Fiber Optics Illustrated Dictionary - Part 77 potx

Fiber Optics Illustrated Dictionary The Internet community of programmers, some of whose contributors included members of The World Wide Web Consortium (W3C) and Compuserve, began work on the development of PNG. The current consensus is that PNG is a good format and it is quickly being adopted by the Web community. The PNG specification was transcribed by Thomas Boutell and Tom Lane and released as RFC 2083 in 1997. The features ofPNG include an open software standard, good lossless compression ratios, 8-bit color palette support, 16-bit grayscale support, 24- and 48- bit truecolor support, alpha blending transparency for supporting different degrees of transparency, gamma correction, two-dimensional interlacing, text chunk support, multiple CRCs for error checking without viewing, security signature, full online references, and source code availability. PNG was not designed for animation support; it was intended for single images. MNG was subsequently developed to support animation. See Graphics Interchange Format, Lempel-Ziv- Welch, magic signature, PNG Development Group, Portable Network Frame, Virtual Reality Modeling Language, See RFC 2083. http://www.cdrom.com/pub/png/png.html Porthcurno The U.K. port location ofhistoric submarine telegraph cables, established primarily by John Pender in the 1870s, Porthcurno (historically Porthcurnow, in southwest England) is now the port link for a new fiber optics cable, installed in 1997. It is also the home of the Centre for the History of In- temational Telegraph Communications, including the Museum of Submarine Telegraphy images and arti- facts documenting the region and telegraphic communications. The collection includes telegraph keys, sounders, relays, synchronizers, and more, some of which may be viewed online. The surrounding landscape includes historic cables under the sand and un- derground tunnels. http://www.porthcurno.org.ukl portrait A descriptive word that refers to the direction of roughly rectangular objects, usually printouts, photographs, or monitors, which are oriented so the long side is vertical and the short side is horizontal. Contrast w.ith landscape. portrule A historic telegraphic device with a metal, toothed bar acting as symbolic contact points to de- fine digits or code symbols. This device was later superseded by the simpler telegraph key. POSIX 1003.0 Portable Operating System Interface UNIX. An open systems standards architectural framework, also known as IEEE 10030.0 POST See power on self test. Post Roads Act Aregulation of the telecommunications industry in the United States begun in 1866 with the Post Roads Act in which authority was granted to the Postmaster General to oversee rates for government telegrams and to assign rights of way through public lands. By 1934, after passing through some intermediate bodies, including the u.s. Department of Commerce, telecommunications became the pti- mary responsibility of the Federal Communications Commission (FCC). 752 Post Telephone & Telegraph administration. Tele- communications operating bodies around the world that are individually controlled by their regional gov- ernments. Postel, Jonathan B. (1943-1998) No dictionary about the Internet would be complete without a reference to Jonathan Postel. From the early ARPANET to the current Internet, he contributed three decades oflow-key, passionate, dedicated service and volumes of fundamental information as a developer, advisor, protocol prototype implementor, and offical RFC documents editor. Like the underlying thread that runs through a tapestry, Postel held quietly to a vision, avoiding the fanfare and business opportunities that constantly presented themselves to pioneers of the computing industry. He chose instead to concentrate on the structure and orderly evolution of this most important communications medium, for the benefit of all. Over the years, Postel worked for a number of educational institutions and high technology companies including the Network Measurement Center at UCLA (ARPANET) and SRI International with Doug Engelbart. See lANA, Request for Comments. postmaster The person responsible for configuring and maintaining a network mail server, often including administering users, setting up mailboxes, distri- bution lists, aliases, filters, etc. Many of the postmaster functions are actual1y handled by computer software such as dragons and mailer daemons. PostScript, Adobe PostScript A powerful, high- level, device-independent page description language and document format widely used in desktop publishing and electronic document design. PostScript, from Adobe Systems, Inc., is used for bitmap and scalable images, scalable fonts, computer monitor display systems, and much more. PostScript originated as the Design System language in 1976 at Evans & Sutherland Computer Corpora- tion, a company renowned for its pioneering flight simulator programs. John Gaffney is credited by John Warnock as the inspiration behind many of PostScript's major design components. In 1978, when John Wamockjoined Martin Newell atXeroxPARC, they reimplemented Design System as JaM (after their first names, John and Mark). At this time, the language was used for experimental applications in VLSI design, printing, and graphic arts, resulting in Xerox's printing protocol called Interpress. Wamockjoined forces with Charles (Chuck) Geschke in 1982 to form Adobe Systems Incorporated. He and Geschke further developed JaM in collaboration with Doug Brotz, Bil1 Paxton, and Ed Taft; PostScript was born of the effort. One of the important developments that helped in- troduce the PostScript language and make consumers aware of its capabilities was the release of the Apple LaserWriter PostScript-capable printer in 1984. Although PostScript doesn't seem as remark- able now, in 1984 most people had 9-pin dot matrix printers and bitmap fonts that provided output that even the most undiscriminating viewer would admit was crude at best. Suddenly, with PostScript, a prosumer- © 2003 by CRC Press LLC priced laser printer could print legible, beautiful text down to 4 points in size in some of the finest fonts in the world. This launched the desktop publishing revo- lution, which is still having far-reaching impact on the publishing market, especially among small presses, self-publishing individuals, and genealogists. PostScript fonts are some of the best computer fonts in the world. Adobe Systems maintains a large library for sale to consumers and service bureaus. PostScript fonts are scalable, in order to print out at the best resolution of the output device. Many people think that PostScript fonts and other scalable fonts are essen- tially the same, but most other scalable fonts are not integrated into a page description language, and so are not as flexible and powerful as PostScript fonts. Since PostScript is a programming language, fonts can be swirled, stretched, and individually rendered so that each letter differs from the previous in some essen- tial way. The possibilities have even now not been fully exploited. PostScript is commonly used to distribute documents on the Web, as is Adobe Acrobat format, a second- cousin to PostScript for displaying text and graphics. It is also possible to send high-quality PostScript documents through email, by sending the file as an email file attachment. This is a means by which people can send professional-looking text and graphics re- sumes, business documents, manuals, and much more over the Internet or be linked to a Web page for in- stant download. See vector fonts. potentiometer 1. An instrument for measuring electromotive forces. 