M

.mil (military) - Pronounced dot mill.The Internet generic Top Level Domain (gTLD) reserved exclusively for the United States military.This is an unsponsored domain. See also gTLD, Internet, and unsponsored domain.

.mobi - Pronounced dot mobi. The generic Top Level Domain (gTLD) reserved for consumers and providers of mobile products and services. This domain was created in 2005 under the sponsorship of mTLD Top Level Domain, Ltd. See also gTLD, Internet, and sponsored domain.

.mp2 - The file extension for audio data encoded in the Moving Picture Experts Group (MPEG) Audio Layer 2 format. See also MPEG-2.

.mp3 - The file extension for audio data encoded in the Moving Picture Experts Group (MPEG) Audio Layer 3 format. See also MPEG-3.

.mpg - The file extension for video and audio data encoded in the Moving Picture Experts Group (MPEG) format. See also MPEG.

.museum - Pronounced dot museum.The generic Top Level Domain (gTLD) reserved exclusively for the museum community. This domain was created in 2002 under the sponsorship of the Museum Domain Management Association. See also gTLD, Internet, and sponsored domain.

M Plane - One of the three entities of frame-relay network management. The Three planes are: The User Plane (the U Plane defines the transfer of information), the Management Plane (the M Plane defines the LMI, Local Management Interface), and the Control Plane (the C Plane is delegated for signaling and switched virtual circuits). The M Plane (also called the Local Management Interface, LMI) reports the status and configuration of connections to the FRAD (Frame-Relay Access Device). It provides notification of the addition, deletion, availability, and presence of all Data-Link Connections (DLCs). It also provides the exchange sequence that maintains the data connections when they are not in use (also called keep-alive data).

M - 1. Mega. From Greek megas, meaning great, translates to million. 2. In transmission systems, MHz (MegaHertz) is a million (10 ⁶ ) Hertz, Mbps (Megabit per second) is a million (10 ⁶ ) bits per second, and MBps (MegaByte per second) is a million (10 ⁶ ) bytes per second. In transmission systems, therefore, a million is exactly 1,000,000, since the measurement is based on a base 10, or decimal, number system. 3. In computing and storage systems, a MB (MegaByte) is actually 1,048,576 (2 ²⁰ ) bytes, because the measurement is based on a base 2, or binary, number system.The term MB comes from the fact that 1,048,576 is nominally, or approximately, 1,000,000.

m - meter. See meter.

M1 - A reference to the Meridian 1 PBX (Private Branch Exchange) switching system manufactured by Nortel Networks.

M12 (Multiplex 1-to-2) - A device used in a digital carrier system to multiplex level one bit streams into a level two bit stream. In a T-carrier system, for example, an M12 multiplexes four T1s into a T2 bit stream. See also bit stream, carrier, multiplexer, T1, T2, and T-carrier.

M13 (Multiplex 1-to-3) - A device used in a digital carrier system to multiplex level one bit streams into a level three bit stream. In an E-carrier system, for example, an M13 multiplexes four E-1s into an E-2 bit stream, and then multiplexes four E-2s into an E-3 bit stream.The corresponding T1 version of an M13 combines 28 T1 bit streams into a T3 bit stream. See also bit stream, carrier, E-1, E-2, E-carrier, and multiplexer.

M24 - Also known as D4.A T-carrier framing convention. See D4 and T-carrier.

Ma Bell - A reference to AT&T—the company that is said to have given birth to the Baby Bells, better known as the RBOCs.

MAC (Media-Access Control) - The protocol (there are several types, e.g., Ethernet MAC) that determines the transmission of information on a local-area network. The MAC is a part of the OSI (Open Systems Interconnect model) data-link layer that interfaces with the physical layer. The MAC is referred to as a sublayer of the data-link layer. Its purpose is to manage the transfer of data to the “wire” or “fiber optic,” as required by the used protocol. See also Data-Link Layer and LLC.

MAC Address (Media-Access Control Address) - A standardized OSI (Open Systems Architecture model) data-link layer identifier that is manufactured (burned into ROM) into every port or device that connects to a LAN. Network-control devices use MAC addresses to create and update routing tables and network data structures. MAC addresses are six bytes long (48 bits). The first 24 bits of the address are a vendor/manufacturer code, and the next 24 bits are the interface serial number (Fig. M.1). The IEEE delegates MAC address number ranges to manufacturing companies worldwide. MAC addresses are also called hardware addresses, MAClayer addresses, or physical addresses. See also Network Address.

MAC Address Learning - Service that characterizes a learning bridge, in which the source MAC address of each received packet is stored so that future packets destined for that address can be forwarded only to the bridge interface on which that address is located. Packets destined for unrecognized addresses are forwarded out every bridge interface. This scheme helps to minimize traffic on the attached LANs. MAC address learning is defined in the IEEE 802.1 standard. See also Learning Bridge and MAC Address.

MAC bridge (Medium Access Control bridge) - See encapsulating bridge

Machine Language - The lowest-level programming language. PROMs are the key to machine language. They contain instructions that assist the microprocessor in decoding the 8-, 16-, or 32-bit instructions into functions that the microprocessor executes. The instructions (machine-language scripts) are burned into the PROM when it is programmed. Typical machine-language instructions include: MOV A,M, which is actually entered as an OP-Code of 167, instructs a microprocessor to move the contents of memory address A to memory address M. Another machine instruction is OUT, entered as an OP-Code of 323, which instructs a microprocessor to move the contents of the previous memory address to a port that is identified in the next instruction.

machine - 1. A simple, unpowered instrument, such as a lever, pulley, or inclined plane, that is used for performing some kind of work by transmitting or changing the direction of energy. 2.A powered mechanical device, such as an automobile or drill press, that consists of a structure and various moving and unmoving parts and is for doing some kind of work. 3. An electronic device, such as a computer or facsimile machine, that can be thought of as operating on a mechanical basis. Such machines have automated many of the functions previously performed by humans. See also human.

MacIP - Network layer protocol that encapsulates IP packets in DDP packets for transmission over AppleTalk. MacIP also provides proxy ARP services. See also DDP and Proxy ARP.

macrobend - A relatively large bend in an optical waveguide, such as a fiber optic cable.A technician may need to bend a cable around a corner, for example, or may need to coil some cable in a span to provide necessary slack in the event that the cable must be spliced in the future, perhaps to repair a break.A technician placing a macrobend in a cable must consider the minimum allowable bend diameter in order to prevent either damage to the cable or bending loss, i.e., loss of signal strength resulting from an excessive bend. See also bend diameter, bending loss, and microbend.

macrocell - In radio systems, an imprecise term referring to a relatively large area of coverage, perhaps an entire metropolitan area of 50 miles in diameter. A macrocell is larger than a microcell and much larger than a picocell. See also cell, microcell, and picocell.

MAE (Merit Access Exchange or Metropolitan Area Exchange) - The exact meaning of the acronym is lost in the mists of time; it means either Merit Access Exchange or Metropolitan Area Exchange. In either case, MAE now is just MAE, a registered trademark of MCI, now (September 2007) a Verizon company, and is an official Network Access Point (NAP) at which an Internet service provider (ISP) can access the Internet backbone and exchange traffic with other ISPs. Some NAPs are known as NAPs, some as Internet Exchanges (IXs), and some as MAEs.Tier 1 MAEs are located in San Jose, California (MAE West);Vienna,Virginia (MAE East); Miami, Florida; and Paris, France.Tier 2 MAE sites currently are located in Chicago, Illinois; Dallas,Texas; Los Angeles, California; and New York, New York. See also Internet, ISP, IX, and NAP.

Magnetic Ink - Ink that is used to print information that will be read electronically. Magnetic ink is made with ferrous compounds. The banking industry uses magnetic ink on some of their printed materials and typical bank-account checks have the account number printed in magnetic ink so that they can be electronically processed.

Magnetic Storage - A method of storing data by magnetizing a tiny section of a tape or disk for each bit (Fig. M.2).Hard-disk drives and floppy-disk drives utilize disks coated with ferromagnetic materials. Data cartridges contain thin plastic tape coated with ferromagnetic materials that are recorded and read in a similar fashion. Analog information can also be stored magnetically; cassette tapes are a common example.

Magnetic Stripe - The stripe on the back of a credit card or other device. Magnetic stripes are usually used to store information, such as a name and account number, in a binary bar-code format.

Mail Bridge - In an e-mail environment, a part of a mail gateway that enforces an administrative policy with regard to what mail it forwards.

Mail Gateway - In an e-mail operating environment, a computer (usually a server) loaded with specialized software that connects two or more dissimilar electronic-mail systems and transfers mail messages between them.

mail transfer agent (MTA) - See MTA.

mail user agent (MUA) - See MUA.

mailbox - A partition of computer memory designated for the temporary storage of messages intended for an individual, department, company, or other authorized user entity. Mailboxes can be associated with e-mail, facsimile mail, or voice mail systems.

Main Distribution Frame - Also called a distribution frame. The place where all the wire, fiber optic, or coax for a network is terminated. The distribution frame is usually placed as close to the central-office switch or PBX as possible. For a photo, see Distribution Frame.

Main Feeder - An F1 (first facility) cable from a central office. The feeder cable runs to cross connect points in the telephone network where F2 (second facility) cable feeds are connected/cross connected. For a photo, see Distribution Cable.

Main Frame - A large computer capable of retrieving information from mass-storage units and calculating/processing the data in a very short time in comparison to a client-server computing process. Main-frame computers have been regaining favoritism in large data-processing environments because of their outstanding reliability and processing power.

Main PBX - A primary PBX that interfaces with the public telephone network via CO (central office) trunk lines. The other type of PBX is an off-premises (remote) PBX, which is connected to the outside world or public network by switching through a main PBX.

maintenance and administration terminal (MAT) - See MAT.

make and break - See soft handoff.

Make Busy - 1. A reference to the activation of the “busy out” feature of an ACD telephone. If the telephone is busied out, the ACD system will not transfer calls to that telephone. This is useful when an agent is on break or their shift is over. 2. A temporary fix or condition of a phone service. To “busy a line out of a hunt sequence.” If a business phone line becomes defective and it is in a hunt or roll-over sequence, calls will not hunt or roll past this line. For example, four lines come into your business. The first line is the main number; if that first line is busy, then calls come in on the second line, etc. If line one goes bad, it can’t be called, so it can’t be busy. Because it is not busy, calls will not hunt or rotate to the next three lines. When you call the phone company repair service, they busy out the bad line, which makes it look busy to the network. Your calls then start coming in on the other three lines. When a repair technician finishes repairing the problem on the bad line, he has it unbusied. Another temporary fix is to call forward the line from the central office. The phone company can do this at the customer’s request.

Malicious Call Trace - A feature offered by local telephone companies. Even though all calls are kept in an archived database, it is sometimes difficult to locate a single call—even if an accurate time is given. The malicious call trace or annoyance call trace “flags” a call when a customer hangs up and dials the call-trace feature code after receiving an annoyance call. Usually, the charge is $2.00 per trace. After the trace or “flag” has been made, telephone company security officials investigate the source of the call. If there are multiple occurrences, then the telephone company will press charges against the malicious caller. The person receiving the malicious calls will never find out who the caller is unless they are summoned to a court hearing.

malware (malicious software) - Software that is harmful or evil in intent. See also spyware, Trojan horse, virus, and worm.

MAN (Metropolitan Area Network) - See Metropolitan Area Network.

Managed Object - In LAN network management, a network device (such as a workstation or server) that can be managed by a network administrator through a management protocol.

managed service provider (MSP) - See MSP.

Management Information Base (MIB) - A data file within a TCP/IPloaded network device, such as a PC or router that contains information about that device. The information that is contained in the MIB include hardware addresses (MAC address), counters, statistics, and routing tables. Each software/information category is referred to as an object. MIB works in conjunction with SNMP (Simple Network-Management Protocol).

management information systems (MIS) - See IS.

management plane - In the ATM reference model, the functions that involve the management of the ATM switch or hub. The management plane is divided into plane management and layer management. Plane management acts on the management of the switch as a whole, with no layered approach. Layer management acts on the management of the resources at each specific layer of the model, e.g., operation, administration, and maintenance (OA&M) information. See also ATM reference model, control plane, and user plane.

Management Plane - One of the three entities of frame-relay network management. The Three planes are: The User Plane (the U Plane defines the transfer of information), the Management Plane (the M Plane defines the LMI, Local Management Interface), and the Control Plane (the C Plane is delegated for signaling and switched virtual circuits). The M Plane (also called the Local Management Interface, LMI) reports the status and configuration of connections to the FRAD (Frame-Relay Access Device). It provides notification of the addition, deletion, availability, and presence of all Data-Link Connections (DLCs). It also provides the exchange sequence that maintains the data connections when they are not in use (also called keep-alive data).

manager of managers (MOM) - See MOM.

Manchester coding - A technique for encoding both the clock and data pulses into a self-synchronizing bit stream. Manchester coding does not send data as a series of raw 1 bits and 0 bits. Rather, each data bit includes a midpoint voltage level transition from positive (+) to negative (–) or from negative (–) to positive (+), with the direction of the transition indicating whether the bit is a 1 bit or a 0 bit.The fact that each bit representation includes both a positive and a negative pulse ensures pulse density and, therefore, ensures proper synchronization.This characteristic also maintains DC balance on the line. Sometimes referred to as phase encoding (PE) and biphase encoding, Manchester coding is a special case of binary phase-shift keying (BPSK). Manchester coding is specified in early versions of IEEE 802.3, also known as Ethernet, and 802.4, also known as token bus. In contemporary high speed networking, more efficient coding schemes, such as 4B/5B and 8B/10B, largely have replaced Manchester coding, which requires two pulses (+/– or –/+) for each data bit. See also 4B/5B, 802.3, 802.4, 8B/10B, BPSK, Ethernet, line coding, ones density, phase, pulse, synchronous, and Token Bus.

