websters new world telecom dictionary phần 7

NMT 900 (Nordic Mobile Telephone 900 MHz) 338 NMT 900 (Nordic Mobile Telephone 900 MHz) A 1G analog cellular radio technology developed and placed into service in the early 1980s in Scandinavian countries.NMT 900 operates in the 900 MHz band, employing frequency division multiple access (FDMA) to derive 1999 channels with a width of 12.5 kHz.NMT 900 employs frequency division duplex (FDD) to achieve bidirectional communications, with the downlink in the 935-960 MHz band and the uplink in the 890-915 MHz band.Within each channel,frequency modulation (FM) is employed.See also 1G,analog,cellular radio,channel,downlink,FDD, FDMA, FM, and uplink. NN (Network Neutrality) Referring to Internet neutrality. See Net neutrality. NNI (Network-to-Network Interface) The boundary or point of interaction between network serv-ice providers.The NNI is both a physical and logical point of demarcation.The NNI serves the technical boundary where protocol issues are resolved and as the point of division between the responsibilities of the individual service providers.NNIs are defined for asynchronous transfer mode (ATM) and frame relay, as examples. See also ATM, logical, frame relay, physical, and protocol. NOC (Network Operations Center) (pronounced knock) Also known as network control center (NCC). A centralized location from which a large,complex network and its component subnetworks and network elements can be monitored, and faults or performance failures can be identified, diagnosed, isolated, and often corrected. See also network, network element, and subnet. node 1. A junction point at which two or more circuits interconnect in a data network.A bridge, for example,interconnects two or more segments of a local area network (LAN).See also bridge,circuit,LAN, and network.2. In a switched network,a switching point that comprises a point of interconnection for cir-cuits,a data switch,and control facilities.In the public switched telephone network (PSTN),for example, a great many circuits terminate in a central office (CO) and a tandem office,each of which comprises one or more switches and Signaling System 7 (SS7) network control logic,multiplexers,a wide variety of other devices.See also access node,CO,PSTN,service node,SS7,switch,and tandem switch.3.A device such as a sta-tion,bridge,computer,repeater,server,switch,or other device that connects to a network.4. In the IBM Systems Network Architecture (SNA), a physical device such as a computer, communications processor (e.g., FEP), terminal controllers, or terminal. See also SNA. noise Unwanted disturbances superimposed on a signal and interfering with its integrity. Noise can be introduced by equipment or can be the result of natural phenomena. Noise can take a number of forms, including amplitude noise,cross-talk,echo,intermodulation noise,harmonic distortion,impulse noise,ran-dom noise, and white noise. nominal In name only,but not in reality.A T1 circuit sometimes is described as having a nominal trans-mission rate of 1.5 Mbps,although in reality the signaling rate is 1.544 Mbps and its payload is 1.536 Mbps. It is easier to say one point five Megabits per second or one and a half Megabits per second than one point five four four Megabits per second. It is not exact, but it is close enough for all but the most obnoxious purists.Similarly,an E-1 is generally described as having a transmission rate of 2 Mbps,although in reality the signaling rate is 2.048 Mbps and the payload is 1.92 Mbps.See also payload,signaling rate,and transmis-sion rate. non-blocking A switch that provides a guaranteed talk path for every terminal; in other words, there exists a 1:1 (one-to-one) relationship between ports and time slots.Such a configuration is expensive,gen-erally considered excessive and, therefore, unusual in all but the most intense applications scenarios, such as call center ACDs and backbone data switches.See Figure N-1. See also ACD,backbone,blocking,and call center. 339 non-wireline carrier Switch CPU Power Supply Figure N-1 non-deterministic 1. Non-predictive. Referring to the inability to objectively predict an outcome or result of a process due to lack of knowledge of a cause and effect relationship or the inability to know ini-tial conditions. 2. In telecommunications switching and routing, the unpredictability of a path between nodes. See also node, path, route, and switch. 