2. A device used to regulate a current by varying the resistances at either end. It can also perform the functions ofa rheostat, which is more limited. Potentiometers are commonly incorporated into dials and computer input devices like joysticks. See rheostat. POTS Plain Old Telephone Service. The basic analog phone service, which has been available from local phone companies and used in homes for years and years. No ISDN, no surcharge services such as Caller ill, Call Waiting, etc. See loop start. potting To embed within an insulating or protective material or layer, usually for the purpose of reducing electrical interference or fire hazards. Potting is sometimes required in cases where higher voltage computer components may be interfaced with lower voltage phone lines. Poulsen arc A device enclosed in a gas atmosphere with a strong magnetic field, which created an electric arc that could generate high frequency radio waves. It was found that larger versions of the Poulsen arc could generate even greater arcs. The rights to market this technology were purchased in 1909 by C. Elwell, who formed the Federal Tele- graph Company to design and build industrial arc transmitters for the newly developing broadcast industry. Eventually the techno logy was superseded by vacuum tube transmitters. See arc converter; Duddell, William; Poulsen, Valdemar. Poulsen, Valdemar (1867-1942) A Danish scientist and inventor who built upon the work of William du Bois Duddell and devised a way to use an electric arc to generate continuous waves at high frequencies by placing the arc in a controlled atmosphere within a strong magnetic field. He collaborated with P.O. Pedersen in inventing a form of wireless telegraphy technology. In 1898, Poulsen recorded electronic waves on a thin conducting wire, a pioneer electromagnetic tape recorder that was called the telegrafon or telegraphone. He was awarded a patent for his magnetic recording device in November 1900 (U.S. #661,619) and the patent for the electric arc genera- tor in 1902. His work with electric arcs provided a means to improve signal strength and stability in crys- tal-based radio sets. One of Poulsen's exciting accomplishments that is uncredited in radio history is that he was broadcasting music from the town of Lyngby, Denmark, by spring 1909. He put a microphone near an early pho- nograph player on March 4, 1909 and transmitted to an amateur radio pioneer in Hellerup. Se~ radio history. power In the human sense, having the capability to exert political, physical, or other force over other objects, phenomena, or people. Aphysically powerful person has the ability to lift heavy objects. Apoliti- cally powerful person has the ability to control the course of human events. In the scientific sense, power has a much more specific meaning. Power is a measure of the rate at which work is done or, seen another way, the level at which work could be done. Thus, a more powerful current can generally drive more or larger electrical components, a more powerful engine can generally drive larger or heavier machinery (we say "generally" because there are other factors that may effect overall efficiency and linearity of the examples). The basic unit of work is the joule (1). Thus, power can be expressed in terms of watts and in its relationship to work (in Joules) over time. See power, electrical. power, electrical Expressed for direct current (DC) in watts, the product of the electromotive force (in volts) and the current (in amperes). Thus, P= EI. In terms ofresistance, according to Ohm's law, this can be expressed as P=1 2 R. Expressing power for alternating current (AC) is a little more complicated as another factor, the alternating phase of the current, must be taken into con- sideration. Alternating current alternates between positive and negative phases, as does the current, in a certain number of cycles per second (Hz). However, the phases of the two, while having the same period- icity, don't necessarily hit the same part of the sinu- soidal phase at the same time. The separation of these phases is expressed in degress and there are desig- nations for different aspects of the power (apparent, real, etc.) that must be considered in any calculations of AC power. See ampere, apparent power, Ohm's law, ohm, power, resistance, volt, watt. power down To initiate or perform a sequence of operations in order to shut down a system. For example, a power down on a computer may involve closing files, asking the user to save data, logging out 753 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary the user, etc. before actually terminating the power to the system. Power down sequences are designed to clean up systems, remove unwanted files, and prevent the accidental loss of data. power hole digger A machine for digging deep narrow holes for utility poles, starting with the early telegraph lines. It was introduced in North America around 1915, although line workers using long spades still dug the holes in undeveloped regions for several decades after the introduction of the power hole digger. See pike pole. Power Macintosh computer, PowerMac The successor to the original Macintosh line, the PowerMac is based upon ffiM POWER RISC chip architecture. This popular line is gradually being succeeded by even faster Macintoshes built with G3 and G4 chips. The PowerMac series is not obsolete, however; a number of third-part developers such as XLR8 and Sonnet have developed reasonably priced PCI - format G3 and G4 accelerator cards that are compatible wi th most of the PowerMac machines, providing speeds ranging from 300- to 600- MHz and higher. See G3, Macintosh computer, POWER. POWER, Power PC Performance Optimization With Enhanced RISC. A complex processor, one of the first superscalar processors, initially implemented by ffiM with three integrated circuits (branch, inte- ger, floating point). This technology was further developed as a microprocessor by ffiM, Motorola, and Apple Computing in the early 1990s. The idea was to create a successor to the Motorola 68000 line and the Intel 80x86 line; the PowerPC was the result of this collaboration. The first version was the PowerPC 601, released in 1993, derived strongly from the ffiM POWER specification. Since then, a series has been released, including the 603, 604, and G3, and the chips are incorporated most familiarly into the Pow- erMacs and Macintosh G3s. power connector See p connector. power hole digger A machine for digging deep narrow holes for utility poles, starting with the early telegraph lines. It was introduced in North America around 1915, although line workers using long spades still dug the holes in undeveloped regions for several decades after the introduction of the power hole digger. See pike pole. power on self test POST. The process of checking internal systems prior to becoming