Manchester Encoding - Also called differential encoding. A physical media transmission format used in IEEE 802.5 and token-ring LANs (Local-Area Networks). Differential encoding combines a clocking signal with the data stream. A binary 1 is denoted by a voltage increase and a binary 0 is denoted by a voltage decrease. The voltage reset between voltage increases and decreases represents the clocking or timing source. By design, differential encoding is less prone to attenuation, but more sensitive to RFI (Radio Frequency Interference) than PCM (Pulse-Code Modulation) formats.

mandrel wrapping - A technique used in multimode fiber (MMF) optics to modify the modal distribution of an optical signal.The wrapping of the MMF around a mandrel results in intentional macrobends and forces modes into higher orders, i.e., away from direct paths through the core and towards the core/cladding interface. If the MMF is fully filled by the source, mandrel wrapping forces the higher-order modes into the cladding, where they are attenuated and lost. If the MMF is underfilled, mandrel wrapping forces some low-order modes into higher-order modes, which redistribution results in modal equilibrium, i.e., equal distribution of power across modes propagating in the core. Mandrel wrapping sometimes is used in jumper cables to intentionally attenuate high-power optical signals in order to prevent damage to optical receivers. Mandrel wrapping also is used in launch cables to achieve modal equilibrium for testing purposes. The diameter of the mandrel and the number of wraps or turns around it are sensitive to the fiber characteristics and the desired modal distribution. See also attenuation, cladding, core, high-order mode, jumper, launch cable, low-order mode, mandrel, MMF, mode, and signal.

mandrel - A rod or spindle around which material such as metal, wire, or glass is cast, molded, bent, shaped, or wrapped. See also mandrel wrapping.

Mann-Elkins Act - In the United States, the act (1910) that granted the Interstate Commerce Commission (ICC) interstate regulatory authority.

Manual Ring-Down Line - Not really a phone line, but two phones connected together via a pair of wires and a talk battery (9 V to 24 V). Signaling, such as ringing, is performed manually, by flipping a switch on and off rapidly, which disconnects and connects the battery. The changing voltage imitates a weak ring voltage. Rescue teams use manual ringdown lines in cave and mine-shaft rescue operations because their radio range is very limited in underground tunnels.

Manufacturing Automation Protocol (MAP) - See MAP.

Manufacturing Automation Protocol/Technical and Office Protocol (MAP/TOP) - See MAP.

MAP (Manufacturing Automation Protocol) - A local area network (LAN) protocol developed by General Motors (GM) in the early 1980s for the interconnection of computers and programmable machine tools in factory or assembly line operations, MAP is based on Token Bus (IEEE 802.4) running at 1, 5, 10, and 20 Mbps. MAP sometimes is referred to as Manufacturing Automation Protocol/Technical and Office Protocol (MAP/TOP). See also 802.4, LAN, and Token Bus.

Map - A reference to “mapping”—a virtual tributary though an Optical Carrier Circuit (OC-3) over a SONET ring or end-to-end path. Mapping the tributary involves telling the SONET equipment which and how much bandwidth within the OC (Optical Carrier) will be designated a channel. The choices are DS0, DS1, DS3, and STS-1. STS-1 is an electrical version of an OC-1.

MAP/TOP (Manufacturing Automation Protocol/Technical and Office Protocol) - See MAP.

Mapping - See Map.

Marine Telephone - A radio telephone that is designated specific operating frequencies by the FCC. It is not cellular (cellular is a short-distance radio application), it broadcasts with more power and a much greater distance. Tellabs manufactures marine telephone equipment.

mark - Referring to a service mark or trademark. See also service mark and trademark.

Marker Tape - A plastic label built into cables that have cable ID and specification information printed on them by the manufacturer. Marker tapes are uncommon in newer polyethylene cables, because it is much easier and less expensive to print the cable designation on the outside of the cable.

Markov source - A statistical model for predicting the occurrence frequencies of letter or word pairs and triplets. Markov source is used in some data compression mechanisms. See also compression.

MARS (Multicast Address Resolution Server) - A mechanism for supporting IP multicast. A MARS serves a group of nodes (known as a cluster); each node in the cluster is configured with the ATM address of the MARS. The MARS supports multicast through multicast messages of overlaid point-to-multipoint connections or through multicast servers.

Martian (Mis-Addressed/Routed Transmission In A Network or Mis-Addressed/Routed Telepacket In A Network) - A data message that ends up in the wrong part of a network. Martians are caused by routing-table inaccuracies. Those inaccuracies are caused by the lack of maintaining static routing table entries or workstations that have been given bogus network addresses.

MARTians - Misaddressed or Routed Telepacket on a LAN or WAN.

maser (microwave amplification by stimulated emission of radiation) - The maser is a device similar to the laser, but emitting microwave radio waves rather than light. In 1953, Charles H. Townes, James P. Gordon, and Herbert J. Zeiger invented the maser, which earned them the Nobel Prize in Physics in 1964. Research continued into the 1950s, leading to the optical maser, or laser, for which AT&T Bell Telephone Laboratories was awarded a patent in 1960. See also laser.

mashing - A process of building new Web-based services from reusable components of other services, mashing is a technique defined in Web 2.0. See also Web 2.0.

Mask - See Address Mask and Subnet Mask.

Mast Clamp - A device used to attach a ram hook to a power mast. The ram hook (also called a ram horn) is used to attach an aerial service wire via a drop clamp.

Master Clock - A reference to a BITSs clock. A central timing device for synchronous networks, such as SONET networks. Bits clocks can be rack mounted, just like other telecommunications equipment.

Master of Network Science (MNS) - A well-known industry certification/training program offered by 3COM. This program is actually referred to as a credential, rather than a certification by 3COM. Several hardware and administration intensive programs are available under the MNS family of certifications. The first is the MNS LAN Solutions track, which includes training on high-performance 3COM LAN switching equipment, seven exams, and a lab test. Another is the MNS LAN Solutions Plus track, which requires completion of the LAN Solutions requirements, and extends the trainee’s knowledge into the ATM products offered by 3COM. Another example track is the MNS Network Architecture, which provides a rounded study of enterprise networking. Other MNS tracks include the MNS Network Management, MNS WAN Solutions, and MNS Remote-Access Solutions. Information regarding the 3COM MNS training programs can be found at http://www.3com.com.

master/slave - Descriptive of a relationship in which one entity, the master, is in total control of another, the slave. In computer networking, master/slave is a network architecture and set of protocols in which one device or program, the master, exerts total control over one or more other devices, the slaves.The master determines the communications priorities of the slaves, for example. A master/slave architecture, such as IBM Token Ring or Synchronous Data Link Control (SDLC), is decidedly different from a peer-topeer architecture, in which computers communicate as equals, sharing the same responsibilities and using the same programs to communicate.As the term master/slave can be offensive to some people, some computer manufacturers prefer the term primary/secondary. Bluetooth specifications provides for ad hoc piconets that can include as many as seven slaves under the control of a master, which assumes that responsibility when initiating the network. See also ad hoc, Bluetooth, client/server, network architecture, PC, peer-topeer, piconet, protocols, SDLC, and Token Ring.

MAT (Maintenance and Administration Terminal) - A PC or other data terminal connected to the maintenance port of a PBX or key telephone system (KTS) in order that authorized users can access the system software for purposes that might include Move,Add, and Change (MAC) activity; Class of Service (CoS) changes; automatic route selection (ARS) programming; requests for traffic and usage statistics; requests for status reports; and diagnostic testing and analysis. Remote maintenance generally can be accomplished over the PSTN via a modem connection.

MAT (Meridian Administration Tools) - A Northern Telecom CTI application that allows a Meridian PBX system to be managed through a GUI environment over a LAN or single PC. It enables a user to make administrative changes to the system by clicking on the picture of an item to be changed (such as a feature button on a telephone or the name display) and typing in the change. It also provides excellent traffic and core analysis tools, which graph the busy hours by network group. Call accounting is also a feature of MAT.

material dispersion - A type of dispersion that occurs in optical fiber due to the interaction of various wavelengths with the physical matter in the crystalline structure of the glass.The refractive index of the glass varies according to the wavelength of the optical signal, i.e., different wavelengths travel at different speeds in the medium.The longer the wavelength, the faster the signal travels. No pulse is perfectly defined, i.e. includes just one wavelength. Rather, an optical pulse emitted by a light source has a certain spectral width, i.e., includes a range of wavelengths of lesser power around the center wavelength. The effect of material dispersion is that the various wavelengths comprising the pulse travel at different velocities through the medium. So, the pulse can spread over a distance simply due to the interaction of various wavelengths with the matter in the crystalline core, which causes some portions of a pulse to arrive earlier than other portions. As the wavelength increases (and frequency decreases), material dispersion decreases. So, optical signals in the 1550 nm window suffer less from material dispersion than wavelengths in the 1310 nm window. Material dispersion, which is synonymous with intramodal dispersion and spectral dispersion, is one factor contributing to chromatic dispersion. Material dispersion and chromatic dispersion are issues in long haul fiber optic transmission systems (FOTS) employing single-mode fiber (SMF) of step-index construction. Multimode graded-index fibers suffer so much from modal dispersion over short distances that material dispersion and chromatic dispersion never become factors. See also chromatic dispersion, dispersion, graded-index fiber, MMF, modal dispersion, refractive index, SMF, spectral width, step-index fiber, and window.

matrix switch - A switch comprising an array of internal buses or circuits laid out in a grid of rows and columns so that connections can be set up anywhere the circuits intersect, and a path can be established between any input port and any output port.There are physical matrixes (with metallic contacts) such as voice crossbar switches, and logical matrixes used in packet switches. A matrix switch can provide full bandwidth to multiple, simultaneous transmissions on a port-to-port, point-to-point basis. If there are congestion issues in a matrix switch, it may have the ability to subdivide its capacity, with the buses becoming shared buses through a process of time division multiplexing (TDM). See also bus, circuit, crossbar, cutthrough switch, LAN switch, port, shared bus switch, switch, and TDM.

Matrix - The part of a switch that carries and routes calls. The matrix is a virtual part of the core that commands which channels to connect with what. As multiplexed bit streams run through a digital switch, they are separated and recombined from inputs (interface cards) to specified outputs (interface cards) by the core (CPU) of the switch. The matrix is not a tangible object; it is a combination of the CPU and interface equipment.

Matthews, Gordon (1937–2002) - The inventor of modern voice processing systems, Matthews filed the basic patents and first commercialized the systems. Matthews was on a business trip in the 1970s and was having trouble reaching his office to pick up his messages due to time zone differences. He mentioned the problem to his wife, Monika, who suggested that he invent a computer so that he and his employees could leave messages for each other. Matthews went to work on the project and founded VMX (Voice Message eXpress) in Dallas,Texas (United States) in 1979. Shortly thereafter, 3M bought the first commercial system, a standalone voice mail system with an interface to the PBX, from which the call was forwarded in the event of a busy or no-answer condition at the user station. Monika Matthews recorded the first greeting on this first commercial system. Note: In 1992, Matthews retired and sold VMX to Octel. Octel subsequently merged with the Enterprise Networks Group of Lucent Technologies, an AT&T spin-off.VMX and Octel systems are now a product line of Avaya, a Lucent spin-off, which is just as well, as Lucent was acquired by Alcatel, a French company, in 2006. See also voice processor.

MAU (Media Attachment Unit) - Generically referred to as a transceiver, this device connects to a computer or other device’s BNC network-interface card port and permits a convenient connection to an RJ45 twisted-pair media. Transceivers have also been called AUIs (Access Unit interface) and Media-Access Units (with the same acronym, MAU).

MAU (Medium Access Unit) - A device that provides a point of access for hosts, workstations, and peripherals into a local area network (LAN).An MAU typically is a multiport device that houses multiple network interface cards (NICs). See also LAN and NIC.

maxCTD (maximum Cell Transfer Delay) - See CTD.

maximum burst size (MBS) - See MBS.

Maximum Burst - An ATM parameter that specifies the largest burst of data above the insured and maximum rates that will be allowed temporarily on an ATM PVC, but will not be dropped at the edge by the traffic-policing function. On average, the traffic needs to be within the maximum rate. This parameter is specified in bytes or cells. See also Maximum Rate and Insured Rate.

maximum frame size (MFS) - See MFS.

Maximum Rate - On an ATM (Asynchronous Transfer Mode) connection, a parameter that defines the total bandwidth that will be permitted to traverse from point to point under any circumstances. The maximum rate is equal to the insured rate and the excess rate combined. When the ATM network that serves the connection has a low level of traffic, the connection is permitted to transmit at the excess-rate value of bandwidth. When the network is congested or very busy, only the insured rate of bandwidth is allocated to the connection. An example of an insured rate for a connection is 256 Kbps, and an example of the maximum rate for that same connection could be 512 Kbps. See also Excess Rate.

maximum transmission unit (MTU) - See MTU.

MB (MegaByte) - Million bytes. In computing and storage systems, a MB (MegaByte) is actually 1,048,576 (2 ²⁰ ) bytes, since the measurement is based on a base 2, or binary, number system.The term MB comes from the fact that 1,048,576 is nominally, or approximately, 1,000,000. See also byte and M.

Mbps (Megabit per second) - Million (10 ⁶ ) bits per second.A measure of bandwidth in a digital transmission system. See also bandwidth, bps, and M.

MBps - MegaByte per second, or million (10 ⁶ ) bytes per second. MBps is a measure of transmission system bandwidth in ESCON, Fibre Channel, FICON, and other select storage area network (SAN) solutions. See also bandwidth, Bps, byte, ESCON, Fibre Channel, FICON, M, and SAN.

MBS (Maximum Burst Size) - In asynchronous transfer mode (ATM), a traffic parameter describing the maximum number of consecutive cells that can transmit within the peak cell rate (PCR), given the burst tolerance (BT), or burst cell tolerance (BCT), of the network. See also ATM, BCT, BT, cell, PCR, and traffic parameter.

MC (Multipoint Controller) - See MCU.

MCLR (Maximum Cell-Loss Ratio) - In an ATM (Asynchronous Transfer Mode) network, the maximum ratio of cells that do not successfully transit a link or node, compared with the total number of cells that arrive at the link or node. MCLR is one of four link signals exchanged between network nodes to determine the available resources of an ATM network. The MCLR applies to cells in the CBR (Constant Bit Rate) and VBR (Variable Bit Rate) traffic classes whose CLP (Cell-Loss Priority) bit is set to zero. See also CBR, CLP, UBR, and VBR.

McNutt, Emma - The first female telephone operator, Emma McNutt was hired by New England Bell in Boston, Massachusetts, and began work on September 1, 1878. Previously, all operators had been young men who reportedly were given to lightening the tedium of their work by roughhousing, shouting at each other, and swearing at the customers.Young ladies of the time were brought up to be gracious, diffident, prim, proper, virtuous, and never profane. The Bell System also required them to be single. (Note: New England Bell did not hire married women until 1942, with the thought being that, by definition, a married woman could not be virtuous, at least not from a male perspective. It was, after all, male chauvinists who did the hiring in those days.) Within a few years, the male operator was extinct, not to resurface until the 1960s. History lost track of Emma McNutt after she retired in 1911.