3. In local area networks (LANs) a contentious medium access control (MAC) technique that does not allow a node to predict when it will be allowed to gain access to the network.Carrier sense multiple access (CSMA),which is used in 802.3 Ethernets,is non-deterministic. See also 802.3, CSMA, deterministic, LAN, MAC, and node. non-dialable toll points A location that a caller cannot dial directly,but must call with operator assis-tance. Such locations are very remote and may be beyond the reach of cable systems and may be too low and sheltered to be reached via satellite,but can be reached via special radio circuits.In the United States, there remain a large number of non-dialable toll points, generally in deep valleys and canyons. non dispersion-shifted fiber (NDSF) See NDSF. non-facility associated signaling (NFAS) See NFAS. non-line-of-sight (NLOS) See NLOS. nonpersistent carrier sense multiple access (Nonpersistent CSMA) See CSMA. Nonpersistent CSMA (Nonpersistent Carrier Sense Multiple Access) See CSMA. non-real-time (nrt) See nrt. non real-time variable bit rate (nrt-VBR) See nrt-VBR. non-repudiation Referring to a mechanism that proves that the originating node sent a message and that the receiving node received it.Therefore,the sender cannot deny sending the message and the receiver cannot deny having received it. Non-repudiation can be effected through digital signatures, confirmation receipts, and timestamps. See also digital signature. non-return-to-zero (NRZ) See NRZ. non-wireline carrier Also known as an A Carrier.A provider of cellular radio service that is not a tra-ditional landline telecommunications services.The distinction between wireline and non-wireline carriers was made primarily for purposes of segregating bidders for radio spectrum assignment during the FCC cellular spectrum auctions.The initial approach toward spectrum assignment was designed to ensure that there was one wireline (i.e.,telephone company) and one non-wireline carrier per market.See also carrier, cellular, FCC, landline, radio, spectrum, and wireline carrier. Nordic Mobile Telephone (NMT) 340 Nordic Mobile Telephone (NMT) See NMT. normal 1. Conforming to an accepted, usual, or typical form, model, or pattern. 2. In geometry and mathematics,the transverse or perpendicular,i.e.,a right angle,which is 90 degrees from a plane or sur-face. Frankly, this seems decidedly abnormal to me, as I have known a lot of people who seemed to be at right angles compared to normalcy. See also counterintuitive, critical angle, out-of-phase, and total internal reflection. North American Numbering Council (NANC) See NANC. North American Numbering Plan (NANP) See NANP. North American Time Division Multiple Access (NA-TDMA) A digital cellular radio standard better known as Digital Advanced Mobile Phone Service (D-AMPS). See D-AMPS. NOS (Network Operating System) Software that provides a local area network (LAN) with multi-user, multitasking capabilities, facilitates communications and resource sharing, and thereby provides the basic framework for LAN operation.The NOS comprises modules distributed throughout the LAN,with some residing in the servers and others in the clients. See also client, client/server, LAN, and server. notation The use of signs or symbols to represent numbers, words, phrases, or even complete concepts in fields such as language, mathematics, chemistry, and music. See also binary notation and hexadecimal nota-tion. NPA (Numbering Plan Administration) The administration of the scheme of logical addresses,i.e., telephone numbers, used in the global switched telephone network (GSTN) and the national public switched telephone networks (PSTNs) that compose it.The ITU-T is responsible for international num-bering plan administration, and individual nations or regions have similar responsibilities within their domains.The North American Numbering Plan (NANP),for example,defines the telephone numbering scheme in the area loosely described as North America.The ITU-T E.164 recommendation (The Inter-national Public Telecommunication Numbering Plan) specifies the current international NPA convention at a maximum of 15 digits, although the number of digits required for calling within a nation varies. In many cases,numbering schemes vary within the same country;for example,six- and seven-digit telephone numbers coexist in Namibia and many other countries. In the countries within the NANP, the dialing scheme is +CC.NPA.NXX.xxxx, with the fields defined as follows: · + The plus sign indicates that there may be leading digits for international dialing. In the United States, the caller dials 011 as an international access code. · CC (Country Code)The country code is one, two, or three digits, established by the ITU-T.As