It's a good time to pray for victims of September 11, 2001 terrorist activities!


See pico-.
pico- (p)

The Institute of Electrical and Electronic Engineers (IEEE) standard
providing the overview and architecture of Integrated Services (IS) LAN
IEEE 802.9 Isochronous services with Carrier sense multiple access with
collision detection (CSMA/CD) Media Access Control (MAC) service. The
Iso-Ethernet standard. See also H.322.

See private automatic branch exchange (PABX) or wireless private
automatic branch exchange (PABX)

The process of sending a predefined quantity of information before
receiving a response acknowledging receipt of the previously
transmitted data.

A BBS program which packs new messages together to be sent out by a
mailer or download by a user for offline mail reading.

A group of bits switched as a unit for transmission over a shared
network. A packet is the basic unit of transmission in a
packet-switched network. Control information is carried in the packet,
along with the data, to provide for addressing sequence, flow control,
and error control at each of several protocol levels. A packet can be
of fixed or variable length, but usually has a specified maximum length
of 1024 bits.

packet assembler/disassembler (PAD)
A device that accepts character streams from a terminal or host
computer and assembles them into packets that can be handled by a
packet-switching network. It also accepts packets from the network, and
disassembles them into character streams that can be handled by the
terminal or host computer on the receiving end.

packet buffer
Memory space reserved for storing a packet awaiting transmission or for
storing a received packet.

packet Internet groper (PING)
1) A program useful in testing and debugging local area network (LAN)
or wide area network (WAN) systems. It sends out an echo and expects a
specified host to respond in a specified time frame. 2) A transmission
control protocol/Internet protocol (TCP/IP) utility that sends packets
of information to a computer on a network. A PING can be used to
determine whether a computer is connected to the Internet.

packet processor
The Cascade switch module that performs frame format validation,
routing, queuing, and protocol conversion for the switch.

packet switched public data network (PSDN)
A packet-oriented public network based on X.25.

packet switching
A transmission protocol in which data is segmented into packets that
can be individually addressed and routed through the network, possibly
using several different routes. The sequence of the packets is
maintained and the destination established by the exchange of control
information, contained in the packets, between the sending terminal and
the network before the transmission starts. The receiving-end node
determines that all packets are received and in the proper sequence
before forwarding the reassembled message to the addressee. Packet
switching allows facility sharing by many users. Packet switching is
being superseded by frame relay and eventually by asynchronous transfer
mode (ATM).

packet switching module
Provides interface between a PBX and an interface packet-switching
module; data terminals are provided with speed, codes, and protocols to
process data calls to packet-switching networks.

packet switching network
A network in which data is transmitted in packets. Packets can be
routed individually over the best available network connection and
reassembled to form a complete message at the destination. See packet
switching, packet, and packet assembler/disassembler.
packet switching
packet assembler/disassembler (PAD)

Packet Switching Node (PSN)
The name of an Arpanet packet switch; PSNs were formerly called IMPS.

packing density
The amount of storage area per unit length, unit area, or unit volume;
for example, the number of bits stored per inch on magnetic tape.

See packet assembler/disassembler.
packet assembler/disassembler (PAD)

This happens when a file that is being transferred ends in the middle
of a block of data. The communications program must add blank data to
fill up the block. Some term programs will "strip" this before saving
the file to disk.

1) Direct attendant access and station-user dial access to loudspeaker
equipment using special telephone sets with internal speakers. 2) A
one-way alert or alphanumeric message service. Messages are normally
left via a bureau with a human or automatic operator.

paging by zone
The use of a telephone access code to page specific groups of
telephones or speakers.

See public access line (PAL) or Phase Alternate Line -- add

PAL Format
For Phase Alteration Line , 625 lines of resolution at 25 frames per

See pulse amplitude modulation (PAM) or pulse modulation (PAM, PPM,

parallel interface
An interface that can handle a group of bits transmitted at the same
time, by sending each bit over a separate wire. Probably the best known
parallel interface of all is the one developed by Centronics, a printer
manufacturer, that has 36 pins and can handle a byte of data at a time.
The transmission of the data is controlled by a computer generated
strobe pulse.

parallel transmission
Simultaneous transmission of all the bits making up a character or
byte, either over separate channels or on different carrier frequencies
on one channel.