MCP (Microsoft-Certified Professional) - A well-known industry certification/training program offered by Microsoft and its training partners. The MCP certification is an in-depth learning track that incorporates Microsoft Networking products, Microsoft Applications, and general applications thereof. Up-to-date information regarding the MCP training program can be found through http://www.microsoft.com.

MCR (Minimum Cell Rate) - A parameter defined by the ATM Forum for ATM Traffic Management. Minimum cell rate is defined only for Available Bit Rate (ABR) transmissions and it specifies the minimum value for the Allowed Cell-Rate (ACR) parameter. A minimum cell rate is necessary when timing-sensitive transmissions are made, such as voice or video.

MCSE (Microsoft-Certified Systems Engineer) - A well-known industry certification/training program offered by Microsoft and its training partners. The MCSE certification is an in-depth study program that incorporates Microsoft Networking products, such as Windows NT and Microsoft Exchange Server. The learning track for this program is extensive in Microsoft data-base applications and, in general, enterprise networking. Information regarding the MCP training program can be found through http://www.microsoft.com.

MCU (Multipoint Control Unit) - In H.323-compliant multimedia networks, a device that supports conferencing among three or more participating terminals.The MCU comprises a Multipoint Controller (MC) and optional Multipoint Processors (MPs). The MC is responsible for call control negotiation to achieve common levels of communication.The MP may process either a single media stream or multiple media streams, depending on the nature of the conference. See also H.323 and multimedia.

MD5 (Message Digest 5) - MD5 is the algorithm used for message authentication in SNMP (Simple Network-Management Protocol). MD5 verifies the integrity of the communication, authenticates the origin, and checks for timeliness.

MDF (Main Distribution Frame) - Also called a distribution frame. The place where all the wire, fiber optic, or coax for a network is terminated. The distribution frame is usually placed as close to the centraloffice switch or PBX as possible. For a photo, see Distribution Frame.

MDU (Multi-Dwelling Unit) - An apartment building, condominium, residence hotel, or other building that is subdivided into multiple residences. An MDU has considerable implications for local loop deployments, particularly with respect to passive optical network (PON). See also local loop and PON.

mean opinion score (MOS) - See P.800.

mean time between failures (MTBF) - See MTBF.

mean time to repair (MTTR) - See MTTR.

Measured Rate Service - Abbreviated 1MR for residential and 1MB for business, this type of telephone service is offered by local telephone companies. Measured-rate service means that a line is billed on a “per call basis.” Telephone companies in the Southern and Western United States have tried to abolish measured service by encouraging customers to subscribe to flat-rate services, abbreviated 1FR for residential and 1FB for business use.

Mechanical Splice - An alternative fiber-optic splice to fusion splicing. Fusion splicing equipment is very expensive ($40,000 is typical for a fusion splicer). Mechanical splices come as a kit, which connectorizes the ends of the fibers. A tool kit is required for mechanical splicing. It consists of a microscope, polishing puck, cleavers, epoxy, and polishing compound. They cost about $1,200. An oven used to “hot cure” the epoxy is also available. With a mechanical splice, you cleave or cut the end of the fiber as square and smooth as possible, then epoxy the fiber end into a connector. The epoxy takes about 12 hours to cure without an oven and about 20 minutes with an oven. After the epoxy has cured, the tip of the connector (which should be flush with the end of the fiber optic) is polished by holding it with a device called a puck (it is shaped like a hockey puck). The puck holds the fiber connector while it is gently rubbed against a pad coated with polishing compound. When the polishing is done, the connector is ready to be mated with another connector and the splice is complete. Mechanical splice kits cost about $15.00 per splice and are available in SC- and ST-style connectors.

mechanical strength - The ability to withstand the stress of physical forces. Cable and wire systems, for example, must be designed in consideration of the amount of twisting and bending (flex strength) they can tolerate and the amount of weight or longitudinal stress a cable or wire can support (tensile strength) without suffering deformation or breaking (break strength). See also break strength, flex strength, strength member, and tensile strength.

Mechanized Line Testing (MLT) - Also called DATU (Direct Access Test Unit). MLT and DATU equipment is either added on or built into a central-office switch. DATU allows a technician or customer-service agent to dial the phone number of the DATU or MLT equipment and execute a test for shorts, opens and grounds remotely. In response to a digital voice, the technician enters a password and a choice of options. The results of the test can be read back to the technician by a digital recording or sent to them via an alpha-numeric pager. DATU units can also send a locating tone on the technician’s choice of TIP, RING, or both TIP and RING. The test unit can also short lines and remove battery voltage for testing.

Media Attachment Unit (MAU) - Generically referred to as a transceiver, this device connects to a computer or other device’s BNC network-interface card port and permits a convenient connection to an RJ45 twisted-pair media. Transceivers have also been called AUIs (Access Unit interface) and Media-Access Units (with the same acronym, MAU). In token-ring networks, a MAU is known as a multistation access unit and is abbreviated MSAU to avoid confusion.

media converter - A device that interfaces disparate transmission media, making the necessary signal conversions at the Physical Layer. For example, a media converter is required to interface a fiber optic transmission system such as Passive Optical Network (PON) to the copper unshielded twisted pair (UTP) used in inside wire applications on the customer premises. See also Physical Layer, PON, and UTP.

Media Gateway Control (Megaco) - See Megaco.

Media Gateway Control Protocol (MGCP) - A predecessor to Media Gateway Control (Megaco). See Megaco.

Media Gateway Controller (MGC) - In voice over Internet Protocol (VoIP) networks, a device responsible for the registration and management of resources at the media gateway (MG). Sometimes referred to as a call agent, call controller, or softswitch. See also media gateway, softswitch, and VoIP.

media gateway - 1. A protocol converter that interfaces a traditional public switched telephone network (PSTN), or device running PSTN protocols, with a device running the Internet protocol (IP) suite. 2. A small IPBX system sized for small business enterprise (SBE) applications up to a dozen or so extensions, or perhaps small-to-medium enterprise (SME) applications up to 50 or so extensions. A media gateway also can be networked with a larger media server, media manager, or communication manager that serves a larger regional office. See also IPBX. 3. In H.323-compliant multimedia networks,a gateway is an optional element used for various levels of protocol conversion.The gateway serves as a protocol converter between devices and networks that have native H.323 capability and those that do not.The gateway also may translate between audio, video, and data formats, and may perform signaling conversions between the H.225 packet protocol and external protocols such as SS7 and Q.931.Alternatively, signaling conversions may be performed by gatekeepers, call processors, or session border controllers. See also H.225, H.323, multimedia, network, packet, protocol, protocol converter, Q.931, session, and SS7.

Media Interface Connector - A fiber-optic connector.

media manager - See media gateway.

media server - See media gateway.

Media-Access Control (MAC) - The protocol (there are several types, e.g., Ethernet MAC) that determines the transmission of information on a local-area network. The MAC is a part of the OSI (Open Systems Interconnect model) data-link layer that interfaces with the physical layer. The MAC is referred to as a sublayer of the data-link layer. Its purpose is to manage the transfer of data to the “wire” or “fiber optic,” as required by the used protocol. See also Data-Link Layer and LLC.

Media-Access Control Address (MAC Address) - A standardized OSI (Open Systems Architecture model) data-link layer identifier that is manufactured (burned into ROM) into every port or device that connects to a LAN. Network-control devices use MAC addresses to create and update routing tables and network data structures. MAC addresses are six bytes long (48 bits). The first 24 bits of the address are a vendor/manufacturer code, and the next 24 bits are the interface serial number. The IEEE delegates MAC address number ranges to manufacturing companies worldwide. MAC addresses are also called hardware addresses, MAC-layer addresses, or physical addresses. See also Network Address.

mediation device - Also known as a set handler. See set handler.

Medical Implant Communications Service (MICS) - See MICS.

medium access control (MAC) bridge - See encapsulating bridge.

Medium Access Unit (MAU) - See MAU.

medium earth orbit (MEO) - See MEO.

Medium Frequency - The range of radio frequencies from 300 to 3000 kHz.

medium voltage (MV) - See MV.

medium - A substance that conveys something, i.e., through which something is carried or transmitted. In the context of telecommunications, a medium is something that passively supports or allows the conveyance or transmission of a signal, and is not necessarily a tangible thing that can be touched. See transmission medium.

Mega (M) - The prefix for million. Sixteen megabytes is equal to 16,000,000 bytes, and would be abbreviated 16 MB. See also M.

Megabit per second (Mbps) - See Mbps.

Megabyte per second (MBps) - See MBps.

Megabyte - One million bytes. Mega is abbreviated “M” and bytes are abbreviated “B.” Sixteen megabytes is equal to 16,000,000 bytes and would be abbreviated 16 MB.

Megaco (Media gateway control) - A joint standardization effort of the ITU-T (H.248) and the IETF (RFC 3525) that defines the call control protocols employed in a physically decomposed gateway with subcomponents distributed across multiple devices that may be in multiple physically distinct locations. Those subcomponents take the form of a Media Gateway (MG) and a Media Gateway Controller (MGC), also known as a softswitch or a call agent.A single MGC can control a large number of MGs, each of which is optimized for a particular gateway application function to convert the media format between a packet network and another form of network, such as a public switched telephone network (PSTN) or an asynchronous transfer mode (ATM) network. The call control and signaling logic are centralized in the MGC and can include features such as dial tone, collect dialed digits, call hold, call transfer, call forward, and call conference. The MGC signals the MGs, which then execute the feature commands and process the call, performing gateway functions as required to interface the incompatible networks or network elements (NEs).There is a master/slave relationship between the centralized MGC and decentralized MGs, much like that of a traditional PSTN, except that the MGs that execute the features and perform the switching are distributed across the network. See also ATM, call transfer, conference call, dial tone, gateway, H.248, hold, IETF, ITU-T, master/slave, protocol, PSTN, and softswitch.

Megahertz - One million hertz. Mega is abbreviated “M” and hertz is abbreviated “H.” Sixteen MHz is equal to 16,000,000 Hz (hertz is another word for cycles in radio frequency). See also MHz.

Megohm - One million ohm. Mega is abbreviated “M,” and the symbol for ohms is “Ω.” Sixteen megabytes is equal to 16,000,000 ohms (ohms are a measure of resistance to electricity) and would be abbreviated 16 MΩ.

Member - Nortel’s name for a trunk. For example, a T1 would contain 24 members. See also Route.

Memory - Electronic memory comes in two families, ROM (Read-Only Memory) and RAM (Random-Access Memory). Memory devices are made from two different technologies, bipolar (TTL) and MOS (MetalOxide Semiconductor). Memory is stored by a technique called writing and retrieved by a technique called reading. ROM devices can only be read and are programmed during manufacture. PROM (Programmable Read-Only Memory) devices can be programmed at a later date by an electronics reseller or electronic assembler for a special application using special equipment. Special ROM devices called EPROMs (Erasable Program-mable Read-Only Memory) can be electronically erased and reused. RAM has read and write capability. The term random access means that any memory address can be read in any order at any time. The two types of RAM are static and dynamic. Static RAM can hold its memory even when power is removed. Dynamic RAM needs constant power to refresh its memory. The following family diagram illustrates the memory types and the technology with which they are made. See also SD RAM and EDO RAM.

MEMS (Micro-ElectroMechanical Systems) - Tiny electromechanical systems on a silicon chip. MEMS comprise integrated mechanical elements, sensors, actuators, and electronics on a common silicon substrate through microfabrication technologies, including the micromachining of the mechanical elements. MEMS are employed in optical projectors as well as in purely optical switches used in fiber optics transmission systems (FOTS), and actually are more along the lines of optical cross-connects. As purely optical devices, they do not require that the incoming optical signal be converted to an electrical signal for processing and then be reconverted to an optical signal. In other words, MEMS are optical-optical-optical (OOO), rather than optical-electrical-optical (OEO). See also cross-connect, FOTS, and switch.

MEO (Medium Earth Orbit or Middle Earth Orbit) - A satellite or satellite constellation (i.e., system) operating at an altitude of 10,062–20,940 kilometers. Unlike a geosynchronous Earth orbiting (GEO) satellite, MEO and LEO (Low Earth Orbit) satellites do not remain in a fixed position relative to the Earth’s surface, so are referred to as mobile satellite systems (MSSs), as opposed to the fixed satellite systems (FSSs) in geostatic orbit. See also FSS, GEO, LEO, MSS, and satellite.

Meridian 1 - A large-scale PBX (Private Branch Exchange System) manufactured by Northern Telecom. For a photo, see Private Branch Exchange.

Meridian Administration Tools (MAT) - See MAT.

Merit Access Exchange (MAE) - See MAE.

mesh topology - A network topology characterized by the intertwining of nodes through links connecting them together directly, rather than through one or more intermediate points of interconnection.There are two types of mesh topologies: full mesh and partial mesh.

• full mesh: A topology that connects every node directly with every other node.A full mesh minimizes propagation delay, latency, and the potential for data errors and loss in transit, as the path is direct and involves no intermediate processing points.A full mesh also provides the greatest number of alternative paths between any two nodes, which has the advantage of extreme network redundancy and resiliency. In the event of a catastrophic failure or performance degradation anywhere in the network, sufficiently intelligent nodes can redirect traffic around the point of failure.A full mesh topology would be highly desirable if it were not for the large number of circuits and ports required.An eight-node full mesh network, as illustrated in Figure M-1, requires 28 circuits, each of which requires two ports, calculated as follows:

X = n(n – 1) / 2

28 = 8(8 – 1) / 2

The cost and complexity of full mesh networks generally makes them impractical for more than three or four nodes, at least in wireline networks.Wireless networking can be quite another matter in some cases. Several Wireless LAN (WLAN) technologies operating in the unlicensed ISM bands support full mesh networking, as the cost of a establishing a link is essentially zero, as is the level of complexity.

• partial mesh: A topology that provides a path by which any node can connect with any node, but not necessarily a direct path, and which provides no common point of interconnection for all nodes. A partial mesh is characterized by a backbone that takes the form of a small mesh of centrally located nodes, through which the more remote end nodes interconnect. A partial mesh provides some of the advantages of a full mesh, but without the extreme circuit and port requirements.

See also infrastructure mesh, ISM, pure mesh, topology, and WLAN.

