Fiber Optics Illustrated Dictionary - Part 9 ppsx

Fiber Optics Illustrated Dictionary that supports mid-range speeds and the transmission of both voice and data over existing copper-pair wires. ADSL is becoming apopular cost-effective option for faster computer network access (e.g., Internet) in households and small businesses. It enables users to be online virtually all the time without interfering with the use of the phone for voice messages or having to dial the service provider each time access is desired. ADSL services are competitive with cable modem. "Asymmetric" refers to the discrepancy between the upstream and downstream transmission speeds. Most users download far more than they upload, so a com- promise is established to balance cost and speed. Thus, download speeds are configured to be faster than upload speeds (e.g., 640 kbps versus 8 Mbps). Installation of ADSL service involves installing a network interface device (NID) that houses a spliner (a low-pass filter) at the subscriber premises. Sepa- rate lines run from the splitter to the phone and from the spliner to the ADSL remote transceiver (some- what like a traditional modem) which, in turn, connects to the computer. Software to handle communications is installed on the computer. The combined telephone and ADSL signals travel from the loop to the subscriber NID where the signal is split. The telephone signal is then directed to the phone set and the ADSL signal is directed to the terminal unit (the remote transceiver) where it is processed and transmitted to a network interface card (NIC) installed in the computer. Much the same happens in the reverse direction. Phone and ADSL signals coming from the subscriber premises are sent to the central office where a splitter sends phone signals to the voice switching mechanisms and ADSL signals to the data network where an Internet Services Provider handles user requests such as Internet access, Web hosting, etc. Copper wire lines are not optimal for ADSL, as bridge taps and load coils on utility poles can interfere with ADSL signals. See Digital Subscriber Line for a fuller explanation. See cable modem, discrete multi tone, G.lite, UAWG. asymmetric transmission A transmission channel in which information flows more readily (faster) in one direction than the other, or moves primarily in one direction or the other at anyone time, or in which a greater volume of information flows in one direction or the other. There are many instances in which information typically flows more in one direction than another, as in interactive TV, where most of the time the user is observing and not transmining but may make an occasional request for a specific movie or file. The medium itself may not be inherently asymmetric. For example, a data upload over a modem is primarily one-way, but the line capacity is two-way, and the direction can be easily switched when upload- ing. The slower channel, or the one with a lower volume capacity, may be called the backchannel. asymmetrical compression In data compression techniques, some types of files can be compressed faster than they can be decompressed and some work the other way around. In designing compression al- gorithms, sometimes optimization in one direction or 72 the other is preferred. In creating animation se- quences, it is usually very important that they decom- press and play quickly; otherwise the illusion ofmo- tion is lost. However, it is usually not a problem if the compression takes longer than the decompression because the computer can handle that while the user is working on other projects. asymmetrical modem A modem designed to favor the transmission of the bulk of the data in one direction over the other. This is appropriate in situations where most of the communication is one-way, as in managing an archive site, where downloads typically outnumber uploads thousands-to-one. See Asymmet- ric Digital Subscriber Line. asynchronous Not synchronous. A concept that ap- plies across many areas of telecommunications, in which the timing of the information being received and transmined is not predefined and may be unpre- dictable, as in many modem communications and interactive radio communications. This type of communication typically requires some means ofindicating the starting and stopping points of the transmission. There are various schemes for handling this, from verbal cues ("Roger"), to start/stop bits, and various handshaking signals. asynchronous balanced mode ABM. In an Interna- tional Business Machines (IBM) Token-Ring network, a service in the logical link control (LLC) at the SNA data link control level that allows devices to send and respond to data link commands. asynchronous communications interface adapter AClA. A data formaning device that translates signals between the computer and aperipheral such as a modem. asynchronous packet assembler/disassembler APAD. A mechanism to assemble a stream of bytes from an asynchronous source (e.g., a computer) into packets and transmit them to a network, and vice versa. In terms of serving atranslation function, it can be thought of as loosely working like a traditional modem, which takes asynchronous digital signals from acomputer and modulates and demodulates them for compatibility with an analog phone system. In the case ofa PAD, however, the data is being packetized and sent over an X.25 network from one or more devices that are not directly X.25 compatible. The ITU- T has defined more than one standard for perform- ing these translation functions to facilitate connections with X.25. Examples include: X,3 basic packet data network assembly/disassembly X.5 packet data network assembly/disassembly for facsimiles X.29 packet data network assembly/disassembly control information and user data exchange procedures X,39 packet data network assembly/disassembly control information and user data exchange procedures for facsimiles . See X Series Recommendations. asynchronous transfer mode ATM. A high-speed, cell-based, connection-oriented, packet transmission © 2003 by CRC Press LLC protocol for handling data with varying burst and bit rates. ATM is a commercially significant protocol due to its flexibility and widespread use for Internet con- nectivity. ATM evolved from standardization efforts by the CCITT (now lTU- T) for Broadband ISDN (B- ISDN) i~ the mid-1980s. It was originally related to Synchronous Digital Hierarchy (SDH) standards. ATM allows integration of LAN and WAN environments under a single protocol, with reduced encap- sulation. It does not require a specific physical transport and thus can be integrated with current physical networks. It provides Virtual Connection (VC) switching and multiplexing for Broadband ISDN, to enable the uniform transmission of voice, data, video and other multimedia communications. See Anchor- age Accord for information on acquiring ATM technical specifications. See the Appendix for details and diagrams on ATM and ATM adaptation layers. AT 1. See access tandem. 