PABX (Private Automatic Branch Exchange) - A private telephone exchange which transmits calls internally and to and from the public telephone network.

Packet - An arbitrary collection of data grouped and transmitted with its user identification over a shared facility.

Packet Port - A port on the CellPath 300 that transmits and receives packet traffic.

Packet Switching - A communications paradigm in which packets (messages) are individually routed between hosts with no previously established communications path. 

Packet Switching Network - A network designed to carry data in the form of packets.

PAD (Packet Assembler Disassembler) - An interface device that buffers data sent to/from character mode devices, and assembles and disassembles the packets needed for X.25 operation.

Paired Cable - A cable in which all of the conductors are arranged in the form of twisted pairs. This form of cable is the one most commonly used for communications.

PAL (Phase Alternate Line) - Largely a German/British development in the late 60s. Used in the UK and much of Europe. Phase Alternate Line is the acronym's expansion. The B-Y and R-Y signals are weighted to U and V, then modulated onto a double-sideband suppressed subcarrier at 4.43MHz.

The V (R-Y) signal's phase is turned through 180 degrees on each alternate line. This gets rid of NTSC's hue changes with phase errors at the expense of de-saturation. The carrier reference is sent as a burst in the back porch. The phase of the burst is alternated every line to convey the phase switching of the V signal. The burst's average phase is -V. (see NTSC for U.S.).

Panic Dump - A listing of information written by the processor when it reaches a non-recoverable condition. Contents of certain memory locations and other program state information useful in determining the cause of the fault condition are recorded.

Parallel Port - An output receptacle often located on the rear of a computer. Unlike serial, there is no EIA standard for parallel transmission, but most equipment adheres to a quasi-standard called the Centronics Parallel Standard. 

Parent Node - The logical group node that represents the containing peer group of a specific node at the next higher level of the hierarchy.

Parent Peer Group - The parent peer group of a peer group is the one containing the logical group node representing that peer group. The parent peer group of a node is the one containing the parent node of that node. 

Parity Bit - A binary bit appended to an array of bits to make them sum all of the bits always odd or always even. 

Part 68 Requirements (Registration) - Specifications established by the FCC as the minimum acceptable protection which communications equipment must provide the telephone network. Meeting these requirements does not certify that equipment performs any task.

patch panel - A generic device that allows for organizing and connecting the fiber optic cables coming from the ASX-4000.

Path Constraint - A bound on the combined value of a topology metric along a path for a specific connection.

Path Scope - The highest level of PNNI hierarchy used by a path.

Payload Scrambling - A technique that eliminates certain bit patterns that may occur within an ATM cell payload that could be misinterpreted by certain sensitive transmission equipment as an alarm condition.

PBX (Private Branch Exchange) - A private phone system (switch) that connects to the public telephone network and offers in-house connectivity. To reach an outside line, the user must dial a digit like 8 or 9. 

PBX Battery - Source of DC power for private branch exchange. Usually on the same premises as the PBX, though PBXs are sometimes fed from the central office over special conductors. 

PC (Personal Computer) - A computer for personal, single user use, as opposed to other types of computers such as mainframes and minis, which are typically shared by many users.

PCB (Printed Circuit Board) - Flat material (fiberglass/epoxy) on which electronic components are mounted. A PCB also provides electrical pathways, called traces, that connect components. PCBs are very sensitive to static electricity and must be handled with care. Also called printed wiring board and printed circuit card.

PCI (Peripheral Component Interconnect) - A local-bus standard created by Intel.

PCM (Pulse Code Modulation) - A modulation scheme that samples the information signals and transmits a series of coded pulses to represent the data.

PCR (Peak Cell Rate) - Parameter defined by the ATM Forum for ATM traffic management. In CBR transmissions, PCR determines how often data samples are sent. In ABR transmissions, PCR determines the maximum value of the ACR. 

PCS (Personal Communications Software) - Personal Communications Software available in ROLM, Cedar, Cypress, and Juniper makes for easy access to external databases, rapid transfer of data files, and one-touch access to most telephone features. Other PCS features include built-in calculator, small phone list, reminder function, and internal clock.

PDN (Public Data Network) - A network designed primarily for data transmission and intended for sharing by many users from many organizations.

PDSC (Power Distribution Servicing Cabinet) - A cabinet containing branch circuit protection for essential AC loads.

PDU (Protocol Data Unit) - A unit of data specified in a layer protocol and consisting of protocol control information and layer user data. 

Peak - That part of the business day in which cellular customers expect to pay full service rates. 

Peak Cell Rate - At the PHY Layer SAP of a point-to-point VCC, the Peak Cell Rate is the inverse of the minimum inter-arrival time T0 of the request to send an ATM-SDU.

Peak Current - The maximum value reached by a varying current during one cycle.

Peak-to-Peak Value - The algebraic difference between the extreme values of a varying quantity.