Mesh - A WAN (Wide-Area Network) physical or logical network topology in which devices are organized in a manageable, segmented manner with many, often redundant, interconnections strategically placed between network nodes. Mesh topologies provide efficient data transport. Many mesh applications are created through virtual private networks. Having many connections through a VPN is cost effective in comparison to a private-line network. A full mesh is when all nodes in the network have a connection to all other nodes. A partial mesh topology is when some nodes are connected to all other nodes.

Message Handling Service (MHS) - See X.400.

Message Handling Service Protocol (MHSP) - See X.400.

message mode service - In asynchronous transfer mode (ATM) a type of service for framed data in which only one interface data unit (IDU) is passed. In other words, it is a single-frame message. Message mode service is supported by ATM Adaptation Layer 3/4 (AAL 3/4). AAL 3/4 also supports streaming mode service, which is used for framed data in which multiple IDUs are passed in a data stream. See also AAL3/4, ATM, IDU, and streaming mode service.

message service - Also known as a messenger call.A service offered in developing countries that involves the telephone company’s sending a messenger to a remote village or other location without telephone service.The messenger carries a message advising a person to expect a telephone call at a particular pay station or telephone company office or agency in another village with telephone service. Messenger service is charged at a premium rate, with the cost of the messenger added to the cost of the call.

message switch - A device that switches complete messages within a data network.A message switch is a store-and-forward device that receives, stores, and forwards messages.

Message Telecommunications Service (MTS) - Synonymous with Direct Distance Dialing (DDD) See DDD.

Message Transfer Part - The function in SS7 networking that packetizes and de-packetizes signal data.

message unit - A collection of bits or characters that represent a fragment or segment (i.e., portion) of a message.A message unit can take the form of a block, cell, frame, or packet. See also block, cell, frame, message, and packet.

message waiting - A condition in which a voice message has been deposited in a voice mail system and is available for the telephone system (key telephone system (KTS), PBX, or Centrex system) user to retrieve.The voice messaging system advises the user of the message waiting by one of several means such as lighting a message waiting lamp on the station set, causing the telephone system to provide stuttered dial tone when the user lifts the handset to place a call, or perhaps ringing the station periodically. See also Centrex, KTS, PBX, and voice mail.

message - A complete thought or idea prepared for transmission. A message may consist of a single discrete set of data prepared for transmission as a whole, or it may be segmented, fragmented, or otherwise divided into multiple parts of the whole in the form of frames, blocks, packets, cells or other sets of data for enhanced effectiveness in transmission, switching or routing, format conversion, storage, etc.At the destination, the fragments or segments are reassembled into the complete message.

messenger call - See message service.

Metadata - From the Greek meta, meaning beside or after, and the Latin datum, meaning what is given. Data about data, that is, data that describes other data. For example, the title, subject, publisher, and author comprise metadata about its contents.

Metcalfe, Robert Melancton (1946–) - Credited as the inventor of the local area network (LAN) concept and the enabling technology. Metcalfe and his associates at the Xerox Palo Alto Research Center (Xerox PARC) developed the first LAN, which originally was known as the Altos Aloha Network as it connected Altos computers through a network based on the AlohaNet packet radio system technology developed at the University of Hawaii.The network later (1973) became known as Ethernet, from luminiferous ether, the omnipresent passive medium once conjectured to pervade all space and to support the propagation of electromagnetic energy, even through a vacuum. See also ether, Ethernet, LAN, Metcalfe’s law, and Xerox PARC.

Metcalfe’s law - The value of a telecommunications network is proportional to the square of the number of users (n ² ) of the system. Robert Metcalfe developed the law to describe the value of Ethernet, which he invented in early 1973. Metcalfe’s law is used to describe the value of network technologies such as telephones, fax machines, the Internet, and the World Wide Web (WWW). See also Ethernet and Metcalfe, Robert Melancton.

meter (m) - The basic SI unit of length, a meter is equivalent to approximately 1.094 yard, or 39.37 inches.The meter was originally determined by Napoleonic scientists at the French Academy of Sciences as one ten millionth (10 ^-7 ) of the distance between the North Pole and the Earth’s equator through Paris, France.The meter was then recorded as the distance between two fine lines engraved on a platinum-iridium bar kept at the International Bureau of Weights and Measures in Paris.The meter is now defined as the distance traveled by light in a vacuum in 1 ⁄299,792,458 seconds. See also SI.

Meters-to-Feet Conversion - One meter equals 3.28 feet. One kilometer equals 3280 feet.

metre - See meter.

Metric (Routing Measure) - A method by which a routing algorithm/ protocol determines that one route is better than another. This information is stored in routing tables. Metrics include bandwidth, communication cost, delay, hop count, load, best packet size, path cost, and reliability.

metric gauge - The measure of the diameter, or thickness, of a conductor, metric gauge is used outside of the United States and England, where American Wire Gauge (AWG) and British Standard Gauge (BSG) are used, respectively. In the metric gauge scale, the gauge is 10 times the diameter of the wire in millimeters (mm), so a 50 gauge metric wire would be 5 mm in diameter. Note that AWG is retrogressive, i.e., the larger the number, the thinner the conductor, but metric gauge is progressive. In order to avoid confusion, metric sized wire generally is specified in millimeters rather than metric gauge. See also AWG, BSG, and gauge.

metro Ethernet (metropolitan Ethernet) - An Ethernet LAN-to-LAN metropolitan area network (MAN) service offering that involves centrally positioning one or more gigabit Ethernet (GbE) or 10- gigabit Ethernet (10 GbE) switches in a metro area. Metro Ethernet offers the advantage of carrying all traffic in native Ethernet format, with no requirement for introducing SDH/SONET, frame relay, ATM or other Physical Layer or Data Link Layer protocols that can increase both complexity and cost, while adding overhead. See also 10GbE, ATM, Data Link Layer, Ethernet, frame relay, GbE, LAN, overhead, Physical Layer, protocol, SDH, and SONET.

Metropolitan Area Exchange (MAE) - See MAE.

metropolitan Ethernet (metro Ethernet) - See metro Ethernet.

Metropolitan Statistical Area (MSA) - A term that refers to the 306 metropolitan areas that the FCC manages cellular and PCS (Personal Communications Service) communications in. There are also RSA M 2/25/00 7:07 AM Page 383(Rural Statistical Area) markets that the FCC determined as separate from each other. 428 RSA markets are in the United States. Each statistical area, 734 in all, has at least two licensed service providers.

Metropolitan-Area Network (MAN) - A computer network that incorporates the local telephone company’s facilities to communicate. MAN networks connect other LANs or computers in a city together. T1 private lines are popular for MAN applications.

MF (Medium Frequency) - MF radio is in the frequency range of 300 kHz – 3 MHz and has a wavelength of 1 km – 100 m. MF radio has applications in navigation, AM radio, and mobile radio. See also electromagnetic spectrum, frequency, Hz, and wavelength.

MFA Forum - A special interest group formed of the MPLS Forum, Frame Relay Forum, and ATM Forum.The MFA Forum is a not-for-profit special interest group of manufacturers, vendors, carriers and others with interests in the development and promotion of multi-vendor, multi-service packet-based networks, associated applications, and interworking solutions.The emphasis, clearly, is on MPLS, frame relay, and ATM solutions. See also ATM, frame relay, and MPLS.

MFD - A less-common abbreviation for microfarad (uF). See Microfarad.

MFJ (Modified Final Judgement - Also known as the Divestiture Decree. In the United States, a negotiated settlement (1982) between the Department of Justice (DOJ) and AT&T as a modification to the 1956 Consent Decree.The MFJ forced AT&T to divest its wholly owned Bell Operating Companies (BOCs), which it later spun off to form the seven Regional Bell Operating Companies (RBOCs). Bell Communications Research (Bellcore) was established for RBOC common R&D support. Local Access and Transport Areas (LATAs) were established, with AT&T and other interexchange carriers (IXCs) permitted to provide interLATA service.The BOCs and other local exchange carriers (LECs) were granted exclusive rights to provide local and intraLATA long distance services.The MFJ established requirements for equal access, which allows a telephone subscriber to access any IXC through the LEC network to place a long distance call with equal ease, i.e., by dialing 1+.The MFJ also removed restrictions on AT&T against computer and related businesses. AT&T retained Long Lines (long distance), Bell Telephone Laboratories (R&D), and Western Electric (manufacturing). AT&T retained the embedded base of customer premises equipment (CPE).The MFJ took full effect January 1, 1984. See also Bellcore, BOC, Consent Decree, CPE, equal access, IXC, LATA, LEC, RBOC, and Telecommunications Act of 1996.

MFR (Multilink Frame Relay) - A service that bundles multiple T1 local loops to provide access to frame relay at speeds between T1 and T3. MFR essentially is a form of inverse multiplexing that also offers a significant measure of redundancy. See also frame relay, inverse multiplexing, local loop, T1, and T3.

MFS (Maximum Frame Size) - In asynchronous transfer mode (ATM), a traffic parameter describing the maximum size of a protocol data unit (PDU), or frame, supported by the network. MFS relates specifically to the guaranteed frame rate (GFR) service category. See also ATM, frame, GFR, PDU, and traffic parameter.

MG (Media Gateway) - See Media Gateway.

MGC (Media Gateway Controller) - See Media Gateway Controller.

MGCP (Media Gateway Control Protocol) - A predecessor to Media Gateway Control (Megaco). See Megaco.

MH (Modified Huffman) - A relatively simple encoding and compression algorithm used in facsimile machines that eliminates signal redundancy using a one-dimensional run-length encoding process to digitize and compress a document prior to transmission.The transmitting machine scans a document from top-tobottom and left-to-right, sensing dots of black and white color at an interval that depends on the resolution setting. Rather than transmitting a set of bits identifying the value (black or white, grayscale, or color) of each dot of each line, the scanning machine looks for redundancy, or runs, of dots of the same value.The machine then can transmit a set of bits identifying that value and the length of the run before the value changes from black to white, then transmit the length of the run of white, and so on.The receiving machine reverses the process, decompressing the data in order to reconstruct a facsimile of the original image. Modified Huffman is a lossless compression technique, as no data is lost during the compression and decompression processes. Group III fax machines operating at 9.6 kbps transmit documents at business letter quality at a rate of approximately 30 seconds per page, using the MH compression algorithm. MH is supported by all Group III devices as the lowest common denominator, yielding a compression ratio of about 20:1 in black and white. See also compression, encode, facsimile, Group III, Huffman coding, and run-length encoding.

Mho - Slang for Siemens, conductance. Conductance is often confused with being the opposite of resistance, which is not the case. Conductance is the reciprocal of resistance. To get the reciprocal of a resistance, simply take one divided by that number, or the resistance. If the resistance of a circuit or component is 500 ohms, then the conductance is equal to 1/500, which is 0.002, 2 millisiemens (2 mS). The higher the number in siemens, the higher the conductance and the lower the resistance.

MHS (Message Handling Service) - See X.400.

MHSP (Message Handling Service Protocol) - See X.400.

MHz (MegaHertz) - Million (10 ⁶ ) Hertz. A measure of bandwidth in an analog transmission. See also bandwidth, Hertz, and M.

MIB (Management Information Base) - A data file within a TCP/IPloaded network device, such as a PC or router that contains information about that device. The information that is contained in the MIB include hardware addresses (MAC address), counters, statistics, and routing tables. Each software/information category is referred to as an object. MIB works in conjunction with SNMP (Simple Network-Management Protocol).

mic (microphone) - See microphone.

Micro - The prefix for one trillionth. Abbreviated “u”, the Greek letter mu. One microfarad is equal to one trillionth of one farad and would be written 0.000,000,000,001 Farad, and abbreviated 1uF.

microbend - An abrupt discontinuity in the core/cladding interface of an optical fiber, a microbend can be in the form of a small bulge, dent, kink, or slight axial displacement. Microbends typically are caused by trauma to the fiber during the manufacturing process when the fibers are being drawn, coated, cabled, and reeled. Microbends also can be created by trauma during the installation process if, for example, metal clips are left on too long or tie wraps (i.e., zip ties) are cinched too tight and the fiber is compressed excessively. Although a microbend does not compromise the physical integrity of the fiber, it can cause a small amount of bending loss. See also bending loss and macrobend.

microbrowser - A simplified version of a browser for use in Web-enabled cellular terminals. See also browser, cellular, and We b.

microbusiness - An enterprise (i.e., for-profit commercial business) with fewer than 10 employees. Synonymous with SOHO. See also SME and SOHO.

microcell - In radio systems, an imprecise term referring to a relatively small area of coverage, of perhaps 6–8 miles in diameter.A microcell is smaller than a macrocell, but larger than a picocell. See also cell, femtocell, macrocell, and picocell.

Microchip - A reference to a VLSI (Very Large-Scale Integration) electronic device. For more information on microchips see Very Large-Scale Integration.

microcircuit - Synonymous with integrated circuit and microchip. See integrated circuit.

Microcom Networking Protocol (MNP) - See MNP.

Microcom Networking Protocol version 4 (MNP4) - See MNP4.

microcomputer - Synonymous with personal computer (PC).A computer built around a single central processing unit (CPU), a microcomputer is less capable than a midrange computer, or minicomputer, and certainly much less capable than a mainframe computer. See also CPU, mainframe computer, and minicomputer.

Microfarad - Usually represented as µF. Farad is the standard unit of capacitance. A capacitor is an electronic device that has two special properties. It only allows alternating current to pass through it, and it can store an electric charge. One of the many applications of capacitors is to filter alternating current (AC) out of DC power supplies and rectifiers. This is done by placing a capacitor from the DC output to ground. The capacitor appears as an easier path to voltage fluctuations and RFI, and as an impossible path to direct current (DC). Physically, a capacitor is two plates of metal, separated by an insulator (mylar is common). The physical size of a 1-F capacitor would be two sheets of tin foil the size of a football field, insulated (or separated) by a thin sheet of mylar. The farad is a huge unit of capacitance. This is why most capacitors are microfarads (uF) in value. For a schematic symbol of a capacitor, see Capacitance.

micron (µ) - One one-millionth ( 1 ⁄1,000,000) of a meter (m). Just to put it in perspective, a human hair is approximately 5–10µ in diameter.The core of a single-mode optical fiber is typically 5–10µ in diameter, and the core of a multimode fiber is typically either 50µ or 62.5µ in diameter. It is through the core of an optical fiber that the optical signal primarily is intended to travel. See also meter and nm.

Micron - A standard unit of measurement that is equal to 1 ⁄1000 of one millimeter or 1 ⁄25,000 of an inch. The core and cladding of fiber optic is measured in microns.

microphone (mic) - A device containing a transducer for converting sound waves into electrical signals that can then be amplified, transmitted, and output through a speaker. See also speaker and transducer.

