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Glossary P-Q

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  • Packet: A group of bits(including data & call control signals) transmitted as a whole on a packet-switching network. Usually smaller than a transmission block.
  • Packet Assembler/Disassembler: (PAD) A device for connecting a terminal or computer to an X.25 network.
  • Packet Data Network: (PDN) Often used to mean packet-switched network.
  • Packet Switching: A wide area communications technique in which data is packeted for transmission over a shared data network rather than over dedicated lines. Packet switching differs from circuit switching in that is uses virtual circuits, i.e. it is made up of bandwidth allocated on demand from a network of shared circuits.
  • PAD: See Packet Assembler/Disassembler
  • PAP: See Printer Access Protocol
  • Parallel Circuit: A circuit in which the identical voltage is presented to all components, with current dividing among the components according to the resistances or the impedances of the components.
  • Parallel Extender: A kit that usually contains a Transmitter, Receiver, and a small wire to connect the two for connecting a parallel port on a computer to a parallel printer.
  • Parallel Processing: Concurrent or simultaneous execution of two or more processes, or programs within the same processor, as contrasted with serial or sequential processing.
  • Parallel Transmission: Transmission mode that sends a number of bits simultaneously over separate lines (example, 8 bits over 8 lines). Usually unidirectional.
  • Parity Bit: A check bit added to a character to make the total number of 1's in the character an even or odd number.
  • Parity Checking: The process of checking that a received character has the correct parity bit. Both the sending & the receiving DTE's must be set to operate for the same parity indicates an error & may cause an appropriate remedial action to be initiated.
  • Pass Through: Describing the ability to gain access to one network element through another
  • Patch Cable: A cable with plugs or terminals on each end of the conductors to temporarily connect circuits of equipment together.
  • Patch Cord: A length of cable with connectors on one or both ends used to join telecommunications circuits at the cross-connect.
  • Patch Panel: A system of terminal blocks, patch cords & backboards that facilitates administration of cross- connect fields for moves & rearrangements.
  • PBX: See Private Branch Exchange
  • PCC: See Premises Communication Cable
  • PCF: See Physical Control Fields
  • PDN: See Packet Data Network
  • PE: See Polyethylene
  • Peak: The maximum instantaneous value of a varying current or voltage.
  • Peer-to-Peer: A system in which two or more nodes or processes can initiate communications with each other. Usually describes a network in which all nodes have the ability to share resources with other nodes so that a dedicated server can be implemented but is not required.
  • Performance Management: Measures & records resource utilization. It is one of the categories of network management defined by the ISO.
  • Phase: An angular relationship between waves.
  • Phase Modulation: A modulation technique. The phase of the carrier sine wave is modified to add the information.
  • Phase Shift: A change in the phase relationship between two alternating quantities.
  • Photodetector: (Receiver) Transforms a light signal into an electrical signal. The silicon photo diode is most commonly used for relatively fast speeds & good sensitivity in the 0.75 um to 0.95 um wavelength region. Avalance photodiodes (ADP) combine the detection of optical signals with internal amplification of photo-current. Internal gain is realized through avalance multiplication of carriers in the junction region. The advantage in using an ADP is its higher signal-to-noise ratio, especially at high bit rates. Physical Address: The MAC-layer address of a node, as opposed to the software-defined network-layer address.
  • Physical Control Fields: (PCF) The Access Control & the Frame Control bytes in a Token Ring header.
  • Physical Layer: The lowest level of the OSI reference model. The Physical layer specifies the physical transmission media, signaling levels, connectors, & related interface features.
  • Pickup: Any device which is capable of transforming a measurable quantity of intelligence (such as sound) into relative electrical signals.
  • Pico: Prefix meaning one-trillionth (or one-millionth of one-millionth) (10-12).
  • Picofarad: one trillionth of a farad
  • Pigtail Wire: Fine stranded, extra flexible, rope lay lead wire attached to a shield for terminating purposes.
  • Pin Configuration: A predetermined relationship between the terminals in a connector & the conductors in a cable that specifies the terminals to which each conductor is to be terminated.
  • Ping: Network management software used to test if a managed device is reachable. The ICMP packets used for this function are called echo packets or "pings."
  • Pinouts: Pin configurations for cabling.
  • Pipe: A device that acts as an interface or buffer between applications & devices.
  • Pitch: In flat cable, the normal distance between the index edges of two adjacent conductors. For connectors, it's the normal distance between contacts along one row.
  • Pixel: Picture element; smallest unit of a graphics or video display; light characteristics (color & intensity) which can be coded into an electrical signal for transmission.
  • Plastic: High polymeric substances, including both natural & synthetic materials.
