Fiber Optics Illustrated Dictionary - Part 77 potx

PostScript, from Adobe Systems, Inc., is used for bitmap and scalable images, scalable fonts, computer monitor display sys-tems, and much more.. The basic ana-log phone service, which ha

Fiber Optics Illustrated Dictionary

The Internet community of programmers, some of

whose contributors included members of The World

Wide Web Consortium (W3C) and Compuserve,

be-gan 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

stan-dard, 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

anima-tion 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 of historic

sub-marine 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

com-munications The collection includes telegraph keys,

sounders, relays, synchronizers, and more, some of

which may be viewed online The surrounding

land-scape includes historic cables under the sand and

un-derground tunnels http://www.porthcurno.org.ukl

portrait A descriptive word that refers to the

direc-tion ofroughly 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

su-perseded 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 A regulation of the

telecommunica-tions 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

govern-ment telegrams and to assign rights of way through

public lands By 1934, after passing through some

intermediate bodies, including theu.s.Department

of Commerce, telecommunications became the

pti-mary responsibility of the Federal Communications

Commission (FCC)

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 ref-erence 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 ofthis most im-portant communications medium, for the benefit of all Over the years, Postel worked for a number of educational institutions and high technology compa-nies 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 includ-ing administerinclud-ing users, settinclud-ing up mailboxes, distri-bution lists, aliases, filters, etc Many of the postmas-ter functions are actual1y handled by compupostmas-ter soft-ware 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 publish-ing and electronic document design PostScript, from Adobe Systems, Inc., is used for bitmap and scalable images, scalable fonts, computer monitor display sys-tems, 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 developedJaMin 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 consum-ers 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,

aprosumer-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

reso-lution 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.Aninstrument for measuring

elec-tromotive forces 2 A device used to regulate a

cur-rent by varying the resistances at either end It can also

perform the functions ofa rheostat, which is more

lim-ited Potentiometers are commonly incorporated into

dials and computer input devices like joysticks See

rheostat

POTSPlain Old Telephone Service The basic

ana-log 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 ofreducing

electrical interference or fire hazards Potting is

some-times 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

elec-tric arc that could generate high frequency radio

waves It was found that larger versions ofthe Poulsen

arc could generate even greater arcs

The rights to market this technology were purchased

in1909by C Elwell, who formed the Federal

Tele-graph Company to design and build industrial arc

transmitters for the newly developing broadcast

in-dustry Eventually the technology was superseded by

vacuum tube transmitters See arc converter; Duddell,

William; Poulsen, Valdemar

Poulsen, Valdemar(1867-1942)ADanish scientist

and inventor who built upon the work of William du

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 electro-magnetic tape recorder that was called thetelegrafon

ortelegraphone He was awarded a patent for his

magnetic recording device in November1900(U.S

#661,619)and the patent for the electric arc genera-tor in1902.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 broadcast-ing music from the town of Lyngby, Denmark, by spring1909.He put a microphone near an early pho-nograph player on March 4,1909and transmitted to

an amateur radio pioneer in Hellerup.Se~radio his-tory

power In the human sense, having the capability to exert political, physical, or other force over other ob-jects, phenomena, or people A physically 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 spe-cific meaning Power is a measure ofthe 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 compo-nents, a more powerful engine can generally drive larger or heavier machinery (we say "generally" be-cause 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 ex-pressedinterms 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=12R

Expressing power for alternating current (AC) is a little more complicated as another factor, the alter-nating phase of the current, must be taken into con-sideration Alternating current alternates between positive and negative phases, as does the current, in acertain number ofcycles per second(Hz).However, the phases ofthe 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 ofthese 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 ex-ample, a power down on a computer may involve closing files, asking the user to save data, logging out

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

pre-vent the accidental loss of data

power hole digger Amachine for digging deep

nar-row holes for utility poles, starting with the early

tele-graph 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

dig-ger See pike pole

Power Macintosh computer, PowerMac The

suc-cessor 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 with

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

de-veloped 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

nar-row holes for utility poles, starting with the early

tele-graph 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

dig-ger 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

com-puters, the system may check memory subsystems,

configuration parameters, electrical voltages, the

presence or absence ofcertain peripherals (e.g.,

moni-tors) before coming online in terms of initiating

ex-ternal data or operating systems that may be contained

on a CD-ROM or hard drive Many laser printers have

selftests and may optionally display the results ofthe

test and basic configuration parameters on a printed

page.Ifthe selftests fail, the system may power down,

flash warning lights, or display a message on an LCD

screen, depending upon how it is programmed to

re-spond to problems and how early in the test sequence

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 deDe-vice 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 synchro-nize 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 If a 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 ofthe electronic components in a com-puter 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 elec-trical 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 moni-tor settings The chip retains its information by be-ing refreshed with power from a battery, usually a small lithium cell This battery may have to be re-placed every 6 years or so