Microprocessor - Also called a CPU (Central Processing Unit). The device within a computer (or switch or other machine that performs complex tasks) that controls the transfer of the individual instructions from one device connected to its bus (the data or I/O bus) to another, such as ROM, RAM, subcontrollers, decoders, and I/O Ports. Some communications equipment manufacturers actually call a certain card or portion of the system the CPU. That is because they include all of the RAM, subprocessors, buffers, clocking circuitry, and ROM as a part of the CPU.

Microsoft Certified Professional (MCP) - A well-known industry certification/training program offered by Microsoft and its training partners. The MCP certification is an in-depth learning track that incorporates Microsoft Networking products, Microsoft Applications, and general applications thereof. Up-to-date information regarding the MCP training program can be found through http://www.microsoft.com.

Microsoft Certified Systems Engineer (MCSE) - A well-known industry certification/training program offered by Microsoft and its training partners. The MCSE certification is an in-depth study program that incorporates Microsoft Networking products, such as Windows NT and Microsoft Exchange Server. The learning track for this program is extensive in Microsoft data-base applications and, in general, enterprise networking. Information regarding the MCP training program can be found through http://www.microsoft.com.

Microsoft Cluster Server (MSCS) - A feature of Windows NT that enables two NT servers that are connected on a network to logically function as one. Microsoft Cluster Server software also provides failure detection and the ability of one server to take over all functions if the other stops operating.

microwave - A form of radio transmission that uses ultra-high frequencies, developed out of experiments with radar (radio detecting and ranging) during the period preceding World War II. Developed by Harald T. Friis and his associates at AT&T Bell Telephone Laboratories, microwave systems are point-to-point radio systems operating in the GigaHertz (GHz) frequency range. The wavelength is in the millimeter range, which is to say that each electromagnetic cycle or waveform is in the range of a millimeter, which gives rise to the term microwave. As such high-frequency signals are especially susceptible to attenuation due to interaction with the physical matter in the atmosphere, terrestrial microwave radio beams must be tightly focused and must be amplified or repeated frequently. Microwave is a Line-of-Sight (LOS) technology as such high-frequency radio waves will not pass through solid objects of any significance. See also frequency, frequency spectrum, Friis, LOS, point-to-point, radar, radio, and wavelength.

MICS (Medical Implant Communications Service) - In the United States, an ultra-low power, mobile radio service for transmitting data in support of diagnostic or therapeutic functions associated with implanted medical devices, such as cardiac pacemakers and defibrillators. MICS requires no licensing, but MICS equipment must be operated by an authorized health care professional. MICS operates in the 402–405 MHz band. The Federal Communications Commission (FCC) regulates MICS, which is in the family of personal radio services. See also FCC and personal radio services.

Mid-Span- A telephone service wire that runs from a pole to a hook attached to a cable strand, then to a house or building.

middle earth orbit (MEO) - See MEO.

middleware - Programs that serve as intermediaries and translators between two different computing platforms, perhaps between client workstations requesting data or programs, and servers that provide them. Middleware is used in cross-platform situations where the clients and servers run on different operating systems (OSs) or where different database file structures are used. See also client, database, OS, server, and software.

midrange computer - See minicomputer.

Mileage of Circuit - The mileage of a private-line circuit is calculated using V and H coordinates. For a table of V&H coordinates, see Airline Mileage. AT&T developed a grid-coordinate system that gives every telephone central office in the United States a vertical and horizontal grid number. To calculate the mileage between two cities, the Pythagorean theorem is used. For an example of calculating airline mileage, see Airline Mileage.

Military Network (MILNET) - See MILNET.

Milli - Milli is the prefix for one-thousandth, abbreviated “m.” Five mA is equal to five thousandths of an amp and is written as 0.005 A or 5 mA.

millimeter (mm) - See mm.

MILNET (MILitary NETwork) - Also known as Defense Data Network (DDN). A packet network formed in 1983 of ARPANET users in European and Pacific Rim continents. See also ARPANET.

MIME (Multipurpose Internet Mail Extensions) - Extensions to the Simple Mail Transport Protocol (SMTP) used in IP-based networks for e-mail. MIME was developed to overcome SMTP’s ASCII limitation, which supports only plain text, i.e., unformatted text. MIME standards, as defined in the IETF RFC 2045, include a number of types and subtypes that support a range of data formats.Those types include the following:

• text type for textual messages. Subtypes include plain text for 7-bit ASCII, and rich text for enhanced text formatting.

• image type for image files. Subtypes include Graphics Interchange Format (GIF) and Joint Photographic Experts Group (JPEG).

• video type for time-varying picture images.The Moving Pictures Experts Group (MPEG) subtype is defined.

• audio type for basic audio data at 8 Khz.

• application type for executable code and any data that doesn’t fit neatly into any of the other types. Subtypes include octet-stream for binary data and postscript for PostScript files.

• message type for encapsulated messages within e-mail. Partial subtype permits a long e-mail message to be fragmented at the transmitter and reassembled at the receiver.

• multipart type supports the combination of multiple types into a single e-mail message.

MIME (Multipurpose Internet Mail Extensions) - This standard allows Internet mail users to attach nontext files, such as graphics (JPG), spreadsheets (XLS), and formatted documents (DOC) to their e-mail messages. The files can be binary, text, or multimedia. This standard is an enhancement to SMTP (Simple Mail-Transfer Protocol). The other important protocol with regard to Internet e-mail is POP (Post Office Protocol), which enables users to retrieve mail from outside networks. See also S/MIME.

MIMO (Multiple-Input Multiple-Output) - A technique for increasing wireless bandwidth by spatial antenna diversity, MIMO is incorporated into IEEE 802.11n specifications for wireless LAN (WLAN) and 802.16 specifications for broadband wireless access (BWA), more commonly known as WiMAX. As radio signals travel from transmitter to receiver in an enclosed space, they propagate along multiple paths. The signal elements traveling a direct path along a line of sight (LOS) arrive first and strongest.Those that travel the least direct paths, having reflected off walls, floors, ceiling, potted plants, people, and other obstructions, not only arrive last, but also suffer the greatest attenuation due to absorption, diffusion, and other contributing factors. MIMO technology employs multiple spatially diverse transmit antennas to actually encourage the signals to traverse multiple paths and multiple receive antennas to extract additional information from the signals that do so. MIMO algorithms in the receive device correlate and recombine the signals, realizing diversity gain, i.e., an increase in signal strength, in the process. MIMO technology doubles the spectral efficiency.The 802.11n MIMO technology, for example, is expected to yield a theoretical maximum signaling rate of 108 Mbps, compared to the 54 Mbps yielded by the earlier 802.11g technology. See also 802.11g, 802.11n, 802.16, absorption, attenuation, bandwidth, BWA, diffusion,gain, IEEE, LOS, spatial diversity, spectral efficiency, WiMAX, and WLAN.

Mini Connector - A physical connector used for PC applications and telecommunication hardware-interface applications.

Mini-T1 - Also called a Mini-T. A means of connecting a T1 circuit from one side of a building, to another. A T1 cross-connect that runs between two DSX (Digital Cross-Connect Panels) within a central office or other telecommunications environment. In central telecommunications environments, there are so many circuits and connections that it is necessary to create a circuit-tracking system just to get a connection made. These Mini-Ts commonly incorporate a building’s horizontal and vertical wiring system as well.

minicom - In the United Kingdom, a printing telegraph service widely used by those with hearing or speech impairments. Also generically known as TTY (TeleTYpewriter), TDD (Telecommunications Device for the Deaf) in the United States, and textphone In Europe. See also telegraph and teletype.

minicomputer - Synonymous with midrange computer. A medium-size computer that is less capable than a mainframe, but more so than a microcomputer.A minicomputer is designed to handle intensive and complex computational tasks, support a large number of users, and make use of large volumes of secondary storage. Minicomputers commonly are networked and share computational tasks in a distributed processing architecture.A minicomputer often is used as a front-end processor (FEP), managing the interface between a wide area network and a mainframe, and serving to manage user access privileges, deal with security issues, and otherwise relieve the mainframe of routine tasks. See also Internet, LAN, mainframe computer, and personal computer.

Minimum Cell Rate (MCR) - A parameter defined by the ATM forum for ATM traffic management. Minimum cell rate is defined only for Available Bit-Rate (ABR) transmissions and specifies the minimum value for the Allowed Cell Rate (ACR) parameter.

minimum point of entry (MPOE) - See MPOE.

MIPS (Millions of Instructions Per Second) - A measurement of how fast a microprocessor or central processor can execute program instructions.

MIS (Management Information System) - Also called IS (Information Systems). The part of a company that cares for data and voice communications/processing. The two have been merging together over the past decade and are becoming one entity as communications technology advances. The latest craze in MIS is CTI (Computer Telephone Integration), which enables users to track telecommunications events and operate telecommunications equipment on a computer, with a GUI (Graphical User Interface, such as Windows). IVR (Integrated Voice Response) is a form of CTI.

MLT (Mechanized Line Testing) - Also called DATU (Direct-Access Test Unit). MLT and DATU is equipment that is either added on or built in to a central-office switch. DATU allows a technician or customer-service agent to dial the phone number of the DATU or MLT equipment and execute a test for shorts, opens, and grounds remotely. In response to a digital voice, the technician enters a password and a choice of options. The results of the test can be read back to the technician by a digital recording or sent to them via an alphanumeric pager. DATU units can also send a locating tone on the technicians choice of TIP, RING, or both TIP and RING. The test unit can also short lines and remove battery voltage for testing.

MLT (Multi-Level Transition) A technique used in 100Base-TX Ethernet to reduce the signaling rate and thereby lower the carrier frequency in consideration of attenuation issues over twisted pair cable.The line coding technique used in 100Base-TX is 4B/5B, which increases the signaling rate to 125 Mbps in support of a datastream of 100 Mbps. MLT-3 is a ternary approach that cycles through three signal levels in the pattern +V, 0V, –V and adds a scrambling step before placing the signal on the line. In combination, these intermediate steps support a signaling rate of 125 Mbps while placing the main spectral energy at a frequency of only 31.25 MHz.That low frequency results in improved signal quality and a reduced potential for interference. See also 100Base-TX, 4B/5B, attenuation, carrier, frequency, line coding, signal, signaling rate, and twisted pair.

mm (millimeter) One one-thousandth (10 ^-3 , or 1 ⁄1,000) of a meter.Your little fingernail is about 1 mm thick and it grows at a rate of about 1 nm (nanometer) per second. If a nanometer were scaled up to the width of your little fingernail, your fingernail would be about the size of Delaware. See also meter.

Mm-Band - The band of frequencies designated by the IEEE between 110 GHz and 300 GHz. For a table, see IEEE Radar Band Designation.

MMDS (Multichannel Multipoint Distribution Services) - A point-to-multipoint microwave technology operating in five bands in the 2.15–2.68 GHz range in the United States and Canada and in the 3.5 GHz range elsewhere, MMDS was developed for television transmission. MMDS subsequently was tweaked for two-way Internet access applications but is bandwidth-limited at only 200 MHz, which does not compare favorably with most alternative access technologies. MMDS operates on the basis of a macrocell up to 31 miles (50 kilometers) miles in radius.The transmit antenna is placed on a hilltop, tall building, or other point with maximum lookdown in order to maximize line of sight (LOS).The antenna may be omnidirectional or may be sectorized in order to improve spectrum efficiency. MMDS has been rendered obsolete and incorporated into WiMAX. See also bandwidth, Internet, LOS,macrocell,microwave, pointto-multipoint, spectral efficiency, and WiMAX.

MMF (MultiMode Fiber) - A type of optical fiber with a relatively thick inner core that allows light rays to propagate along multiple modes, or physical paths, through the fiber.The number of modes is sensitive to the core diameter, the numerical aperture (NA), and the wavelength.A core diameter that is large in relationship to the wavelength supports a large number of modes. MMF typically has a core diameter of 62.5 microns or 50 microns.The light source used in an MMF transmission system generally is either a light-emitting diode (LED) or a vertical cavity surface-emitting laser (VCSEL). LEDs operate in the 850 nm range, emit poorly focused light beams, and couple effectively to 62.5 micron MMF.VCSELs typically operate in the 1300 nm and 1310 nm ranges, emit well-focused light beams, and couple effectively to both 62.5 micron and 50.0 micron fiber.The numerical aperture mathematically describes the angle of acceptance, which defines the light-gathering ability of the fiber. These interrelated terms all establish the size of the angle at which the light source can effectively inject a signal into the fiber.The wider the angle from axial, the higher the mode, the more modes supported, the more light reaches the far end. So, a fiber optic transmission system (FOTS) employing an LED connected to a fiber with a 62.5 micron core and a relatively large numerical aperture supports a great many modes. A FOTS employing a VSCEL connected to a fiber with a 50.0 micron core and a relatively small numerical aperture supports many fewer modes of light.The latter example is preferable.There are two general categories of modes:

• Low-order modes are relatively straight paths that signals or signal elements travel as they propagate.As low-order modes are relatively direct, the signals encounter and interact with relatively little physical matter and attenuate relatively little. Such signals also reach a distant point in the fiber circuit relatively soon as they have traveled a short distance.

• High-order modes are relatively transverse paths signals or signal elements travel as they propagate through the fiber.As these paths are highly indirect, the signals encounter and interact with considerable physical matter and, therefore, attenuate to a greater extent than those propagating along loworder modes. Such signals also reach a distant point in the fiber circuit relatively late, as they have traveled a long distance.

Most MMF also is graded-index fiber, rather than step-index. Graded-index fiber compensates for high order modes by accepting errant light rays into the cladding, which comprises a great many layers of glass of slightly and progressively lower refractive index, or index of refraction (IOR).As a result, the errant signal components gradually increase in velocity and refract, or bend, back towards the core, where they rejoin other signal elements that propagated along other modes, i.e., took more or less direct paths. To some extent, graded-index fiber mitigates issues of pulse dispersion, a type of inter-symbol interference that occurs when various signal elements of various strengths overrun each other and that is especially problematic in high-bandwidth applications, as bit times (pulse lengths) are very short and pulses must be very close together. Issues of attenuation and pulse dispersion combine to limit MMF to relatively short-haul, low-speed applications such as local area networks (LANs) running at 1 Gbps or less. See also cladding, core, graded-index fiber, IOR, LED, MMF, mode, numerical aperture, pulse dispersion, reflection, refraction, SMF, stepindex fiber, VCSEL, and wavelength.

