Index - A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A-Z
MAIN DISTRIBUTION FRAME (MDF) - The point where outside plant cables terminate and from which they cross connect to terminal or central office line equipment. Synonym: Main Distribution Frame; Main Distributing Frame; Mainframe; Main Frame.
MAINFRAME - 1.) One of the telephony synonyms for Main Distributing Frame; 2.) Data processing term descriptive of very large computers.
MAIN PBX - A PBX directly connected to a tandem switching exchange via an access trunk group, bypassing the local end office switching machine.
MAN (METROPOLITAN AREA NETWORK) - A non-specific term arising from the Cable TV industry's description of use of its transmission facilities throughout a city area, with a nominal range of 50 miles. The term has been adopted by LECs to describe fiber-based ring structures with transmission capacity large enough to connect LANs in various parts of a city together.
MANUAL TIE LINE - A tie line which requires the assistance of an attendant at both ends of the circuit in order to complete a connection; incapable of passing dialing down the link. Synonym: Manual Trunk, Ringdown Trunk, Ringdown Tie Line.
MAP (MANUFACTURING AUTOMATION PROTOCOL) - General Motors' data protocol fitting guidelines of the OSI Reference Model, optimized for the short, random messages typical of a factory floor communications environment; most used on broadband coaxial LANs. Contrast: TOP. MAPPING -In network operations, the logical association of one set of values, such as addresses on one network, with quantities or values of another set, such as devices on a second network; this might be name-address mapping, internetwork-route mapping, or as mundane as telephone jack location-extension number mapping, hence the telephony synonym is Assignment Sheet, Assignment Record, or perhaps even Telephone Directory, as all take the form of columns of equalities listed side by side.
MARK - The signal state on a binary channel representing a "1." Corresponds to current on, hole in paper tape, and (usually) negative voltage, as in EIA RS-232. Antonym: Space; current off; 0; no hole; positive voltage. Telegraphic circuits (with the notable exception of Telex trunks) hold a mark state when idle as a form of circuit assurance alarm technique.
MASTERGROUP (MG) - 10 supergroups each comprised of 5 groups of 12 channels summing up to 600 circuits transported as a unit in an analog FDM carrier system; first used in Bell's type L1 carrier systems on intercity coaxial cable.
MEGAHERTZ (MHZ) - a unit of a million Hertz; meaning millions of cycles per second of AC current.
MESSAGE - In telecommunications, a complete transmission of data or information; often synonomous with "block" in data communications, as 256 characters approximates the length of a world-standard 50-word telegram.
MESSAGE SWITCHING - A telegraphic/data communications technique for receiving an entire message, perhaps storing temporarily if need be, and routing the message on to another switch or a terminal. Compare to Packet Switching and Circuit Switching.
MESSAGE TELEPHONE SERVICE (MTS) - The tariff name for basic long distance telephone calling service; Telegraphic equivalent is Message Telegram Service, to draw a comparison.
MESSAGE TRANSFER PART - That part of a common channel signaling system that transfers signaling messages, error control and signaling link security related to the transfer; the "protocols" of such telephony networks. See also: CCIS, CCITT Signaling System Number 6; CCITT Signaling System Number 7.
MESSAGE UNIT (MU) - A local dial telephone charging plan that is time and distance sensitive; see LMS.
MICROWAVE (M/W) - Radio transmission using very short lengths, corresponding to a frequency of 1,000 megahertz or greater. - Synonym: Microwave Radio; Line of Sight; LOS.
MODEM - Contraction of the term Modulator/Demodulator; device that modulates and demodulates signals on and off a "carrier" frequency; not limited to computer data use, thus the telco-specific term "data set" for data modems.
MODIFIED FINAL JUDGMENT (MFJ) - The consent decree agreement between the U.S. Department of Justice and AT&T governing the breakup of the monopoly-era Bell System into AT&T, 7 Regional Bell Holding Companies (RBHC) and other entities. On August 26, 1982, U.S. District Court Judge Harold Greene accepted, with modifications, an AT&T/Justice Department settlement terminating the government's 1974 antitrust suit against AT&T. Judge Greene's decree did away with the provisions of the 1956 consent decree that had kept AT&T out of competitive, unregulated ventures, but left many details for refinement, a process that continues to this day.
MODULATION - Alterations in the characteristics of analog carrier waves, impressed on the amplitude, phase and/or the frequency of the wave.
MONITORING - Listening in on telephone calls in progress. Subject to severe restrictions as to the purpose and use of information obtained in doing so.
MONITORING DEVICE - Records data on calls placed through a company's telephone system: number called, length of calls, calling location.
MOST ECONOMICAL ROUTE SELECTION (MERS) - - Synonym: Least Cost Routing.
MSU (MODEM SHARING UNIT) - A hardware device, most often a simple contention switch operating on RTS (Request to Send) leads of DTE interfaces, that permits only one terminal at a time to use the modem.
MTBF (MEAN TIME BETWEEN FAILURE) - A statistical method developed and administered by the U.S. military for purposes of estimating maintenance levels required by various devices and systems. Since accurate statistics require a basis of "failures per million hours of operation," an MTBF estimate on a single device is not very accurate; it would take 114 years to see if the device really had that many failures! Similarly, since the MTBF is an estimate of averages, half of the devices can be expected to fail before then, and half after. MTBF cannot be used as a guarantee. Telecommunications systems operate on the principle of "Availability," for which there is a body of CCITT Recommendations.
MTTR - (MEAN TIME TO REPAIR) - A U.S. military statistical method for estimating electronics repair time on hardware devices; not appropriate to telecommunications facilities "restoration," which is the appropriate term.
MULTILEAVING - An IBM Bisync-era method of interspersing message blocks for various applications on a single line. Compare: Interleaving, in its second sense.
MULTIPLE ACCESS - In satellite communications, the capability of a communications satellite to function as part of the communications linkage between more than a single pair of ground stations. When accomplished with analog methods, FDMA is the term; if digital, TDMA.
MULTIPLEX/MULTIPLEXING - Transmitting more than a single message simultaneously on a physical transmission path; if analog, the technique is FDM, but if digital it is TDM.
MULTIPLEXER/MULTIPLEXOR - The hardware device performing combination and decombination of communications signals to and from a larger-capacity "composite" signal on line between multiplexers. Note: the spelling ending "-or" is properly used only for optical units; some sales people attempt it as a stylized name for wireline data units.
MULTIPOINT/MULTIDROP - An arrangement of communications facilities ranging from across a floor to across the globe in which one common facility is shared by all; one station at a time, usually under central polling control, sometimes contention for the channel, as in many LANs, has a history running deep into telegraphic communications. Contrast: Point to Point.
MULTIPLEXING - The act of combining a number of individual message circuits for transmission over a common path. Two methods are used: (1) frequency division, and (2) time division.