  • Plenum: A space within the building created by building components, designed for the movement of environmental air (a space above a suspended ceiling or below an access floor).
  • Plug: The part of the two mating halves of a connector which is moveable when not fastened to the other mating half.
  • Point-to-Point Link: Communication link connecting two DTE's
  • Point-to-Point Protocol: (PPP) A standard TCP/IP related protocol used to communication over a serial point-to-point link such as T-1 trunk between routers.
  • Polarity: A condition when there are two opposing voltage levels.
  • Polling: An access method with which a hub asks each node in turn if it has data to transmit.
  • Polyethylene: (PE) A type of plastic material used to make cable jacketing. Having excellent electrical properties.
  • Polymer: A substance made of many repeating chemical units or molecules. The term polymer is often used in place of plastic, rubber, or elastomer.
  • Polypropylene: A thermoplastic similar to polyethylene but stiffer & having a higher softening point (temperature).
  • Polyurethane: Broad class of polymers noted for good abrasion & solvent resistance, Can be in solid or cellular form.
  • Polyvinyl Chloride: (PVC) A general purpose thermoplastic used for wire & cable insulation & jackets.
  • Port: A point of exit or entry for a data channel in a network.
  • Port Number: A field in the TCP & UDP headers that specifies which applications are sending & receiving the messages. The port field is the layer interface that enables TCP & UDP to transfer messages to any application.
  • Potting: Sealing by filling with a substance to exclude moisture.
  • Power: The amount of work per unit of time. Usually expressed in watts.
  • PPP: See Point-to-Point Protocol
  • Premises Communication Cable: (PCC) CSA (Canadian Standards Association) Cable Designation.
  • Presentation Layer: Layer six of the ISO reference model; provides standards for restructuring data into the required format, character set, or language.
  • Print Spooler: An application that manages print requests or jobs so that one job can be processed while other jobs are placed in a queue until the printer has finished with preceding jobs.
  • Printer Access Protocol: (PAP) An AppleTalk protocol governing transmissions between workstations & printers or similar devices.
  • Printer Server: An intelligent device used to transfer information to a series of printers.
  • Private Branch Exchange: (PBX) A private telephone exchange.
  • Processing Unit: A unit of a computer that contains the circuits controlling the interpretation & execution of commands. It is the heart of the computer.
  • Programmable Read-Only Memory: (PROM) A nonvolatile memory chip that stores data or programs permanently. Compare with volatile memory.
  • PROM: See Programmable Read-Only Memory
  • Propagation delay: The time required for data to travel from transmission point to destination.
  • Proprietary: A protocol or communications system developed by a company, as opposed to those emanating from a standards organization.
  • Protected mode: CPU (Central Processing Unit) mode in which applications must request memory allocations from the operating system, & these allocations are then protected from other applications" requests.
  • Protective Ground: (GND) One of the signals in the DTE-DCE interface. Protective Ground discharges harmful electrical current, thereby protecting the equipment & users.
  • Protocol: A standardized set of rules that specify the format, timing, sequencing, and/or error checking for data transmissions.
  • Protocol Multiplexing: A technique for unambiguously transmitting more than one protocol over the same link. For example both Ethernet & PPP allow protocol Multiplexing.
  • Protocol stack: A representation of the hierarchical nature of a protocol suite.
  • Protocol Suite: A hierarchical set of related protocols.
  • Proxy: Allows the LAN to connect to the internet through addressing. This will not allow the internet to access the Local Area Network (LAN)
  • PSTN: See Public Switched Telephone Network
  • Pubic Network: A network operated by common carriers or telecommunications administrations for the provision of circuit switched, packet-switched, & leased-line circuits to the public.
  • Public Switched Telephone Network: (PSTN) Any switching communications system such as Telex, TWX, or public telephone networks that provides circuit switching to many customers.
  • Publishing: Making resources available to network users.
  • Pulling Eye: A device used to pull cable into or from a duct or conduit.
  • Pulse: A current or voltage which changes abruptly from one value to another & back to the original value in a finite length of time. Used to describe one particular variation in a series of wave motions.
  • Punchdown: A method for securing wire to a quick clip in which the insulated wire is placed in the terminal groove & pushed down with a special tool. As the wire is seated, the terminal displaces the wire insulation to make an electrical connection. The punchdown operation may also trim the wire as it terminates. Also called cut down.
  • PVC: See Polyvinyl Chloride
  • QBE: See Query By Example
  • Query By Example: (QBE) A database front-end that requests the user to supply an example of the type of data to be retrieved.
  • Query Language: A programming language that permits users to retrieve information from a database.
  • Queue: An ordered list of items waiting to be processed.
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