Fiber Optics Illustrated Dictionary - Part 74 doc

Fiber Optics Illustrated Dictionary Parabolic Antenna Examples This roofmounted parabolic antenna is about 81eet across and uses a meshparabola to reduce weight and wind resistance. the motion of objects and are used in the manufacture of reflectors and antennas. See parabolic antenna, parabolic reflector. concentrate and direct reflecting beams. See parabola, parabolic antenna. paradigm A clear or typical example, a standard, ideal, or archetype. paradigm shift A fundamental, significant change in the way something is perceived or understood, particularly if it has been taken for granted, or assumed to be true for a long time, or by amajority of the popu- lation.ln other words, the situation or thing itselfhas not changed, but our way ofunderstanding it has. A general paradigm shift occurred when humans, most of whom believed that the Earth was the center of the solar system and even the universe, acknowl- edged that the Earth revolves around the sun. The dis- covery that matter at the atomic level (quantum mechanics) did not behave according to accepted models of classical mechanics represented a paradigm shift in physics. Paradigm shifts often take a long time, sometimes decades or centuries (although tran- sition periods are collapsing as education and televi- sion become widespread), and those who first pro- pose new ideas and ways of looking at things are often pilloried or persecuted (even beaten to death or hanged) for their assertions. The suggestion that computers could be taught to be "intelligent," or to play games intelligently, was met with almost universal contempt in the 1960s and 1970s. In 1997, a computer beat a grandmaster chess player, an event that added credence to the argument that intelligent computers could be developed, and may someday surpass humans in specific or generalized intelligence, or develop machine intelligence ofwhich humans are not capable. parallel port An interface port on a computing system that permits the connection of parallel devices for the simultaneous transfer of data across multiple transmission wires. Most microcomputers are now standardized to 25-pin parallel D connectors, communicating with Centronics-compatible parallel protocols (although there are individual makers who use slight variations of the standard). Due to the increased speed of transmission over serial communications, parallel ports are commonly used for outputting to printers and other types ofperipherals like cartridge drives. See serial port. parallel processing Carrying out two or more tasks, more or less concurrently, usually with the intention of carrying out the processing at a faster speed, or otherwise more efficiently. See concurrent programming. parameter Aproperty which records, embodies, or determines a characteristic of an object or system. In communications, parameters affect many characteristics such as size, shape, speed, timing intervals, ad- dresses, identities, etc. parametric amplifier A type oflow noise, radio- fre- quency amplifier which employs high-frequency alternating current (AC) for power. Used with microwave frequency electron beam devices. parametric design The process ofusing general parameters, rather than individual measures, to automate computer-aided design and drafting (CAD) and One olthe bigger challenges in telecommunications is designing antennas and transmissions technologies that can communicate over vast distances in the in- clement, radiation-high, temperatllre-flllctllating environments characteristic 01space. The Cassini Sat- urn probe shown here in its testingphases, in 1996, is equipped on top with a parabolic radio antenna provided by the Italian Space Agency (AS1). [NASAIJPL image detail.} parabolic antenna An antenna designed with a characteristic parabolic "dish" shape that captures a directional beam and focuses it, usually through afeed horn. This shape is especially appropriate for very short, directional transmission waves, such as micro- waves, and the diameter of the antenna is designed to correspond with a multiple of the length of the wavelength being received. Parabolic antennas may be made from a variety of materials: solid metal, mesh metal, fiberglass. This style of antenna is commonly used for microwave satellite transmissions, though it is also used for some long-distance space applications, such as space probe communications. See antenna, feed hom, microwave antenna, low noise amplifier. reflector An antenna, or other reflector, which uti- lizes the characteristics of the shape ofa parabola to feed horn parabolic reflector supporting struts 722 © 2003 by CRC Press LLC computer-aided manufacturing (CAM). USPTO Patent Resources IlIet!IlIds ed systems far9JlNlfdal~ dIIIlJ1Slnyetl1l'ltt: IaxtDnjJay R.(8t!l!n9ham, WA); SDlIt: (StUmpllll, \VA): saao: DanJ.cetIlin9"1ln, WA). AeJlgnoe:~, (8lilllngnut, WA). Aflpl." oct. 3D, tams IilI1L a. : 0Il8f 3114 a.nmu.s. a.:MI13S1;3M114 t;3GSlI4I8;3G1IIISeRllllaf sa.dl:3I4/l senZ3" 3R,"·4' U.S. PI1'tn1 DocUlltlllltJ ~tl.,'I84~SoIOf713~OtL 'i8!Sllttsnlct:3MI'!Il'~\I .• 1S85L1ylnt"'" 1~7KatoetaI.SlI2/41)( ~~H8tteOtl;OIlYv .4.U1st11nfbtJt!tltw:HetndOI1,H R. ~,I#gtUJ:I4f'F11I4HlJgtlOC&Multat AmmOii tot generDng aparamtVie doal;n GIl. computer wlthoutthe u •• of. plogrll\ll'll!ng language A ~ to CflttUt uwltr Cffawlftg1rcmUlftICh oll'ltr drawtng. Of dlfr.rem llimomiont tanl!ton bo syll!he'lJel1 by llIodll1t CfmWlglntIJttd tsfOaeh dIm_nslllnln "'.m r CItlaWlng 1I#ln9 gl"e" I ~ll vlIllJe, It ial}l\>en a lablll. ,",e •• lab l'lln ~~ etlm ICltlt!htld.rpttYld •• MCSlllljntJont ~jCh ate c.alcuiafOd at d •• tlftltdln adtt~ pl5n WIlf 1\Ill, lIleaY'. ua •• ~.,4fI1U.to P'OIItp'~ unribr "~h detlgn vw. qIIlCOfporUti Irlt respCll\t, \IIftIl ~ lrda!he ~ plan 1f., JI'Of"e i. uncceor. a.equfJ't 1111l~. to, clartA1:aan. A' adrds1llan WO'lfd do llItl'P' Iw ltIit."alun 'M1Il dete. fnral boll"" 1ffl'9"plan and 1M IMfW' dt1lWlngto cr.e a ~stIod Cl1~ p.lr1%DQ¢ ."gn. lIle lS • ., UlKb thIt col\fl'ollirlg mlgn pI" to bt und lit a n.su OUM nap. Acing 4Jlll'!O The U.S. Patent and Trademark Office is endeavor- ing to make patent and trademark information available online to the public. Patent abstracts, descrip- tions, and diagrams are currently availablefor recent patents and images are availablefor historicpatents. Parametric design incorporates a form ofexpert system and is particularly valuable in situations where many small variations on a basic design (bolts, boxes, modem covers, PC boards, telephone handsets, etc.) need to be designed and manufactured. In these cases, a computer program can be used to automate the design process, by providing guidelines, rather than single-part measurements, to turn out the many needed variations thousands of times faster than a CAD operator could draw each one by hand. One of the early patents for an applied parametric design computer program was awarded to Synthesis (OfficeCad), in Washington State, in the 1980s. It can be accessed online, along with other patents filed since the mid-1970s, on the u.s. Patent and Trade- mark Office's Web site. See CAD, expert system. http://patents.uspto.gov/ parametric equalizer A component device used in sound systems to selectively manipulate selected frequencies in order to adjust the sound, usually to suit the taste of the listener. parasiteAn organism or process which feeds off another without providing a return. In