PRB Private Radio Bureau

Precise Positioning Service PPS One ofthe precise location data signals transmitted from Global Posi-tioning System (GPS) satellites This signal is for military and general government use, requires a

zontal and vertical accuracy are about 22 to 28 m,

respectively, and time accuracy is 100 nsec See Global

Positioning System, StandardPositioning SetVice (SPS)

Preece, WilliamA 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

conduc-tivity method

Predictor Compression ProtocolPCP Amethod for

transporting multiprotocol datagrams over PPP

en-capsulated links proposed in the mid-1990s PCP is

based on Predictor, a freely available high-speed

com-pression algorithm implemented by Timo Raita in the

mid-1980s While not considered the fastest

compres-sion algorithm, it had the advantage of availability

See Point-to-Point Protocol, RFC 1978

preformIn fiber optics production, a rod that is

cre-ated by a process ofdeposition and consolidation that

is subsequently used as a blank or source rod for

melt-ing and drawmelt-ing the medium into a thin fiber The tube

within which the preform is created through a vapor

deposition process may be retained as part ofthe

pre-form See boule See vapor deposition for a fuller

ex-planation of the process

prepaid phone cardAcredit card-like monetary

stor-age medium which is charged or credited with a

cer-tain amount ofprepaid 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

Avariety ofvendors 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 StampPTS In MPEG-2

encod-ing, 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) Avideo decoder synchronizes the

MPEG video data with the STC, with the assumption

that the audio decoder follows suit If the

synchroni-zation 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

quickly be accessed later Thus, in video and audio editing, cuts and dubs are sometimes preset; in com-puter programs, times or online activities may be pre-set Pushbutton radios can be preset to instantly tune

to a desired frequency

President's Task Force on Telecommunications PolicySee Telecommunications Policy, President's Task Force on

PRESTCentre for Policy Research in Engineering, Science and Technology U.K group

Pretty Good PrivacyPGP Apowerful high-security encryption scheme developed in the early 1990s by Philip Zimmermann, based on the Blowfish encryp-tion technology

PGP provides privacy and authentication oftransmit-ted messages Only the person intended to see the message can read it.Anintercepted 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 ofTechnology (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 maintenanceRegular 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 equip-ment is turned off and probably even unplugged Don't use a metal nozzle for vacuuming and ground yourselffirst 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 sys-tem See screen saver

Price Cap RegulationA means by which local mo-nopolistic 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 staffor adopt more cost-effective, newer technologies, it was intended that Price Cap Regulation

Fiber Optics Illustrated Dictionary

would provide incentives for innovation Many

com-panies changed from Profit Cap Regulation to Price

Cap Regulation in the mid-1990s

Primary Rate InterfacePRJ One oftwo major

cat-egories of ISDN services, PRJ caters to higher-end

customers and businesses See Basic Rate Interface,

ISDN

primitiveArepresentation ofa basic unit in

comput-ing 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 A primitive is some type

ofba-sic building block, usually one frequently used or

re-used In networking, a primitive is an abstract

repre-sentation across a layer service access point, where

information is exchanged between auser and provider

principalMain, central, overriding; the highest

au-thority or administrator

principle Ageneral, or fundamental concept,

state-ment, or truth A basis for decision-making, actions,

or operations

print server, printer serverA system that handles

the logistics of requests to one or more printers on a

network Frequently there will be a variety of types

of printers 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

ser-vice; 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 inturnmay be relayed to the user

or the appropriate service center

print spoolerAn application which manages and

schedules a printing job to a printing 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

min-utes 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 of multitasking systems and printers with

large buffers, the use of spoolers is diminishing

On larger networks, a print server may handle

print-ing 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

printed circuit boardPCB A board upon which electronic circuits are mounted, with the circuit con-nections etched, foiled, or blasted onto the surface of the board, usually on the side opposite the majority

of the components The etched electrical pathways, calledtraces,provide flat, convenient electrical con-tacts without wires This is a very practical, light-weight method ofdoing 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 cop-per, 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 tech-nology 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 print-ing medium is often paper, card stock, metal plates,

or other portable media

printer control characterA character which has a specific control effect on the action of a 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 send-ing the document, in order ot set up the printsend-ing pa-rameters, 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 ap-propriate 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 ca-pabilities, is often used because the control charac-ters cannot always be entered from the keyboard, as they lie beyond the range ofthe alphabet Printer con-trol characters are often not displayable, or may dis-playas unusual symbols

printer control languageA language designed to utilize the capabilities of a particular type of printer,

or one conforming to a common standard such as Hewlett Packard Graphics Language (HPGL), widely used on plotters, for example

printer driverA file or program providing infonna-tion on the physical, operainfonna-tional, and control charac-teristics of a printer This may include relevant con-trol codes, available font shapes and sizes, paper feed controls, etc Typically an operating system or appli-cations program will interact with a printer through

a printer 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

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 ofa 1928

cabinet radio discovered by Jonathan Winter, curator

andfounder ofthe America Radio Museum (the wires

were added later) This is currently the earliest known

radio based upon a "printed" circuit board.

