Subscriber Line. A form of DSL technology where the upstream and downstream speeds differ. Generally the downstream speed is higher. For example, a 384/128 line would have a downstream [to the user] speed of 384Kb/s and an upstream speed of 128Kb/s.

AES/EBU – Internationally accepted professional 2-channel digital audio interface transmitted via a balanced line connection using XLR connectors; specified jointly by the Audio Engineering Society and the European Broadcast Union.

affiliateednet affiliates are sites whose ISDN lines are managed by ednet, who receive free technical support 24 * 7, and reduced service rates on bridging services. In addition to this, affiliates receive booking referrals through ednet, and international promotion.

AIM — Ascend Inverse Multiplexing. An Ascend proprietary protocol used to combine multiple ISDN calls to create one aggregate data pipe. Available on Ascend equipment provided with DolbyFax gear, however, BONDING is generally preferred, as it’s compatible with non-Ascend devices.

algorithm – A procedure for solving a mathematical problem in a finite number of steps that frequently involves repetition of an operation. Algorithm here refers specifically to a procedure that encodes audio information (so that it can be sent at high speed across data lines) and decodes the transmitted information into audio at the receiving end.

apt-X – A proprietary real-time digital audio data reduction algorithm capable of compressing 16-bit PCM audio samples by a factor of 4:1 with no perceptible audible degradation. apt-X is used predominantly with APT codecs. Uses predictive coding.

associateednet associates receive reduced service rates for bridging services. ednet does not manage their ISDN lines. In addition to this, associates receive booking referrals through ednet, and international promotion.

asynchronous – 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 (especially PCs) and mainframes, lower speed transmission, and less expensive computer transmission systems.

auxiliary data – Data transmitted in a subsidiary or reserve capacity. For example using AC-2 1200 baud is reserved for auxiliary data, which can be used to control equipment remotely or send timecode.


B8ZS — Bit Eight Zero Stuffing. A means of encoding 8 bit data via leased line [generally T-1] so all-8 bits in each transmission frame can be used to carry data.

bandwidth – The amount of data that can be transmitted in a fixed amount of time. For digital devices, the bandwidth is usually expressed in bits per second (bps) or bytes per second [Bps]. For analog devices, the bandwidth is expressed in cycles per second, or Hertz (Hz).

baud – The number of signaling elements that occur each second; from J. M. E. Baudot (died 1903) French inventor of baudot telegraph code. At slow speeds, only one bit of information (signaling element) is encoded in each electrical change. The baud, therefore, indicates the number of bits per second that are transmitted

bearer channel – (B – channel) Portion of the ISDN line that is used to transmit encoded digital data. There are two B-channels per ISDN line, each with a 64Kbps capacity.

BERT test – Bit Error Rate Test. A test performed by the Telephone companies to test ISDN lines. A known data pattern is sent to the equipment and bit errors are counted in its return.

bit — The smallest unit of data storafe. A bit for most purposes is a binary notation, either on [1] or off [0]. Bits are combined to makeup bytes — a byte consists of 8 bits.

bit rate – (data bandwidth) This is the speed at which two terminal adapters talk to each other. It is usually a multiple of 56Kbps or 64 Kbps.

BRI – Basic-Rate Interface. The basic ISDN configuration, which consists of two B-channels that, can carry voice or data at rate of 64Kbps, and one D-channel, which carries call-control information. Another type of ISDN configuration is called Primary-Rate Interface (PRI), which consists of 23 B-channels (30 in Europe) and one D-channel.

BONDING – Industry standard ISDN B channel aggregation protocol used to create one large data pipe from inverse multiplexing smaller connections together. Developed by the Bandwidth on Demand Interoperability Group.

bridge – In transmitting high quality audio over data lines, both codecs must operate using the same algorithm. A bridge is necessary to exchange audio between non-compatible codecs, e.g. APTx to Dolby AC2. Up to 10 locations can be bridged. Each codec is dialed from ednet and the audio from each side is fed to the other(s).

broadband — 1. A type of data transmission in which a single medium (wire) can carry several channels at once. ISDN networks use broadband transmission. In contrast, baseband transmission allows only one signal at a time. Most communications between computers, including the majority of local-area networks, use baseband communications.
2. A general term for any high speed Internet access, generally referring to speeds of 384Kb/s or above.