technology, the term can refer to a process, or a mechanical or electrical device that monitors or uses transmissions clan- destinely, or without the usual compensation to the provider of the transmission. Small wiretap devices are sometimes called parasites, especially if they draw their power from the line being tapped. PARC, Xerox PARC See Palo Alto Research Center. parity Equality, state ofbeing the same, equivalent, matching. parity bitAbit which is included in a transmission for error checking or status purposes. In telecommunications over a modem, most protocols allow the use of a parity bit appended to a data stream ofa speci- fied length, the parity bit set to zero or one, depending upon the preceding data. Parity values calculated and stored as the sent bits are checked against parity values calculated from the received bits. See parity checking. parity checking A simple means of checking data integrity after a transmission by comparing the calculated value of the parity at the receiving end with the value calculated and stored at the sending end. Parity checking is very commonly used in file transfer through modems over phone lines. First the transmitting and receiving ends negotiate a common protocol, for example, ZModem, then the parity setting is selected as odd or even (or none). Assume aparity setting of even for this example. Par- ity is calculated prior to sending, by tallying the ones or zeros in a group of bits (usually seven), and then assigning a parity value of zero if there is an even number of one bits and of one if there is an odd number of one bits, (or the converse, by looking at zero bits for odd parity). The sender transmits the data and its associated parity bit. The receiver calculates the parity of the received bits and checks to see if there is a match with the transmitted parity bit. If not, there is a problem. The system is not foolproof; a match does not guar- antee that the data were correctly transmitted, as the parity bit itself may have become altered along with the data, but mechanisms in most software evaluate the frequency ofparityerrors so that the user may be alerted and the transmission aborted, restarted from an earlierpoint, or resumed later, depending upon the protocol. park drive In hard drives, "parking" the drive is a means to secure any moving mechanisms that may be damaged by being jiggled in transit. Some hard drives park automatically when not in use, and some use mechanisms to prevent damage if the unit is trans- ported (e.g., drives in laptops). Older drives were often equipped with software-parking, and it was quite important to run the software command to park the drive before moving the system or removing the drive. This system is now uncommon. Mobile computers are equipped with self-parking drives. park phone In telephony, parking is the process of putting a line through to a particular phone so that it can be picked up at another station, or to put a line on "soft hold" so the conversation can be continued from another phone. park timeout In telephony, a time limit on aparked line after which it hangs up the line if the call is not resumed on another line (or the same line). parking 1. In telephony, parking is the process of putting a line through to a particular phone so that it can be picked up at another station, or putting a line on "soft hold" so the conversation can be continued 723 . • •. : •. :.: , ;.~~~,: i:,:i © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary from another phone. 2. In computing, the process of securing a device so that any moving parts that might be damaged or that might damage other components are kept in check. For example, the read/write head ofa hard disk drive could damage the head and the magnetic media if it skitters across the drive when it is moved. Parking the drive through software or built- in electronic sensors ensures that this type of damage doesn't occur. Depending upon the operating system and type of drive, a drive may have to be unparked or mounted after it has been parked. Older OSs and drives tend not to be auto-parking. It may be necessary to run a software utility to park the drive when powering down the system to remove the drive or to move the computer system. 3. In general consumer electronics, the process of tying down, bolt- ing, or otherwise securing moving parts so they are not damaged or do not cause damage in transit. It is very common for laserdisc and compact disc players to have a transit bolt in the back to prevent the trays from moving around during shipment. Always take care to remove the transit bolt before use, save it by taping it to the manual or the underside of the player, and always reinsert the same bolt (the length may be important) before moving the equipment, especially if it is being shipped by a third party. Parkinson'slaw C. Northcote Parkinson wrote in the 1950s that work expands to fill the time available for its completion. (For those who are perfectionists, and believe that ifajob is worth doing, it's worth doing right, this is doubly true.) partial response/maximum likelihood PRML. PRML is a means of digitally encoding analog data and reconstructing it. This concept can be applied to many aspects of technology but has been particularly useful in the development of improved data broad- casting and storage devices. PRML-technology hard drives, for example, can provide high disc capacities and faster transfer rates than earlier technologies based on peak detection (the detection of voltage spikes resulting from magnetic flux reversals). Peak voltages become harder to detect as data are more densely packed (the peaks become dif- ficult to distinguish from the noise). To overcome this problem, a new approach, based on digitally sampling the analog signal, was developed. Vendors like Seagate have applied a PRML digital sampling and data reconstruction approach to the development of high-capacity drives that use partial response (PR) in magnetoresistive (MR) hard drive heads. These heads detect and sample an analog signal prior to Viterbi detection decoding. Together, PR and MR eliminate overhead in the electronic equal- ization (undershoot filtering) process, freeing up as much as an additional storage space. Maximum likelihood (ML) is used in the conversion of analog wave- forms into digital data. Through Viterbi detection, all possible combinations of data are checked for the best match of least error with the incoming data. The as- sumption is that the least error pattern will most likely be correct and, in practice, it works quite well. To- gether PR and ML enable faster data transfer rates 724 through run length limited (RLL) coding and significant areal density increases over peak detection meth- ods are possible. As PRML technology caught on and was adopted by a number of vendors, the algorithms and underlying technology were improved to the point where the higher performance versions were called extended partial response/maximum likelihood (EPRML) to reflect further significant improvements over the earlier PRML drives. See Super DLTtape. partition Subset, class, section, or division. partition, drive On hard drives, a usually contiguous section of a disk individually initialized and handled by the operating system as a distinct unit. Some systems can format the individual partitions in a variety of formats, Le., a I-Gbyte hard drive with a NeXTStep 400-Mbyte volume on one partition, a 