2. advanced technology 3. AudioTex. A commercial telephony-based information service, offering announcements, messages, music, meeting schedules, etc. AT, PC/AT Advanced Technology. The common name for a series of 80286-based personal computers introduced by International Business Machines (IBM) in the mid-1980s. This model was released about a year later than the Apple Lisa, at about the same time as the Apple Macintosh, and about a year before the Amiga 1000, Apple IIGS, and Atari ST computers. This is historically significant in the development of user interfaces, as most of the compet- ing computers were evolving graphical user interfaces (GUIs) and included built-in serial ports and sound cards, while most of the AT systems were text- oriented (primarily MS-DOS), with sound and various interface cards optional. The IBM AT and li- censed clones from other manufacturers were pur- chased primarily by business users, in part because the IBM name was well known in the business industry, and also because IBM had a decades-old tradition at the time of providing service and repair options to business owners. Two of the chief software products used on the AT were spreadsheets and word processors. AT commands, Hayes Standard AT Commands A very simple control and reporting language built into Hayes Microcomputer Products, Inc. modems, and Hayes-command-compatible modems from other manufacturers. Originally modems were "dumb" devices; they had no significant memory or algo- rithms incorporated into the device to process commands or data from the computer. Hayes introduced "smart" modems in the early 1980s that could process a limited command set and enhance the utility of modems. This instruction set has since been incorporated into almost every make and model of computer modem, usually with enhancements by individual manufacturers. The AT command set allows computer control of a modem and provides a way for the modem to report information back to the computer software. The AT stands for "attention" and is a way of alerting the modem that there is an instruction set fo Howing the "AT" which is to be acknowledged or executed. When you run a telecommunications program through your modem, the software is talking to the modem with AT commands along the path provided by the serial cable that typically connects the modem to the computer. If your software can be set to interactive mode, you can type the AT commands directly to your modem and see what happens. The AT commands are usually listed at the back of the manual that comes with a modem. Many modem manufacturers have included supersets of the basic Hayes command set to provide control of proprietary or enhanced features specific to their products, so AT commands usually include most or all of the Hayes commands, and additional ones as well. AT commands fall into a number of categories. There are commands for querying the status of the phone line, for querying the status of the modem, and for carrying out operations such as dialing, setting the transmission speed, setting the number of redials, setting the length of wait periods, etc. Modems contain a number of registers in which information is stored, often in the form ofa toggle (true or false) or integer setting. Thus, setting the register to zero signifies one thing, and setting it to one or another integer, when appropriate, signifies another. Thus, AT 80=0 sets the "8' register to zero. Since register SO determines how many rings to AutoAnswer, setting it to zero effectively turns off AutoAnswer. AT SO=l instructs the modem to AutoAnswer after it detects one ring. If you are running a computer bulletin board, or a friend is calling to send you a file over the phone line, AutoAnswer can be turned on (or you can type ATA "attention, answer" when you hear the phone ring). Remember to set AutoAnswer off when you are finished transmitting, or the next voice caller may get a nasty modem-blast in the ear. Some modems have enhancements that allow them to autodetect whether the in- coming call is voice or data and to react accordingly so this doesn't happen. AT 80=0 M1 DT 555-4321 W DT 123 attention; set autoanswer to zero rings set speaker to be on (M!) during establishment of call (so you can hear dial tone and dialing) and off during connection (so you don't have to hear the modem sounds) dial tone mode 555-4321 wait for dial tone dial tone mode 123 (to dial an inner extension, for example). AT commands can be combined. You needn't type AT in front of each individual instruction. For example, you might wish to initialize your modem, and dial out as a single string of commands. 73 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary AT &T American Telephone and Telegraph Company. A company established almost 150 years ago to cre- ate practical commercial applications from the early telegraph and telephone patents filed in the 1870s, primarily those of Alexander Graham Bell and Elisha Gray. Some of the patents became the property of the Bell System, and some served simply as competitive motivation to implement the new ideas and technologies. The American Telephone and Telegraph Company (AT &T) began as a long-distance subsidiary of the American Bell Telephone Company in 1885. In 1899 the two companies were again merged into one under the AT&T name. In the 1900s, AT&T was reor- ganized, becoming aholding company, the parent of the Bell companies and Western Electric. In the en- suing years, several additional reorganizations oc- curred, some voluntary, some mandated by u.S. jus- tice authorities. In the early 1900s, there was a period of substantial change in the phone industry, since the original Bell patents, protected for a term of 17 years, were expir- ing and independent companies were entering the phone market in substantial numbers. This situation resulted in independents collectively holding almost half of the phones until, by 1913, AT&T was again the majority holder, due to mergers and acquisitions, and was legally restrained from acquiring any more independents. AT&T was also mandated to permit independents to use the AT&T toll lines. The Communications Act of 1934 further regulated the industry and established the Federal Communi- cations Commission (FCC), which was given jwis- diction over the telephone and broadcast industries, a responsibility it still holds. In 1956, the u.s. gov- ernment and AT&T entered into an agreement that AT &T would offer only phone-related services and not engage in common carrier communications such as computer network services. AT&T was further re- quired to license Bell patents for royalties to inter- ested applicants. A number of antitrust suits ensued in the 1970s charg- ing AT&T with monopolistic practices, and there were calls for divestiture resulting in divestiture proceedings in the 1980s. During this same period, AT &T was granted limited permission to engage in computer-related services. While its political history was undergoing many ups and downs, the researchers in the Bell Laboratories provided an enormous amount ofresearch