fully operational that occurs in many electronic devices immediately after the system is powered on. For example, in computers, the system may check memory subsystems, configuration parameters, electrical voltages, the presence or absence of certain peripherals (e.g., monitors) before coming online in terms ofinitiating external data or operating systems that may be contained on a CD-ROM or hard drive. Many laser printers have self tests and may optionally display the results of the test and basic configuration parameters on a printed page. If the self tests fail, the system may power down, flash warning lights, or display a message on an LCD screen, depending upon how it is programmed to respond to problems and how early in the test sequence 754 the problem occurs. See power up sequence. power save mode See sleep mode. power up sequence The operational bootstrap and test sequence that a computer goes through when first powered on. This usually includes loading very low level routines, often from read-only memory (ROM), which then make it possible to load other routines and operating system capabilities from a hard disk, floppy, cartridge, or CD-ROM drive. It is very common for a computer to run through a hardware systems check in the power up sequence to test memory, sound, graphics, and other basic input/output devices. De- vice drivers and external device checks may also be performed, in addition to locating and interfacing with a network, if applicable. If many devices are attached to a computer, you may have to power them up in the right order. If you tum on the computer before turning on external hard drives, CD-ROM drives, or video signal sources, the computer may not recognize the device or synchronize correctly with the signal. As a general rule, turn on peripherals before turning on the computer. Give a hard drive a moment to "spin up," that is, get the drive revolutions up to speed, before turning on the computer. Similarly, with a device such as a scanner or printer, which may also have test sequences, count to five before you turn on the computer. Ifa system is being powered up right after being shut down, it is important to wait 30 seconds or so before turning it back on. Some of the electronic components in a computer will retain current after the system is shut down, and a sudden surge of additional current may stress the circuitry. Give the current a few moments to drain off, then turn the system back on. Newer peripheral bus technologies such as FireWire are more flexible in terms of monitoring a live electrical connection or data stream. They may be hot swappable and configurable on-the-fly, thus freeing the user from worrying about startup sequences. PPDN Public Packet Data Network. PPJ 1. pixels per inch. See resolution. 2. See plan position indicator. PPP See Point-to-Point Protocol. PPS 1. packets per second. A means of quantifying network traffic by tallying the number of packets transmitted through a given point in a given amount of time. 2. Path Protection Switched. See SONET. 3. See Precise Positioning Service. 4. pulses per second. PPSN Public Packet Switched Network. PPTP See Point-to-Point Tunneling Protocol. PRAM programmable random access memory. A chip that is sometimes used on computers to save semipermanent configuration settings such as monitor settings. The chip retains its information by being refreshed with power from a battery, usually a small lithium cell. This battery may have to be replaced every 6 years or so. PRB Private Radio Bureau. Precise Positioning Service PPS. One of the precise location data signals transmitted from Global Posi- tioning System (GPS) satellites. This signal is for military and general government use, requires a © 2003 by CRC Press LLC specially equipped receiver, and is encrypted. Hori- zontal and vertical accuracy are about 22 to 28 m, respectively, and time accuracy is 100 nsec. See Global Positioning System, Standard Positioning SetVice (SPS). Preece, William A British researcher who experi- mented in the late 1800s with conductivity methods for sending wireless communications. He was able to send a message a distance of 5 miles. See conductivity method. PredictorCompression Protocol PCP. A method for transporting multiprotocol datagrams over PPP en- capsulated links proposed in the mid-1990s. PCP is based on Predictor, a freely available high-speed compression algorithm implemented by Timo Raita in the mid-1980s. While not considered the fastest compression algorithm, it had the advantage of availability. See Point-to-Point Protocol, RFC 1978. preform In fiber optics production, a rod that is created by a process of deposition and consolidation that is subsequently used as a blank or source rod for melt- ing and drawing the medium into a thin fiber. The tube within which the preform is created through a vapor deposition process may be retained as part of the preform. See boule. See vapor deposition for a fuller ex- planation of the process. prepaidphonecardA credit card-like monetary stor- age medium which is charged or credited with a certain amount of prepaid phone access. This phone card can then be inserted in a card-compatible phone and will automatically allow access to calls up to the amount charged on the card. Copying machine cards are somewhat similar. Unfortunately, many phone cards are not rechargeable, which is an unfortunate waste of resources since a phone card can last many years, as do copy cards. This is mainly due to the way the accounting is done. The value of the card is not simply embedded in the card as it is on a copy card, rather it is handled through accounting software at the switching center. The best reason to get a phone card is to avoid inserting coins into a telephone, especially for a long-distance call during which you might be interrupted by an operator to add more change (which might not be handy). The denominations on a phone card vary from region to region, but amounts such as $4.95, $9.95, and $19.95 are common. A variety of vendors offer phone cards; the service is not necessarily directly provided by the local phone company. This accounts for the different designs on the cards, the different ways in which they are pro- moted, and the different denominations that are available. Presentation Time Stamp PTS. In MPEG-2 encoding, a timestamp that is encoded into the elementary packet stream. This is used for synchronization of different streams by comparing it against the System Time Clock (STC). A video decoder synchronizes the MPEG video data with the STC, with the assumption that the audio decoder follows suit. If the synchronization is within acceptable parameters, the decoded picture is displayed; othelWise, it is repeated, the STC is readjusted, or the next B or P frame is skipped over to maintain synchronization. preset A setting configured in advance so it can quickly be accessed later. Thus, in video and audio editing, cuts and dubs are sometimes preset; in computer programs, times or online activities may be preset. Pushbutton radios can be preset to instantly tune to a desired frequency. President's Task Force on Telecommunications Policy See Telecommunications Policy, President's Task Force on. PREST Centre for Policy Research in Engineering, Science