PACS: Personal Access Communication System
PAD: Packet Assembly/Disassembly
PAL: Phase Alternating Line; European videostandard with image format 4:3, 625 lines, 50 Hz and4 Mhz video bandwidth with a total 8 Mhzof video channel width. PAL uses YUV.
PALC: Plasma-Addressed Liquid-Crystal Display
PARC: Palo Alto Research Center
Passband signal:A line code that is modulated with a crrier of cosine and / or sine waves.
Pb: Petabit; 1,125,899,906,842,624bits
PB: PetaByte; 1,125,899,906,842,624bytes
PBX: Private Branch eXchange
PC: Personal Computer
PC: Politically Correct; the actual definitionof this term, can NOT be defined, by definition.
PCI: 1. Peripheral Component Interconnect.2. Peripheral Chip Interface
PCM: Pulse Code Modulation; Coding where inputsignal is represented by a given number of fixed-width samples per/sec.Often used for the coding employed in the telephone network.
PCR: Peak Cell Rate, (ATM)
PCR: Program Clock Reference
PCS: Personal Communications Service
PCS: Personal Conferencing Specification
PCS: Process Control System
PCVS: Point to Point Switched Virtual Connections,(ATM)
PD: Packetization Delay
PDA: Personal Digital Assitant
PDGS: Product Design Graphics System; CAD/CAMapplication co-developed by Ford Motor Company and PRIME computer systems.
PDH: PlesiochronousDigital Hierarchy; A transmission system for voice communication usingplesiochronous synchronization.
PDH is the conventional multiplexing technology for network transmissionsystems. PDH is being replaced by SONET and
other SDH (Synchronous Digital Hierarchy) schemes.Service levels are described with terms like DS1, asin ISDN.
PDK: Peripheral Developer Kit
PDM: Product Data Management
PDN: Premises Distribution Network
PDN: Packet Data Network
PDP: A line of mid-range computers developedby Digital Equipment Corporation, (DEC) throughout the70's and 80s.
PDP: Plasma Display Panels; or Plasma DischargePanels;
PDU: Packet Data Unit
PDU: Protocol Data Unit
Peering Aggreements / Arrangements:It is a requirement for an ISP, coming into a MetropolitanArea Exchange (MAE), to have peering or transit arrangementswith the other ISPs connected to the MAE.The operator of the MAE cannot arrange peering, it canonly provide guidelines or introductions. There is no single ISPin charge of the peering. Peering agreements are bilateral agreements betweenindividual ISPs. Each ISP must negotiateindependently and needs to contact every ISP they wishto peer with individually. (see also MAE, NAP,ISP)
Pel: Picture element.
PEP: Protocol Extension Protocol; a protocolbuilt into HTTP/1.1 to ease the addition of features.
Perl: Practical Extraction Resource Language
PES: Packetised Elementary Streams (MPEG)
Petabit: (Pb) 1,125,899,906,842,624 bits,1,024 Terabits.
PetaByte: (PB) 1,125,899,906,842,624 Bytes;1,024 TeraBytes.
PEX: PHIGSExtensions to X (referring to X11window system)
PGP: Pretty Good Privacy (Al Zimmerman)
PHIGS: Programmers Hierarchical InteractiveGraphics System
PHRACK: Since 1985, Phrack has been providingthe hacker community with information on operating systems, networkingtechnologies, and telephony, as well as relaying other topics of interestto the international computer underground. (check out, PHRACK)
PHY: PHYsical layer designation for FDDIand other network topologies.
PIM: Protocol-Independent Multicast; is anIP multicast protocol that works with all existing unicastrouting protocols. PIM has two modes that allow it to work effectivelywith two different types of multicast traffic distribution patterns: densemode and sparse mode.
PIM-DM: Protocol-Independent Multicast -Dense Mode; Dense mode PIM is designed for the following conditions:
pipeline: In computers, a pipeline isthe continuous and somewhat overlapped movement of instructions to theprocessor or in the arithmetic steps taken by the processor to performan instruction. Pipelining is the use of a pipeline. Without a pipeline,a computer processor gets the first instruction from memory, performs theoperation it calls for, and then goes to get the next
instruction from memory, and so forth. While fetching (getting) theinstruction, the arithmetic part of the processor is idle. It must waituntil it gets the next instruction. With pipelining, the computer architectureallows the next instructions to be fetched while the processor is performingarithmetic operations, holding them in a buffer close to the processoruntil each instruction operation can be performed. The staging of instructionfetching is continuous. The result is an increase in the number of instructionsthat can be performed during a given time period.
pixel: An abbreviation of picture element;the minimum raster display element, represented as a point with a specifiedcolor or intensity level. One way to measure picture resolution is by thenumber of pixels used to create images.