and development in telephone technologies, beginning in the late 1800s and early 1900s. AT&T researchers developed the first two-wire telephone circuit, which is still in use today, the first practical transistor, and many other inventions that are in broad use. See Bell, Alex- ander; Bell Laboratories; Bell System; Carty, John 1.; Kingsbury Commitment; Modified Final Judg- ment; Vail, Theodore. AT&T TeleMedia Connection A Microsoft Win- dows-based videoconferencing product from AT&T Global Information Solutions providing audio/video, file transfer, and application-sharing utilities over ISDN through ITU- TH Series and Q Series Recom- 74 mendations standards and encoding techniques. Atanasoff, John Vincent (1903-1995) An American physicist and inventor who developed a vacuum tube calculating device in the mid-1930s that foreshad- owed the famous ENIAC computer that was opera- tional in the post-World War II years. In 1939, with a small grant from Iowa State College, he pioneered the development of a binary logic computer called the ABC, or AtanasofI-Berry Computer, with assistance from Clifford Berry a recent graduate in electrical engineering. Unfortunately, the War brought the project to a halt. He left his academic position to become Chief of the Acoustics Division of the u.S. Naval Ordnance Laboratory where he worked on computing devices for the Navy along with atomic testing. In the 1950s, Atanasofftook a number of cor- porate positions and retired in 1961. See Atanasoff- Berry Computer; Berry, Clifford E. Atanasoff-Berry Computer ABC. Apioneering binary, direct logic computer with a regenerative memory, designed and built by J. V. Atanasoffwith assistance from Clifford E. Berry. After two years on the drawing boards, it was prototyped in 1939. It is significant not only for its historic place in the early history of computers, but also because it was designed with aseparation between memory and data processing functions. The electricity needed to keep the memory refreshed, so the information wasn't lost, was provided by rotating drum capacitors. Atanasoff had been working on the ideas that led up to the ABC since 1935 and related that the idea for the ABC came to him in aroadhouse in 1937 after he and his graduate students had developed a calculator for complex mathematics manipulation. Punch cards, which had been developed to store information for electromechanical devices in the late 1800s, were used to enter data into the ABC. In 1940, Atanasoff and Berry authored Computing Machines for the So- lution of Large Systems o/Linear Algebraic Equations with illustrations, in preparation for a patent application that was never completed due to circumstances associated with World War ll. Much of the information aboutAtanasoff's invention did not come to light until a long court battle in the 1970s between Sperry Rand and Honeywell. Unfor- tunately, after Atanasoff left for a position with the u.S. Navy, the computer was dismantled, without notifying the inventors. The Ames Laboratory is building a working replica of this historic invention. See ENIAC; Zuse, Konrad. Atari Corporation Ahistorically significant games and computer company established in 1972 by Nolan Bushnell. Atari shipped the first computer game to achieve wide commercial acceptance. "Pong" was a simple monochrome game with a ball and two paddles, a form of electronic table tennis that became wildly popular. Atari continued developing games but also subsequently introduced a number of microcom- puters, including the Atari 800 and the Atari 520ST. The 520ST had a graphical interface and built-in MIDI and was competitive with the Amiga for the home market in the mid-1980s. © 2003 by CRC Press LLC ATB See all trunks busy. ATCA See Antique Telephone Collectors Association. ATCP See AppleTalk Control Protocol. ATCRBS air traffic control radar beacon system. ATD 1. asynchronous time division. 2. Attention Dial. A modem command from the Hayes set that instructs a modem to dial the number following the command. Often a T or P will precede the number to indicate whether to dial as a tone or pulse signal. For example, Attention Dial Tone would be ATDT 555-1234. 3. advanced technology demonstration. ATDRSS See Advanced Tracking and Data Relay Satellite System. ATEL See Advanced Television Evaluation Labora- tory. ATG 1. See address translation gateway. 2. Art Tech- nology Group Inc. An e-commerce platform development vendor. Athena project, Project Athena A project of the Massachusetts Institute of Technology (MIT) Com- puter Science Lab begun in 1984. The goal was to take various incompatible computer systems, and develop a teaching network that could utilize the different resources of each in a consistent manner. The development of The X Window System originated from efforts to provide a graphical user interface (GUI) for Athena. See X Window System. ATI 1. Accelerated Technology Incorporated. A commercial supplier of realtime operating system (RTOS) source code for embedded systems, based upon the Nucleus PLUS multitasking kernel. 2. Advanced Telecommunications, Inc. A commercial vendor of telecommunications-related system design, installation, and training. ATI is one of several firms associated with Applied Cellular Technology. 3. See Ad- vanced Telecommunications Institute. ATIS 1. Advanced Travelers Information System. A forum of SAE International, an engineering society for advancing transportation mobility. 2. See Alliance for Telecommunications Industry Solutions. ATM 1. See asynchronous transfer mode. 2. See Au- tomated Teller Machine. ATM-PON asynchronous transfer mode passive optical networks. A type of optical distribution network, promoted as a means to implement large-scale, full- service subscriber telecommunications services. See fiber to the home. ATM Adaptation Layer AAL. A layer in an ATM network. See asynchronous transfer mode in the Ap- pendix for extended information and diagrams. ATM cell The basic unit ofinfonnation transmitted through an ATM network. An ATM cell has a fixed length of 53 bytes, consisting ofa 44- or 48- byte pay- load (the information transmitted), and a 5-byte header (addressing information) with optional4-byte adaptation layer information. Interpretation of signals from different types of media into a fixed length unit of data makes it possible to accommodate different types of transmissions over one type of network. See asynchronous transfer mode; see the Appendix for details and diagrams. ATM cell rate In ATM networks, a concept that expresses the flow of basic units of transport used to convey data, signals, and priorities. Common cell rate concepts include leaky bucket and cell rate margin. See ATM Cell Rate Concepts Table. ATM endpoint In an ATM network, the point at which a connection is initiated or terminated. See asynchronous transfer mode. ATM endpoint address A location identifier func- tionally similar to a hardware address in an ATMARP environment, although it need not be tied to hardware. See asynchronous transfer mode, ATM