CLEC — Competitive Local Exchange Carrier. This term denotes any of a new class of local telco’s who are providing local dialtone and extended services [such as DSL] in the wake of deregulation.

central office — Refers to the telco office, usually the one closest to the user’s facility, that houses the switching equipment that terminates the local pair of wires which are said to “serve” the user’s ISDN, POTS, DSL or other telco line.

channel bank – Equipment in the central office that performs various necessary functions so that the ISDN circuit can operate properly. Multiplexes lower speed digital channels into a higher speed composite channel, among other things. Also may be used as CPE on T1 or other high-speed data circuits.

clear channel – The concept whereby individual ISDN data calls are placed one by one, rather than by other call set-up protocols such as BONDING (see entry). These individual data streams are later IMUXed (see entry) together by the decoder of the far end codec.

codec – – Acronym for COder/DECoder. Any audio or video device that employs a mathematical algorithm to compress/decompress data, usually for transmission over a fixed bandwidth telco network

CO – Short form for telephone company Central Office (See Central Office)

coding delay – The delay a processor takes to transform incoming audio/video into a compressed state suitable for transmission over a network. Usually expressed in milliseconds.

CPE — Customer Premise Equipment [sometimes Customer Provided Equipment]. Equipment connecting to a telco circuit provided by the customer, such as a CSU/DSU or modem.


data channel – The out of band signaling channel in a 2B + D ISDN circuit (see entry). Constitutes 16kbps of bandwidth, which is in addition to the 128kbps of B channel data possible with ISDN.

digital I/O – Refers to the circuitry in an audio codecs that supplies digital input and output connectors. Although all codecs send material in the digital domain across the telco network, codecs with direct digital input/output connectors allow the digital audio to be directly interfaced with outboard digital gear, thereby eliminating an additional digital-to-analog or analog-to-digital conversion.

digital patch – i original MPEG network was known as the “digital patch” from the formerly acquired company Digital Patch Systems. This network consisted of Musicam [then CCS] CDQ2000 audio codecs.

DS0 – One 64kbps portion of telecommunications circuit bandwidth. Term used for an individual channel of a larger bandwidth circuit, such as a T-1 (see entry).

DS-3 – Equal in bandwidth to 28 T-1 (see entry) circuits, or approximately 45Mb/sec.

DSL — Digital Subscriber Line. This technology allows high speed synchronous data to be carried over commonly found copper telco wiring, such as the local loops installed in almost every residence and business in the US. Not without limitations [such as an 18k ft. distance limit for most types], DSL allows high-speed data access far more easily and cheaply than before.


E-1 – A dedicated connection from point A to point B, this is the European version of a T-1 (see entry). Instead of providing 24 DS0s (see entry) it provides 30, gives a maximum throughput of 1.92 MB/sec.

edlinkednet‘s “bridging” service. Technically, the service which transcodes between two or more codecs employing incompatible algorithms.

ESF — Extended Super Frame. A T1 framing format.

ethernet — A networking specification for LANs to allow the use of a large number of network devices such as computers, printers, and routers, in a single physical topology. Uses twisted pair [10-Base-T or coaxial [10-Base-2] wiring for the physical connection.


f/x – A telco acronym for an ISDN circuit that has been “foreign exchanged”, meaning that the line is not served by the closest central office (see entry). Instead, usually due to technical limitation at the nearest CO, a special circuit is built from another CO to the user’s site.

Frequency Masking – Principle where louder sounds render soft sounds inaudible in nearby frequency bands. This is the principle behind perceptual encoding.

FTP — File Transfer Protocol. A standard and efficient interactive protocol for transferring files via TCP/IP connections.

full duplex – Telco communication that is bi-directional. ISDN is full duplex, so each end of the connection can simultaneously transmit to the other.


G.711 – Refers to the transmission of audio via a POTS (Plain Old Telephone) circuit. Frequency response is limited to about 3.5kHz.

G.722 – A coding technology developed in the late 70s and designed primarily for speech. Uses one 56 or 64 kbps data call and codes only 50Hz-7kHz of audio frequency. G.722 is popular in the broadcast community due to the very low coding delay. Data reduction is achieved by coding only the difference between successive samples.

G.722 Turbo – An algorithm proprietary to Comrex codecs whereby two 56 or 64 data calls are placed using BONDING (see entry). Yields the same low coding delay as G.722 but increases the frequency response to 15kHz.