and Technology. U.K. group. PrettyGood Privacy PGP. A powerful high-security encryption scheme developed in the early 1990s by Philip Zimmermann, based on the Blowfish encryption technology. PGP provides privacy and authentication of transmitted messages. Only the person intended to see the message can read it. An intercepted message cannot be deciphered. Authentication provides assurance of the authenticity of the sender and that the message has not been changed. PGP is freely distributed to U.S. and Canadian citizens for noncommercial use by the Massachusetts Institute of Technology (MIT) in cooperation with Zimmermann and with RSA Data Security, Inc., which licenses patents to the public- key encryption technology incorporated into PGP. PGPfone has now been developed to provide for se- cure online digital phone conversations. In 1998, Network Associates acquired PGP technology. See Blowfish; International Data Encryption Algorithm; PGP Inc.; Zimmermann, Philip. There is a useful PGP-related informational FAQ on the Web. http://cryptography.org/getpgp.htm preventive maintenance Regular inspection, testing, adjusting, and maintenance of equipment in order to prevent problems before they cause damage or affect service. Computers (especially floppy disk drives and the area around the fan) tend to accumulate dust every couple of years; the fuzz should be gently brushed out or vacuumed with a low-power, fine- nozzled vacuum, making sure the computer equipment is turned off and probably even unplugged. Don't use a metal nozzle for vacuuming and ground yourself first by touching the power supply casing to drain off accumulated static electricity. A good time to clean is when swapping or installing memory. Also gently check the various chips on the motherboard to ensure that they are firmly seated. Chips occasion- ally work their way up out of their seating or may loosen when a system is transported. Monitors should be turned off when not in use, and should have a screen saver active when in use. Bat- teries in phones that have extra features (like LCD readouts) should be replaced regularly, before you lose all the phone numbers programmed into the system. See screen saver. Price Cap Regulation A means by which local monopolistic phone companies are regulated so that rates remain the same for a specified period. Unlike Profit Cap Regulation, which did not carry large incentives to pare back staff or adopt more cost-effective, newer technologies, it was intended that Price Cap Regulation 755 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary would provide incentives for innovation. Many companies changed from Profit Cap Regulation to Price Cap Regulation in the mid-1990s. PrimaryRate Interface PRJ. One of two major cat- egories of ISDN services, PRJ caters to higher-end customers and businesses. See Basic Rate Interface, ISDN. primitiveArepresentation of a basic unit in computing. As examples, a graphics primitive may be a circle, line, or square; an audio primitive may be a phoneme or sound; a programming primitive may be a routine, procedure, or object. Aprimitive is some type ofba- sic building block, usually one frequently used or re- used. In networking, aprimitive is an abstract repre- sentation across a layer service access point, where information is exchanged between a user and provider. principal Main, central, overriding; the highest authority or administrator. principle A general, or fundamental concept, state- ment, or truth. A basis for decision-making, actions, or operations. print server, printer server A system that handles the logistics of requests to one or more printers on a network. Frequently there will be a variety of types ofprinters shared among users. These might include plotters, laser printers, dot matrix printers, high-speed page printers, and specialized color dye sublimation or thermal wax printers. The print server handles queuing; messages to users if a printer is not in service; alternate routing if the printers have been reor- ganized; scheduling, if some types ofjobs (e.g., big ones) are to be run at night or after hours; and priori- tizing, if some users have higher precedence. The print server can also be used to send messages to maintenance personnel if there is trouble with paper jams, empty trays, etc. Some printers have sufficient processing power to send status and error messages to the server, which in turn may be relayed to the user or the appropriate service center. print spooler An application which manages and schedules aprintingjob to aprinting device in such a way that the computer is not tied up, waiting for the print job to fmish. For example, imagine sending a large plotting job to a plotter from a CAD program. If it is a single-tasking system and cannot handle the print job in the background, and if there isn't a large buffer in the plotter itself, it might take 10 to 40 minutes for the plot to finish, and the computer would be unusable for that period of time. In order to reduce wait time on this type of system, print spoolers were developed so that a plot could be printed to disk rather than to the plotting device, a process which might take 2 minutes instead of20. The plot can then be spooled to the printer during a lunch break, after hours, or when the plotter is not tied up by another user. With the spread ofmultitasking systems and printers with large buffers, the use of spoolers is diminishing. On larger networks, a print server may handle printing tasks as a type of"smart spooler." In other words, the print job might be sent to a file, or sent directly to the print server, and scheduled and spooled from there rather than from the originating machine. See spool. 756 printed circuit board PCB. A board upon which electronic circuits are mounted, with the circuit connections etched, foiled, or blasted onto the surface of the board, usually on the side opposite the majority of the components. The etched electrical pathways, called traces, provide flat, convenient electrical con- tacts without wires. This is a very practical, light- weight method of doing away with wires and enables mass production of PCBs. The conventional wisdom is that printed circuit boards were first invented in the 1940s, but the Ameri- can Radio Museum has a radio in its collection dat- ing from the late 1920s which is designed with a copper, blasted circuit on the underside of the board as shown in the following photos. Thus, the founder of the museum has fascinating evidence that the technology was introduced almost 20 years before its pre- viously acknowledged invention. printerA device for transcribing information onto a medium which can be read directly or otherwise un- derstood directly, or with a minimum of manipula- tion (as in mirror writing), by someone familiar with the communications medium (writing, illustrations, Morse code, seismographic charts, etc.). The printing medium is often paper, card stock, metal plates, or other portable media. printer control character A character which has a specific control effect on the action ofa printer. The effects include line feeds, page feeds, carriage returns, mode changes, font changes, page length control, and other features that might be specific to the printer. Control characters