endpoint. ATM Forum, The An international nonprofit organization founded in 1991 to further the evolution and implementation of asynchronous transfer mode (ATM) technology as a global standard. The Forum provides educational information onATM and specifications and recommendations to the lTU-T based on standards of interoperability between vendors, with consideration to the needs of the end-user com- munity. The ATM Forum is a membership-by-fee group which includes a number of technical commit- tees to discuss and report on specific issues such as signalling, traffic management, emulation, security, testing, and interfacing. See asynchronous transfer mode, UNI. http:/www.atmforum.com/ ATM hardware address The individual IP station address. See asynchronous transfer mode, ATM endpoint address, Internet Protocol. ATM line interface ALI. A device at the physical layer enabling connection to a variety of physical media allowing, for example, the accommodation of different line speeds. ATM Link Enhancer ALE. A commercial error-cor- recting mechanism for satellite communications developed by COMSAT. The Header Error Control (HEC) specified for asynchronous transfer mode (ATM) is suitable for transmissions carried through low error rate media such as fiber optic cables. It be- comes inadequate, however, in bursty transmissions environments such as wireless networks, particularly those that are satellite-based. To compensate for this limitation, COM SAT developed an ALE module which is inserted in the data paths before and after the satellite modems, to isolate ATM cells from burst errors. This module allows selective interleaving of ATM cells before they are transmitted through the satellite link, thus providing a lower bit error rate (BER) and an improved cell loss ratio (CLR). See asynchronous transfer mode, cell rate. ATM models There are a variety of types and imple- mentations of ATM networks, including Classical IP, LANE, IP Broadcast over ATM, and others. See asynchronous transfer mode, ATM Transition Model, Classical IP Model, Conventional Model, Integrated Model, Peer Model. See Appendix B for details and diagrams. ATM slotA time indicator for the duration of one cell, usually described in microseconds. It will vary depending upon the cell-carrying medium. In ATM, one use of the term slot is to describe delay in switch performance. See asynchronous transfer mode, ATM cell. 75 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary AIM switch processor ASP. A modular component from Cisco Systems that provides cell relay, signal- ing, and management processing functions. It includes an imbedded IOO-MHz MultiChannel Inter- face Processor (MIP) R4600 RISC processor, with ATM access to the switch fabric, to provide high call setup rates and low call setup latencies. It includes an Ethernet port and dual serial ports. The ASP works in conjunction with a field-replace- able feature daughtercard which supports advanced ATM switch functions, including intelligent packet discard, dual leaky bucket traffic policing, and available bit rate (ARR) congestion control mechanisms. See asynchronous transfer mode. AIM traffic descriptor A list of network traffic parameters, such as cell rates and burst sizes, and, op- tionally, a Best Efforts (BE) indicator, within an asynchronous transfer mode (ATM) virtual connection. This information is used to determine traffic characteristics and to allocate resources. See asynchronous transfer mode, BEC, cell rate, PCR, SCR. AIM Transition Model A model lying between the Classical IP Models and the Peerand IntegratedMod- els. See ATM models. AIM Wireless Access Communication System AWACS. An ACTS project to support and influence emerging ATM wireless standards. The project con- sidered various link level and system level simula- tions in order to research system concepts based on a 19-GHz air interface. It also addressed the feasibil- ity of different modulation schemes and of directional antenna technology. See Advanced Communications Technologies and Services. AIMARP ATM Address Resolution Protocol. ATMARP is the ATM Address Resolution Protocol (ARP) with extensions to support address resolution in a unicast server environment. ATMARP provides a means of resolving Internet Protocol (LP) addresses to ATM addresses. ATMARP use of public UNI addresses or ATM endpoint addresses is similar to Ethernet addressing; ATM addresses need not be tied to hardware. lnATMARP (Inverse ATMARP) is used AIM Cell Rate Concepts Abbreviation Name Notes ACR allowed cell rate A traffic management parameter dynamically managed by congestion control mechanisms. ACR varies between the minimum cell rate (MCR) and the peak cell rate (PCR). CCR current cell rate A traffic flow control concept that aids in the calculation ofER. The CCR may not be changed by the network elements (NEs). CCR is set by the source to the available cell rate (ACR) when generating a forward RM-cell. CDF cutoffdecrease factor Controls the decrease in the allowed cell rate (ACR) associated with the cell rate margin (CRM). CIV cell interarrival variation Changes in arrival times of cells nearing the receiver. If the cells are carrying information that must be synchronized, as in constant bit rate (CBR) traffic, then latency and other delays that cause interarrival variation can interfere with the output. GCRA generic cell rate algorithm A conformance enforcing algorithm which evaluates arriving cells. See leaky bucket. ICR initial cell rate A traffic flow available bit rate (ARR) service parameter. The ICR is the rate at which the source should be sending the data. MCR minimum cell rate Available bit rate (ABR) service traffic descriptor. The MCR is the transmission rate in cells per second at which the source may always send. PCR peak cell rate The PCR is the transmission rate in cells per second that may never be exceeded, which characterizes the constant bit rate (CBR). RDF rate decrease factor An available bit rate (ABR) flow control service parameter that controls the decrease in the transmission rate of cells when it is needed. See cell rate. SCR sustainable cell rate The upper measure of a computed average rate of cell transmission over time. 76 © 2003 by CRC Press LLC on AIM networks supporting penn anent virtual connections (PVCs). Inverse Address Resolution Proto- col (InARP) supports dynamic address resolution enabling a protocol address corresponding to a given hardware address to be requested. See asynchronous transfer mode and the Appendix for a fuller explanation of ATM. See RFC 1293, RFC 1577. atmosphere 1. Ambience, mood, feeling about a location or room. 2. A gaseous mass enveloping a ce- lestial body. See atmosphere, Earth's. atmosphere, Earth's The gaseous envelope sur- rounding the Earth which provides breathable air, moisture, weather variations, protection from the sun's radiation, especially the ultraviolet rays, and particles which deflect radiant energy that can be harnessed for telecommunications. Atmospheric pressure at sea level is approx. 