Detail close-up ofcopper blasted traces on the

un-derside 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 emulationAny 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

paper and avoids problems such as slippage through the fax machine

printingPrinting is the production and reproduction

of characters, symbols, and images on physical me-dia for the purposes of preserving infonnation or ar-tistic works and/or to communicate or distribute them

to others Printing has long been associated with print-ing presses that enable many copies of a sprint-ingle 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.Inthe mid-1400s Johann Gutenberg in-troduced 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) Amodem 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 tradi-tional ink presses which usespot color while running

the paper through the press several times, once for each color, toprocess color, which uses cyan,

ma-genta, yellow, and black dots to simulate awide 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 priorityAlevel ofaccess 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 process-ing time, than windows in the background On most network systems, system administration functions take priority over user functions

Priority Access and Channel AssignmentPACA

A Supplementary Bearer Service (SBC) scheme for handling radio communications transmission access and channel assignment PACA is ofinterest to emer-gency 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 sup-port up to 15 priority levels to supsup-port emergency service Personal Communications System (PCS) us-ers and is described in ANSI Tl.706-I997 In 1998, the Technical Subcommittee TIPl submitted a draft proposal to the American National Standards Institute

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 oflocal or national

emer-gencies This can overload land-basedtrunklines 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

commu-nications 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

ef-ficiency 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 Aprogram 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 be-cause wireless airwaves are not unlimited and are fre-quently congested during emergency situations Pri-ority access provides some level ofguarantee ofcom-pleting an important national security or emergency-related call See National Communications System, Wireless Priority Services http://pas.ncs.gov/ prism A physical component for separating propa-gating light into its component parts or an algorith-mic method for separating modeled light into its com-ponent 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 com-monly 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

A Selection of Common Commercially Available Prism Lenses

This illustration includes a number ofcommon prismatic lenses for directing and separating light into its compo-nent parts They are also usefulfor projecting, reverting and inverting images.

A - equilateral prismwith three 60 0

its component colors.

B -Littrow prisma type ofdispersing prism, similar to the equilateral prism in that it can break white light into its components Some versions will have a coating on the long suiface (the plane ofthe hypotenuse) to divert the light beam such that the image is not inverted See Littrow configuration.

C- right angle prism,a means ofdirecting the light 90 0

from the incoming (incident) angle This prism can be used

to reverse and image left ot right or to invert the image, depending upon the orientation ofthe prism 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 prisman interestingly-shapedprism with the top surface coated, this prism will rotate an image twicefor one rotation ofthe prism relative to the viewer (in the longitudinal direction) Dove prisms come coated and uncoated Assembled blockprisms madefrom individual blocks o/bonded glass or synthetics are not shown here, but they are

a specialized type ofprism designed to split light beams for selectively directing or polarizing light.

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 of prism 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

attenu-ation 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 ExchangePABX, PBX.Aprivate 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 handleoutgoin~ calls;

connections can be made by first dialing "9' to

ac-cess an outside line PABX 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 PABX

and PBX are now used interchangeably See Centrex

Private Cable OperatorPCO.Anindependent cable

operator providing video and telephony services to

subscribers in niche markets such as multiple

dwell-ing units Many markets that are too small or

special-ized 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 ofapartment, 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

pub-lic messenger service or telecommunications service

provider that mayor may not be in competition with

a dominant commercial carrier or government-funded

service

private lineIn the early days ofphone service, a

pri-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.Itwas not uncommon in the early part of

the century for hundreds ofwires 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 ofa

neigh-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

gan to take on a different meaning, similar to its early meaning, referring to a direct connection between two businesses, between a home and a business, or be-tween different departments in a business or institu-tional complex

Private Line Automatic RingdownPLAR Ameans

of interconnecting two lines to form a "hotline" di-rect connection

privileges 1.On a telephone system, particular func-tions and services available on particular consoles or

to particular individuals in a company, sometimes through keying in an access code 2 On a data net-work system, access to specific applications, pro-cesses, devices, or data files More specifically, file privileges are a record of the actions an individual or group member can take on a file, typicallyread, write, execute,ordelete.