400-Mbyte Linux volume on another, and a 200- Mhyte Macintosh volume on a third, all recognized by the OS and readable/writable without any unusual technical expertise or demands upon the user. On many microcomputer operating systems, disk volumes and files cannot cross partitions, but many Unix and workstation operating systems can handle volumes that cross partitions transparently to the user, e.g., two 500-Mbyte hard drives used together might appear to the user as a I-Gbyte virtual drive. There are many schools of thought as to whether a hard drive needs to be partitioned. A few operating systems can only handle up to four partitions, each with up to 2 Gbytes of space and, consequently, a larger hard drive must be sectioned into smaller pieces in order to be handled by the operating system. Others don't have this limitation on the number of partitions, and can manage larger-sized partitions. In terms of disk management, in the case of problems, it may be easier to rebuild partitions or handle data recovery procedures if there are several partitions rather than just one. Redundant array drives are another way of handling error recovery. Often a small 200- to 500-Mbyte partition will be set aside as a "swap drive" and not used for other purposes. See RAID. partition, memoryIn computer memory, a !jnked or contiguous section, separate from other sections, that is allocated for a specific purpose or process, such as video display or frame buffering. party I. One of the individuals in a transaction. A common legal term used to stipulate an individual or organizational entity. To be party to a transaction is to listen in or participate. In telecommunications, the transaction might be a telephone call, a conversation, or a computer communication. party line In telephony, a line shared by two or more subscribers, so if one or more subscribers pick up the line and listen when someone else is engaged in the call, they can hear the conversation, and can't make further calls until the current conversation is discon- nected. Party lines were very common on older shared phone circuits until the 1960s; they are now uneommon in North America. On ISDN lines and Frame Relay networks, a sort of party line system exists, but is rarely a hindrance to the user, unless too many © 2003 by CRC Press LLC subscribers are assigned to the line. party line, following Following the party line is a phrase from politics that indicates acceptance and promotion of the administration's point of view. The administration might be a political party, a business entity, or other institution. It is sometimes used as a derogatory phrase for ambitious compliance, or for a person who doesn't think for him- or herself, but pro- motes the current popular point of view. PAS 1. see profile alignment system. 2. See Priority Access Service. pascalAn SI unit of pressure equal to one newton per square meter. Pascal A programming language descended from ALGOL, developed by Niklaus Wirth in 1970. Pas- cal became especially popular in the 1980s for teach- ing programming concepts and techniques. A structured, typed language, Pascal is somewhat similar to Modula IT, and fits somewhere between C and higher level languages like BASIC and FORTRAN. It is less cryptic than C, but also less preferred by programmers in commercial development environments, yet is generally preferred over the less structured BASIC in educational environments. See Modula IT, C. Pascal, Blaise (1623-1662) A talented French inventor and mathematician, Pascal devised one of the ear- liest calculators, a"Pascaline," while still in his teens. It was a numerical base ten, movable dial, wheel calculator designed to assist his father in carrying out his duties as a tax collector. Pascal appears to have come up with the design independently, and probably was not aware of the earlier calculator developed by Schickard at about the time ofPascal's birth. Pascal also did research in fluid dynamics. See Schickard, Wilhelm. pass through v. To move through a component device or leg ofa network without significantly alter- ing the characteristics of that which has just been passed through, or without being altered by that which is passed through. See passthrough device, tunneling. passband 1. The range of transmission frequencies that can pass through a filter without a significant de- crease in amplitude (attenuation). A passband filter allows selective screening out of irrelevant or undes- ired frequencies in order to create a device for a specific purpose, or to simplify its operation. 2. A signal that loses no spectral energy at direct currents (DC), unlike a baseband signal. A Manchester-encoded signal is one example ofa passband signal. passthrough device 1. A device chained between two other devices, which passes data through without changing them. For example, an external memory module might be attached to a computer, with an external hard drive attached to the memory module. The memory module passes through the hard drive signals in such a way that the hard drive works just as though it were directly attached to the computer. See daisy chain. 2. A device that provides access to and passes back the signals transmitted by another. Some- times used as a diagnostic tool. password A word or combination of characters which, when provided by a person or entity wishing to gain entry to a system or situation, is checked against certain characteristics, or a list of those who are authorized to have access. If a match is found, entry is permitted. Password protection systems are very common on computers and networks. It is very unwise to tape passwords to monitors or desks where anyone can see them. It is also unwise to use common words as passwords; a moderately long password with a combination of letters and symbols is safer. See anonymous FTP, back door, back porch. patch v. To connect one circuit with another, usually through an intermediate line. For example, on old telephone switchboards, the operator would patch through a call by taking ajack connected at the other end to the main switchboard, and plugging it into the phone receptacle for the individual getting the call. A patch is a temporary connection, one subject to frequent change or used for diagnostic purposes. patch, software n. In software, a patch is a piece of code that is inserted into the original code to over- ride some of the original programming, or to add capabilities or data which weren't in the original code and perhaps should have been. A patch is distin- guished from an upgrade in that it typically is intended to correct oversights or errors, whereas an upgrade is usually ofgreater scope, intended to enhance or ex- tend the capabilities of the program. In many products, the two are combined. patch,sound In electronic music, a sampled segment of sound stored digitally. The sound is measured and recorded, that is, "quantized," at rapid intervals in order to create a digital impression of the analog sound wave. For the most part, the more frequent the sampling, up to the limits of human perception, the more true to the original the sample tends to sound (the capabilities of the playback mechanism contribute as well). Sound patches can be generated by and used with many commercial sound synthesizers and computer synthesizer software. MIDI is a common protocol used in the music industry for communicating digitized sound between MIDI-compatible instru- ments and