14.7 pounds per square inch, with local weather variations, and decreases some- what uniformly as altitude increases. Barometers are used to measure atmospheric weather, and baromet- ric altimeters indicate altitude through changes in pressures in the atmosphere. The atmosphere has been divided into three main re- gions. From the surface going away from the Earth, they are the troposphere, stratosphere, and ionosphere. See ionosphere. ATN See Aeronautical Telecommunications Net- work. atomA fundamental unit of energy or matter (depending upon how you look at it) that is the essential building block of molecules which, in tum, are fundamental building blocks ofelements. An atom is chemi- cally indivisible. However, from a physics point of view, atoms are described in terms of even smaller components, including protons, neutrons and their associated electrons. In the weird and wild world of quantum physics, there are even smaller units of energy called quarks and other atomic interactions yet to be fully understood. atomic clock An instrument devised in the 1940s for precise timing and synchronization, it is now particularly important in the u.S. Global Positioning Sys- tem (GPS) and many scientific research applications. An atomic clock uses the frequency associated with a quantum transition between two energy levels in an atom as its reference. It exploits the unique frequency characteristics of photons in a given transition. Atomic clock is actually ageneral category name for oscillators whose characteristics are based on quantum mechanical energy state transitions. Advanced atomic clocks can be accurate to within fractions of a second over hundreds of thousands of years. Space- based atomic clocks can be designed to be more accurate than Earth-based atomic clocks due to the lesser influence of the Earth's gravity. Coordinated Universal Time (UTC) reporting centers make use of atomic clocks for establishing an international time reference. Atomic clocks can be used to validate satellite data for integrity and accuracy for use in navigational applications. Synchronization between transmitting and receiving telecommunications stations can be maintained by means of atomic clocks or by a set of less expensive timing devices which, in tum, can derive their timing from the more expensive atomic clocks. In the early 1990s, atomic clocks were improved with the introduction of a Hewlett-Packard cesium-beam clock which was more rugged and more stable than previous models. Europe's Geostationary Navigation Overlay System (EGNOS) is being designed to use cesium and ru- bidium atomic clocks to provide System Time (ST) for calculating precise navigation infonnation for GPS-based land, marine, and air transportation systems. By using atomic clocks and GPS data from sat- ellites, rather than traditional beacon-based navigational methods, accuracy can be established within seven meters. Computers that are permanently or frequently connected to the Internet will sometimes be configured to poll the U.S. Naval Observatory atomic clock to synchronize their system clocks with the time on the Navy's clock. This synchronization is useful for time- sensitive file and database management and for time- critical e-commerce applications such as stock and auction transactions. Accurate time-stamp information is also useful for computer-based legal transactions and event tracking. The National Institute of Standards and Technology (NIST) sponsors a Web site called "A Walk through Time" that features infonnation and illustrations on time-keeping through the ages and the development of atomic clocks. See Coordinated Universal Time, Datum Corporation, Global Positioning System. http://physics.nist.gov/GenInt/Time/time.html atomic laser A device or process that emits matter in the same general sense as an optical laser stimu- lates the emission ofcoherent pulses of light. Such a laser was developed out of research on Bose-Einstein condensates in the mid-1990s by W. Ketterle et al. at MIT. Rather than using mirrors to deflect light within an optical cavity, they used magnetic fields to deflect matter in a magnetic cavity, using sodium atoms, which are magnetically sensitive, as the "ammuni- tion" for the atomic laser "gun." As energy is built up, a pulse of coherent matter manages to break through the magnetic barrier in much the same way as pulses of light break through the semitransparent mirrors of an optical cavity. The system was success- fully demonstrated and described in 1997. By Spring 2002, the scientists had found a way to emit a continuous stream of atoms. The potential for this technology in terms ofdesign- ing complex crystal lattices, diffraction gratings, circuit boards and other fabrications important to the semiconductor industry may be very great. The system works in the environment of a vacuum, so it's not quite as easy to set up, but it is fascinating technology which will no doubt by harnessed in exciting ways. For their discoveries, the inventors received a Nobel Prize in physics in 2001. See laser. atomic number Anumber characteristic determined by experimentation, since the atom is far too small 77 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary to be seen by any natural or microscopic means. This number is used to represent an element in a periodic table and describes electrons in relation to the protons in a neutral atom. ATS 1. See Applications Technology Satellite program. 2. Automation Tooling Systems. ATSC See Advanced Television Systems Committee. ATSC Digital TV Standard - Examples Doc. Date Description Al80 Jul 99 Modulation and Coding Requirements for Digital TV (DTV) Applications over Satellite. Modulation and data coding for satellite communications are defmed for a variety of programming types, including video, audio, data, multimedia, or others. It includes multiplexed bit streams such as MPEG-2. Al64A May 00 Transmission Measurement and Compliance for Digital Television describing test, monitoring, and measuring methods. Al65A May 00 The Program and System Information Protocol for Terrestrial Broadcast and Cable, providing a methodology for transporting digital television data and electronic program guide data with an amendment on Directed Channel Change (DCC) for program tailoring. Al90 JulOl The Data Broadcast Standard defining protocols for data transmission compatible with digital multiplex bit streams according to ISOIIEC 13818-1 (MPEG-2 systems) standards. The standard encompasses both non- TV and TV programming, including Webcasting, streaming video, etc. Al53B Aug 01 The Digital Television Standard for advanced television (ATV) systems. The document specifies the parameters and video encoding input scanning format, along with preprocessing and compression parameters of the video encoding. It describes audio encoder signal formats, preprocessing, and compression, as well as the service multiplex and transport layer characteristics and specifications. ATSC Digital Television Standard ATSC DTS. The 78 Advanced Television