Parc Universal Packet (PUP)
In the internet system developed by Xerox Corporation, a PUP is the
fundamental unit of transfer, just as the IP datagram in a TCP/IP
internet. The name was derived from the name of the laboratory at which
the Xerox internet was developed, the Palo Alto Research Center (PARC).

The maintenance of the sameness of data by checking during transmission
to detect whether the data has been altered.

parity bit
A binary digit appended to a collection of digits to make the sum of
the digits always odd or always even.

parity check
The addition of non-information, or parity bits to data, making the
number of ones in a grouping of bits always even or always odd. Parity
checking detects single-bit errors and can be applied to characters,
blocks, or any convenient bit grouping.

A feature that enables calls to be transferred to a busy extension; the
call can be connected to the extension when it is free. See camp-on.

part 68
Federal Communications Commission (FCC) specifications indicating the
minimum acceptable protection that communications equipment must
provide to the telephone network.

The subcomponent elements of an aggregate object.

A participant in a call.

party line
A telephone line that is shared by multiple subscribers.

party line stations
Two-party telephone service that is expanded to support multiparty

A range of frequencies passed by a device or network.

A special code that only you know which the BBS, or some other entity,
asks for each time you logon. Passwords should be changed frequently
and should be something you can remember but that others won't guess.

password protection
The use of passwords as a security measure to protect a system against
unauthorized access.

past due balance
The balance resulting from the failure to pay an invoice or bill by the
specified due date.

A temporary jack-and-cable connection.

End-to-end transport of a service, usually consisting of multiple lines
and sections. (SONET)

path attenuation
The losses undergone by a wave in transit between a transmitter and a

path circuit
A circuit or connection route.

See private automatic telex.
private automatic telex

See private automatic exchange.
private automatic exchange (PAX)

pay per minute
See measured service.
measured service

pay phone
A public or private telephone that accepts coins or encoded credit

The ability to select and view the cable television programming of
one's choice for a fee.

The process of paying or the receipt of a revenue item.

See private branch exchange.

PBX attendant position
The equipment used by the PBX operator for manually controlling calls
and connecting functions.

PBX extension
A telephone station connected to and/or served by a private branch
exchange (PBX).

PBX main station
The designated primary telephone instrument associated with a PBX.

PBX station line
The permanent electrical circuit and any incidental components between
the appearance of the PBX station line circuit and point of connection
with the station equipment.

PBX station line circuit
A network of circuit elements used to connect a PBX to one of its
associated lines.

PBX tie line
See tie line

PBX trunk
The transmission path between a PBX and a commercial central office.

See personal computer (PC)

See private computerized branch exchange (PCBX)

See peripheral component interconnect (PCI)

See pulse code modulation (PCM) or physical connection management (PCM)

See personal communications network

See personal communications service (PCS)

Low cost alternative to the ActionMedia card. See ActionMedia.

See personal digital assistant.
personal digital assistant (PDA)

See pulse duration modulation (PDM)

See public data network.

See public document switching service

See protocol data unit (PDU)

See private digital exchange (PDX)

peer communications
A form of communications in which two parties contact each other as
equals rather than in a master/slave relationship. A program and a
terminal form a master/slave combination, but two programs form peer
communications. Peer communications protocols usually provide more
powerful interaction facilities.

A network model with no centralized servers. Network users can
independently initiate communications sessions at their discretion in
order to share resources with others on the network. Communications
tasks are assigned so that data transmission between logical groups or
layers in a network architecture is accomplished between entities in
the same layer of the open system interconnection (OSI) model.

peer-to-peer model
See peer-to-peer

peer-to-peer network
See peer-to-peer

peer-to-peer network communications architecture
See peer-to-peer

peer-to-peer resource sharing
An architecture that allows any station to contribute resources to the
network while still running local application programs.

peg count
A rough count of some event, usually the number of calls made or
received in a given time period.

See picture element (PEL and pixel)

See privacy-enhanced mail (PEM)

The submarine cable between peninsular Spain and the Balearic Islands.