PLATO: Programmed Logic for Automatic TeachingOperations
PLB: Picture Level Benchmark
PMD: Physical Media Designator
PMT: Program Map Table; see ISO/IEC13818-1 Sections 220.127.116.11 and 2.6.8
Plesiochronous: Nearly synchronised;A term describing a communication system where transmitted signals havethe same nominal digital rate but are synchronised on different clocks.
According to ITU-T standards, corresponding signalsare plesiochronous if their significant instants occur at nominally thesame
rate, with any variation in rate being constrained within specifiedlimits.
PNG: Portable Network Graphic (Format)
P-NNI or PNNI:Private Network to Network Interface, (ATM)
POP: Point of Presence; usually means a cityor location where a network can be connected to, often with dialup phonelines. So if an Internet company says they will soon have a POP inBelgrade, it means that they will soon have a local phone number in Belgradeand/or a place where leased lines can connect to their network.
POP: Post Office Protocol; A protocol designedto allow single user computers to retrieve electronic mail from a server.There are (in 1994) three versions: POP, POP2, and POP3. Later versionsare NOT compatible with earlier ones.
POSIX: Portable Operating System Interface;is a set of standard operating system interfaces based on the UNIX operatingsystem. The need for standardization arose because enterprises using computerswanted to be able to develop programs that could be moved among differentmanufacturer's computer systems without having to be recoded. UNIX wasselected as the basis for a standard system interface partly because itwas "manufacturer-neutral." However, several major versions of
UNIX exist so there was a need to develop a common denominator system.
Informally, each standard in the POSIX set is defined by a decimal followingthe POSIX. Thus, POSIX.1 is the standard for an application program interfacein the C language. POSIX.2 is the standard shell and utilities interface(that is to say, the interactive command inteface with the operating system).These are the main two interfaces, but additional interfaces, such as POSIX.4for thread management, have been developed or are being developed. ThePOSIX interfaces were developed under the auspices of the IEEE.
PostScript: A Page Description Language,(Adobe Systems, Inc.)
POTS: Plain Old Telephone Service; The onlyname recognized around the world for basic analog telephone service. POTStakes the lowest 4 kHz of bandwidth on twisted pairwiring. Any service sharing a line with POTS must either use frequenciesabove POTS or convert POTS to digital and interleave with other data signals.
PPH: Pixels per Hour (used to refer to the'Cannon 600 Bubblejet printer').
PPTP: Point to Point Tunneling Protocol
PPV: Pay Per View
PRA: Primary Rate Access; An ISDNaccess method that uses maximum data rates of 2.048 Mbit/s in Europe, or1.544 Mbit/s in the US and Japan.
PRDB: Policy Routing Database; the routing configuration database,which was used to configure the NSFNET routers since1986. With the introduction of the RIPE-181language, which provided better functionality in recording global routingpolicies, the PRDB was to be retired in 1995 for full RADBfunctionality.
PRI: Primary Rate Interface; ISDN'scarrier or large user interface comprising 30 B Channelsand 1 D Channel (30B+1D) channels in Europe, supportingaround 1,920 Mbit/s. Primary Rate Interface (PRI) ISDN,in the US is primarily designed for business applications and consistsof 23 B Channels and 1 DChannel (23B+D). In essence, it is the same as a full T1(1.544 Mbps) apllication with the same per channel electrical and protocolcharacteristics of BRI ISDN. However,the ability to bond multiple B Channels allowsfor significantly higher bandwidth facilitating even higher throughputand special applications such as Large Screen Video Conferencing on demand.In addaition, the newer versions of PBXs (Private BranchExchanges) are being eqipped to take a direct BRI inputand are also designed to provide for alternate Voice and Data transmission.
PSC: Public Service Commission; a locally appointedgovernment body that votes on, amoung other things, 'local loop', (seeLEC) boundaries.
PSK: Phase Shift Keying; a modulation methodfor compressing a digital communications stream.
PT: Payload Type
PTI: Payload Type Identifier
PTS: Presentation Time Stamp; frequently usedbetween demultiplexing and decoding phases of a transciever.
PVC: Permanent Virtual Connection/Circuit;An ATM logical connection (rather than physical) betweenendpoints. A PVC is a connection set up by some external mechanism, typicallynetwork management, in which a set of switches between an ATMsource and destination ATM systems are programmedwith the appropriate VPI / VCI values.PVCs always require some manual configuration.
PVCC: Permanent Virtual Channel Connection
PVM: Parallel Virtual Machine
PVPC: Permanent Virtual Path Connection