Systems Committee (ATSC) Technology Group on Distribution released the ATSC Digital Television Standard in September 1995 (Document AJ53) along with Document A/54 which describes use of the DTS. The DTS is based upon the ISO/IEC MPEG-2 Video Standard, the Digital Au- dio Compression (AC-3) Standard, and the ISOIIEC MPEG-2 Systems Standard. It was part of an ongo- ing effort to upgrade consumer broadcasting programming and equipment to reflect improvements in technology. The Digital Television Standard was, in large part, adopted by the Federal Communications Commis- sion (FCC) in December 1996 as well as by Canada and some Asian and South American countries. This influential document was revised by the ATSC and released asAJ53AinApri12001. It specifies the technical parameters of advanced TV systems. Examples of standards include those listed below. See Advanced Television Standards Committee. ATSE Academy of Technological Sciences and En- gineering. http://www.atse.org.au/ ATT See Automatic Toll Ticketing. attachment Something connected to or with. In data communications, a note or file that is attached to the end of an existing file or other electronic communication. Commonly, binary files are sent with email messages as attachments because the message text part of many email systems cannot transcribe or transmit 8-bit binary code. The system will convert the binary attachment to a compatible mode (e.g., 7-bit text) and reconvert it back to binary at the destina- tion. An email binary attachment allows you to send apicture, sound file, Adobe PostScript document, or other nontext transmission in conjunction with regu- lar text. attachment unitinterface, autonomous unitinterface AUI. Certain cables and connectors used to at- tach equipment to Ethernet transceivers. Commonly Ethernet connections are made via a printed circuit board installed in a slot in acomputerwith a BN C or RJ-45 connector protruding from the computer for making the connection to the Ethernet transceiver and cable. The ANSI/IEEE standard 802.3 (originally released as Document 1802.3-1991) defines an AUI physical layer interface called DB-15 or DIX. attack time The time it takes for asignal or sound to go from its initiation to its full volume or power. On a violin, for example, it's the time interval from the moment the bow begins to move and a consistent note achieves its full volume and tone. The attack time on an electronic system is the time it takes from the initiation ofapulse, signal, or power-on action until the system reaches its intended activation threshold, output, or throughput level. See decay time. ATTC See Advanced Television Test Center. attempt An effort to initiate or establish a communications connection. In some systems that are billed on a flat rate or per-call basis, attempts are not billed. In other systems, such as those that bill by air time, the attempts are charged by the minute or second whether or not the call is connected. © 2003 by CRC Press LLC attenuation The decrease between the power of the initial transmission and its power when received or measured at specified points, usually expressed as a ratio in decibels. Loss in power can result from distance, transmission lines, configurations, faults, and weather. See absorption, contrast with gain. attitudeandarticulation controlsubsystem AACS. A spacecraft guidance system employed on the Cassini spacecraft mission to permit dynamic control of rotation and translation maneuvers. The AACS uses star and sun sensors to establish reference points for determining its position. The main engine and smaller engines are used for propulsive maneuvers. Sensors estimate attitude and rate of both the base body and the articulated platforms. A series of vec- tors, kinematically propagated in time, aids the system in detennining motion of various bodies in relation to the base frame. The AACS works in conjunction with the command and data subsystem (CDS), which is the main processor on the craft. The CDS receives RF signals from Earth and sends information and control parameters to other systems, such as the AACS, accordingly. See Cassini. atto-(symb. - a) Used as a prefix to represent a very minute quantity, one quintillionth of, 10- 18 • See femto ATU See African Telecommunications Union. ATU-C ADSL transceiver unit-central office. A modem-like device installed at telephony central offices to process data communications received from the subscriber that are then fOlWarded through a data network to a subscriber-chosen data services provider. See Asymmetric Digital Subscriber Line. ATU-R ADSL transceiver unit-remote. A modem- like device installed on the subscriber premises to process data communications. It typically interfaces between the computer and a network interface device splitter. See Asymmetric Digital Subscriber Line. ATV 1. See advanced TV. 2. See amateur television. ATVEF See Advanced Television Enhancement Fo- rum. ATVEF Enhanced Content Specification A foun- dation specification developed by the Advanced Tele- vision Enhancement Forum for the creation of HTML-enhanced television content. It focuses mainly on existing technologies rather than promoting new ones, laying out a means for providing and viewing broadcast programming on the World Wide Web or through specialized viewing software similar to Web browsers. It promotes the reliable transmission ofa variety of types of broadcasts through Internet, cable, and land-based networks to computers, enhanced televisions, and dedicated enhanced TV consumer appliances. The specification is intended to encompass both one-way and two-way systems and both analog and digital systems. See Advanced Television Enhancement Forum, broadcast data trig- ger. audible ringing tone An audible signal transmitted to the calling party to let the caller know that the called number is ringing. See busy signal. audible sound Sound waves that are perceived by the ear/brain ofa particular species. Audible sound ranges vary from species to species, with humans hearing generally between the ranges of20 to 20,000 hertz. The upper ranges tend to drop off during the teenage years and decline gradually throughout a person's lifetime. Illnesses, very sudden loud noises, protracted loud noises, and sustained low level noises can have profound negative effects on a person's hearing. See audio, sound. audio Pertaining to sounds, primarily those within range of human perception, from frequencies of about 20 to 20,000 hertz (the upper range especially tends to diminish as people get older). The comfortable hearing range varies in loudness from a few decibels to about 80 decibels. At volumes near and above 160 decibels, permanent hearing damage is almost certain. Sudden loud sounds, frequent exposure to loud sounds, or even long-term exposure to medium level sounds can damage the sensitive structures associated with hearing. The types of sounds most commonly used for communication are speech and music. Most hearing is done with the ears, although some people augment their