software programs. Speech and music sound patches are often used to enhance multimedia CD-ROM educational and entertainment products. More recently, messages composed from speech patches are becoming common on the Web. See quan- tize, sampling. patch bay, patch board A hardware panel designed with multiple connecting ports such that the configuration of the patched in cables can be readily changed. In other words, it is set up so that temporary circuits, or those which are frequently changed, can easily be rewired. Dishwasher-sized patch bays are often equipped with wheels so they can be moved in or out of a work area, and usually have receptacles or ter- minals for easy insertion and removal of patch cords and/or wires. Patch boards are useful for prototyping, monitoring, and testing new circuit layouts. See patch panel. patch cord A short length of wire or cable used to connect circuits. The connectors at either end vary, but are often RCA jacks or BNC connectors. Patch 725 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary cords are commonly used with patch bays, patch panels, and electronics components. Videographers and musicians often refer to video and audio connecting cables as patch cords, since video equipment connections are frequently reconfigured. patch panelA hardware device, often wall-mounted, that facilitates the connection and reconfiguration of temporary circuits. Patch panels are often mounted in areas that are accessible to technicians but not to casual passersby, such as in maintenance closets. A patch panel may resemble a distribution frame, in that it has a grid of openings or connectors through which circuits can be routed. It commonly has mounted receptacles to match the types ofjacks used in that par- ti cular circuit. Fiber optic patch panels are typically made with greater precision and strain relief assemblies than CAT-5 Ethernet panels, for example, because the integrity of the coupling in fiber optic connections is crucial to its effectiveness. Patch Panel- Fiber Optic Patch panels faCilitate the coupling and quick reor- ganization of wire orfiber optic connections. The panels are commonly installed on walls or in wiring closets where casualpassersby can ~ knock ortamper with the connectors. This panel illustrates banks of common SC- (top) and ST- fiber optic connecting ports. Connectors may have locking mechanisms with alignment slots and knobs (e.g .• bayonet mounts) to prevent accidental disconnection Depending upon the type of panel and connectors. the panel may be passive. linking the connections straight across, or active, with electronics built in to the panel to influence the signals (e.g .• providing am- plification). Patel, C. Kumar N. (1938- )An Indian-born Ameri- can physicist with an interest in optics, especially molecular spectroscopy and laser systems. Patel stud- ied in India and at Stanford University, then began his career at Bell Labs in 1961 where he became Executive Director of Research, Materials Science, Engineering and Academic Affairs, a position he held until 1993. He then served as Vice Chancellor ofRe- search at UCLA until 1999 and as President & CEO of Pranalvtica. Patel holds over 30 patents and has received many honors, including the OSA Lomb Medal and the Na- tional Medal of Science (1996) for the invention of 726 the first nitrogen CO 2 laser in 1964. He was also in- strumental in the development of the Raman laser, a tunable laser demonstrated in 1969. Patel has continued to actively pursue applications of lasers. In June 1997 he and his colleagues submitted a patent application for an optical bit rate converter suitable for time division multiplexed (TOM) multiaccess communications networks. See Javan, Ali. patentAregistration process fonnally established in the United States in April 1790 which provides a record of the ownership, development, and date and method of creation of unique products and processes. The first American patent was granted on 31 July 1790. By 1802, applications had increased to the point where a separate Patent Office was set up, and more rigorous scrutiny was established by 1836. In the United States, the documents are processed and stored in a central government repository that is open to the public and intended to further technological progress by the encouragement of the dissemination of ideas. Japanese patents have been available over networks for some time now, and recent U.S. patents are now searchable on the Web through the U.S. Patent and Trademark Office site. The Clinton Ad- ministration announced on June 25, 1998 that over 20 million pages of patent and trademark infonna- tion would be provided free to the public on the In- ternet by year's end. Content is supplied through the Commerce Department's large database of text and images. The collection will include the full text of2 million patents dating from 1976, 800,000 trademarks and 300,000 pending registrations dating from the 1800s. Tiff images are available for historic patents. Patent applications must follow very specific fonnat and content guidelines laid out by the patent office. Patent registration grants exclusive intellectual and certain commercialization protections to the inventor for a tenn of 17 years in the U.S. (international patents are similar). In cases of others coming up with the same idea simultaneously or previously, without knowledge that the idea has been patented, preference for the idea now goes to the inventor who first is granted the patent. This is a change from historical procedures in which an earlier inventor, if she or he had documents to prove the case, could have apatent from a later inventor overturned. Many people incorrectly assume that the patent process exists to explicitly prevent others from infring- ing on patents, but it is the responsibility of the patent owners, not the patent office, to police the use and abuse of patented ideas. The patent does, however, defme the nature and extent of the legal protection available to the inventor through the justice system. Granting of a patent does not include granting ofa right to manufacture a product incorporating the idea, since other patents for other aspects of the invention may exist. The most important aspect of the patent and the sub- mission of patent applications is the Claims section, in which the inventor lays out, in point form, the characteristics which make the invention unique and nonobvious. Some or all of these claims may be © 2003 by CRC Press LLC accepted by the patent office, and the document is cri- tiqued and rejected or returned to the applicant for revisions. Since uniqueness is often evaluated in a historical context in the Prior Art section, historical antecedents and current similar inventions must be described by the applicant thoroughly and succinctly. The invention must also be more than a half-baked idea, since the patent application must include a clear description of how to build or otherwise recreate the invention itself, without undue difficulty to a layper- son or someone appropriately skilled in the area of specialization appropriate to a specialized invention. Hardware patents usually fall under the products category and software patents under the process category. Note that patents, copyrights, and other legal registration procedures may grant ownership to the employer of the inventor rather than the inventor, if the employee undertook the invention in