G.728 – Audio compression algorithm found on video codecs, where little bandwidth is allocated for the audio transmission [generally implemented at 16Kbps]. Designed for voice and limited in frequency response, typically only about 50Hz-3.5kHz.


H.221 — An early teleconferencing method for combining the bandwidth of two 56kbit calls which allows compatibility between 2 Switch 56 and 2 B channel ISDN calls. Used in CCS Musicam codecs and compatible units from other manufacturers.

H.261 — An early video codec standard which is in heavy use in videoconferencing applications. A precursor to MPEG-1, H.261 is optimized for low data rates and low motion content.

H.263 — An update of the H.261 video codec standard, H.263 is also used primarily in videoconferencing. Generally higher quality than H.261, especially at lower bit-rates.

H.320 – Video teleconferencing standard that combination of H.261 video compression and various suitable audio compression standards (G.711, G.722, etc.). Generally refers to videoconferencing data transmission via ISDN networks.

H.323 – Video teleconferencing standard defining how conferencing data is to be sent over IP networks, including the Internet.

Handshaking – Protocols usually implemented in hardware that let one data device tell another that conditions are right (or wrong) for communications. A simple example: a printer telling a computer that it is OK to print.

house sync – A precise clock pulse from a central generator that may be used by multiple devices in a facility so that they all work in step at the same speed. This might be a digital audio word clock, or a video sync signal.

http — Hyper Text Transfer Protocol. A TCP/IP protocol for the transmission of material containing multiple data types, such as text and graphics. The underlying protocol of the World Wide Web.


IDSL — ISDN Digital Subscriber Line — DSL, which uses the 2B1Q line coding of ISDN to obtain speeds of 128Kb/s symmetrically. Slower than most other forms of DSL, but able to be deployed up to 24,700 feet from the central office.

ILEC — Incumbent Local Exchange Carrier. Basically Ma Bell, or one of the major local telcos created in the wake of deregulation. These are the telcos who own all of the copper wire going to businesses and residences and provide dialtone, ISDN, dedicated circuits, and a host of other products. Temples of bureaucracy.

IMUX – – Inverse MUltipleXer. Circuitry in an audio codec that takes data from 2 or more individual multiplexed data calls and reconstitutes it to a single larger data block.

initialization – The process by which an ISDN terminal adapter is registered as on line to the telco central office (see entry). Generally, initialization occurs while powering on the ISDN equipment and is accomplished through a series of “handshaking” steps. Once initialized, the ISDN gear is capable of placing and receiving calls.

ISDN – Integrated Services Digital Network. Virtually all ednet supplied ISDN circuits are BRIs (Basic Rate Interface) in the format of 2B + D. The B refers to “Bearer-channels”, each capable of transmitting 64kbps of synchronous (see entry) data. The D refers to “Data-channel”, a 16kbps out of band signaling channel.

isochronous – Refers to processes where data must be transmitted within certain time constraints, for example when streaming audio and video simultaneously for a multimedia event. Less rigid than synchronous transmission (see entry).

IXC – Inter Exchange Carrier. A telco acronym for the long distance company.


J.52 — An ITU recommendation for the transmission of MPEG audio via up to three 64Kb/s lines for mono, and six for stereo. Used by Musicam on their Prima codecs for multi-line transmission.

Joint Stereo — A method of encoding stereo material, which takes advantage of the redundancy between channels in order to maximize the quality of, encoded material by not encoding redundant data twice. Used most commonly in MPEG Layer 2 and Layer 3 at 128 to 256Kb/s.


LAN — Local Area Network. Any combination of interconnected network devices at a single physical site. These could include computers, printers, and servers, and are usually connected via ethernet. See also WAN.

LEC — Local Exchange Carrier. This term generally refers to the ILEC, but can mean any local telecommunication service provider.

land patch — Synonym for Digital Patch.

last mile – The euphemism for the wiring that connects a telephone or data customer to the PSTN or a CO.

line card – The circuit card in the telephone switch in a CO that receives the “last mile” line from a customer location.

local loop — See last mile.


M-JPEG — Movie-Joint Photographic Experts group. A compression definition for moving images based on sequences of JPEG images. Of fairly high quality and easy to edit, as each frame is digitized distinctly, M-JPEG requires high bitrates and isn’t nearly as efficient as MPEG standards.