can be sent to a printer before sending the document, in order ot set up the printing parameters, or may be imbedded in the document itself to set typefaces, font sizes, text attributes, space, line feeds, etc. Printer control characters are handled transparently by word processing programs, which send the appropriate characters through a printer driver without explicit programming by the user. In cases where a user is imbedding printer control characters in the document, a hex editor, or ASCn editor with hex capabilities, is often used because the control characters cannot always be entered from the keyboard, as they lie beyond the range of the alphabet. Printer control characters are often not displayable, or may dis- playas unusual symbols. printer control language A language designed to utilize the capabilities ofa particular type ofprinter, or one conforming to a common standard such as Hewlett Packard Graphics Language (HPGL), widely used on plotters, for example. printerdriverA file or program providing infonnation on the physical, operational, and control charac- teristics ofa printer. This may include relevant control codes, available font shapes and sizes, paper feed controls, etc. Typically an operating system or applications program will interact with a printer through aprinter driver stored as a computer file. Many printer drivers may be available, and if the relevant one is not online, often a substitute can be found from a maker with a similar printer. Many different laser © 2003 by CRC Press LLC printers will function with the same commands as Hewlett Packard or Apple laser printers, and many impact and inkjet printers will work with Hewlett Packard or Epson printer drivers. Historic First Printed Circuit Board - 1928 Copper traces blasted onto the underside of a 1928 cabinet radio discovered by Jonathan Winter, curator andfounder of the America Radio Museum (the wires were added later). This is currently the earliest known radio based upon a "printed" circuit board. Detail close-up of copper blasted traces on the underside. Small bolts and nuts were used to provide the electrical connection to the vacuum tube components on the top side. This historic example of one of the first printed circuit boards in existence is part of the American Radio Museum collection. printer emulation Any software which fonnats and outputs text to a device as though it were outputting to a printer. This way, for example, a word-processed program with all the text formatting, margins, and images can be sent through a facsimile transmission wi thout first being printed and scanned. This saves paper and avoids problems such as slippage through the fax machine. printing Printing is the production and reproduction of characters, symbols, and images on physical media for the purposes ofpreserving infonnation or ar- tistic works and/or to communicate or distribute them to others. Printing has long been associated with printing presses that enable many copies ofa single mas- ter to be created. There is evidence that movable type, in the fonn of clay discs, may have been used in Crete as early as 1500 BC, and type was used in southeast Asia by the 11 th century. In the mid-1400s Johann Gutenberg introduced movable type to the west. Type was set by hand until the early 1800s, when the first typesetting machines began to appear. Mass market microcomputer printers were introduced in the 1970s, and the home and prosumer desktop publishing markets became widespread in the mid- and late-1980s. Dry printing processes (e.g., photo- copying with toner) became prevalent in the 1970s and have replaced a large proportion of wet printing processes (e.g., ink). A modem desktop laser printer costing $1000 is easier to use and more flexible than the letter presses of the 1960s that cost $30,000 or more. Color printing processes are numerous, from traditional ink presses which use spot color while running the paper through the press several times, once for each color, to process color, which uses cyan, ma- genta, yellow, and black dots to simulate a wide range of colors. Computer printers use thermal wax, dye sublimation, inkjet, and colored ribbons to create printouts that rival commercial color photocopies and photographs, and may someday supersede them. priorityA level of access or usage which ranks higher than others. For example, on a computer system, operating system functions usually take precedence over user or network requests. On a server, such as a print server or network server, certain types of tasks may be handled first. In graphical user interfaces, a window which is clicked to the front may be assigned a higher priority, and greater proportion of processing time, than windows in the background. On most network systems, system administration functions take priority over user functions. Priority Access and Channel Assignment PACA. A Supplementary Bearer Service (SBC) scheme for handling radio communications transmission access and channel assignment. PACA is of interest to emergency service administrators and providers because it can be used to queue priority calls (e.g., emergency calls) when all channels are busy. ANSI standard 664 describes PACA queuing for priority call handling. Enhanced Priority Access and Channel Assignment (PACA-E) was developed in the mid-1990s to support up to 15 priority levels to support emergency service Personal Communications System (PCS) users and is described in ANSI Tl.706-I997. In 1998, the Technical Subcommittee TIPl submitted a draft proposal to the American National Standards Institute 757 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary for a Stage 2 Service Description for PCS-based PACA-E. This document defined and described call setup procedures for priority access and priority egress for PCS systems. Typically, many more calls are made during storms, natural disasters, and times of local or national emer- gencies. This can overload land-based trunk lines and result in "fast busy" signals. Under these conditions, mobile networks also tend to become congested and PACA queuing has been studied as a means to handle busy channels in private and public wireless communications. PACA services can be accessed by the caller through a designated high-priority line or through dialing an assigned access code. In studies of the efficiency of PACA queuing, static queuing, and dy- namic queuing conducted in the late 1990s, PACA compared favorably to the other methods. Priority Access Service PAS. A program of the U.S. government, in association with the National Com- munications System (NCS), to provide a means for national security and emergency preparedness (NS/EP) telecommunications users to obtain priority access to available wireless channels when needed for initiating emergency calls. PAS was established because wireless airwaves are not unlimited and are frequently congested during emergency situations. Pri- ority access provides some level of guarantee of com- pleting an important national security or emergency- related call. See National Communications System, Wireless Priority Services. http://pas.ncs.gov/ prism Aphysical component for separating propagating light into its component parts or an algorith- mic method for separating modeled