MMR (Modified Modified Read) - A compression algorithm used in Group III and Group IV facsimile machines operating at 14.4 kbps or better and specified in ITU-T Recommendation T.6, MMR uses a two-dimensional compression technique that permits the transmitting modem to view and consider multiple lines of data during the encoding process.At 28.8 kbps, Group III machines can transmit a page in approximately four (4) seconds using a V.34 modem employing Quadrature Amplitude Modulation (QAM). At 33.6 kbps, Group III machines can transmit a page in about three (3) seconds using a V.34bis (aka V.34+) modem employing Trellis Coding Modulation (TCM). See also compression, encode, facsimile, Group III, Group IV, ITU-T, modem, QAM, T. 6, TCM, V.34, and V.34bis.

MMS (Multimedia Messaging Service) - A messaging service offered on many digital cellular networks, MMS is an evolution of Short Message Service (SMS) that supports text messages with audio, image, and video attachments. See also SMS.

Mnemonic - A computer programming command that is an abbreviation or shortened version of what the command does. PRT is a mnemonic in Nortel Networks applications software that makes a switch “print” a specified list of information. LOGI is a mnemonic for “log in.”

MNP (Microcom Networking Protocol) - An early protocol for modem communications, MNP was among the first to include error correction. MNP subsequently was incorporated into the ITU-T V.42 Recommendation. See also ITU-T, modem, protocol, and V Series.

MNP 4 (Microcom Networking Protocol class 4) - An enhancement to the MNP family of modem protocols, MNP 4 added variable packet assembly, which adjusts the packet size downward to compensate for line conditions that cause dropped packets. (Note: MNP supports packets as small as 64 bytes and as large as 256 bytes.) Reducing the packet size reduces the raw packet efficiency, as the ratio of payload to overhead drops, but increases throughput under such conditions, as smaller packets are more likely to transit the connection without error and, therefore, unlikely to require retransmission. See also byte, MNP, modem, overhead, packet, payload, protocol, and throughput.

MNS (Master of Network Science) - A well-known industry certification/training program offered by 3COM. This program is actually referred to as a credential, rather than a certification by 3COM. Several hardware and administration intensive programs are available under the MNS family of certifications. The first is the MNS LAN Solutions track, which includes training on high-performance 3COM LAN switching equipment, seven exams, and a lab test. Another is the MNS LAN Solutions Plus track, which requires completion of the LAN Solutions requirements, and extends the trainee’s knowledge into the ATM products offered by 3COM. Another example track is the MNS Network Architecture, which provides a rounded study of enterprise networking. Other MNS tracks include the MNS Network Management, MNS WAN Solutions, and MNS Remote-Access Solutions. Information regarding the 3COM MNS training programs can be found at http://www.3com.com.

mobile satellite system (MSS) - See MSS.

mobile station (MS) - See MS.

mobile telephone switching office (MTSO) - See MTSO.

mobile traffic switching office (MTSO) - See MTSO.

Mobile - A communications link made by portable radio.

Mobitex (Mobile text) - Low-speed, packet-switched wireless data networks deployed in Europe and the United States alongside cellular radio networks. Developed jointly by Ericsson and Swedish Telecom, Mobitex offers runs in Europe in the 400–450 MHz band and in the United States in the 800 and 900 MHz bands, although it will run in any band. Mobitex channel spacing of 12.5 kHz supports theoretical data transmission rates of 8 kbps through Gaussian minimum-shift keying (GMSK) modulation. Mobitex packets are up to 512 octets, including overhead, using a slotted Aloha protocol. Mobitex networks support short message service (SMS), e-mail, and Internet access. See also cellular radio, channel, e-mail, GMSK, Internet, overhead, packet switch, protocol, slotted Aloha, and SMS.

modal bandwidth - The measure of the capacity of a multimode fiber (MMF) in Gbps applications, modal bandwidth is expressed in MHz/km. A MMF with a higher modal bandwidth will support data transmission at a given rate over a longer distance. Modal bandwidth is determined by the dispersion characteristics of the fiber, including both modal dispersion and chromatic dispersion. MMF core diameter (50µ vs. 62.5µ) is one of the fiber attributes that influence modal bandwidth. See also chromatic dispersion, dispersion, MMF, and modal dispersion.

Modal Dispersion - As light travels down a fiber optic, each individual light ray/particle takes a different path. Imagine that a bunch of small rubber balls are shot down a long tube at the same time. Each ball will bounce differently as they make their way around curves. At the end of the tube, the balls will come out at different times. Light behaves the same way. A sudden pulse of light on one side of a fiber optic will disperse itself as it traverses down the fiber, causing the pulse of light at the far end to be more of a “blip.”

modal equilibrium - More correctly known as equilibrium mode distribution. Referring to a state in which optical power is evenly distributed across all modes, i.e., physical paths in an optical fiber. See also mode and optical fiber.

Modal Loss - The attenuation of a light signal as it travels through a fiber optic because of tight bends. See Modal Dispersion.

modal noise - 1. Noise caused by interactions between the fiber and the connectors, modal noise results in power fluctuations at the receivers, increasing the signal-to-noise ratio (SNR) and limiting the length of the fiber link. Modal noise occurs only when high power lasers are used in conjunction with multimode fiber (MMF). See also SNR. 2. Noise generated in a multimode fiber optic transmission system (FOTS) by the combination of mode-dependent attenuation and fluctuations in the distribution of optical energy, i.e., optical power density, among the guided modes or in their relative phases. Synonymous with speckle noise. See also MMF and power density.

mode field diameter - A measure of the diameter of the area in which an optical signal propagates through a single-mode fiber (SMF).Although most of the signal is confined to the core, some of the signal travels in the cladding, so the mode field diameter is of greater significance than the core diameter. See also cladding, core, optical fiber, and SMF.

mode filter - A device that attenuates high-order modes in an optical fiber.As high-order modes can be lost in the cladding and, therefore, serve no useful purpose, a mode filter essentially strips them out of the transmitted signal. See also attenuation, high-order mode, and optical fiber.

mode - The physical path a signal or signal component follows as it propagates through a waveguide. Some signal components travel directly through the center of the waveguide, at least theoretically, and, therefore, travel the shortest possible distance between the point at which they enter the waveguide and the point at which they exit the waveguide. Other modes take more transverse paths, striking and reflecting back and forth off of the interface between the core and cladding as they propagate through an optical fiber, for example. Low-order modes take modestly transverse paths, while high-order modes take considerably more transverse paths. Some modes at the transmitter can be so transverse as to strike the corecladding interface at less than the critical angle and, therefore, penetrate the interface and be permanently lost in the cladding. Figure M-4 illustrates the differences between these paths. See also cladding, core, critical angle, and waveguide.

Modem (Modulate/Demodulate) - A device that transmits digital information over a telephone line (standard POTS line) or a private circuit (56K line). Modems modulate the digital information before transmitting it. One standard of modulation is FSK (Frequency-Shift Keying). Each M 2/25/00 7:07 AM Page 389positive (1) bit is sent as a frequency or “pitch” of sound and each (0) bit is transmitted as a different frequency or “pitch” of sound.

Modem Eliminator - A device similar to the baseband modem in that it does not do any actual modulation, and allows connection of two DTE devices. It is intended for very short distances, for example, from one device to another right next to it. Modem eliminators connect at the ITU/T V.24 and V.28 (or EIA 232-D, where only the names of the pins are different) interface-level standard. Some modem eliminators are simply a null/modem cable. Some have their own clock source added for conditioning or buffering the transmission.

Modem on Hold (MoH) - A feature of V.92 modems that puts a data session on hold when it detects a voice call, either incoming or outgoing, through a call waiting indication, and gracefully resumes that session when the voice call is terminated.Thereby,V.92 allows a single analog line to be used for both voice and data. MoH requires that the line be equipped with call waiting. See also call waiting, hold, modem, and V Series.

Modem Standards- Standard XFR rate Modulation Duplex V.21 / Bell 103 300 FSK Full duplex V.22 1200 DPSK Full duplex V.22 bis 2400 QAM Full duplex V.23 / Bell 202 1200/75 FSK Half duplex Bell 212A 1200 DPSK Full duplex V.32 9600 QAM Full duplex EC V.32 bis 14,400 TCM Full duplex EC V.32 ter 19,200 TCM Full duplex EC V.34 28,800 TCM FULL DUPLEX EC V.90 56,600 TCM EC�Error Correction

Modified Final Judgement (MFJ) -See MFJ.

Modified Huffman (MH) - See MH.

Modified Modified Read (MMR) - See MMR.

Modified Read (MR) - See MR.

Modular Adapter - A device used to interconnect one wire/cable type with another, without the use of termination blocks. Also called harmonica adapters. See also 258A Adapter.

Modular Jack - A jack that is equipped with a plug so that devices can be easily attached and detached. Old jacks, still found in old homes, are hard wired, which means that the telephone cord had to be permanently affixed to the terminals inside the jack with screws. The same went for nonmodular or hard-wired telephones. If you wanted to have a longer cord, you couldn’t buy one at the store and just plug it in. You had to call the phone company and they would send a telephone technician out to install a longer cord for you.

Modular - A reference to equipment that is equipped with plug-in type interfaces, rather than being hard wired.

modulate - 1. Change or vary in some way. 2. In acoustics, modulation involves varying the pitch, tone, or volume of an audio signal, such as the human voice. 3. In physics, modulation involves varying the characteristics of an electromagnetic waveform, generally by varying the amplitude, frequency, or phase, or some combination. 4. In telecommunications, modems perform signal modulation and demodulation processes to encode information from digital devices onto signals carried by analog circuits. Digital Service Units (DSUs) and various other devices modulate carrier waves to place digital signals on digital circuits. See also AM, FM, modem, PM, and PSK. 5. In telecommunications, codecs code analog signals into digital format prior to transmission over a digital circuit, and decode them on the receiving end of the connection. Codecs use a variety of modulation techniques, including adaptive differential pulse code modulation (ADPCM), differential pulse code modulation (DPCM), and pulse code modulation (PCM). See also ADPCM, analog, codec, digital, DPCM, and PCM.

Modulation - A method of varying a radio carrier frequency so that a signal (the variations) can ride on it. After the carrier signal has the variations imposed on it, it is amplified and transmitted. The variations in the signal are then detected by the receiver. The variations in the carrier signal are actually voices, music, or whatever is to be transmitted. The different methods of modulating a carrier frequency are AM (Amplitude Modulation), FM (Frequency Modulation), and PM (Phase Modulation).

modulo - 1. An integer that leaves the same remainder when it is the divisor of two other integers. For example, 6 modulo 4 = 2 and 14 modulo 4 = 2. In other words, 6 divided by four results in a remainder of 2, and 14 divided by 4 leaves a remainder of 2. 2. In telecommunications, referring to the window size, which identifies the maximum number of bytes, frames, or packets that a device can transmit without an acknowledgement from the receiver.As an example, the X.25 protocol has a windowing mechanism that specifies the number of packets that one router can transmit to another without receiving an acknowledgement.TCP has a similar mechanism that is expresses in bytes.Windowing serves as flow control and error control mechanisms. Modulo 8, for example, allows the transmission of 7 datasets without an acknowledgement, but requires an acknowledgement after the 8th dataset. See also error control, flow control, TCP, and X.25.

MoH (Modem on Hold) - See Modem on Hold.

MOH (Music On Hold) - A feature of PBX and key systems that allows an audio signal from a tape recorder, radio, or other audio device to be fed to callers that are on hold. The PBX or key system user manual designates how to cross connect the audio signal into the system.

MOM (Manager Of Managers) - A high-level network management system (NMS) that gathers and correlates alarms and alerts from multiple element management systems (EMSs). See also EMS and NMS.

monomode fiber - Synonymous with single-mode fiber (SMF). See SMF.

Monopole Antenna - An antenna mast of one pole extending from the ground. These are popular with cellular and PCS wireless services.

monopoly - A condition in which a single company is the exclusive manufacturer of a product or provider of a service or controls an entire industry, thereby allowing the company to fix prices.A monopolistic condition can arise when a company invents and patents a product that is so compelling that an entire industry builds up around it. If the company continues to develop and patent further versions of the product, it can extend that monopolistic condition, perhaps acquiring or overwhelming competitors. Natural monopoly, a concept developed by political economist John Stuart Mill (1806–1873), refers to utility services that are so capital-intensive and right-of-way intensive that it just doesn’t make sense to have more than one provider. Natural monopolies include transportation infrastructure such as roads, bridges, ferries, subways, and railroads, as well as utility infrastructure such as water, natural gas, electricity, sewer, cable television, and wireline telephone.Well, cable television and wireline telephone infrastructure used to be considered natural monopolies, but it’s not quite that simple any longer. See also Graham-Willis Act.

monotonic - 1. Unvarying in quality or characteristics, such as pitch, tone, style, or color. 2. In mathematics, steadily increasing or decreasing in value. See also oscillator.

Moore, Gordon E. (1929–) - A co-founder of Intel, Moore is best known for his 1965 prediction that the number of transistors on an integrated circuit would roughly double every year for the foreseeable future. Moore updated the prediction in 1975, stating that the number of transistors on an integrated circuit for minimum component cost doubles approximately every 2 years.The prediction, known as Moore’s Law, has proved largely true for the last 40+ years. A chemist and physicist by training, Moore retired as Chief Executive Officer (CEO) of Intel in 1987. See also Moore’s Law.

Moore’s Law - The observation of Gordon E. Moore (1929–), co-founder of Intel, that the complexity of semiconductor components had roughly doubled per year since the first prototype microchip and that the rate would remain nearly constant for at least 10 years. Moore stated the observation in an article entitled “Cramming more components onto integrated circuits” that appeared in the April 19, 1965 edition of Electronics magazine. In the article, Moore predicted that “With unit cost falling as the number of components per circuit rises, by 1975 economics may dictate squeezing as many as 65,000 components on a single chip.” In 1975, Moore updated the prediction, stating that the number of transistors on an integrated circuit for minimum component cost doubles approximately every 2 years.As a point of interest, the first microprocessor had 2,200 transistors. In 2007, Intel placed more than 1,700,000,000 transistors on its Itanium chip.See also Moore, Gordon E.

MOP (Method Of Procedure) - When network engineers design an addition to a network (a new node in a SONET ring is a good example), they write a MOP. The MOP instructs technicians step by step which circuits to reroute, which circuit cards to swap and when, and when to activate the new node. MOPs are a crucial communication tool between engineers and technicians.