MPEG — Moving Pictures Experts Group. An ISO standards organization which defines standards for audio and video compression.

MPEG 1 video — A compression definition originally designed to create high quality video and audio at a data rate of 1.5Mb/s. The MPEG video codecs work by digitizing a new frame only occasionally, and storing only differential and interpolated date between digitized [or I] frames. In practical use, MPEG 1 is usable from rates as low as 300Kb/s. MPEG 1 decimates the original source material by using only 30 of the 60 original fields and reducing the resolution to 352 x 240 pixels [for NTSC], hence it’s not generally acceptable for entertainment or broadcast use.

MPEG 2 video — A second MPEG video compression specification design to meet the needs of the broadcast industry. MPEG 2 supports the full 60 fields in each frame and a 704×480-frame size.

MPEG Layer 2 audio — The three layers of audio compression specified in the MPEG 1 and MPEG 2 protocols increase in complexity and quality from Layer 1 to Layer 3. Whereas Layer 1 was designed for use at 192Kb/s and is rarely used, Layer 2 has found great success as an easily implemented yet high quality algorithm for use at rates of 128Kb /s to 384Kb/s for stereo material. This is the algorithm most common to ednet MPEG sites, and is supported in every MPEG device we’ve sold, from the Musicam CDQ2000 onward.

MPEG Layer 3 audio — Layer 3 audio is designed for high quality audio transmission at bitrates from 64Kb/s to 320Kb/s. Advantages over Layer 2 include full range frequency reponse for single channel transmission at 64Kb/s and discrete stereo operation at 128Kb/s. Disadvantages include a high encoding processing time and subjectively more audio artifacts than Layer 2 at 128Kb/s and above. This is the native algorithm of the Telos Zephyr and is also supported in current Musicam devices.

master clock – A precise clock pulse from a central generator that may be used by multiple evices in many locations so that all work in step at the same speed. National timekeepers such as the National Bureaus of Standards in the US and the Greenwich Observatory in England are often the ultimate sources for these accurate timings for telephone, data, and satellite systems.

mix minus — in studio applications, an audio feed to a device without the output of that device included, to avoid a feedback loop. For instance, when connecting an audio codec to a studio console, you’ll want to send it the mixed output from the console without including it’s own output, or else the remote end will hear themselves back. This can be accomplished by using bus outputs in most cases.

modem – A device for sending data over telephone lines by turning the data into audio tones. Combines a MODulator and a DEModulator, hence MODEM.

multiplexing – The mixing of signals onto a common medium so that they may be carried together but separated at their destination (de-multiplexed) without loss.


NPA — Numeric Planning Area. The technical term for what we call an area code.

NXX — Telco nomenclature for the prefix of a North American telephone number. [i.e. 212 NXX-2133].

NT-1 – The device that terminates a 2 wire ISDN line and changes the U (2 wire) interface to the S/T (four wire) interface. In Some countries the telephone company supplies this and the customer plugs his equipment into the S/T interface. In the US the customer must supply the NT-1 and plug into the U interface. Many ISDN devices for use in the US include this circuit internally.


OC-3 – one of the Sonet family of optical fiber connection carrying 3 DS-3 circuits (155Mbits/sec)

OC-12 – one of the Sonet family of optical fiber connection carrying 12 DS-3 circuits (600Mbits/sec)

OC-N – one of the Sonet family of optical fiber connection carrying “N” DS-3 circuits


PCM – Pulse Code Modulation. A sampling technique for digitizing analog signals, especially audio signals. PCM samples the signal 8000 times a second; 8 bits for a total of 64 Kbps represent each sample. There are two standards for coding the sample level. The Mu-Law standard is used in North America and Japan while the A-Law standard is use in most other countries. PCM is used with T-1 and T-3 carrier systems. These carrier systems combine the PCM signals from many lines and transmit them over a single cable or other medium.

POTS – Plain Old Telephone Service. Standard analog phone lines used for voice and computer modem operation.

perceptual coding – Digital audio data reduction technique. Uses the concept of frequency masking to economize on bandwidth. Dominant signals are encoded while imperceptible signals in neighboring frequency bands are discarded. This is a moderately quick data reduction technique (about 80-125 ms), and results in data reduction of 8:1 to 12:1. MPEG L2 and L3 use this scheme.

predictive-adaptive coding – Digital audio data reduction technique. Instead of encoding all samples as 16-bit PCM digital audio, only the four-bit difference between samples is encoded. This is a very fast encoding method (about 7ms) and results in a data reduction of about 4:1. APTX and G.722 use this model.

psychoacoustic modeling — A model of how the human auditory system processes sound. Psychoacoustic modeling assumes loud sounds will drown out quiet neighboring sounds, like a busy highway might obscure a conversation. See also frequency masking.