examples, the United States is 1, South Africa is 27, and Luxembourg is 352. · NPA (Numbering Plan Area)The NPA, or area code, is a three-digit number that corresponds to a geographic area.The NPA follows the pattern NXX, with N indicating that only numbers 2–9 are allowed, as 0 or 1 would confuse the network, and X indicating that any number is allowed.The area code is used only when a call crosses an area code boundary. In such a case, the dialing sequence is 1.NNX.NNX.xxxx. N-PCS (Narrowband Personal Communications Services) See PCS. NPAC (Number Portability Administration Center) In the United States,the Federal Communi-cations Commission (FCC) established the NPAC to supervise and perform clearinghouse functions in support of local number portability (LNP) and local routing numbers (LRNs). See also LNP and LRN. NREN (National Research and Education Network) The first (1990) asynchronous transfer mode (ATM) network in the United States,NREN was a test-bed gigabit network sponsored by the Advanced 341 NT1 (Network Termination 1) Research Project Agency (ARPA) and the National Science Foundation (NSF).Previously (1987),a con-sortium of European carriers,end users,and universities sponsored a similar project known as the Research for Advanced Communications in Europe (RACE) project 1022 (1987). See also RACE. nrt 1. near-realtime. Referring to a quality of service (QoS) level designed for applications that do not require transmission to take place in real time,but nearly so.That is to say the transmission must take place within a reasonably short time from the exact moment as the event itself takes place in the real world. Near-realtime QoS is essential in many applications directly involving humans and their perception of time.Transaction processing, for example, must take place in near-realtime to avoid customer dissatisfac-tion.See also QoS and realtime.2. non-realtime. Referring to a quality of service (QoS) level designed for applications that do not require transmission to take place in real time, that is to say that the transmission need not take place at the exact moment and in the exact sequence as the event itself takes place in the real world.Internet access,for example,need not be available instantly on demand.e-mail need not be sent across a network to be received instantly, but can tolerate a considerable level of error, latency, loss of sequence, loss of data, and retransmission. See also latency, QoS, and realtime. nrt-VBR (non real-time Variable Bit Rate) In asynchronous transfer mode (ATM),a class of traffic that is bursty, with periods of intense activity and periods of low or no activity, and of a non real-time nature that is not dependent on loss or delay because there is time to recover through retransmission.Traffic parameters include peak cell rate (PCR), cell delay variation tolerance (CDVT), sustainable cell rate (SCR), maximum burst size (MBS), and burst tolerance (BT).The quality of service (QoS) parameter is cell loss ratio (CLR).ATM also defines available bit rate (ABR), constant bit rate (CBR), real-time Vari-able Bit Rate (rt-VBR), unspecified bit rate (UBR), and variable bit rate (VBR) traffic classes. Examples of nrt-VBR traffic include data traffic such as X.25,frame relay,transaction processing,LAN-to-LAN,and non real-time buffered voice and video traffic. See also ABR, ATM, BT, CBR, CDVT, CLR, compression, frame relay, LAN, MBS, PCR, QoS, realtime, rt-VBR, SCR, time slot, UBR, and VBR, and X.25. NRZ (Non-Return-to-Zero) A binary line coding technique in which 1 bits are represented by a high value significant condition (e.g., +V) and 0s are represented by a low value significant condition (e.g., –V), that is, opposite polarity, with no neutral or rest condition (e.g., 0V). See also line coding, Man-chester coding, and polarity. NSF (National Science Foundation) An independent agency of the United States government formed in 1950 “to promote the progress of science; to advance the national health, prosperity, and wel-fare; to secure the national defense, according to the NSF…” The mission of the NSF includes support for all fields of fundamental science and engineering. In telecommunications, the NSF has taken the ini-tiative projects such as the development of the very-high-speed Backbone Network Service (vBNS), which formed the initial backbone infrastructure for Internet2. See also Internet2 and vBNS. NT (Network Termination) In ISDN networks, a set of functions accomplished through the use of programmed logic variously embedded in the carrier network and the customer premises equipment (CPE).NT