The submarine cable between peninsular Spain and the Canary Islands.

percent error-free seconds
The percentage of elapsed test seconds that do not contain errors.

percentage of interstate usage (PIU)
The percentage of time that a facility or circuit is used for
interstate transmissions. PIU is used to allocate access services
between state and federal jurisdictions for pricing purposes.

performance monitoring
The collection of data, on either a part-time or full-time basis, so
that the overall efficiency of a circuit may be determined.

perigee The point in a satellite's orbit that is closest to the earth.

peripheral component interconnect (PCI)
PCI provides high speed, auto configuring interconnection between the
cards in a PCs motherboard, the system memory, and the CPU.

peripheral device or equipment
Equipment that works in conjunction with a computer or processor and
provides the system with outside communications.

permanent virtual circuit (PVC)
1) A virtual connection, permanently established, using scheduling
techniques to generate, capture, and accommodate
connection-provisioning requests. 2) In data networking services, a
circuit that is defined in a static manner, with static parameters, but
that is not tied to any physical path through the network.

permanent virtual connection
See permanent virtual circuit (PVC)

An operator-assisted telephone call that is billed only if the
requested person accepts the call.

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person-to-person call
1) A type of long distance call. Charging begins only when the person
calling begins speaking to the person to whom they have specified they
wish to speak. 2) The rate charged when a caller wishes to speak to a
specific person, department, room, or extension.

personal communications network
A type of wireless telephone system that communicates through low-power
antennas and uses light, inexpensive hand-held handsets.

personal communications service (PCS)
Individualized telecommunications services permitting users to
communicate regardless of location. The low power, wireless
communications technology uses lightweight, inexpensive pocket
telephones and personal computers to transmit voice, fax, and data from

personal computer (PC)
Any computing system for use primarily by one person. Synonym: desktop

personal digital assistant (PDA)
An electronics device that acts as a personal carry-along database,
calculator, alarm clock, and personal communicator. It looks like a
palmtop computer, and communications are transmitted through telephone
lines or wireless.

personal identification number (PIN)
A four-digit code at the end of a calling card number.

personalized response system (PRS)
A computer assistance system which permits operators to pre-record
their greeting to customers and other frequently used messages, thereby
relieving stress on their voices and increasing operator productivity.
(See voice response.)
voice response (VR)

phantom circuit
A circuit configured so that two pairs of wires can provide three
speech paths.

Phase Alteration Line (PAL)
Video format used in most of western Europe, Australia and others.

Phase Alternate Line -- add
The European 625-line, 25 frame color-television standard. The system
was developed in West Germany that minimizes phase errors and improves
color performance.

Phase II costing
A prospective, incremental, growth-oriented method of costing for
telecommunications carriers that deals with new and existing products
and services.

Phase III costing
A historically-oriented method of accounting and costing in which
categories of services are studied over a one-year test period to
determine whether broad categories of service are meeting their revenue

phase jitter
See jitter.

phase modulation (PM)
Modulation in which the angle relative to the unmodulated carrier
changes according to the value of the amplitude of the modulating

phase-shift keying (PSK)
A modulation technique in which the phase of the carrier is modulated
by the state of the input signal.

The submarine cable between the Philippines and Singapore. Synonym:

A substance that emits light when struck by electrons. This substance
coats the back of a cathode ray tube (CRT) video display.

photo CD
A product developed by Eastman Kodak that places photos on a compact
disc and allows users to view them on a their television or computer.

photo CD compatibility
A product that displays photos stored on a compact disc. Photo
CD-compatible products can support what is described as Single Session
(capable of displaying just one set of photos from the CD) or
Multisession (capable of displaying more than one set of photos from
the CD.)

A device that detects optical power and converts it to electrical

See physical layer protocol (PHY)

physical change
The modification of an existing circuit, dedicated access channel or
port, at the request of the customer.

physical connection
The full-duplex layer association between adjacent physical layer
protocols (PHYs) in a fiber-distributed data interface (FDDI) ring,
that is, a pair of physical links.

physical connection management (PCM)
In a fiber-distributed data interface (FDDI), that portion of CMT that
manages the physical connection between adjacent physical layer
protocols (PHYs). This includes the signaling of connection type, link
confidence testing, and the enforcement of connection rules.

physical layer
Layer 1 of the open system interconnection (OSI) model; it defines and
handles the electrical/optical and physical media connections.

physical layer protocol (PHY)
A portion of the fiber-distributed data interface (FDDI) standard that
defines symbols, line states, clocking requirements, and the encoding
of data for transmission.

physical link
The simplest path, by way of physical medium dependent (PMD) and
attached mediums, from the transmit function of one physical layer
protocol (PHY) entity to the receive function on an adjacent physical
layer protocol (PHY) concentrators, repeaters, or station entity in a

physical medium
See link, bridge, or gateway

physical medium dependent (PMD)
A portion of the fiber-distributed data interface (FDDI) standard that
defines the medium and protocols to transfer symbols between physical
layer protocols (PHYs).

physical port
Each input/output card supports a number of physical communications
ports. The ports can be configured for different types of frame relay
interfaces and direct trunks.

physical topology
The actual arrangement of cables and hardware that make up a network.
For example, bus, ring, or star.