understanding of auditory information by read- ing lips or sensing physical vibrations through their fingers or bodies. Helen Keller was known for "lis- tening" to symphonies through a sensitive sound board placed in the symphony hall under her chair. Many deaf or hard-of-hearing people use their fin- gertips pressed against the larynx ofa speaker to aid in sensing auditory vibrations. While humans can hear a broad range of frequencies, not all these frequencies are used in human speech. We can detect pitches up to about 18,000 to 20,000 hertz but don't utter sounds that high in conversation. Thus, telephone and other speech circuits typically are not designed to transmit the full hearing range of frequencies and will be optimized for the frequencies associated with the information being transmitted. See acoustic. AudioMsual Service Specific Convergence Sub- layer AVSSCS. A multimedia convergence protocol for transmitting video over AAL5 using available bit rate (ABR) services. There is a particular focus on supporting MPEG over ATM as ATM has become a dominant networking medium and MPEG is a widely supported video format. ATM is capable of supporting simultaneous video and other data transmissions. See asynchronous transfer mode, MPOA. AudioApplications ProgrammingInterface AAPI. A library of functions designed to facilitate the design of audio applications. The functions can be called by compatible applications programs in order to in- teract with audio servers. Thus, the conversion, play- back, or recording of audio can be accomplished without each aspect of the application being written from the ground up (Le., without reinventing the wheel). Most operating systems now have AAPIs available for developers. Audio Engineering Society AES. Since 1948, the AES has been promoting and fostering the development and advancement of audio technologies. The AES Standards Committee contributes information 79 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary and technical expertise that supports national and international audio standards development. The Au- dio Engineering Society Historical Committee (AES HC) researches, collects, and preserves historical information and artifacts related to audio history. AES publishes the Journal of the Audio Engineering So- ciety and various papers and conference proceedings. http://www.aes.org/ audio frequency AF. A spectrum of wavelengths that can be heard. For humans this is from about 30 hertz up to about 20 kilohertz, although the upper level de- clines to about 16 to 18 kilohertz by adulthood. Audio Interchange File Format AlFF, Audio IFF. AIFF is a widely used audio file storage and exchange format descended from Interchange File Format (IFF). IFF is a flexible, multiplatform means of digitally encoding avariety of types ofmedia-related information (not just sound). IFF was developed in the mid-1980s by Electronic Arts and Commodore- Amiga. In 1985, the format quickly became standard on the Amiga computer. Later variations of the concept and the file format were ported to other platforms to provide compatibility with Amiga files. While TIFF, JPEG, and BMP have now superseded IFF for the exchange of image files, the Audio Inter- change File Format concept has survived and mi- grated to other platforms and has been adapted by Apple Computer, Inc. as the standard audio file format for Macintosh systems. AlFF facilitates the data storage and transmission of monaural (mono) and multichannel sound samples using a chunky format. On the Macintosh, it is stored in the data fork. AlFF is also supported on a number of professional workstations, including Avid Tech- nology and Silicon Graphics (SGl), and has further been adopted as a standard audio format by the Open Media Format Interchange (OMPI) group. The original IFF format is documented in the Amiga ROM Kernel manual, Appendix H. Details of Apple Computer's AIFF are available from Apple Devel- operTechrUcalSupport. Audio Messaging Interchange Specification AMIS. An analog telephony protocol that facilitates the exchange of voice mail messages among users on voice mail systemsfromdifferentvendors.AMIS specifications were released in the early 1990s. Not all the features of commercial voice mail systems can be directed through AMIS. Depending upon the implementation, AMIS may not permit broadcasting to multiple users on another system, and there may not be a full complement of confirmation messages available from the other systems. A number of commercial products implementing AMIS systems or interfacing with AMIS systems have been developed by large vendors such as Toshiba and Lucent. Active Voice Corporation claims to be the first voice processing systems manufacturer to incorporate AMIS standards into its products. See Voice Profile for In- ternet Mail. audio tape A type of magnetic storage medium used for audio recordings. Most audio tapes are small, so they can be used in portable tape decks or car stereos, 80 with playing times ranging from 10 to 120 minutes. Common music tapes are 30, 45, or 60 minutes per side for a double-sided tape. Some audio tapes are designed as a continuous loop with the tape ends fused for continuous playing. Video tapes are sometimes used as high quality audio tapes. Eight-track tape cartridges were introduced in the early 1960s and were popular for a few years. Cas- sette tapes were introduced soon after eight-tracks and eventually superseded them. By the 1980s, video tape-based audio recording approached CD sound quality. Computers in the late 1970s and early 1980s used large magnetic tape spools and small audio tapes (e.g., cassette tapes) for recording data. Various types of magnetic tape systems (e.g., DAT) are still used for data backups. As CD players become less expensive and more prevalent they provide higher quality sound reproduction than most tape systems and a less volatile alternative to data tape backups. audio-follow-video AFV In many broadcast systems, audio and video are recorded and/or transmitted separately. In AFV, the audio signals are automati- cally routed together with their associated video signals audio-on-demand AoD. Audio services provided to auser on request. AoD is one of the earliest services- on-demand (SoD) systems implemented in the telecommunications industry. In the days of operator- managed telephone services, imaginative service pro- viders realized they could place a phone at the switch- board center near a radio or gramophone player and play music for the subscriber on request. It was an unsophisticated system, but the concept was timely, and the idea is now implemented with digitally au- tomated technologies in the form of video-on-demand, and other custom request services. See services-on-demand, video-on-demand. AudioGram DeliveryServices ADS. A Nortel subscriber telephone service option that enables callers who get a busy signal or no answer to their ring to leave a message that will be delivered to the callee at a later scheduled time. Essentially it's a phone line answering