0-9  A  B  C  D  E  F  G  H  I  J  K  L  M  N  O  P  Q  R  S  T  U  V  W  X  Y  Z packet In general usage, a unit of information transmitted as a whole from one device to another on a network. In packet-switching networks, a packet is defined more specifically as a transmission unit of fixed maximum size that consists of binary digits representing (1) data and (2) a header containing an identification number, source and destination addresses, and, sometimes, error-control data. packet switching A message-delivery technique in which packets of information are relayed through stations in a computer network along the best route currently available between source and destination. A packet-switching network handles information in small units, breaking long messages into multiple packets before routing. Although each packet may travel along a different path, and the packets composing a message may arrive at different times or out of sequence, the receiving computer reassembles the original message. Packet-switching networks are considered fast and efficient. To manage the tasks of routing traffic and assembling/disassembling packets, these networks require intelligence from the computers and software that control delivery. Packet switching allows for efficient sharing of network resources, since packets from different sources can be sent over the same channels in the same bitstream. passive component A passive component guides or manipulates light without an external input to alter the signal. Lenses, mirrors, prisms, splitters, combiners, attenuators, isolators, circulators, and couplers are usually passive components. peering The arrangement of traffic exchange between ISPs. Larger with their own backbone networks agree to allow traffic from other large ISPs in exchange for traffic on their backbones. They also exchange traffic with smaller ISPs so that they can reach regional end points. percent of 52-week high This figure is a useful relative measure of the market's current vie of the company and its level of price depreciation from its recent trading history. Calculated by dividing current stock price by the highest closing price within the last 52-week period. percent of 52-week low This figure is a useful relative measure of the market's current view of the company and its level of price appreciation from its recent trading history. Calculated by dividing current stock price by the lowest closing price within the last 52-week period. performance monitoring In network management, (a) a set of functions that evaluate and report the behavior of telecommunications equipment and the effectiveness of the network or network element and (b) a set of various subfunctions, such as gathering statistical information, maintaining and examining historical logs, determining system performance under natural and artificial conditions, and altering system modes of operation personal communications system (PCS) Advanced cellular communications and the inter networking of both wire and wireless networks that offer new communications services via very small portable handsets. The network relies on micro cellular technologically low-power, small-coverage cells-and a common channel-signaling technology to provide a wide variety of features in addition to basic two-way telephone service. personal computer (PC) A computer for one's own use conceived in 1981. The name served as a contrast to the other types of computers at the time-mainframes and mini-computers--which were often shared by many users. Personal Computer Memory Card International Association (PCMCIA) An international standards and trade association founded in order to establish hardware standards for connecting peripherals to portable computers. The initial standard and its subsequent releases is known as the PC card, a credit-card-sized memory or input-output device that fits into portable computers. personal digital assistant (PDA) A portable computing device capable of transmitting data. personal information management (PIM) The organization of names and addresses and random notes for fast retrieval. Most PIM applications provide a combination of features such as a telephone list with automatic dialing, calendar, scheduler, and news ticker. petabit (Pb) 2 to the 50th bits. photo diode A semiconductor diode that produces, as a result of the absorption of photons, (a) a photo voltage or (b) free carriers that support the conduction of photo current. photodetectors A transducer capable of accepting an optical signal and producing an electrical signal containing the same information as in the optical signal. photonic bandgap (PBG) materials or structures A new class of dielectrics that direct the flow of light in a manner somewhat analogous to what semiconductors do with electrons. While semiconductors facilitate the coherent propagation of electrons, photonic bandgap materials facilitate the coherent localization of photons. PBG materials exclude light transmission in all directions for specific wavelength ranges, similar to the way semiconductors exclude electron propagation for certain energy bands. photonics The technology of generating and harnessing light and other forms of radiant energy whose quantum unit is the photon. This particle of light is faster and more effective than the electron upon which legacy electronics systems depend. The science of photonics includes light emission, transmission, deflection, amplification, and detection by optical components and instruments, lasers and other light sources, fiber optics, electro-optical instrumentation, related hardware and electronics, and sophisticated systems. The range of applications of photonics extends from energy generation to detection to communications and information processing photonics packet switching An all-optical network in which packets (time slots) are switched optically from an input to an output at a photon ic switch. physical layer Layer 1 (often referred to as the Physical Layer) of the Open Systems Interconnection (OSI) model, which includes all electrical and mechanical aspects relating to the connection of a device to a transmission medium, such as the connection of a work station to a LAN .This layer contains issues specific to the manner in which a device gains physical access to the medium and how it goes about inserting bits into or extracting bits from the wire. physical topology The physical layout of the network (for example, bus, star, tree, mesh). piezo-electric