A computer that enables carriers to offer enhanced services by: 1)
Acting on the format, content, code, protocol or similar aspects of
transmitted information. 2) Providing additional or restructured
information. 3) Involving subscriber interaction with stored data, such
as translating 800 numbers to a plain old telephone service (POTS)
number or a trunk group. SCPs connect to signalling points, which
connect to switches.

PIC charges
A local exchange carrier (LEC) charge for changing the PIC. Often paid
by the new interexchange carrier (IEC). If a LEC sends a PIC charge to
a customer, the new IEC will typically credit the customer's account.

PIC request
A request record sent to a local exchange carrier (LEC) asking for an
automatic number identification (ANI) to be activated, deactivated or
changed in some way.

PIC response
A response record sent by a local exchange carrier (LEC), corresponding
to a previous primary exchange carrier (PIC) request, with a response
code that indicates whether the request was performed. Some LECs return
non-standard PIC response codes.

pico- (p)
The prefix indicating one trillionth of a unit.

picture element (PEL and pixel)
The smallest discrete part of a video image, the size of which is
controlled by the analog-to-digital conversion sampling process and
subsequent other compression processes. The more picture elements per
line, the higher the resolution of the image. To convert the number of
H pixels to a close approximation of TV lines of resolution for the
NTSC system, simply multiply the number of H pixels by 0.78.
Furthermore, each 80 TV lines of resolution (NTSC) requires 1 MHz of
analog bandwidth for transmission.

picture-in-picture display (PIP)
A video display mode in which a one-quarter- size video image (or
smaller) is superimposed over one quadrant of a full-screen video
image. PIP is especially useful as a preview monitor for one-monitor
videoconferencing installations and for TV receivers.

See property imposed fee.
property imposed fee (PIF)

pilot model
A model of a system. The model is used for program testing purposes; it
is simpler than the system it represents. The files used on a pilot
model can, for example, contain fewer records than the operational
files; there can be fewer lines and fewer terminals per line.

pilot tone
A tone of a specific frequency that is associated with a certain
transmission system.

See personal identification number (PIN) or positive intrinsic negative

PIN number
See personal identification number (PIN)

See packet Internet groper.
packet Internet groper (PING)

See picture-in-picture display (PIP)

See percentage of interstate usage (PIU)

See picture element (PEL and pixel)

See public key system (PKS)

See private line (PL)

plain old telephone service (POTS)
The basic service provided by a public telephone network, without any
added facilities such as conditioning.

The foundation of a system on which subcomponents depend.

A ready-made station that can be moved from one location to another and
activated by inserting it into a socket.

Production Level Video. Higher quality video similar to VHS.

See phase modulation (PM)

See private manual branch exchange (PMBX)

See physical medium dependent (PMD)

See private mobile radio (PMR)

purchase order

point of presence (POP)
The physical location at which the responsibility for managing
inter-LATA circuits changes from the local telephone company to the
long-distance company.

point-to-multipoint circuit
A circuit that connects a single node to a switch.

point-to-multipoint network
A network configuration interconnecting a point to multiple sites.

A private, direct connection established for data transmission between
two stations.

point-to-point connection
An uninterrupted link between two pieces of equipment.

point-to-point network
A network configuration that interconnects only two points. The
connection can be dedicated or switched.

point-to-point protocol (PPP)
The Internet standard method for transmitting Internet protocol (IP)
packets over serial point-to-point links. PPP supports both
asynchronous and synchronous lines. PPP has a number of advantages over
serial line Internet protocol (SLIP): it is designed to operate both
over asynchronous connections and bit-oriented synchronous systems; it
can configure connections to a remote network dynamically, and test
that the link is usable.