RJ11 – A standard 4 pin telephone connector. POTS lines are generally delivered by the phone company on RJ11’s.

RJ12 – A standard 6 pin phone connector. Often for specialized, non-telco related uses.

RJ45 – A standard 8 pin telephone connector. ISDN lines are generally delivered by the phone company on RJ45’s. On a standard U-interface ISDN installations, signal will be on the middle two pins (4 & 5) and phase is not important.

router — A network device that routes traffic between different networks, for instance from a LAN to a WAN, or the Internet. Usually the traffic routed is IP in nature, but routers can also be used for transmission of AppleTalk, IPX, and other forms of data traffic.

RS-232 – electronic specification for serial data connections between digital terminal equipment (DTE) and data communications equipment. (DCE) Signal is unbalanced. May be either synchronous or asynchronous. Can reside on multiple connector sizes, but most commonly appear on DB9/ DB25 connectors. 50′ transmission limit.

RS-422 – Designed to extend the 50′ limit of RS232, this is a specification for serial data connections between digital terminal equipment (DTE) and data communications equipment (DCE). Signal is balanced. May be either synchronous or asynchronous. 5000′ limit.

RS-449 – Specification for putting RS-422 electrical connections into DB37 connectors. 5000′ limit.

RS-530 – Specification for putting RS-422 electrical connections into DB25 connectors. 5000′ limit.

RTP — Real Time Protocol

RTSP — Real Time Streaming Protocol. A TCP/IP protocol designed for transport of streaming data, such as audio and video, which has a high reliance on packet sequence. Used by Quicktime and Real G2 for packet delivery.


SDSL — Symmetrical Digital Subscriber Line. A DSL circuit with the same speeds both upstream and downstream.

SMPTE – The Society of Motion Picture and Television Engineers. This professional society sets the standards and practices for movies and TV, and as such has lent their initials to many times. A most common usage refers to SMPTE [standard] timecode.

S/PDIF — Sony/Philips Digital InterFace. Standard 2-channel digital audio interface found on many consumer-oriented products.

SPID — Service Profile Identifier. An identifying numerical string, which is assigned by the telco to each B-Channel on a BRI line in North America, configured for multipoint service [including National ISDN-1 lines and DMS-100 lines]. The number is often arbitrary, yet for the ISDN equipment to work properly, it’s SPID configuration must match that configured in the telco switch. Recently, most telcos have standardized on a format of NPA-NXX-XXXX-0101.

S/T interface – The four-wire interface of ISDN line terminated by an NT-1 circuit. (See also U- interface and NT-1)

SW56 — Switched 56. A precursor to ISDN, offering switched data service of 56Kb/s per line. ISDN and SW56 circuits can interoperate.

sample rate — The rate at which an analog signal is sampled, or digitized. For instance, when digitizing audio for a CD, the audio is captured at a sample rate of 44.1KHz, or 44,100 times per second, creating a very close, but not perfect, digital representation of the analog waveform.

switch type — Generally refers to the telco switch protocol used on an ISDN line, e.g. NI-1 or DMS-100.

sub-band — A range of audio spectrum that can be filtered, evaluated for audio energy within that range. In the scheme of data compression called sub-band coding, the value arrived at is combined by mathematical means (see algorithm) with values for other active bands sub-and used to encode the entire audio waveform in less data than the original signal. These coding methods depend on an idiosyncrasy of human audio perception, namely that the ear cannot detect soft sound when they occur at frequencies that are close to those of loud simultaneous sounds. The theory goes “since the ear cannot perceive them, there is no point in encoding them, thus using less data”. Example uses of sub-band coding are the MPEG and Dolby AC-2 algorithms.

Synchronous — Refers to data transmission wherein the transmitter and receiver are synchronized and data is sent at a fixed rate. Synchronous transmission eliminates the need for start and stop bits when compared to asynchronous transmission, and is therefore more efficient. Most high-speed data circuits, from ISDN to T3, are synchronous.