light into its component parts. Prisms can be more broadly defmed as separating electromagnetic energy into its component parts, but the term is largely used to describe prismatic effects in the optical spectrum. Physical prisms come in many shapes, sizes and ma- terials but are generally transparent to the wave- lengths of interest. Thus, glass and crystals are commonly used for prisms for optical frequencies. What they have in common is the ability to refract light such that different frequencies are refracted in different directions. ASelection of Common Commercially Available Prism Lenses This illustration includes a number of common prismatic lensesfor directing and separating light into its compo- nentparts. They are also usefulforprojecting, reverting and inverting images. A- equilateral prism with three 60 0 angles, commonly called adispersing prism since it disperses white light into its component colors. B- Littrow prism a type of dispersingprism, similar to the equilateralprism in that it can break white light into its components. Some versions will have a coating on the long suiface (the plane of the hypotenuse) to divert the light beam such that the image is not inverted. See Littrow configuration. C- right angle prism, a means of directing the light 90 0 from the incoming (incident) angle. This prism can be used to reverse and image left otright or to invert the image, depending upon the orientation of theprism to the source and viewer. D - pentagonal prism, similar to the right angle prism in that it can direct light 90 0 from the incident angle, but does so without inverting or reverting the image due to the light path being reflected twice within the prism at 450. E- dove prism an interestingly-shapedprism with the top surface coated, this prism will rotate an image twicefor one rotation of the prism relative to the viewer (in the longitudinal direction) Doveprisms come coatedanduncoated. Assembledblockprisms made from individual blocks o/bondedglass orsynthetics are not shown here, but they are a specialized type of prism designed to split light beams for selectively directing orpolarizing light. 758 © 2003 by CRC Press LLC Traditional triangular prisms will refract light in the colors of the rainbow as well as infrared or ultravio- let light in frequencies invisible to humans (but vis- ible to some insects, snakes, and birds). Some mate- rials have natural refractive properties and others can be growtl or manipulated to enhance their prismatic qualities. A beamsplitter is a specific type ofprism that sepa- rates and directs the separated paths of light so light of the desired properties is available for sending through optical components and undesired light is discarded through redirection, absorption or attenuation. Beamsplitters are commonly found in viewing scopes, interferometers, spectrophotometers, and many other instruments. See Iceland spar, Nicol prism, polarization, refraction. Private Automatic Branch Exchange, Private Branch Exchange PABX, PBX. A private telephone exchange, usually located in a business or educational institution, which can handle switching and other functions automatically. In an automated exchange, an operator is not needed to handle outgoin~ calls; connections can be made by first dialing "9' to access an outside line. P ABX was derived from Private Branch Exchange (PBX) which originally was at- tended by a switchboard operator. Since private ex- changes are almost all automated, the terms P ABX and PBX are now used interchangeably. See Centrex. PrivateCableOperator PCO. An independent cable operator providing video and telephony services to subscribers in niche markets such as multiple dwelling units. Many markets that are too small or specialized to be readily served by local exchange carriers (LECs) and thus alternative service providers have found viable ways to provide telecommunications services to these subscribers. These markets largely consist of apartment, motel, college, and housing co- operative dwellers. PCOs work in close cooperation with multiple dwelling unit (MDD) owners and man- agers. PCOs are supported, in part, by the Indepen- dent Cable &Telecommunications Association. private carrierAprivately owned, commercial public messenger service or telecommunications service provider that mayor may not be in competition with a dominant commercial carrier or government-funded service. private line In the early days of phone service, apri- vate line was a line that went from one business or person to another, without necessarily going through a public phone exchange, or from one floor or room to another. It was not uncommon in the early part of the century for hundreds of wires to crisscross over a street between one building and another. As more people were connected through public wiring systems that could handle multiple connections, the meaning of the phrase changed and, until about the 1960s, a private telephone line came to mean one that was not a party line. That is, the phone line was dedicated to only one user, and there was no possibility of aneigh- bor on the same exchange listening to a conversation or tying up the connection so another subscriber couldn't dial a call. As private lines became the norm and party lines began to disappear, "private line" began to take on a different meaning, similar to its early meaning, referring to adirect connection between two businesses, between a home and a business, or between different departments in a business or institu- tional complex. PrivateLineAutomatic Ringdown PLAR. A means ofinterconnecting two lines to form a "hotline" direct connection. privileges 1. On atelephone system, particular functions and services available on particular consoles or to particular individuals in a company, sometimes through keying in an access code. 2. On a data network system, access to specific applications, processes, devices, or data files. More specifically, file privileges are a record of the actions an individual or group member can take on a file, typically read, write, execute, or delete. PrivLM Private Land Mobile. PRMApacket reservation multiple access. PRML See Partial Response/Maximum L~kelihood. probe Adetection or measuring device, often with a narrow tip, used to assess temperature, wind, humid- ity, current, voltage, amperage, polarity, or other properties of air or electrical circuits. Aprobe is often used in conjunction with an analog or digital readout displaying the results. Aprobe may be used as a diagnostic tool to troubleshoot or configure a network. On a computer system, a probe is a software process that seeks out specified information or detects certain ~~~~t~:H~:~fr~~~~;~~:::~i:!{;~l!