the course of his or her normal work hours or duties. One of the most famous patent clerks in history was Albert Einstein, who worked as ajunior clerk in the Swiss Patent Office when unable to find work as a teacher or research scientist. While working there, he wrote some of his most startling, insightful treatises on relativity. See copyright, trademark. http://www.uspto.gov/ Paterson, Tim Paterson developed a simple but his- torically important disk operating system for Seattle Computer Products in the late 1970s. The product was derived from Gary Kildall 's CP 1M operating system, which was the most successful and well known at the time, with over halfa million copies distributed. Pater- son created a basic operating system called QDOS (Quick and Dirty Operating System) which he has stated was derived in part from the program interface described in a CPM manual from the mid-1970s. Microsoft bought it, fIXed it up a little, and provided it to ffiM soon after. ffiM released it initially as PC DOS 1.0. Meanwhile, Seattle Computer Products re- tained the rights to QDOS. Microsoft subsequently bought out all QDOS distribution rights for $50,000. The Microsoft financial empire essentially sprung from this transaction as the product was developed into MS-DOS and, eventually, after many facelifts and enhancements, evolved into Windows. See Digi- tal Research; Kildall, Gary; Microsoft Corporation. path A route, track, directional identifier, runway, conduit, or other end-to-end, hop-to-hop, or as-you- go means of delineating the track followed by a person, process, transmission, or data unit while travel- ing from one point, node, or endpoint to another. A file path is one which indicates the hierarchical organization and location ofa specific file or grouping of files. A transmissions path is the specific or general direction of radiant energy travel. path information unit PIU. In packet networking, a message unit consisting of a transmission header (TM) or a transmission header combined with a following basic information unit (BIU) or segment. See datagram. Path Terminating Element See SONET path terminating element. pattern matching, pattern recognition The process of comparing text, symbols, images, or other elements to determine whether they are the same, similar, or mathematically equal. The process of pattern matching is widely used in database search and analysis mechanisms, and its cousin, pattern recognition, is common to artificial intelligence applications including expert systems, robotics, and others. Pattern recognition was in its infancy in the late 1950s and early 1960s, when computing systems were ex- pensive, cumbersome, and programmed with punch cards. Nevertheless, early researchers at the time, sensing its potential, developed equipment and algorithms which could read a few handwritten letters, if they were plainly written. See Perceptrons. pay phone, pay telephone See payphone. payload The user information, and sometimes ac- counting and network administration information, carried in the upper layers in a layered architecture, within a cell, frame, packet, or other network data transmission unit. Separate from but associated with the payload, there is frequently signaling, header, error checking, and other data which relate more to the type and manner of transmission than to the information content from the user or process sending the transmission. Payload Data Segment PDS. In communications satellites, the data services that are made available to authorized users. See Unified User Interface. Payment Extension Protocol PEP. An HTTP payment extension protocol described by the JEPI project in August 1996 in conjunction with seven examples of the Universal Payment Preamble (UPP) that could be used over PEP. The purpose of the system was to develop apractical, automatable payment system for running over the widely distributed HTTP applications on the Web. PEP enables UPP to be embedded in HTTP to support Web client/server payment trans- actions. Examples of basic payment mechanisms include queries to determine what types of payment forms are supported, presentation of payment options, demand payment options, payment acceptance/rejec- tion, and payment option queries. See e-commerce, JEPI, Universal Payment Preamble. payphone, paystation phone Any self-contained public or private telephone unit that requires a per- call or per-minute fee, usually directly transacted with the phone. Although some human-operated stations exist most require payment by coin or stripe card. The first pay telephones were attended by operators who collected the fees for the calls. One of the early coin box patents was issued in 1885, and William Gray installed a public coin phone in Connecticut in 1889 while employed by Pratt & Whitney. payphone postpay Payphone calls paid after completion, usually with a calling card or credit card. payphone, private Also known as COCOT, this is a customer-owned coin-operated phone, as might be found in a hotel lobby or tavern. COCOTs may provide only limited access to long-distance carriers. PBX Private Branch Exchange. See Private Auto- matic Branch Exchange. 727 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary PC 1. personal computer. While many people use PC to refer specifically to IBM and third-party licensed hardware, in fact, PC correctly refers not only to Intell IBM computers, but also to any personal computer or microcomputer priced in a consumer or small business price range. 2. printed circuit. See printed circuit board. 3. program counter. 4. protocol control. PC card See PCMCIA card. PC, IBM/Intel colloq. In general and marketing terms, PC is understood as a subset of personal computers, consisting of Intel-based IBM hardware, or third-party licensed hardware, running the IBM OS/2 software or, more commonly, running the Microsoft Windows graphical operating environment in conjunction with MS-DOS. For information on specific IBM desktop computers, see the listings under IBM Personal Computers. PCA 1. point of closest approach. In a satellite communications system, a point on a segment of the orbit or ground track when the satellite is closest to a specific ground station. 2. Premises Cabling Associa- tion. 3. protective connecting arrangement. Commer- cial connecting rental agreement, required by AT&T / Bell prior to divestiture for telecommunications devices that were not AT &T /Bell, were connected to the AT &T !Bell system. See Carterfone decision. PCB 1. power control box. 2. power control box. 3. process control block. 4. See printed circuit board. 5. protocol control block (in TCP and similar network protocols ). PCCA See Portable Computer and Communications Association. PCF See photonic crystal fiber. PCI 1. See Peripheral Connect Interface. 2. Protocol Control Information. PCIA Personal Communications Industry Associa- tion. F onnerly known as Telocator, PCIA is a national association representing the mobile communications industry. PCL See printer control language. PCM 1. See phase conjugation mirror. 