Morse Code - In 1836, Samuel F.B. Morse built the first working telegraph. He also derived a code that enabled people to exchange information. The Morse Code is still in use today. It is used by amateur radio operators, ships at sea, etc.

Morse, Samuel Finley Breese (1791–1872) - Generally recognized as the inventor of the electric telegraph and the Morse code cipher. Although not actually the inventor of the original electric telegraph, Morse partnered with Leonard Gale and Alfred Vail, who improved on Morse’s early telegraph models, and in 1837 filed for a patent that was finally granted in 1840. Perhaps just as importantly, Morse is credited with developing the binary telegraphic cipher known as Morse code, although many claimed at the time that Vail actually invented the code. In 1844, Morse secured funding for the first intercity telegraph line in the United States, which ran from the railway depot in Baltimore, Maryland, to the Supreme Court Room in the United States Capitol in Washington, D.C. The first message sent over that line was the biblical phrase “What hath God wrought!,” which was chosen by Annie Elllsworth, the daughter of a classmate at Yale University. See also Morse code and telegraph.

MOS (Mean Opinion Score) - See P.800.

MOS - Another reference to CMOS (Complementary Metal-Oxide Semiconductor). The reason why many computer and other high-speed components are static sensitive. CMOS’ largest advantage over TTL is their low power consumption (less than 1 ⁄10 of TTL); they switch on without drawing very much current in contrast to TTL technology. Because very little current is drawn, very little power is consumed and very little heat is given off. This allows the devices to be much smaller.

Mosaic - An Internet browser that provides a consistent user interface available in versions to support Macintosh, Microsoft Windows, and Unix–X Windows. Mosaic can be used over dedicated or dial-up connections. In dial-up mode, the Internet service provider (ISP) must support either Serial Line Internet Protocol (SLIP) or Point-to-Point Protocol (PPP). Mosaic enables the easy browsing of WWW resources through menus that support hypertext. Selected files can include audio and graphics, both of which can be viewed without the requirement to download the subject file. Mosaic was developed by a team led by Marc Andreessen at the National Center for Supercomputing (NCSA) at the University of Illinois Urbana-Champaign campus. Mosaic technology is licensed by the NCSA for commercial application. Spyglass, Inc. licensed well over 12 million copies of Mosaic to IBM, DEC, and others who intended to resell the company’s Enhanced Mosaic, which includes security mechanisms based on Secure Hypertext Transport Protocol (S-HTTP). Ultimately, Spyglass Mosaic was licensed to Microsoft, where it formed the basis for Internet Explorer (IE). Mosaic also is known as NCSA Mosaic. Note: Marc Andreessen later developed the Netscape Navigator browser, as well. See also browser, hypertext, Internet, Internet Explorer, ISP, Mozilla, Netscape Navigator, PPP, S-HTTP, SLIP, and WWW.

mote - From Old English mot, and akin to Middle Dutch and Fris meaning sand or grit. 1. A speck of dust or other tiny particle. 2. In telecommunications, a wireless sensor so tiny as to compare to a speck of dust. About the size of a grain of sand, a mote comprises sensors, a processor, a bidirectional antenna, and a power supply.Also known as smart dust, future applications for motes are many.The military is developing motes that can be spread from the air to gather and transmit information about enemy troop movements. Civil engineers intend to embed motes in concrete to monitor and report on the condition of bridges and roadways. Spread around a warehouse housing weapons, financial records, or other sensitive materials, motes can be used to sense and report security violations.The ZigBee Alliance is involved in the development of standards for mote mesh networking. See also ZigBee and ZigBee Alliance.

motion picture quality - Referring to video quality at a frame rate of 24 frames per second (fps) or more. See also broadcast quality and frame rate.

Motion-JPEG (Motion Joint Photographic Experts Group) - A version of JPEG designed specifically for use in editing of digital video. See also JPEG.

Mouse - A serial-bus I/O device used to point and select objects on a computer monitor screen. There are many manufacturers of mouse hardware and many variations thereof. Some mice have fixed roller balls, some are used with the thumb, others with the forefinger. The three major types of mice interfaces are: USB, serial, and PS2. They are distinguishable by their connector interface.

Moving Picture Experts Group (MPEG) - See MPEG.

Mozilla - Originally a code name for Netscape Navigator, Mozilla is a contraction of Mosaic killer, referring to the hope that it would unseat Mosaic as the top Web browser, and Godzilla, referring to the fictional monster of Japanese science fiction movies. Mozilla now refers to an open source application suite based on the Netscape Navigator source code, which was released by Netscape in 1998 under an open source license. See also browser, Firefox, Mosaic, Netscape Navigator, and We b.

MP (Multipoint Processor) - See MCU.

MPEG (Motion Picture Experts Group) - A widely used menu of standards for compressing video. MPEG1 is a bit-stream standard for compressed video and audio optimized to fit into a maximum bandwidth of 1.5 Mbps and with less resolution, MPEG2 is intended for higher-quality video-on-demand applications and runs at data rates between four and nine Mbps. MPEG4 is a low-bit-rate compression algorithm intended for 64-Kbps connections.

MPEG-1 - The ISO/IEC International Standard (IS 11172) for storage and retrieval of moving pictures and audio on storage media such as Compact Disc (CD). MPEG-1 provides VHS quality at 1.544 Mbps and is compatible with single-speed CD-ROM technology. MPEG-1 integrates synchronous and isochronous audio with video, and permits the random access required by interactive multimedia applications such as video games. Intended for limited-bandwidth transmission, it provides acceptable quality and output compatible with standard televisions. MPEG-1 supports video compression of about 100:1. MPEG-1 standards are the basis for the MP3 (MPEG-1 Audio Layer 3) audio data encoding system. See also audio, bandwidth, compression, encode, IEC, ISO, isochronous, MP3, MPEG, synchronous, and video.

MPEG-2 - The ISO/IEC International Standard (IS 13818) for digital television (DTV). MPEG-2 was conceived as an encoding and compression standard for broadcast television based on interlaced scanning of images at 720 × 480 pixels at a rate of 30 frames per second (fps). Although MPEG-2 supports compression rates as high as 200:1, it is much more bandwidth-intensive (4–100 Mbps) than MPEG-1. MPEG-2, however, provides much better resolution and image quality. MPEG-2 is used in direct broadcast satellite (DBS) services and is the compression technique of choice in a convergence scenario. MPEG-3, designed for high definition television (HDTV) application, was folded into MPEG-2. See also bandwidth, broadcast television, compression, convergence,DBS,DTV, fps,HDTV,IEC, interlaced scanning,ISO,MPEG,MPEG-1, and resolution.

MPEG-21 - The ISO/IEC international standard officially is known as the Multimedia Framework, is an ongoing effort to determine how various multimedia components fit together and to identify new multimedia infrastructure standards that may be required. MPEC-21 also deals with issues of content identification, description, and security. In large part, the focus of MPEG-21 is on the protection of intellectual property through security mechanisms designed to prevent unauthorized access and modification of multimedia content. See also intellectual property, MPEG, and multimedia.

MPEG-3 - The ISO/IEC international standard for high definition television (HDTV), MPEG-3 was folded into MPEG-2 in 1992. See also HDTV, IEC, ISO, and MPEG-2.

MPEG-4 - The ISO/IEC International Standard (IS 14496) for multimedia applications. MPEG-4 is a low bit-rate standard for encoding and compression intended for application in broadcast television, videophones, and mobile phones and other small handheld devices. MPEG-4 is designed for IMT2000 wireless applications at rates of up to 384 kbps upstream and 2 Mbps downstream. MPEG-4 deals with the coded representation of audiovisual objects, both natural and synthetic, and their multiplexing and demultiplexing for transmission, playback, and storage. See also compression, downstream, encode, IEC, ISO, MPEG, multimedia, multiplex, and upstream.

MPEG-7 - The ISO/IEC international standard officially known as the Multimedia Content Description Interface, MPEG-7 is intended to be the content representation standard for multimedia information search, filtering, management, processing, and retrieval. MPEG-7 essentially is a metadata standard based on XML (eXtensible Markup Language) for describing multimedia content features in order that one can easily search for multimedia content on the Web. See also MPEG, multimedia, We b, and XML.

MPI (MultiPath Interference) - See multipath fading.

MPI specter (MultiPath Interference specter) - Referring to the ghosting effect, which occurs when the multiple paths of a television (TV) video signal are relatively long and when some reflected signals, therefore, arrive on a significantly delayed basis in a phenomenon known variously as multipath fading and delay spread.This ghosting effect is particularly evident in poorly installed coax-based CATV systems, and in traditional broadcast radio TV reception in mountainous areas. See also broadcast, CATV, coaxial cable, delay spread, ghosting, multipath fading, path, radio, TV, and video.

MPLS (MultiProtocol Label Switching) - Defined by the IETF in RFC 2702 (1999) as a labelswapping framework with Network Layer (Layer 3) routing, MPLS integrates Data Link Layer (Layer 2) information about network links into Layer 3 routing logic. MPLS enables routers to make packet forwarding decisions very quickly on the basis of short labels, rather than making complex routing decisions after analyzing lengthy packet headers. MPLS is designed to work through routers at even higher speed than ATM switches, while realizing much of the flexibility of an Internet Protocol (IP) network. MPLS works on the basis of forwarding equivalence classes (FECs) and flows. A flow consists of packets between common endpoints identified by features such as network addresses and port numbers.An FEC is a class of packets, all of which are treated the same in terms of destination, priority level, and so on.At the ingress edge of the carrier network, a label edge router (LER) identifies the flow based on the IP header, the interface through which the packet arrives, the packet type (unicast, multicast, or anycast), or perhaps information in the IPv4 Type of Service (ToS) field.The LER attaches a 32-bit MPLS header that includes a 20-bit label, or tag, to that packet and to each subsequent packet of the flow. The LER uses a Label Distribution Protocol (LDP) to distribute the labels or tags to each intervening Label Switching Router (LSR) in the network core, identifying the treatment that should be afforded all packets in the flows on that particular Label Switched Path (LSP). If the traffic engineering options are exercised, traffic is balanced between optimum and non-optimum paths, and congestion is minimized. Otherwise, the traffic takes the same paths that IP packets would take, as MPLS nodes use IP routing protocols, such as the Border Gateway Protocol (BGP), Open Shortest Path First (OSPF), and Routing Information Protocol (RIP) to distribute the labels. From edge-to-edge through the core of the network, each LSR makes note of the incoming port number and analyzes the label associated with each packet in order to select the appropriate Label Switched Path (LSP) over which the packet is to be forwarded on its way to the next LSR.The LSR then switches the existing label for a new one, and forwards it.Thereby, and through a series of links, the end-to-end path is set up and maintained for a given traffic flow.The more complex processes of complete header analysis and routing table lookup are performed only at the ingress edge of the network. In the core of the network, only the abbreviated MPLS label is analyzed in order to make a relatively simple and straightforward packet forwarding decision. All in all, MPLS simplifies the routing process and reduces latency. At the egress LER, the tag is stripped away, as it no longer has any purpose. The structure of the 32-bit MPLS header is as follows:

• Label: 20 bits matching the packet to the LSP.

• Experimental (EXP): 3 bits indicating the precedence, or packet queuing priority, for class of service (CoS) purposes.

• Stack (S): The stacking bit is set at 1 to indicate the last (i.e., innermost) MPLS header in a stack of headers. Outer tags carry a 0 bit in this position. MPLS virtual private networks (VPNs) involve hierarchical routing logic that requires multiple headers.As many as four MPLS headers can be contained within a stack.

• Time To Live (TTL): Copied from the IP TTL.The TTL is a hop count, with a default value of 64.

MPLS is based on several vendor-specific protocols, including Cisco’s Tag Switching, Ipsilon’s IP Switching, and IBM’s ARIS technology. See also anycast, ATM, BGP, congestion, CoS, Data Link Layer, endpoint, FEC, flow, header, hop, IETF, IP, IPv4, IPv6, label, latency, LDP, LER, link, LSP, LSR, multicast, Network Layer, OSPF, packet, port, queue, RIP, router, routing, To S, traffic engineering, TTL, switch, unicast, and VPN.

MPLS Forum - A not-for-profit special interest group of manufacturers, vendors, carriers and others with interests in the development and promotion of Multiprotocol Label Switching (MPLS) technology. The MPLS Forum merged with the ATM Forum and Frame Relay Forum to form the MFA Forum. See also MFA Forum and MPLS.

MPOA (Multiprotocol Over ATM) - An ATM Forum standardization effort that specifies how existing and future network-layer protocols, such as IP, IPv6, AppleTalk, and IPX run over an ATM network with directly attached hosts, routers, and multilayer LAN switches. See also LocalArea Network Emulation.

MPOE (Minimum Point of Entry) - The closest logical and practical point within the customer domain for the placement of a demarcation point (demarc), which sets the boundary of responsibility between the PSTN carrier and the customer. In a high-rise office building, for example, the MPOE typically is defined as a point of the entrance cable 12 inches from the inside wall. See also carrier, demarc, and PSTN.

MPPP (Multilink Point-to-Point Protocol) - Based on Internet Engineering Task Force (IETF) RFC 1990, MPPP supports the linking, or bonding, of multiple links between systems to increase the available bandwidth. MPPP applications include narrowband ISDN (N-ISDN) and analog modem connections. See also AODI, bonding, IETF, modem, and N-ISDN.

MQA (Multiple Queue Assignment) - A reference to the ability of an ACD system to allow agents to log into multiple queues. A Northern Telecom Meridian PBX with MQA software is capable of allowing agents to log into and receive calls from five separate queues. When properly used, MQA makes call centers more efficient by allowing agents to share the incoming call load more effectively. See also Skills Based Routing.

MR (Modified Read) - An optional compression algorithm used in some Group III facsimile machines, MR scans and compresses the first line using Modified Huffman (MH) compression. Subsequent lines are scanned and compared to the first line, and only the differences (deltas) are encoded and transmitted.This process continues for some predetermined number of lines in a group, at which point the process is reset and the first line in another group is encoded using MH, and so on. MR is particularly effective if there are few differences between lines in a document. See also compression, facsimile, Group III, and MH.

MS (Mobile Station) - A wireless portable terminal device used in a radio network designed to establish and maintain connections between mobile terminals or between mobile terminals and one or more fixed base stations (BSs) while in motion. Such networks include cellular radio and specialized mobile radio (SMR). See also BS, cellular radio, and SMR.

MS-DOS (MicroSoft Disk Operating System) - The single-tasking, single-user operating system (OS) with a command-line user interface, released for use in IBM PCs in 1981. See also OS and PC.