~~[~ ~. locate aparticular site, user, address, archive, or other type of information. See protocol analyzer. processAsoftware activity consisting of carrying out a set of predetermined or situation-influenced logical instructions, which may be low-level background processes integral to the operating system, router, or intelligent switcher, or higher-levelprocesses related to the running of an applications program. process switching On a network, packet processing at process level speeds, without the use of a route cache, as is used in fast switching. A Cisco Systems distinction. processor configuration register PCR. processor configuration register. Acomputer processor-related programming register that typically contains a variety of bootstrap, break, data rate, and software configuration information. When spelled in capitals, it refers more specifically to the PCR in the Motorola 68000-family CPU. Prodigy One of the earlier commercial online network services, established by ffiM and Sears Roe- buck. Prodigy used proprietary graphical user interface to provide access to the Internet. Many parents signed on to Prodigy to give their children educational access to online services. Like most of the largest commercial services, Prodigy earned revenues through ads on viewer pages. This practice is uncommon on the smaller, independent Internet Services Providers. Now that freely distributable Web browsers 759 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary are available, proprietary software is only used on some services (AOL). However, the ads remain, as many Web sites are subsidized by ad revenues. Producers Advocacy Group PAG. An ad hoc col- lective of independent public radio producers formed in October 1995. PAG members are responsible for some of the best known and respected public radio programs in North America, including drama, docu- mentaries, comedy, and popular music programs such as The Thistle and the Shamrock. They have also provided educational programs at home and abroad. PAG funding is from diverse sources including charitable trusts and endowments, the Corporation for Public Broadcasting, and corporate and individual donors. See Association ofIndependents in Radio. PROFIBUS process field bus. An internationally standardized, open data bus standard suitable for a wide range ofmanufacturing and process automation applications. PROFIBUS facilitates communications between devices from different manufacturers. Origi- nally a basic industrial communication protocol, PROFIBUS is now an extensive automation communications technology. It enables distributed digital controllers to be interconnected. Using PROFIBUS, a variety of automation and visualization systems can be jointly controlled and operated. PROFIBUS International supports technical commit- tees and working groups to maintain the open, ven- dor-independent nature of PRO FIB US technologies. See INTERBUS. http://www.profibus.org/ PROFlnet An open, Ethernet-based automation implemention of PROFIBUS technology. See PROFIBUS. profile alignment system PAS. In fusion splicing of fiber optic filaments, an automated, video-based alignment and measurement system. See fusion splicing. profile alignment system, lens L-PAS. Similar to a profile alignment system with video-based alignment of fiber optic cladding and then lens effect associated with the fiber core. Profile F, TIFF-F A black-and-white subset of the TIFF specification suitable for minimal facsimile document encoding but which has some extensions to the basic Profile Sspecification. See TIFF-FX. Profile S, TIFF-S A basic black-and-white subset of the TIFF specification suitable for minimal facsimile document encoding. See TIFF-FX. ProfitCap Regulation, Rate of Return Regulation Prior to the mid-1990s, the predominant means by which local monopolistic phone companies were regulated. Excess profits were required to be passed back to consumers as, for example, a rate reduction. By the mid-1990s, many companies changed to Price Cap Regulation. See Price Cap Regulation. Program ClockReference Asynchronization reference clock used, for example, in MPEG decoding. The PCR can synchronize a Station Time Clock (STC). An MPEG-2 video decoder chip can be designed to include an internal counter useful in a Sta- tion Time Clock, which can in tum be accessed by other components through an interface. 760 program counter In general terms, a display or internal reference that keeps track ofa location in apre- sentation (e.g., video or laserdisc program, TV broadcast, computer animation, etc.), sometimes to provide information to the viewer and sometimes as a reference point for searches or editing. In computer software execution, aprogram counter is areference that monitors the location in a program that is currently being accessed. This is handy when debugging, testing a program, or tracing a logical path. programmable Any device which can be controlled or altered through logical instructions without recon- figuring the physical connections. programmable array logic PAL. In the design and manufacturing of computer circuits, a PAL is a circuit in which the OR array is predefmed and cannot be changed, but the AND array is programmable. This was a simpler approach that followed the development ofprogrammable array logic (PAL). See programmable logic. programmable logic Circuit logic designed so that it can be reconfigured, as through linked flip-flops. In conjunction with memory circuits, programmable logic enables stored logic functions to be called upon and executed to configure the circuit. Programmable logic devices range from simple to complex (complex programmable logic devices [CPLDs D. The programmable logic array (PLA) is a more complex forerunner ofprogrammable array logic (pAL). See programmable array logic. programming language Instructions used by a pro- grammer to control computer operations. Program- ming languages are roughly divided into low-, medium-, and high-level languages. Low-level languages are those which most directly translate into machine instructions and interact most directly with the hardware architecture of the system. Machine language and assembly language are considered low- level programming languages. Machine language programs are typically written in binary, with ones and zeros. Assembly language is similar to machine language, except that instructions are more symboli- cally represented, and routines can be written to pass control to different parts of the program. Machine language and assembly language are more difficult and time consuming for some to learn, and more difficult to trace and debug than higher-level languages. Medium-level languages include those which are reasonably powerful, somewhat cryptic in their instruc- tion sets and syntax, but comprehensible enough that some of the commands resemble written English. C is a common, somewhat medium-level language. It is powerful, but requires a good understanding of memory allocation, pointers, and arrays, and takes some time to learn and to apply. C is a compiled language, which means that the code is compiled down to machine code in advance, before the program is run. Higher-level languages like BASIC and various authoring systems were designed to be easy to learn and to use, with commands and syntax that are fairly close to written English. They often are run as interpreted languages (although compilers may exist), and © 2003 by CRC Press LLC so do not require knowledge of how to configure and run a compiler before they can be used. Interpreted languages are translated to machine code as the program is run, and thus will execute more slowly than a program which is precompiled. Interpreted languages tend to be more limited, but also more portable, than lower-level languages. programming overlay, configuration overlay A