A signal stream in which all one bits are the same voltage polarity
(either positive or negative). All zero bits are the opposite polarity
from the one bits.

polar orbit
An satellite orbit that the crosses the poles.

polar return-to-zero
A polar signal with a 50 percent duty cycle.

polar transmission
A method of transmitting teletypewriter signals, whereby the marking
signal is represented by direct current flowing in one direction and
the spacing signal is represented by an equal current flowing in the
opposite direction. Synonym: polar keying

A procedure that allows stations on a multipoint circuit to transmit
without contending for lines. The communications device or computer
queries each terminal by transmitting a message that the terminal
acknowledges by indicating its need for service. If a negative response
is received by the polling device, polling continues with the next
terminal in sequence until all terminals on the polling list are
queried. If the terminal has a message to send, the poll activates the
terminal. Polling avoids the problems of contention.

polling list
The order in which stations are polled and maintained in a list
associated with each channel. A line polling list may also be used to
provide priority in line service.

See point of presence (POP) or post office protocol (POP)

1) A network entry or exit point. 2) A measure of customer premises
equipment (CPE) equipment capacity, generally based on the sum of the
number of station lines and trunks. A private branch exchange (PBX)
with 100 station lines and 20 trunks would have 120 ports. 3) A
connection between a computer and an external device such as a printer
port. 4) A connection point on a multiplexer. 5) The process of
transporting something, such as an application program, from one
environment to another. 6) The entrance or access point to a computer,
multiplexor device or network where signals may be supplied, extracted
or observed.

A device that allows unlike systems to communicate over a common
network link.

positive intrinsic negative (PIN)
A type of photodetector used to sense lightwave energy and convert it
to electrical signals.

To save a message that you have written on a BBS so that other people
can see it.

post office protocol (POP)
An E-mail protocol that lets users access their e-mail using a
graphical format mail program. The mail program (client) connects to
the mail server only while transferring messages.

Postal Telephone and Telegraph (PTT)
Authorities 1) A foreign government agency responsible for regulating
communications outside North America. 2) The government agency that
acts as a common carrier in most countries outside North America.

See plain old telephone service.
plain old telephone service (POTS)

An ordinary telephone number.

power budget
The difference between transmit power and receiver sensitivity,
including any safety margins.

power failure transfer
A private branch exchange (PBX) feature that provides limited service
to and from the exchange network when the PBX is not receiving enough

power level
The ratio of signal power to an arbitrary amount of power chosen as a
reference. Power level is expressed in decibels based on 1 milliwatt
(dBm) or 1 watt (dBw).

power penalty
The total loss introduced by planned-for splices in the fiber link.
Typically, extra splices are planned but not immediately implemented.

See pulse modulation (PAM, PPM, PWM)

See point-to-point protocol (PPP)

See Frame Relay Configuration Quote System.

See primary rate access (PRA)

See pseudo-random binary pulse sequence (PRBS)

predictive dialing
Automated dialing feature in which the systems predicts from pre-set
algorithms when an agent/operator will become free and makes the call
in advance.

The interruption of a lower priority call or message to use the same
circuit to transmit a higher priority message.

Any digit dialed before a telephone number; a prefix signals
predetermined instructions to the telephone system.

The space occupied by a customer, or authorized or joint user in a
building or buildings on continuous property, not separated by a public
highway. Railroad rights-of-ways, and so forth are not included in this

presentation layer
The sixth layer of the open systems interconnection (OSI) model of data
communications. It controls the formats of screens and files. Control
codes, special graphics, and character sets work in this layer.

preset call forwarding
A feature that enables a user to re-route incoming calls to a
predetermined secondary number.

presubscribed interexchange carrier (PIC)
See primary interexchange carrier (PIC)

A Bell operating company (BOC)-tariffed service that permits each
customer served from an equal access switching system to route, without
the use of access codes, the customer's interLATA traffic to the one
interexchange carrier (IC) the customer has chosen. The customer may
use other IC networks by dialing the appropriate carrier-access code,
10XXXX. Also called dialing parity.

preventive maintenance
Periodic inspection, cleaning, and adjustments intended to prevent
system malfunctions.

preview dialing
Automated dialing feature in which the system determines the next call
to be made but allows the agent/operator as a supervisor to check and
activate the call.