Peak Voltage - Maximum voltage occurring during a cycle. For a sine wave, peak value is 1.4142 times the rms value.

Peer Entities - Entities within the same layer.

Peer Group - A set of logical nodes which are grouped for purposes of creating a routing hierarchy. PTSEs are exchanged among all members of the group.

Peer Group Identifier - A string of bits that is used to unambiguously identify a peer group.

Peer Group Leader - A node which has been elected to perform some of the functions associated with a logical group node.

Peer Group Level - The number of significant bits in the peer group identifier of a particular peer group.

Peer Node - A node that is a member of the same peer group as a given node. 

Peripheral Equipment - Equipment which itself has no on-line role but works closely with on-line equipment.

per-VC queuing - Refers to the buffering of information on an individual virtual circuit basis.

Phase - One of several (usually three) windings that comprise the armature. Three phase windings have their generated voltages 120 degrees apart. Each winding represents a Phase A, Phase B and Phase C. 

Phase Hit - Unwanted and significant shifting in phase of an analog signal, defined by AT&T as any case where the phase of a 1004 Hz test signal shifts more than 20 degrees. Also, error-causing events more severe than phase jitter, especially for data transmission equipment using PSK modulation.

PHY (Physical Layer) - The actual cards, wires, and/or fiber-optic cabling used to connect computers, routers, and switches.

Physical Layer (PHY) Connection - An association established by the PHY between two or more ATM-entities. A PHY connection consists of the concatenation of PHY links in order to provide an end-to-end transfer capability to PHY SAPs.

Physical Link - A real link which attaches two switching systems. 

Picofarad - A ten to the negative twelfth power farad. One millionth of a microfarad. 

Pigtail - A flexible conductor attached to a component or device.

Pigtail Antenna - The standard cellular antenna for a car. The term "pigtail" refers to the spring-like section in the lower third of the antenna, the phasing coil. 

ping (Packet Internet Groper) - A program used to test reachability of destinations by sending them an ICMP echo request and waiting for a reply.

Pin Jack - A small single-contact jack used for temporary circuit connection.

Plant - A general term to describe any telephone company equipment used to provide communications services.

PLCP (Physical Layer Convergence Protocol) - A framing protocol that runs on top of the T1 or E1 framing protocol.

Plesiochronous - Two signals are plesiochronous if their corresponding significant instants occur at nominally the same rate, any variation in rate being constrained within specified limits.

PLM (Physical Layer Module) - Interface card in the CellPath 300 that provides the logic to support the physical layer of the network link. A PLM has the actual physical port mounted on it. Various PLMs support various physical layers, such as OC-3c/STM1 or DS3.

PLP (Packet Level Protocol) - Network layer protocol in the X.25 protocol stack. Sometimes called X.25 Level 3 or X.25 Protocol.

PM (Physical Medium) - Refers to the actual physical interfaces. Several interfaces are defined including STS-1, STS-3c, STS-12c, STM-1, STM-4, DS1, E1, DS2, E3, DS3, E4, FDDI-based, Fiber Channel-based, and STP. These range in speeds from 1.544Mbps through 622.08 Mbps.

PM (Protocol Module) - Interface card in the CellPath 300 that provides the logic supporting the protocol layer of the network link. Various PMs support various protocols, such as ATM cell, Frame Relay, or CBR traffic.

PMD (Physical Medium Dependent) - A sublayer concerned with the bit transfer between two network nodes. It deals with wave shapes, timing recovery, line coding, and electro-optic conversions for fiber based links.

PNNI (Private Network Node Interface or Private Network-to-Network Interface) - A protocol that defines the interaction of private ATM switches or groups of private ATM switches.

PNNI Routing Control Channel - VCCs used for the exchange of PNNI routing protocol messages.

PNNI Routing Domain - A group of topologically contiguous systems which are running one instance of PNNI routing.

PNNI Routing Hierarchy - The hierarchy of peer groups used for PNNI routing.

PNNI Topology State Element - A collection of PNNI information that is flooded among all logical nodes within a peer group.

PNNI Topology State Packet - A type of PNNI Routing packet that is used for flooding PTSEs among logical nodes within a peer group.

PO (Proper Operation) - A discrete status indicator whichreports that an engine/alternator system has transferred and is supplying AC in the central office within proper limits.

Point-to-Multipoint Connection - A collection of associated ATM VC or VP links, with associated endpoint nodes, with the following properties:
1. One ATM link, called the Root Link, serves as the root in a simple tree topology. When the Root node sends information, all of the remaining nodes on the connection, called Leaf nodes, receive copies of the information.
2. Each of the Leaf Nodes on the connection can send information directly to the Root Node. The Root Node cannot distinguish which Leaf is sending information without additional (higher layer) information. (See the following note for Phase 1.)
3. The Leaf Nodes cannot communicate directly to each other with this connection type. Note: Phase 1 signaling does not support traffic sent from a Leaf to the Root.

Point-to-Point Connection - A connection with only two endpoints.