MSA (Metropolitan Statistical Area) - A term that refers to the 306 metropolitan areas where the FCC manages cellular and PCS communications in the United States. The FCC has determined 428 RSA (Rural Statistical Area) markets as being separate from each other. Each statistical area, 734 in all, has at least two licensed service providers.

MSB (Most Significant Bit) - The bit in an octet that carries the most value. You can better understand this by comparing it to our base 10 numbering system. Imagine a “most significant number.” If you are 43 years old, the 4 is the most significant number and the three is the least significant number. If the 4 were lost, then you would only be three (a very significant difference). If the 3 were lost, you would still be 40 (not so significant).

MSC (Mobile Switching Center) - A place where cellular telephone call traffic is controlled. A cellular switch is used to perform the functions of the MSC. Bandwidth and cells are switched between users, and trunks that interface to landlines are also managed here.

MSCS (Microsoft Cluster Server) - A feature of Windows NT that enables two NT servers that are connected on a network to logically function as one. Microsoft Cluster Server software also provides failure detection and the ability of one server to take over all functions if the other stops operating.

MSF (Multiservice Switching Forum) - A global association of manufacturers and service providers working to develop and promote interoperable multiservice switching systems based on an open architecture.The MS Forum, the European Telecommunications Standards Institute (ETSI), and the Alliance for Telecommunications Industry Solutions (ATIS) have adopted the IP Multimedia Subsystem (IMS) as the foundation for their next-generation infrastructure strategies. See Appendix A for contact information. See also architecture, ATIS, ETSI, and IMS.

MSO (Multiple System Operator) - An operator of multiple CATV systems.The systems generally are standalone CATV islands rather than being interconnected. See also CATV.

MSP (Managed Service Provider) - A company that delivers and manages network-based services, applications, and equipment for a fee. An MSP may load a company’s application data on its servers, customizing it as necessary, and operating the service at a remote data center.An MSP might manage a company’s entire wide area network (WAN), perhaps including dedicated leased lines, a frame relay network, and an IP-based virtual private network (VPN). See also ASP, frame relay, IP, server, and VPN.

MSS (Mobile Satellite System) - A constellation (i.e., system) of satellites placed at altitudes and in orbits such that they move around the Earth at a different speed than the Earth rotates on its axis and, therefore, appear to be in motion.The MSS classification includes LEO (Low Earth Orbit) and MEO (Middle Earth Orbit) systems. An MSS is in contrast to an FSS (Fixed Satellite System), in which the satellites appear to be fixed in space due to their positioning in geosynchronous Earth orbit (GEO). See also FSS, GEO, LEO, MEO, and satellite.

MTBF (Mean Time Between Failures) - An indicator of component or system reliability based on the known failure rate calculated as the average period of time, expressed in hours, between total breakdowns.

MTS (Message Telecommunications Service) - Synonymous with Direct Distance Dialing (DDD). See DDD.

MTS/WATS Decision (Message Telecommunications Service/ Wide Area Telecommunications Service Decision) - In the United States, the Federal Communications Commission (FCC) decision (1978) that permitted MCI and others to offer switched MTS and WATS voice services in competition with AT&T. See also FCC, MTS, and WATS.

MTSO (Mobile Telephone Switching Office or Mobile Traffic Switching Office) - In a cellular radio network, a switch that serves to interconnect fixed base station (BS) antennas and, thereby, to interconnect radio cells and the mobile stations (MSs) within them. See also antenna, BS, cell, cellular radio, MS, and switch.

MTTR (Mean Time To Repair) - An indicator of the performance of service personnel based on the known elapsed period of time required to perform corrective maintenance and restore a component or system to operational status.

MTU - 1. Multi-Tenant Unit. An office building or mixed-use (i.e., commercial/residential) building housing more than one entity.An MTU has considerable implications for local loop deployments, particularly with respect to passive optical network (PON). See also local loop and PON. 2. Maximum Transmission Unit. In Internet Protocol version 6 (IPv6), all networks must support a packet of at least 1280 octets. The recommendation, however, is that all networks be configured to support an MTU of 1500 octets or greater in order to support encapsulation of Ethernet payloads without incurring fragmentation. See also encapsulate, Ethernet, fragmentation, IPv6, octet, packet, and payload.

mu (µ) - The Greek letter µ, used to denote one-millionth, as in µm, a micrometer, or micron. See micron and mu-law.

mu-law (µ-law) - A voice companding technique specified in the ITU-T G.711 Recommendation for pulse code modulation (PCM).This technique, which is used primarily in the North American and Japanese digital hierarchies (i.e.,T-carrier and J-carrier, respectively), converts 14-bit linear PCM samples into 8-bit compressed samples. A-law is a similar, but not exactly compatible, companding technique used in the European hierarchy (i.e., E-carrier). In an international circuit, if one national network uses A-law and the other uses mu-law, a gateway is used to resolve the incompatibility. In the absence of a gateway, the voice signal is intelligible, if a bit odd-sounding. See also A-law, companding, E-carrier, G.711, gateway, ITUT, J-carrier, PCM, and T-carrier

MUA (Mail User Agent) - e-mail client software responsible for effecting compatibility with the e-mail server, which provides message storage and transport through a Mail Transfer Agent (MTA). See also client, e-mail, server, and software.

Muldem (Multiplexer Demultiplexer) - Another name for a multiplexer.

multi-dwelling unit (MDU) - See MDU.

multi-level transition (MLT) - See MLT.

multi-step fiber - A type of step-index optical fiber comprising multiple layers of cladding with sharp steps in the index of refraction (IOR) at the boundaries. Multi-step fiber compounds the effect of stepindex fiber. See also cladding, IOR, and step-index fiber.

multi-tenant service - An optional PBX software feature package that allows a single PBX to serve multiple tenants, or user organizations. Logical software partitions allow each entity to have its own attendant console, trunk groups, and blocks of telephone numbers.Thereby, each organization has a unique identity through a logical PBX that is part of a single physical PBX.

multi-tenant unit (MTU) - See MTU.

Multi-Use Radio Service (MURS) - See MURS.

multicast address - In Internet Protocol version 6 (IPv6), an address that identifies a group of nodes, each of which can belong to multiple groups. A packet sent to a multicast group is delivered to every interface in the group. Multicast addresses begin with the prefix 11111111. In IPv4, a multicast address is any Class D address. See also broadcast, interface, IPv4, IPv4 address, IPv6, IPv6 address, node, and packet.

multicast - A transmission mode in which a signal or packet is sent to multiple receivers, but not all receivers on a network. An e-mail distribution list is an example of multicast transmission. See also broadcast, multicast address, packet, signal, and unicast.

Multichannel Multipoint Distribution Services (MMDS) - See MMDS.

Multihop - A reference to microwave links that require two or more links to get to a destination. Multi-hop links can extend distance and enable a more flexible path to go around buildings or mountains.

multilink frame relay (MFR) - See MFR.

Multilink Point-to-Point Protocol (MPPP) - See MPPP.

multilocation extension dialing - In the advanced intelligent network (AIN) specifications, a virtual private network (VPN) service of the public switched telephone network (PSTN) that provides for network routing of calls based on abbreviated numbers.This VPN service resembles a coordinated dialing plan in a networked PBX environment. See also AIN, coordinated dialing plan, PBX, PSTN, and VPN.

multimedia conference - A call involving two or more parties and incorporating not only voice and video, but also other media such as text, graphics, and whiteboarding, perhaps on an interactive basis. See also collaborative computing and whiteboarding.

multimedia messaging - 1. Synonymous with integrated messaging and unified messaging. See unified messaging. 2. Multimedia Messaging Service (MMS). See MMS.

multimedia - A method of communications incorporating a combination of media, such as audio, video, text, graphics, and whiteboarding, perhaps on an interactive basis. See also Smell-O-Vision.

Multimeter - An electronic test device used to measure voltage levels, electric current, and circuit resistance. Some multimeters are analog and some are digital. For a photo of a digital multimeter, see Voltmeter. For a photo of an analog cable test meter, see 145A.

multimode fiber (MMF) - See MMF.

Multimode - The alternative to Single-Mode fiber optic. Multi mode has a larger core (50 to 100 micron). Therefore, it accepts more light and more frequencies of light. Multi mode is used for shorter-distance applications, such as LANs. Single-mode fiber optic has a smaller core (5 to 15 micron), but is capable of longer-distance transmissions. It is used in the public network more often and is the choice for SONET applications. Multi-mode fiber optic is made with an orange-colored tube or insulation, and single mode is made with yellow.

MultiNAM - A cellular phone that is programmed to have multiple phone numbers, usually two. MultiNAM cell phones can have numbers that are subscribed to from different cellular companies.

multipath fading - Also known as multipath interference (MPI). Signal attenuation and distortion due to multipath propagation.Wireless radio or optical signals bounce off of physical obstructions they encounter between a transmitter and a receiver.Those signal elements that travel the most direct routes not only arrive soonest, but also suffer less absorption and diffusion attenuate the least and, therefore, are the strongest. Those that travel the least direct routes arrive last and are weakest. In broadcast television and poorly installed cable television, ghosting is the result of multipath fading. In broadcast television and poorly installed cable television, MPI specter, or ghosting, is the result of multipath fading. Signals that travel different paths but arrive at approximately the same time can cancel each other.All of these factors contribute to multipath fading. See also attenuation, diffusion, distortion, ghosting, MPI specter, multipath absorption, and propagation.

multipath interference (MPI) - See multipath fading.

multipath propagation - Referring to the fact that wireless radio or optical signals take multiple physical paths between transmitter and receiver as they bounce off of various physical obstructions. See also propagation.

Multiple Domain Network - SNA network with multiple SSCPs. See also SSCP.

Multiple Queue Assignment (MQA) - A reference to the ability of an ACD system to allow agents to log into multiple queues. A Northern Telecom Meridian PBX with MQA software is capable of allowing agents to log into and receive calls from five separate queues. When properly used, MQA makes call centers more efficient by allowing agents to share the incoming call load more effectively. See also Skills Based Routing.

multiple system operator (MSO) - See MSO.

multiple-input multiple-output (MIMO) - See MIMO.

Multiplex - Multiplexing is the process of encoding two or more digital signals or channels on to one. Channels are multiplexed together to save money. When we use all of the wires in a cable and need more, it costs less to add electronics on the ends of a cable than to install a new one (imagine the expense from LA to NY). A T1 encodes 24 channels into 1 by using frequency-division multiplexing. In a simpler explanation, a T1 makes it possible to place 24 lines that once needed 24 pairs on only 2 pairs. When a group of signals are multiplexed together, they are all sampled at a high rate of speed, faster than the combined speed of all the channels being multiplexed. For a diagram on the multiplexing process, see Time-Division Multiplexing.

Multiplexer - An electronic device that encodes several digital signals into a single digital signal for transmission on a single medium (such as a pair of wires). For a diagram on the multiplexing process, see TimeDivision Multiplexing.

Multipoint Control Unit (MCU) - See MCU.

Multipoint Controller (MC) - See MCU.

Multipoint Line - An older name for a bus physical topology. In Ethernet, a bus is a communications line, twisted pair or coax, with multiple points of connection. In bus physical topology, all points of connection must be terminated to a workstation (host) or a line terminator. See also Bus Topology.

Multipoint Processor (MP) - See MCU.

Multiprotocol Lambda Switching - The term once applied to what is now known as Generalized MPLS (GMPLS). See also GMPLS.

MultiProtocol Over ATM (MPOA) - An ATM Forum standardization effort specifying how existing and future network-layer protocols, such as IP, IPv6, AppleTalk, and IPX, run over an ATM network with directly attached hosts, routers, and multilayer LAN switches. See also Local-Area Network Emulation.

Multipurpose Internet Mail Extensions (MIME) - See MIME.

multirate ISDN - A feature of ISDN primary rate access (PRA) and primary rate interface (PRI) that aggregates or bonds multiple bearer (B) channels to yield a transmission rate in excess of the single-channel rate of 64 kbps. The resulting channels are known has high-speed (H) channels, which are specified at a number of levels. Multirate ISDN also is known as bonding, channel aggregation, and Nx64. See bonding, H channel, ISDN, PRA, and PRI.

Multiservice Switching Forum (MSF) - See MSF.

multislot service class - In General Packet Radio (GPRS) cellular radio networks, the multislot service class determines the number of time slots in each direction, with each time slot supporting a theoretical transmission rate of 21.4 kbps. Of the 12 classes, the simplest is service class 1, which supports one timeslot in each direction.The most capable is service class 12, which supports four time slots in each direction. See also cellular radio, GPRS, time slot, and transmission rate.

munitions - Military supplies such as weapons and ammunition. The government of the United States and many other countries classified cryptology as munitions for many years.Those policies were relaxed in the 1990s, due to the rise of the Internet, which made the policies impossible to enforce. See also encryption and Internet.

MURS (Multi-Use Radio Service) - In the United States, a Citizens Band (CB) Radio Service established in 2002 for private, two-way, short distance voice or data communications service for personal or business activities of the general public. MURS operates in the 151.820, 151.880, 151.940, 154.570, and 154.600 MHz bands. See also CB Radio Service.

Mushroom Board - Also called a white board or peg board. It is placed between termination blocks (such as 66M150 blocks) to provide a means of support for routing cross-connect wire. For a photo, see White Board.

music on hold (MOH) - A voice telecommunications system feature that interfaces the system to an external audio source that provides background music, promotional messages, or other audio content while callers are either in queue or on hold.

must-carry rules - In the United States, FCC rules that require CATV providers to provide channels for all commercial and public local television broadcasters within a 50-mile radius of the cable companies’ service area.The CATV providers are not required to support multiple stations with redundant programming.The broadcast stations are allowed a choice of being carried under the must-carry rules or under more recent regulations that require cable companies to obtain retransmission consent prior to carrying a broadcast signal.The latter rules afford the broadcasters more freedom to negotiate favorable terms of carriage. See also broadcast TV, CATV, and FCC.

mute - The voluntary silencing of a microphone or speaker.

Mux - A shortened name for multiplexer. For a diagram of the multiplexing concept, see Time-Division Multiplexing.

MV (Medium Voltage) - An amount of electromotive force (emf) between low voltage (LV) and high voltage (HV).The power utilities use MV, generally at 7,200 volts, in their distribution networks. Access broadband over power line (Access BPL) technology can make use of those MV lines as local loops for broadband data communications. See also Access BPL, emf, HV, LV, volt, and voltage.