2. See pulse code modulation. PCMCIA Personal Computer Memory Card Inter- face Association. A professional association of electronics peripherals and semiconductor manufacturers and software engineers. See PCMCIA card, PCMCIA standards. PCMCIA card, PC card A standardized computer peripheral card fonnat, not much bigger than a fat wallet card, which is commonly used in portable computing applications. PCMCIA cards (since the mid- 1990s called PC cards because it's easier to say) are microminiaturized devices with a thin edge connec- tor, including memory cards, hard drive cards, fax/ modem cards, network interface hookups, and more. They are used in radio phones, laptop and palmtop computers, digital cameras and camcorders, and vari- ous other portable electronic devices. The most common cards are called Type I or Type II (Type III is less common, and Type IV is vendor-specific). Most laptop peripherals use Type II cards, and it pays to have at least one Type II slot on a portable computer. 728 Hard drives and radio devices tend to use the thicker Type III cards. PCMCIA standards A set of 8-bit bus standards which bears the same name as the organization which developed the standards, the Personal Computer Memory Card Interface Association. PCMCIA standards were developed and tested in the late 1980s and released for general use in 1991. While there is fairly good adherence to the standards, compatibility is not absolute. It's advisable to try cards before buying them, or to get them with a good return policy. The set of standards includes Type I, Type II, Type III, and Type IV. See PCMCIA card. PCMIA Personal Computer Manufacturer Interface Adaptor. PCN See Personal Communication Network. PCO See Private Cable Operator. PCP 1. See Predictor Compression Protocol. 2. Pri- vate Carrier Paging. PCR 1. See peak cell rate. 2. See phase change re- writable. 3. problem/change report. 4. See processor configuration register. 5. See Program Clock Refer- ence. PCS 1. See Personal Communications Service. 2. personal communications software. PD See phase drive. PDA See PDA microbrowser, PDA macrobrowser, Personal Digital Assistant. Web-Compatible PDA Macrobrowser A full color, graphics-capable Palm personal digital assistant (PDA) connected via radio link to the Internet and installed with the SojtSource/Catarra HTML-compatible macrobrowser client, which provides thefull-featured Web surfing of a desktop computer, with a pen to scroll, click, enlarge, or cany out other typical browser actions. This fully HTML-compatible combination of hardware and software has many advantages over more limited microbrowsers and WAP technologies, including the convenience of accessing standard Web pages and securityfeatures rather than requiring special software designed for WAP-based devices. WAP is appropriate for limited resource devices, but for full Web browsing, the SojtSource/Catarra server/client combination is currently the only product that provides unrestricted graphical Web-surfing on PDA mobile devices. © 2003 by CRC Press LLC PDA macrobrowserA software application providing full Web compatibility on limited-resource portable devices through quick conversion and display algorithms transparent to users, Web page designers, and security providers. Macrobrowsers include display software technology installed on a Personal Digi- tal Assistant (PDA) working in conjunction with a proxy server. Thus, unlike microbrowsers, information providers don't have to maintain two sets of Web pages or a separate type of digital certificate - a macrobrowser supports the existing Web infrastructure. Macrobrowsers began appearing in 2001 as PDAs with better memory and display technologies were released. They will likely co-exist with microbrowsers for a while, but may supersede them due to the im- proving power and resolution of handheld wireless devices and the relative ease of implementing Web pages and security features compatible with macrobrowser-enabled devices. See PDA microbrowser, SoftSource, Wireless Application Protocol. PDA microbrowser A software application designed to provide limited Web access compatibility for con- strained-resource devices. Microbrowsers began to appear on the market in 1999. In general, they imple- ment limited-set, proprietary, or specialized adapta- tions of current Web browsing languages to run effectively on Personal Digital Assistant (PDA) devices with limited memory and display resolutions. The most common strategy for micro browsers is to run a Web proxy gateway and to adapt Web pages to the limited-set languages compatible with these devices, through simplified/specialized markup languages. Microbrowsers are a reasonable way to support con- strained-environment handheld computing devices, but put an extra burden of time and expense on Web page designers, programmers, and security providers, as two sets of Web pages and digital certificates must be maintained if microbrowsers and regular HTML browsers are to be supported on the same Web site. Microbrowsers will remain viable for a while for limited-resource devices but may eventually be superseded by PDA macrobrowsers for general purpose browsing, as handheld devices become more powerful and feature-rich. See CHTML, PDA macrobrowser, Personal Digital Assistant, W AP Forum. PDC See Personal Digital Cellular. PDF See Portal Document Format. PDL See page description language. PDP 1. See plasma display panel. 2. See power distribution panel. PDP- A series of Digital Equipment Corporation (DEC) Programmed Data Processors (PDPs) that would today be called minicomputers. Right from the beginning, the PDP-x series filled a need for powerful, smaller-scale, lower-cost computers. The PDP-l sold for only a tenth of the price of many computer behemoth mainframes. This made the PDP-line mar- ketable to educational institutions and businesses that couldn't afford million-dollar computing systems and they became very popular with computer science stu- dents, with many user (and hacker) groups springing up around the machines. DEC's first computer, the 18-bit PDP-I was released in 1960 and a PDP-3 was built by a DEC client. The PDP-4 and PDP-5 followed in 1962 and 1963 and DEC released about one a year from then on. By the mid-1960s, DEC had launched a desktop model of the PDP-8. To be useful, it needed lots of peripherals, and its price was far beyond the range of personal computer owners, but for under $20,000, it was a tran- sitional machine to the smaller scale mini- and, eventually, desktop computers of the late 1970s and beyond. By the early 1970s, the series was up to the PDP-16, but many purchasers were still using PDP-8, PDP-I0, and PDP-II machines into the 1980s. The PDP-x series was gradually superseded by DEC's VAX computers in the mid-1980s, but hobbyists still like to pick up the PDP-x computers at auctions and computer salvages. See VAX. PDS See Payload Data Segment. PDU See Protocol Data Unit. PDUS Primary Data User Station. The combination of a ground station and a satellite image processing system. peak cell rate PCR. In ATM networking, a traffic flow measure that describes the upper cell rate limit, which may not be exceeded by the sender. See cell rate. peer entities In layer-oriented network models, entities within the same layer, usually diagramed and visualized as horizontally related. peer model A networking model built with the as- ;r~E:~i~:~:tf~:~;~~E:;£~~::~t~:n:~~ I. internetwork layer routing can be exchanged. See in- tegrated model. peering The voluntary exchange of routing an- nouncements in order to effectively establish data paths among providers. PEG Regulated Public, Educational or Government access. See cable access. Pel See picture element. Pender, John (ca. 1860-1896) A British merchant who succeeded in establishing ambitious historic