Polarity - A particular state either positive (+) or negative (-) with respect to some other state, often ground.

Polling - Usually refers to some form of data network arrangement whereby a central computer asks each remote location in turn (and very quickly) whether they want to send some information. The purpose is to give each user or each remote data terminal an opportunity to transmit and receive information on a circuit or using facilities which are being shared. Polling is typically used on a multipoint or multidrop line. Polling is done to save money on telephone lines.

Pop - Short for "population." One "pop" equals one person. In the cellular industry, systems are valued financially based on the population of the market served.

Portable - A one-piece, self-contained cellular telephone. The newest ones are so small - weighing as little as 10 ounces - that they can be folded up and carried in a suit pocket or purse. Portables normally have a built-in antenna and rechargeable battery and operate with six-tenths of one watt (0.6) of power.

Positive - (1) Describing the terminal of a storage battery from which the conventional current leaves the battery; (2) having the ability to attract electrons; and (3) the opposite of negative.

Pot - A potentiometer.

Potential Difference - The difference in voltages between two points.

Potential Drop - The difference in potential, often due to a voltage drop across a resistance.

Potentiometer - A three-terminal adjustable voltage divider.

POTS (Plain Old Telephone Service) - The basic service of supplying standard single line telephones, telephone lines and access to the public switched network. No added features like Call Waiting or Call Forwarding are included in POTS.

Potting - Sealing of components under a plastic cover to keep out moisture.

Power - The rate at which energy (or work) is used; units include watts, horsepower, and foot pounds per second.

Power Board or Bay - A frame mounted power distribution panel containing switches, circuit breakers, and fuses mounted on the face of the panel to control the standby power equipment contained in the system. Other components, such as terminal strips, relays, and capacitors are mounted behind the panel.

Power Circuit Breaker - (1) A circuit breaker for use on AC circuits rated in excess of 1500V; and (2) the primary switch used to apply and remove power from equipment.

Power Cord - A three-wire (sometimes two-wire) cord used to make connection with an AC public power supply (commercial power).

Power Density - (1) Power in watts per hertz, or the total power in a band of frequencies divided by the bandwidth in hertz; and (2) in optoelectronics, a colloquial synonym for irradiance.

Power Down - The sequence of actions necessary in order to turn off a computer or telephone system. Not following the correct power down procedures can cause a loss of data.

Power Factor - Ratio of total watts to total root-mean-square volt-amperes, i.e., the active power to the apparent power.

Power Failure Backup - If AC power fails, a telephone system, computer, etc. can still operate by switching to a backup battery supply, often called a UPS (Uninterruptible Power Supply).

Power Loss - Ratio of total power delivered to a line to the power from line into load, expressed in dB.

Power Plant - The equipment necessary to supply processed power to a switch or other device requiring battery backup.

Power Rack - Rack on which such items as rectifiers, tone generators and meters are mounted in a small central office.

Power Rated Fuse - Fuse rated to carry a specified current indefinitely. Currents 50% greater than the specified value will lead to the fuse blowing within five minutes.

Power Supply - That part of switches, computers, etc. which converts the normal 120 or 240 volts AC power to AC and DC at the various voltages and frequencies needed by various components and circuits of the system.

Power Unit - A component or module which provides a power supply at an appropriate voltage for a particular item or items of equipment.

Power Up (or Power On) - The sequence of actions necessary in order to turn a computer or telephone system on.

Precise Dial Tone - Mixture of 350 Hz and 440 Hz tones at -13dBm.

Primary Winding - Transformer winding which receives an input signal from a source, thereby creating magnetic flux in a core. This flux induces current in a secondary winding.

Priority Loads - In plants where load management schemes are used, a priority is assigned to each load center. Loads with the highest priority are powered first and shed last.

Private Network - A series of offices connected together by leased and non-leased phone lines, with switching facilities and transmission equipment owned and operated by the user or by the carrier and leased to the user.

Pro-Active - Taking the initiative.

PROM (Programmable Read Only Memory) - A chip that acts like non-volatile memory and is difficult to re-program.

Proportional Load Sharing - Characteristics of battery chargers in parallel that enables them to share total load current in proportion to their output rating.

Proprietary - Equipment which will only work with one vendor's telephone system.

Protected AC Load - One that must operate during prolonged loss of AC power and can tolerate an interruption of from 0.15 to 5 seconds in the transition from commercial to standby power.

Protocol - A specific set of rules, procedures or conventions relating to format and timing of data transmission between two devices, typically including such things as framing, error handling, transparency and line control. There are three basic types of protocols: character-oriented, byte-oriented and bit-oriented.

PTT (Post Telephone & Telegraph Administration) - PTTs, usually controlled by their governments, provide telephone and telecommunications services in most foreign countries.

PUC (Public Utility Commission) - State body charged with regulating phone companies. Also called Public Service Commission.

PWB - Printed Wire Board.

PWR - Power.