devices operate to interface the four-wire customer wiring to the physical two-wire UTP local loop, performing functions similar to those provided by digital service units (DSUs) and channel service units (CSUs) in non-ISDN digital networks.See also CPE,CSU,DSU,four-wire circuit,ISDN,NT1,NT2, and two-wire circuit. NT1 (Network Termination 1) In ISDN, the logical interface to the carrier side of the connection, performing such functions as signal conversion,synchronization,multiplexing,frame alignment,echo can-cellation, line maintenance, and performance monitoring of the local loop. Such functions correspond to Layer 1 (Physical Layer) of the OSI Reference Model.See also Echo canceller,ISDN,local loop,multiplexing, NT, NT2, OSI Reference Model, and synchronization. NT2 (Network Termination 2) 342 NT2 (Network Termination 2) An interface to an intelligent ISDN-compatible device (e.g.,PBX or router) responsible for the user side of the connection to the network,performing such functions as mul-tiplexing and switching. Such functions correspond to Layer 2 (Data Link Layer) of the OSI Reference Model.An NT2 commonly is actually an NT1/2 device, performing the combined functions, and oper-ating at Layers 1,2,and 3 of the OSI Reference Model.See also ISDN,NT,NT1,and OSI Reference Model. NTACS (Narrowband Total Access Communications System) A narrowband version of the TACS 1G analog cellular radio technology developed for use in the United Kingdom. NTACS operates in the 900 MHz band, employs frequency modulation (FM), and supports 400 channels of 12.5 kHz.As an analog system,TACS derives channels using frequency division multiple access (FDMA) and bidirec-tional communications is achieved through frequency division duplex (FDD) with the downlink in the 860–870 MHz band and the uplink in the 915–925 MHz band.See also 1G,analog,cellular radio,downlink, ETACS, FDD, FDMA, FM, narrowband, TACS, and uplink. NTSC (National Television Standards Committee) The initial standard (1953) for broadcast tele-vision, NTSC was named for the committee that established it in the United States. NTSC is character-ized as analog in nature, with 525 interlaced scan lines.There are 640 pixels per line, 485 of which are dedicated to the active picture.The frame rate is 30 fps, 60 fields interlaced, and the aspect ratio is 4:3.As an early analog standard that is viewed by some as overly complex and ineffective in a contemporary digital context, NTSC sometimes is referred to by its detractors in the pejorative as Never The Same Color.NTSC is defined in ITU-R Recommendation 1125 and served as the baseline for subsequent stan-dards,Phase Alternate Line (PAL) and SECAM (SÉquential Couleur Avec Mémoire).See also analog,aspect ratio, broadcast television, frame, frame rate, interlaced scanning, ITU-R, PAL, pixel, and SECAM. null 1. Valueless; amounting to nothing; zero. 2. In some computer programs, a field into which noth-ing is entered,not even a zero (0).In such programs,even a 0 can affect calculations.See also negative and positive. null modem Referring to a metallic wire cable used to connect two computers directly without the use of modems.A null modem cable simply crosses the transmit and receive wires so that the wire used by one machine for signal transmission is used by the other machine for signal reception.A null modem cable can be created by manually crossing the wires.Alternatively,a null modem adapter can be used to accom-plish the necessary crosslinks. (Note:A null modem is much less expensive and much prettier.) See also cable, modem, and wire. numbering plan administration (NPA) See NPA. Numbering Plan Area (NPA) See NPA. number portability Referring to the ability to port a number across carriers, i.e., move a telephone number from one carrier to another in a competitive environment.The United States first required num-ber portability, initially with respect to toll-free numbers.The Telecommunications Act of 1996 required local number portability (LNP). In 2003, the Federal Communications Commission required wireless number portability (WNP), extending portability to cellular telephone numbers. Number portability is possible in many countries with respect to toll-free numbers and landlines,in general.Portability is possible in fewer countries with respect to cellular service.There are restrictions,however.For example,it generally is not possible to port a number across landline and cellular domains.Neither can numbers be ported across countries. See also LNP. Number Portability Administration Center (NPAC) See NPAC. ... - tailieumienphi.vn