See primary rate interface and integrated services digital network.
primary rate interface (PRI)
integrated services digital network (ISDN)

price caps
A method of rate regulation in which a carrier may adjust prices within
certain ranges. The ranges may be adjusted periodically to account for
changes in inflation, productivity, or other factors. The carrier is
allowed to retain some or all profits above the permitted rate of
return in exchange for a limit on the ability to obtain rate increases.

primary area
A customer's local telephone calling area.

primary block
See primary group

primary carrier
See primary interexchange carrier (PIC)

primary center
A class 3 central office; a control center connecting toll centers.

primary domain controller
The server at which the master copy of a domain's user accounts
database is maintained. The primary domain controller also validates
logon requests. A LAN Manager term.

primary group
The lowest level of the multiplexing hierarchy in which a group of
basic signals are combined by multiplexing.

primary interexchange carrier (PIC)
A subscriber's first choice provider of long-distance service. The
interexchange carrier (IC) designated by the subscriber provides
interLATA service automatically when the customer dials 1 + the
10-digit telephone number. In an equal access office, the subscriber
can choose another carrier by dialing a 950-xxxx or 10xxx number.
Synonyms: primary interLATA carrier and presubscribed interexchange

primary interLATA carrier (PIC)
See primary interexchange carrier (PIC)

primary path
The preferred route from one switched node to another.

primary rate access (PRA)
An ISDN access method that uses maximum data rates of 2.048 Mbit/s in
Europe, or 1.544 Mbit/s in the US and Japan.

primary rate interface (PRI)
An integrated services digital network (ISDN) circuit transmitting at
T1, or DS-1, speed providing the equivalent of 24 voice-grade channels.
The "D" channel is used for signaling, leaving 23 "B" channels for data
and voice communications.

primary routing point
The switch designated as the control point for a long-haul telephone

primary station
A station responsible for controlling a data link; it controls one or
more secondary stations.

An element of the services provided by one entity to another.

print server
A computer and/or program providing local area network (LAN) users with
access to a centralized printer, in which print jobs are usually
handled in the order in which they are received.

printer driver
A program that controls printing and sets options such as print quality
and paper size for a particular printer. For example, in LAN Manager,
each printer queue has a single printer driver associated with it.

The ranking of precedence, importance or preference.

priority indicators A code in a message header that determines
transmission priority: urgent, rush, routine, or deferred.

priority trunk queuing
A private branch exchange (PBX) feature that places a caller with a
high, self-chosen trunk access level ahead of callers waiting for the
same trunk group.

privacy and privacy release
A telephone system feature that prevents others from entering a
conversation in progress.

privacy-enhanced mail (PEM)
An Internet security system.

private automatic branch exchange (PABX)
A small, local telephone switch for a business in which users must dial
9 to access a local line. Synonym: PBX

private automatic exchange (PAX)
Small local telephone switch that serves inside extensions only, with
no ability to connect calls to the public telephone system. Synonym:
private exchange

private automatic telex
A telephone switch used for a telex network exchange within an

private branch exchange (PBX)
A private telephone system switch used by medium and large companies.
The switch is connected to the local public telephone network and
performs in-house routing and switching. Users usually dial 9 to get
outside the system to the local lines. Modern PBXs offer numerous
software-controlled features such as call forwarding and call pickup. A
PBX uses technology similar to that used by a central office switch,
but on a smaller scale. The acronym PBX originally stood for "plug
board exchange."

private carrier
A carrier that is not a common carrier. Do not confuse private carrier
with private line carrier or recognized private operating agency.

private central office line
See direct department calling (DDC)

private computerized branch exchange (PCBX)
A private branch exchange that is computer controlled, allowing the
capabilities and designations of each circuit to be programmed and
stored in memory.

private digital exchange (PDX)
A local telephone switching service that uses digital technology.

private exchange (PX)
See private automatic exchange.
private automatic exchange (PAX)

private line (PL)
1) A telephone system that uses dedicated circuits to connect a
customer's equipment at both ends of the line. A private line does not
provide any switching capability unless it is supported by customer
premises equipment. It includes two local loops and an interexchange
carrier (IEC) circuit. The most common form of private line is a tie
line connecting two pieces of a user's own telephone equipment. Billing
is at a flat rate rather than being usage sensitive. 2) A leased
communications path, local or toll, assigned for the private use of one
customer and having no connection to the public telephone system.

private line service
An outside exchange that operates independently of a private branch
exchange (PBX).

private manual branch exchange (PMBX)
A local telephone system with manual switching under the control of an

private mobile radio (PMR)
A non-cellular based mobile radio system, standardized by ETSI
ETS300.279. PMR is used for private data and voice exchange.

private network
A communications network established and operated by a business or
organization for its exclusive use. Private networks are usually made
up of private lines, with some private branch exchange (PBX) switching.