PrivLMPrivate Land Mobile

PRMApacket reservation multiple access

PRML See Partial Response/MaximumL~kelihood.

probeA detection or measuring device, often with a narrow tip, used to assess temperature, wind, humid-ity, current, voltage, amperage, polarhumid-ity, or other prop-erties ofair or electrical circuits Aprobe is often used

in conjunction with an analog or digital readout dis-playing the results A probe may be used as a diag-nostic 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 a particular site, user, address, archive, or other

type of information See protocol analyzer

processA software activity consisting ofcarrying out

a set of predetermined or situation-influenced logi-cal instructions, which may be low-level background processes integral to the operating system, router, or intelligent switcher, or higher-level processes related

to the running of an applications program

process switchingOn 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 registerPCR processor configuration register A computer processor-related programming register that typically contains a vari-ety of bootstrap, break, data rate, and software con-figuration information When spelled in capitals, it refers more specifically to the PCR in the Motorola 68000-family CPU

ProdigyOne of the earlier commercial online net-work services, established by ffiM and Sears Roe-buck Prodigy used proprietary graphical user inter-face 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 uncom-mon on the smaller, independent Internet Services Providers Now that freely distributable Web browsers

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 GroupPAG 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

pro-vided 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 of Independents 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

commu-nications 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 ofPROFIBUS technologies

See INTERBUS http://www.profibus.org/

PROFlnetAn open, Ethernet-based automation

implemention of PROFIBUS technology See

PROFIBUS

profile alignment systemPAS In fusion splicing of

fiber optic filaments, an automated, video-based

alignment and measurement system See fusion

splicing

profile alignment system, lensL-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-FA black-and-white subset of the

TIFF specification suitable for minimal facsimile

document encoding but which has some extensions

to the basic Profile S specification See TIFF-FX.

Profile S, TIFF-SA basic black-and-white subset of

the TIFF specification suitable for minimal facsimile

document encoding See TIFF-FX

Profit Cap Regulation, Rate ofReturn 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 Clock Reference Asynchronization

refer-ence clock used, for example, in MPEG decoding

The PCR can synchronize a Station Time Clock

(STC) An MPEG-2 video decoder chip can be

de-signed to include an internal counter useful in a

Sta-tion Time Clock, which can in tum be accessed by

other components through an interface

program counterIn general terms, a display or in-ternal reference that keeps track ofa location in a pre-sentation (e.g., video or laserdisc program, TV broad-cast, computer animation, etc.), sometimes to provide information to the viewer and sometimes as a refer-ence point for searches or editing In computer soft-ware execution, a program counter is a reference that monitors the location in a program that is currently being accessed This is handy when debugging, test-ing a program, or tractest-ing a logical path

programmableAny device which can be controlled

or altered through logical instructions without recon-figuring the physical connections

programmable array logicPAL In the design and manufacturing of computer circuits, a PAL is a cir-cuit 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 devel-opment ofprogrammable array logic (PAL) See pro-grammable logic

programmable logicCircuit 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 (com-plex programmable logic devices [CPLDsD.The pro-grammable logic array (PLA) is a more complex fore-runner of programmable array logic (pAL) See pro-grammable array logic

programming languageInstructions used by a pro-grammer to control computer operations Program-ming languages are roughly divided into low-, me-dium-, and high-level languages Low-level lan-guages are those which most directly translate into machine instructions and interact most directly with the hardware architecture of the system Machine lan-guage and assembly lanlan-guage 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 ofthe program Machine lan-guage and assembly lanlan-guage 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 rea-sonably 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 lan-guage, 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 inter-preted languages (although compilers may exist), and

run a compiler before they can be used Interpreted

languages are translated to machine code as the

pro-gram is run, and thus will execute more slowly than

a program which is precompiled Interpreted

lan-guages tend to be more limited, but also more

por-table, than lower-level languages

programming overlay, configuration overlay A

covering made from membrane, plastic, cardboard or

another material that provides information on a

key-board, 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 scanningAmethod ofdisplaying

broad-cast 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

Project AthenaSee 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 ofElectrons in the Synchotron

Acceleratorfor his Ph.D thesis Following this,

Prokhorov researched a range of quantum

electron-ics and radiospectroscopy topelectron-ics In the 1950s, he was

appointed as head of the laboratory of oscillations at

the Institute ofAtomic Energy in Russia

Together with Basov, Prochorov contributed

impor-tant 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

sug-gested 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 modeIn data networks, an open mode

in which the network interface controller (NIC) passes

all the frames which it receives, regardless ofthe

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

promptn. 1 A mechanism for gaining the attention

of the user to indicate that the system is ready for

in-put or that inin-put 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 Aprompt 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

Studies Founded in 1989 as a result of reorganiza-tion ofthe 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 conceptA 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,

re-sources were made available to develop and imple-ment the technology Proofofconcept 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

propagationThe 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

ways to compose, encode, transmit, and route ana-log and digital signals.Italso 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 ofphysical 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, grayline (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 ra-dio or computer communications, programmers have developed modeling programs that enable users totry different scenarios for efficient propagation If the software is sophisticated enough to develop the dif-ferent options as well as running unattended, a great deal ofdatacan 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