machine service. audiographics A multimedia network communications system suitable for distance learning, in which remote computer screens are shared as a conference and lecture interactive medium for dynamically sharing images, video, and text. Electronic Classroom, written by Robert Crago for the Macintosh, is an example of this type of application, designed to work over public switched telephone networks (PSTNs). Audiographics is sometimes called telematics. Some people like to make a distinction between audiographics, which is the transmission of still images and sound, and videoconferencing, the transmission of motion video and sound. With improvements in technology, the distinction is blurring. See whiteboard- ing, electronic; videoconferencing. . audiometer, sonometer An instrument for measuring hearing acuity invented by Alexander Graham Bell. Bell's use of the Audiometer to test hearing was © 2003 by CRC Press LLC reported in October 1884 in the DeafMute Journal. At the April 1885 meeting of the National Academy of Sciences, Bell is reported to have demonstrated his Audiometer devised from two flat coils of insulated wire adjusted with graduated distances such that electrical cutrent from an armature between magnetic poles was passed through one coil (interrupted by a rotating disk), while a phone was attached to the other coil. Thus, the current could be used to control the intensity of the sound, and the responses of the chil- dren being tested could be recorded and analyzed. About 10% of the students tested with this early instrument were found by Bell to be hard of hearing in their better ear. While the Audiometer was initially used to test human hearing, many of the components developed for the audiometric industry (speakers, jacks, amplifiers, tone generators, transmission components, etc.) have since been adapted for telecommunications devices and testing systems (P.A. systems, telephony components,. transmission line testing equipment, etc.). Audiometers have become very sophisticated since their invention by Bell, and the term has become generic to a wide variety of audiometric instruments. Commercial audiometers now commonly include keyboards, internal digital storage for saving hundreds of audiograms, programmable functions, and serial interfaces for connecting to computers. Audion & Electron Tube Controlling Grid grid The triode electron tube (left), developedfrom the Fleming valve by Lee de Forest, is one of the most significant inventions in electronics history. The third element, a controllinggrid, added by de Forest to the two-element Fleming valve, enabled the flow of electrons, from the cathode to the anode, to be controlled. Electron tubes are now more streamlined and sophisticated than the original Audion electron tube which resembled a lightbulb with a plate, filament, andgrid inside and two wires running out the top. Audion An extremely significant invention of the early 1900s, evolutionarily descended from simple flame detectors, that led to the three-element vacuum electron tube patented by American inventor Lee de Forest. The Audion was a tantalum lamp with a mostly evacuated glass globe sealed around a filament and plate. A simple wire bent in a zigzag pattern became a grid, providing control over the flow of the electrons from the filament to the plate in a way that had not been previously possible. Thus, electron tubes could be used to amplify signals, not just rectify them, as in the Fleming oscillation valve upon which de Forest's Audion was based. This triode electron tube's control grid represented breakthrough technology which de Forest sold to AT &T at the bargain price of $50,000. It was used for decades throughout the electronics industry until it was superseded by the transistor for most consumer applications. Repeater devices based on the Audion enabled long-distance telephony. Interestingly, like many inventions through history, the inventor himself didn't understand the detailed mathematics/physics behind why the Audion worked, creating problems in manufacturing. The only way to know if the tube was good was to test it, and the sensitivity varied from tube to tube. Edwin 4rmstrong was one of the few early scientists to grasp some of the physics associated with the Audion's functioning. He authored an article in Electrical World in Decem- ber 1914, explaining the action of the Audion and how it could be more effective if more gases were removed from the bulb in manufacturing. The term Audion was originally trademarked but has become generic for three-element tubes. See de F or- est, Lee; Edison effect; electron tube; flame detec- tor; Fleming oscillation valve. Auditory Research Laboratory ARL. A lab at McGill University in Montreal, Canada specializing in the study of the perceptual organization of sound. augerA tool designed for boring, or a bit that fits into a drill designed to make large bore holes, which can be used for wiring installations. Augustine, Saint A philosopher who authored De civitate Dei (The city of God) in 428 AD. This important record of western knowledge includes historic observations of magnetic phenomena. AUI See Attachment Unit Interface. AUP See Acceptable Use Policy. aural Heard or perceived through the ear; auditory. See acoustic, sound. aurora Solar flare, anuclear effect from the sun that can sometimes be seen by its influence on the Earth's upper atmosphere. The ionization that results causes the undulating light shows we know as the aurora bo- realis and aurora australis. Aurora 1A regional communications satellite in geostationary orbit over Alaska. AUSEAnet The Australian-Asian network which supports multination VLSI project communications of the Assocation of Southeast Asian Nations (A SEAN) for sharing project information among par- ticipating countries. Australian CommunicationsAuthority ACA. The governing body of Australia responsible for regulat- ing telecommunications and radiocommunications, including the management of the radio frequency spectra and the National Numbering Plan. ACA also 81 © 2003 by CRC Press LLC . player and play music for the subscriber on request. It was an unsophisticated system, but the concept was timely, and the idea is now implemented with digitally au- tomated technologies in the form of video-on-demand, and other custom request services. See services-on-demand, video-on-demand. AudioGram DeliveryServices ADS. A Nortel subscriber. product from AT&T Global Information Solutions providing audio/video, file transfer, and application-sharing utilities over ISDN through ITU- TH Series and Q Series Recom- 74 mendations standards and encoding techniques. Atanasoff, John Vincent ( 190 3-1 99 5) An American physicist and inventor who developed. a vacuum tube calculating device in the mid- 193 0s that foreshad- owed the famous ENIAC computer that was opera- tional in the post-World War II years. In 193 9, with a small grant from Iowa State College, he pioneered the development of a

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