T-1 – A 1.5 Mbit/sec telephone circuit that carries 24 digital phone calls of 64 kbits each, multiplexed together on a single four-wire circuit. Commonly used to supply telephone service where multiple lines are required at the same location. The Internet has produced another application for these lines, supplying a 1.5 Mbit last mile from Internet Service Provider (ISP) to customer.

T-2 – A 6 Mbit circuit made up of four multiplexed T-1s on two pairs of copper wires. This signal travels only short distances and hence this services; though in theory practicable, is never deployed.

T-3 – A 45 Mbit circuit made up of 28 multiplexed T-1s. This circuit might be used to carry 672 phone calls, compressed video, or lots of Internet traffic, and forms a building block of high-speed digital communications. This is the highest practical speed copper circuit that is deployed on the PSTN; faster circuits are almost always fiber optic.

TA – Terminal Adapter (see reference)

TCP/IP — Transport Control Protocol/Internet Protocol. Two protocols which usually work in conjunction at the transport and network layers to provide a basis for a wide range of data networking protocols. TCP maintains an open connection between sender and receiver and makes sure that the receiver receives the exact data that was sent and IP handles the addressing and delivery of data. The basis for the Internet.

TEI — Terminal Endpoint Identifier. A dynamically assigned identifier assigned to ISDN CPE by the telco switch as part of the line initialization process.

tandem office — Also tandem switch. Refers to a telco switching point that passes traffic between the local exchange carrier and interexchange carrier [long distance carrier].

telco – Telephone company or service provider

terminal adapter – A device that terminates an ISDN or Switch 56 line that can dial and answer calls on the Public Switched Network (PSTN). Sometimes called a dialer. Short form is TA. Some

timecode — A signal that contains information such as time, date, and other specific useful information which can be recorded and used as a time reference for bookkeeping and synchronization tasks. The popular SMPTE timecode is an 80 bit digital word that occurs once per video or film frame. SMPTE
timecode is at a rate (about 5 kHz) that allows it to be recorded on audio tracks. Some devices (codecs, recorders, etc.) have special digital timecode tracks, while others just use analog tracks for this purpose.

trunk — Generally refers to a high capacity telco circuit which aggregates a number of voice and/or data calls for delivery between switches. Often carried on T1 circuits.


U interface – The two wire ISDN interface method. See also S/T interface, and NT-1

UDP – User Datagram Protocol. Similar to TCP and also operating on the transport layer, but with lower overhead, as it doesn’t perform end-to-end reliability checks or maintain a continuous negotiated connection. Most streaming media packets use UDP as their underlying protocol.

URL —Universal Resource Locater. A standard from of passing address information to a TCP/IP application. For instance, will access with a username of bob and a password of graft using the http protocol.


V.35 — Technically an ITU standard governing transmission at 48Kbps over 60-108 KHz group band circuits, in practice this refers to the large blocky connector generally used for high speed serial DTE interfaces.

videoconferencing – The use of digital video transmission systems to communicate between sites using audio and video compressed and sent via data networks, usually via switched ISDN called or via high-speed IP networks. Videoconferencing systems usually consist of camera, codec, network access equipment, network, and audio system in one unit.


WAN — Wide Area Network. A data network consisting of multiple sites often connected via T1 or other high-speed data communications technologies. Usually denotes a private network, although the Internet could be considered a very broad WAN.

webcasting — the broadcasting of information, generally in the form of audio and/or video via the Internet. Whereas static web information is pulled by the viewer, webcast material is generally pushed, or streamed, to the viewer, either through a web browser or dedicated application, such as the RealPlayer, Quicktime MoviePlayer, or Windows Media Player. Allows delivery of almost any kind of multimedia content.


X.21 — An ITU standard governing the serial interface between DCE and DTE, generally synchronous data on a DB15. Includes connector, electrical, and dialing specifications

XLR – Originally a series of mating connectors made by Cannon starting in the 1950’s with various numbers of pins (e.g. XLR-3 with three pins, XLR-4 with four, and so forth). The terms “XLR” and “Cannon Plug” generally now describe the three pin connectors most often used for microphones in a professional environment. Mating variations of these connectors are now available from many manufacturers (Switchcraft, Neutrik, et al.) and are used for balanced microphone, line level, and AES/EBU digital audio signals.