crystal A type of crystal which, when subjected to mechanical stress, generates current; or which, when subjected to varying electrical stresses, generates mechanical movement. The most familiar type is Rochelle Salts crystal. pigtails A short length of optical fiber that is permanently affixed to an active device, e.g, LED or laser diode, and is used to couple the device, using a splice or connector, to a longer fiber plain old telephone service (POTS) Standard voice service on an analog telephone line. planar devices Components that operate on a flat material such as a thin film, an example of which is a "planar lightwave circuit." planar lightwave circuit An array of optical components and their interconnections that is produced on a flat piece of material such as a silicon wafer plasma A gas made up of electrons and ions. plastic optical fiber (POF) An optical fiber having a plastic core and plastic cladding. plesiochronous A network driven by two different clocks that agree within tight limits. point of presence (POP) A long distance carrier's network access facility, located within the service area of a local telephone company. Data exchange point between disparate networks point-to-consecutive-point A network in a ring configuration, in which each node communicates with its neighboring nodes. point-to-multipoint (PMP) A communications network that provides a path from one location to multiple locations (from one to many). point-to-point (PTP) A communications system that carries a signal between two end points without branching to other points. polarization Alignment of the electric and magnetic fields that make up an electromagnetic wave normally refers to the electric field. If all the light waves have the same alignment, the light is polarized. polarization-mode dispersion The smearing of an optical signal caused by imperfections in the shape of a fiber, stress on the fiber from bending or twisting, that causes light in each mode to travel at a different speed and arrive at a different time. polarizer A passive optical component that aligns the electric and magnetic fields that make up an electromagnetic wave. Normally refers to the electric field. If all light waves have the same alignment, the light is polarized. pooling A method of accounting used in mergers and acquisitions in which the balance sheets of the two companies are combined line by line resulting in no negative impact on the future earnings of the combined company (thus, this method is favored over the purchase method of accounting, which results in the creation of goodwill that must be written off). Most companies therefore prefer the pooling of interests method of accounting because it results in higher reported earning="1"an under the purchase method. However, there are strict requirements that must be met in order to for this treatment. post office protocol 3 A commonly used email server using SMTP-formatted messages that stores messages until a user selectively downloads them. price-to-earnings ratio (P/E) The P/E, also known as a multiple, gives investors an idea of how much they are paying for a company's earning power. The higher the P/E, the more investors are paying and, therefore, the more earnings growth they are expecting. The P/E is calculated by dividing the price of a stock by its earnings per share, which is often used for comparing comparable companies. The P/E ratio may either use the reported earnings from the latest year (called a trailing P/E) or employ an analyst's forecast of future earnings (called a forward P/E). primary rate interface (PRI) ISDN equivalent of a T-1; 23 bearer channels + 1 signaling channel. private branch exchange (PBX) A telephone switching system located at a private network site. professional services automation (PSA) Business software for professional services organizations. property, plant, and equipment Measures the value of long-term assets of a durable nature, such as land, buildings, equipment, furniture, and machinery, acquired for use in operations over a number of years. Recorded on the company's balance sheet at historical cost, which reflects the cash price of obtaining the asset, rather than market value, since it is assumed that the business will hold these assets rather than resell them immediately in the marketplace. These costs are allocated to future periods on the company's income statement through depreciation. Any related costs incurred after initially buying the asset (e.g., additions or improvements) are added to the company's balance sheet through capital expenditures. protocol A set of rules for communication. Computer networks use a protocol stack, such as IP for UNIX and the Internet. These are packages of programs dedicated to various functions needed for computers to connect. Routers connect different protocol stacks together and interpret between them. public limited company A U.K. form of a public company in which the shareholders are not personally liable for the debts of the company. public switched telephone network (PSTN) Refers to the existing worldwide telephone network accessible to all those with telephones and access privileges. In the U.S., it was formerly called the Bell System. pump laser The semiconductor laser that provides the light that excites atoms in a fiber amplifier, putting them in the right state of amplified light. pumping The action of an oscillator that provides cyclic inputs to an oscillating reaction device. Examples of pumping are the action that results in amplification of a signal by a parametric amplifier, and the action that provides a laser or maser with an input signal at the appropriate frequency to sustain stimulated emission. purchase Accounting method used in any merger that is not treated as a pooling of interests in which the purchasing company treats the acquired company as an investment, adding the acquired assets to its own balance sheet, and recording any premium paid above the fair market value as goodwill. Since goodwill will be amortized and charged against future earnings, the reduction in net income results in this method being less favored than the pooling method, which does not result in the creation of goodwill. pure play Stock-market jargon for a company that is virtually all devoted to one line of business. An investor who wants to invest in that line of business looks for such a company. The opposite of a pure play is a widely diversified company, such as a conglomerate.