Private Transatlantic Telecommunications Cable System
A transatlantic, fiber-optic submarine cable operated on a
private-carrier basis. PTAT-1 extends from New Jersey to the United
Kingdom, with spurs to Bermuda and Ireland. It is owned by Spring Cable
and Wireless.

private use network
Two or more private line channels contracted for by a customer and
restricted for use by that customer only.

privilege level
For user-level security, one of three settings -user, admin or guest is
assigned for each user account. The privilege level defines interfaces
was drawn up in 1980, known as Recommendation X.25. Hence packet
switched networks are often referred to as X.25. In some cases X.25 is
being superseded by frame relay and eventually by ATM.

An item of hardware of software provided to the customer.

product group
A number assigned to group automatic number identifications (ANIs) that
have the same product assigned to them.

A set of parameters defining the way in which a device acts. In the LAN
world, a profile is often used by one or more workstations to determine
the connection they will have with other devices. Profiles work like
batch files, executing a number of commands to save a user time and

program circuit
A voice-frequency circuit which has been equalized to handle a wider
range of frequencies than what ordinary speech signals require.

programmable read-only memory (PROM)
Nonvolatile memory, permanently programmed by the equipment
manufacturer into a computer. PROM can be modified only with special
equipment that erases the previous program. It is unaffected by power

progressive conference
A feature allowing parties to be added and sometimes deleted from a
conference call in progress.

project codes
See account codes

See programmable read-only memory (PROM)

propagation delay
The time it takes for a signal to travel between two points on the
network. Propagation delay is useful in determining the response time
of a device to a signal.

property imposed fee (PIF)
A surcharge charged to the end user and given back to the premises, or
agent, or split between both.

property name
The name of the customer or property.

property number
A billing system generated number for new accounts with embedded code
to indicate the platform used.

property surcharge
A per-call or per-minute charge assessed on an operator-assisted call
by the property owner from which the call was placed. This charge is
separate from the call type surcharge, and monies from this charge are
usually assigned to the property owner as part of the compensation

A set of procedures for establishing and controlling communications.
These procedures or rules govern format, timing, sequencing, and error

protocol analyzer
A device or software application that allows a user to analyze the
performance of network data to ensure that the network is operating
within the parameters of the network specifications.

protocol converter
An application-specific node that connects otherwise incompatible
networks. Converts data codes and transmission protocols to enable
interoperability. Contrast with bridge.

protocol data unit (PDU)
Information delivered as a unit between peer entities that may contain
control information, address information, data from a service data unit
(SDU) at a higher layer, or any combination of those three data types.
For example, the fiber-distributed data interface (FDDI) media access
control (MAC) PDUs are tokens and frames.

protocol filtering
A feature in which some bridges can be programmed to always forward or
always reject transmissions that are originated under specific

protocol vital signs (PVS)
A systematic method of analysis and display of protocol operational
parameters to aid in determining the cause of performance degradtion.

protocol-independent router
A routing device that provides the functionality of protocol-specific
routers, such as transmission control protocol/Internet protocol
(TCP/IP) or DECnet routers, but is independent of protocols.

The process by which a requested service is designed, implemented and
tracked, providing the subcomponent parts.

proxy agent
A network management agent that sits in front of a device attached to a
network that needs to be managed, but has no intrinsic network
management capabilities. The proxy agent provides network management
"by proxy" for that device.