telegraph cable links between Western Europe and the Far East and Australia. In 1856, John Pender became a director in the Atlantic Telegraph Company and thus was involved in the first transatlantic cable enterprise spearheaded by Cyrus W. Field. Pender's subsequent ventures indicate that he was inspired by the success of the Atlantic telegraph cable installation and its future economic impact. Wanting to get in on the ground floor of the new industry, in 1864, Pender formed the Telegraph Con- struction and Maintenance Company (Telcon), fore- seeing the future need for cable manufacture and maintenance. Not satisfied with this alone, however, he then founded the British Indian Submarine Tele- graph Company, in 1869, with the goal of linking Britain and India. For building the local Falmouth link, Pender formed the Falmouth-Gibralter-Malta Telegraph Company but soon changed it to the more generic Eastern Telegraph Company as plans and 729 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary locations changed as the project advanced and the port location was changed to Porthcurnow (later Porthcurno - PK). By 1879 Pender was not only a significant telecommunications magnate, but had realized the remarkable feat of building a telegraph cable link between London, England, and Bombay, India. In 1882, Douro mail steamer and passenger ship sank off Cape Finisterre following acollision with a Span- ish steamer. The John Pender telegraph ship, part of Eastern Telegraph's fleet, was nearby and took offa number of passengers, providing them with basic needs and enabling them to telegraph their loved ones with reassurances. See Field, Cyrus West; Porthcurno. penetration Gaining access to a system, circuit, fa- cility, or operation, usually for security reasons or unlawful access. Physical penetration of circuits or networks can be done through means of taps or black boxes. Logical penetration can be done through password-guessing, Trojan horses, viruses, and back doors. Bodily penetration can be done through over- riding electronic security measures, entering as an impostor, or using insider privileged access in an un- ethical manner. See back door, Trojan horse. penetration tap I. Any means by which aconductor is accessed by piercing the outer layers ofshielding and grounding and connecting to the current circuit, with the intention of not disrupting current transmissions. 2. A network connection technique which enables devices to be attached to the network cable without interrupting current network operation. The tap is carried out with a sharp tool which can pierce the outer and inner ground shielding of the network cable, such as a coaxial cable commonly used in Ethernet implementations. penetration testing Testing a system for the integrity of its security. This is sometimes done by inter- nal staff, contractors installing the security measures, or outside experts hired to try to penetrate the system. In the telephone and computing worlds, known "hackers" are sometimes hired to try to penetrate a system to try to identify security holes before the system is opened up to employees or the public, depending upon its nature. In 1998 it was found that cash cards, which were generally considered reasonably safe from decryption and unauthorized use, could be penetrated by measuring their electrical emanations and properties, a finding that calls into question the use of cash cards in place oftraditional means of cur- rency exchange. Pentium An Intel Corporation 80586-based central processing unit (CPU), designed to succeed the 80486, introduced in 1993. Originally released at 66 MHz clock speed, other versions came out, including a 100 MHz version with a l6-bit cache and a 64- bit memory interface, and eight 32-bit general-purpose processing registers. The name is derived from the "5" in the processor line 80x86 due to a court rul- ing that a number cannot be trademarked. Pentium II An Intel Corporation central processing unit (CPU) similar to the Pentium Pro. Unlike the Pentium Pro, which incorporates the level 2 (L2) 730 cache into the chip with the CPU, the Pentium II op- erates with a cache inserted in a slot on the motherboard, thereby increasing the amount of time it takes for the two to communicate. It also incorporates MMX circuitry intended to improve graphics and multimedia-related operations. Pentium MMX Pentium Multimedia Extension, Pen- tium Matrix Math Extension. The MMX is essentially a Pentium Pro chip enhanced with a number of new data types and floating point instructions that enhance computing-intensive operations such as graphics. Applications are becoming increasingly visual in nature, with more graphical user interfaces, image processing, rendering and raytracing, videoconferencing, realtime games, and virtual reality applications, so support for commonly executed graphics and math- intensive computing processes on the chip is intended to support these growing areas ofinterest. Also, by incorporating capabilities similar to those supplied by direct memory access (DSP), Intel can reduce its re- liance on the DSP technologies ofother vendors The Pentium MMX incorporates what Intel calls Single Instruction, Multiple Data (SIMD) techniques to allow several processes to be carried out with a single instruction. See Pentium II, reduced instruction set computing. Pentium Pro, P6 An Intel Corporation 80686 central processing unit (CPU) in the Pentium brand name line, introduced in 1995 as a successor to the Pentium processor. The Pentium Pro originally shipped as a 133-MHz CPU and shares a number ofcommonali- ties with the Pentium, including a 64-bit memory interface. It is a two-part chip in the sense that it has a CPU and a level I memory cache, plus a level 2 (L2) memory cache layered into the CPU rather than re- siding separately on the motherboard. It is a hybrid chip with an underlying RISC structure, but also includes a CISC-RISC translator for downward compatibility. The clock speed of the first version was 133-MHz, with other versions following. People's Communication Charter A global move- ment by a number of international communications associations to demand the protection of the quality ofcommunication services, their accessibility, afford- ability, and ease of use by the public in order to safe- guard basic human rights. The Charter grew out of concerns about new and existing communication technologies conscripted around the world by self- interested governments or allocated preferentially to private parties for use as conduits for information delivery for propaganda or for-profit ventures, at the expense of communications supporting education, community needs, and civil rights. See Milan Decla- ration on Communication and Human Rights. http://www.waag.org/pcc PEP I. Packetized Ensemble Protocol. A high-speed, proprietary, full duplex transmission protocol from Telebit. It has error-correcting mechanisms and is said to handle line noise well; it is no longer in general use. 2. See Payment Extension Protocol. 