covering made from membrane, plastic, cardboard or another material that provides information on a keyboard, keypad, or graphics tablet setup. Overlays were especially prevalent before graphical user interfaces, when complicated, difficult-to-remember control code combinations were used to run word processors and graphics programs. progressive scanningA method of displaying broadcast video signals in which each frame is transmitted one after the other, rather than dividing the frame into sets of two fields interlaced. See interlaced. ProjectAthena See Athena project. Prokhorov,A1eksandr Mikhailovich (1916-2002) An Australian-born Russian physicist, Prokhorov (sometimes transliterated as Prochorov) studied propagation in radio waves and pioneered the study of coherent radiation, in 1947. In 1951, he published Coherent Radiation of Electrons in the Synchotron Accelerator for his Ph.D. thesis. Following this, Prokhorov researched a range of quantum electron- ics and radiospectroscopy topics. In the 1950s, he was appointed as head of the laboratory ofoscillations at the Institute of Atomic Energy in Russia. Together with Basov, Prochorov contributed important developments in microwave spectroscopy and ammonia-based molecular oscillators (the forerunner of masers and lasers). By 1957, Prochorov and Manenkov had suggested that ruby could be used in the construction of lasers. In 1958, Prohnorov suggested that a laser could be used to generate wave- lengths in the infrared spectrum and that a open reso- nating cavity could be utilized (similar to an FP inter- ferometer). For his contributions to fundamental prin- ciples in laser technology, he was coawarded a Nobel Prize for physics in 1964. See laser; laser history; Townes, Charles. promiscuous mode In data networks, an open mode in which the network interface controller (NIC) passes all the frames which it receives, regardless of the des- tination address, to high-level layers in the network. This is usually only done in diagnostic situations, or by users gaining unauthorized access to information from the system. In normal operations, frames are evaluated and selectively passed along if the desti- nation address maps to that device. prompt n. 1. A mechanism for gaining the attention of the user to indicate that the system is ready for input or that input is required before continuing. 2. A prompt on a computer system may be in the form of a cursor, dialog box, flashing area, audible tone, or spoken message. 3. A prompt on an automated phone system may be a spoken question or suggestion to which the user can respond by typing in codes or, in some cases, by clearly speaking numbers or words. PROMPT Institute for Prospective Technological Studies. Founded in 1989 as a result of reorganiza- tion of the Joint Research Centre to monitor and ana- lyze new sciences and technologies. Monitoring is carried out by by the European Science and Technol- ogy Observatory (ESTO). proof of concept A strategy for communicating an idea which is not readily accepted when communi- cated through verbal means alone. Proof of concept usually involves producing a prototype which is par- tially or mostly functioning, at least enough to show that the idea can work. Many new inventions or ideas are not believed until they are actually demonstrated. Edwin Annstrong spent years going against the stated assumption that frequency modulation was math- ematically impossible, but eventually succeeded in his attempts. When it was shown that it was possible, resources were made available to develop and imple- ment the technology. Proofof concept demonstrations are created to attract interest, support, or research and investment dollars. propagate 1. Pass along, continue, extend. 2. To travel through a material or space, to cause to spread out over a greater area. propagation The concept of propagation is intrinsic to every aspect of communication. When you send a message, sound, computer packet, modulated radio frequency signal, etc., you are propagating a phenom- enon through space/time and any data along with any information coded into the propagation of the phe- ~~e:t~:~:~ef.~~~~i~l~::~~:~~ii~ 1. ways to compose, encode, transmit, and route analog and digital signals. It also is dependent upon math- ematical theories and applied engineering techniques for determining and implementing the most effective use of limited resources. Radio wave propagation, for example, can be facili- tated by a number of physical phenomena associated with the Earth, its atmosphere, and various solar in- fluences. The ionosphere is often used to propagate radio waves, but there are other methods, including auroral, gray line (the sunrise and sunset zones), tro- pospheric scatter, and more. Since it can be time-consuming and impractical to physically test alternative propagation models for radio or computer communications, programmers have developed modeling programs that enable users to try different scenarios for efficient propagation. If the software is sophisticated enough to develop the different options as well as running unattended, a great deal of data can be generated in a short amount of time, with the software even suggesting the best al- ternatives from those discovered. These can then be tested on real systems. Propagation models are often used to develop prediction models. The u.S. Department of Commerce NTIA/lnstitute for Telecommunication Sciences makes software available online for modeling high-frequency radio wave propagation. See attenuation, backscatter, hop, ionosphere, routing. 761 © 2003 by CRC Press LLC . Instructions used by a pro- grammer to control computer operations. Program- ming languages are roughly divided into low-, medium-, and high-level languages. Low-level languages are those which most directly. A means by which local monopolistic phone companies are regulated so that rates remain the same for a specified period. Unlike Profit Cap Regulation, which did not carry large incentives to pare back staff or adopt more cost-effective, newer technologies, it was intended that Price Cap Regulation 755 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary would provide incentives for innovation. Many companies changed from Profit Cap Regulation to Price Cap Regulation in the mid-1990s. PrimaryRate. Assignment PACA. A Supplementary Bearer Service (SBC) scheme for handling radio communications transmission access and channel assignment. PACA is of interest to emergency service administrators and providers because it can be used to queue priority calls (e.g., emergency calls) when all channels are busy. ANSI standard 664 describes PACA queuing for priority call handling. Enhanced Priority Access and Channel Assignment (PACA-E) was developed in the mid-1990s to support up to 15 priority levels to support emergency service Personal Communications System (PCS) users and is described in ANSI Tl.706-I997. In 1998, the Technical Subcommittee TIPl submitted a draft proposal to the American National Standards Institute 757 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary for a Stage 2 Service Description for PCS-based PACA-E. This document defined and described call setup procedures for priority

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