See primary routing point

See personalized response system (PRS)

PSC public service commission
See Public Utilities Commission (PUC)

See public switched digital service (PSDS)

pseudo-random binary pulse sequence (PRBS)
A test pattern having the properties of random data, but generated in
such a manner that another circuit, operating independently, can
synchronize on the pattern and detect transmission bit errors.

pseudo-random noise modulation
A spread-spectrum communications technique in which each digital bit is
chopped into chips that are phase-shifted in a random pattern by codes
to stimulate noise. The chip pattern can be rephased by matched-filter

See phase-shift keying (PSK)

See public switched network (PSN) or Packet Switching Node (PSN)

See packet switched public data network (PSDN)

See public switched telephone network (PSTN)

See Private Transatlantic Telecommunications Cable System

PTN public telephone network
See public switched telephone network (PSTN)

See Postal Telephone and Telegraph (PTT) Authorities

public access line (PAL)
Pay phone public data network A shared-resource data network that
offers data communications services to public subscribers. See packet
packet switching

public dial port
A dial-in port which provides access to a system or service, such as a
packet network, from a terminal connected to the public telephone

public document switching service
A service providing the transfer from point-to-point or from
point-to-multipoint of electronic images of documents; a high quality
facsimile transmission network.

public key system (PKS)
An asymmetrical, two-key encryption algorithm that transforms data from
plain text to cipher text with one key that is made public, and
converts cipher text back to plain text with a different key that
remains secret.

public network
A switched communications network with unrestricted access.

public service commission (PSC)
See Public Utilities Commission (PUC)

public switched digital service (PSDS)
A service that provides alternate voice and data on a 2-wire user loop.

public switched network (PSN)
Any switching system that provides circuit switching to many customers.
In the U.S., there are four: telex, teletypewriter exchange (TWX),
telephone, and the broadband exchange.

public switched telephone network (PSTN)
The voice telephone network available to anyone, worldwide, with a
telephone and access privileges.

Public Utilities Commission (PUC)
A state agency that regulates intrastate telecommunications and
telephone service.

See Public Utilities Commission (PUC)

A sharp change in the current or voltage produced in a circuit used to
operate an electrical switch.

pulse amplitude modulation (PAM)
A form of modulation in which the pulse carrier's modulation varies
according to a characteristic of the original analog signal; the pulse
width is constant.

pulse code modulation (PCM)
A form of modulation in which information signals are sampled at
regular intervals, and a series of pulses, coded to represent the
amplitude of the information signal at the time of the sampling, are

pulse dialing
See rotary dial

pulse duration modulation (PDM)
A form of pulse modulation in which the durations of pulses are varied.

pulse modulation (PAM, PPM, PWM)
Transmission of information by modulation of a pulsed or intermittent
carrier. Pulse width, count, position, phase, and/or amplitude can be
the varied characteristic. Pulse code modulation (PCM) is the most
common modulation technique used in the telephone industry. pulse
stuffing See bit stuffing.

pulse width modulation (PWM)
An uncommonly used method of modulating a signal, in which the duration
of a pulse width is varied according to some characteristic of the
modulating signal.

pulse-link repeater
A device that connects one E&M signaling circuit directly to another.

Sending pulses of current through the circuit to transmit a telephone
number, in digital form, to the telephone company.

punch-down block
Telephony term describing the connector arrangements for distributing
and connecting unshielded twisted pair (UTP)/STP wiring inside a
building. Typically found in phone wiring closets.

See Parc Universal Packet.
Parc Universal Packet (PUP)

push button dialing
The use of keys or push buttons instead of a rotary dial to generate a
sequence of digits to establish a circuit connection. The signal form
is usually multiple tones. Synonyms: tone dialing, touch-call,
dual-tone multiple frequency, and touch-tone

A feature that allows use of push button conversion telephones even
when touch-tone circuits are not provided or are not available from the
central office (CO).

push-down queue
A method of prioritizing a list of items waiting to be processed in
which the last item added to the list is the first item processed.
Synonym: last in, first out (LIFO)

push-up queue
A method of prioritizing a list of items waiting to be processed in
which the first item added to the list is the first item processed.
Synonym: first in, first out (FIFO)

pushbutton telephone
A telephone set or system in which each instrument has a series of
buttons for selecting the line to be used, holding a line, or other
functions. This does not refer to the technique used for dialing calls.

See permanent virtual circuit (PVC)

See protocol vital signs (PVS)

See pulse modulation (PAM, PPM, PWM)

PX private exchange
See private automatic exchange (PAX)

Similar to MPEG, but adapted to slower bit rate. Typically used for
video conferencing over an ISDN phone line.

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Since November 20, 1999

Created by Jim Needham

İVector Graphics 1995

Revised: February 16, 2011
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