3. See Pub- lic Exchange Point. PER See Packed Encoding Rules. © 2003 by CRC Press LLC Percent Local Usage PLU. A measure of telecommunications usage by time. PLU is a ratio of the local minutes to the sum of local and intraLATA long- distance minutes between exchange carriers, sent over Local Interconnection Trunks. Switched access and transiting calls are not included. Perceptrons Self-organizing, pattern recognition systems built in the early 1960s at Cornell University. These systems were rudimentary, barely managing to recognize simple letters, yet studies and experiments of this kind led to the optical character recognition and handwriting recognition systems we now take for granted. At the same time, at the Massachusetts Institute of Technology (MIT), researchers were developing pattern-matching systems for medical diagnosis, with a system designed to screen for cancer cells through a microscope. See neural networks, pattern matching. perforatorA tool to make a hole, to penetrate a substance, to punch an opening. Common three-hole punches are perforators. Electronic perforators are widely used to turn electronic signals into code pattern holes in punch cards and paper tapes. See chad, Hollerith card, punch card. performance category See category of performance. perigee The point in an orbit nearest the gravitational center of the body being orbited. See apogee, periapsis. The perigee is the closestpoint of an orbitingobject to the body being orbited. period 1. Cycle, interval of time, portion of time en- compassing a distinct culture (historical period). 2. Geologic time division that is part of an era and longer than an epoch. 3. The time interval between two con- secutive orbits ofa satellite through a specific point (usually the perigee) in the orbit. 4. In electronics, one interval ofa regular, repeating event. Peripheral Component Interconnect, Peripheral Connect Interface PCI. A very popular local bus standard developed by Intel in the early 1990s to support 32/64 bit data that was compatible with the new Pentium processors coming out at the time. It was designed with a newer chipset, to improve on the ISAs and VLBs that were then common, and to include bus mastering (use of the system bus). Since PCl's development, PCI slots have become common in Apple Macintosh and Intel-based mM-licensed machines, along with upgraded versions of the VESA VL bus. The PCI Mezzanine Card (IEEE P1386.1) was designed to work with the PCI specification. peripheral device 1. Apiece ofequipment which is not a main component of a system, but which, when connected to that system, enhances its functionality, speed, or storage capabilities. Peripheral devices generally cannot perfonn useful functions unless connected to the main system. Monitors, 'speakers, key- boards, scanners, video cameras, and printers are examples of peripheral devices. CD-ROM drives are an exception in that some are now designed to play audio CDs even if not connected to a computer. 2. In the telephone industry peripherals may also be called outboard processors, applications processors, or ad- junct processors. Perl Practical extraction and reporting language. A powerful, flexible, general-purpose, interpreted scriptin~ language (originally spelled with a lower- case "p' ) developed by Larry Wall in 1986, and now extensively used for platform-independent scripting on multiple platforms on the Internet. The syntacti- cal structure ofPerl is quite remarkable (perhaps ow- ing to Larry Wall's expertise as a linguist); useful, powerful routines can be written in a few lines or sometimes even in a few characters. An important tool for shell scripting, Common Gateway Interface (CGn development, and much more. When combined with Penguin, it may be a serious contender with Java for object-oriented, Web-related interface design and Automation. The Perl Journal gives practical assis- tance to Perl programmers. Permanent Number Portability PNP. A way for a ::~~n:~j~~tit~f:;~~~~~:~e~:~~n~~:;~~ • to a different service provider in the same locality. permanentvirtualconnection,permanentvirtual circuit PVC. A logical communications channel (which may differ from the physical topology over which it is laid) established to stay the same for some time. In an ATM environment, there are two types of PVCs: permanent virtual path connections (PVPCs) and permanent virtual channel connections (PVCCs). PVCs provide manually configured connections between end systems. The addressing information, Vir- tual Path IdentifierNirtual Channel Identifier (VPI/ VCI), must be put into both devices for connectivity. 2. In Frame Relay networks, a PVC is a logical link, with network management-defined endpoints and Class ofService (CoS). The link consists of an origi- nating element address, data link control identifier, terminating element address, and termination data link control identifier. See RFC 1577. permeability The porosity orpenetrability ofa substance. The degree to which liquids or gases can pass through a substance. Contrast with reluctance. permeability, magnetic The property of amagnetiz- able material that determines the degree to which it will modify the magnetic flux in a region it occupies within a magnetic field. See magnetic field. persistence 1. Perseverance, endurance, running the course, keeping on or with, tending to continue. (A quality essential to writing areference of this magni- tude, since documenting the telecommunications industry is like trying to gas up a car that's driving 731 © 2003 by CRC Press LLC . identifier, runway, conduit, or other end-to-end, hop-to-hop, or as-you- go means of delineating the track followed by a person, process, transmission, or data unit while travel- ing from one point, node, or endpoint to another. A file path is one which indicates the hierarchical organization and location ofa specific file or grouping of files. A transmissions path is the specific or general direction of radiant energy travel. path. private Also known as COCOT, this is a customer-owned coin-operated phone, as might be found in a hotel lobby or tavern. COCOTs may provide only limited access to long-distance carriers. PBX Private Branch Exchange. See Private Auto- matic Branch Exchange. 727 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary PC 1. personal computer. While many people use PC to refer specifically to IBM and third-party licensed hardware, in fact, PC correctly refers not only to Intell IBM computers, but also to any personal computer or microcomputer priced in a consumer or small business price range. 2. printed circuit. See printed circuit board. 3. program counter. 4. protocol control. PC. Processors (PDPs) that would today be called minicomputers. Right from the beginning, the PDP-x series filled a need for powerful, smaller-scale, lower-cost computers. The PDP-l sold for only a tenth of the price of many computer behemoth mainframes. This made the PDP-line mar- ketable to educational institutions and businesses that couldn't afford million-dollar computing systems and they became very popular with computer science stu- dents, with many user (and hacker) groups springing up around the machines. DEC's first computer, the 18-bit PDP-I was released in 1960 and a PDP-3 was built by a DEC client. The PDP-4 and PDP-5 followed in 1962 and 1963 and DEC released about one a year from then on. By the mid-1960s, DEC had launched a desktop model of the PDP-8. To be useful, it needed lots of peripherals, and its price was far beyond the range of personal computer owners, but for under $20,000, it was a tran- sitional machine to the smaller scale mini- and, eventually, desktop computers of the late 1970s and beyond. By the early 1970s, the series was up to the PDP-16, but many purchasers were still using PDP-8, PDP-I0, and PDP-II machines into the 1980s. The PDP-x series was gradually