PABX: Private Automatic Branch Exchange
Private Automatic Branch Exchange (PABX) is an automatic telephone switching system within a private enterprise. Originally, such systems - called private branch exchanges (PBX) - required the use of a live operator. Since almost all private branch exchanges today are automatic, the abbreviation "PBX" usually implies a "PABX."

PAD Switching
PAD Switching refers to a technique of automatically cutting a transmission loss pad into and out of a transmission circuit for different operating conditions.

Pair Cable
Pair Cable refers to a cable in which all of the conductors are arranged in the form of twisted pairs. This form of cable is, by far, the most common form of cable used for communications.

Pair Gain
Pair Gain refers to the number of customers served by a communication system less the number of wire pairs used by that system. Pair gain can be achieved by multiplexing and by concentration.

Paired Disparity Code
Paired disparity code is a code used in telecommunications in which some or all of the characters are represented by two sets of digits of opposite disparity that are used in sequence so as to minimize the total disparity of a longer sequence of digits.

PAM: Pulse Amplitude Modulation
Pulse Amplitude Modulation (PAM) is a form of signal modulation in which the data is encoded in the amplitude of a series, or train, of regularly recurrent signal pulses. PAM is used less frequently than PCM (Pulse-Code Modulation).

Parallel Transmission
Parallel Transmission is a method of data transmission in which the bits of a data character are transmitted simultaneously over a number of channels/ports. In parallel transmission, coded information are transmitted via a system with multiple ports/channels. The port 1 is used to transport the first MSB (Most Significant Bit) and the second port carries the second MSBs, so on and so forth.

Parity Bit
Parity bit is the additional bit inserted into the string of user information in the telecommunications data stream for the purpose of error correction and checking.

Partial Dial Tone
Partial Dial Tone is a steady high tone in telephone system that is used to notify the calling party that he/she has not commenced dialing within a pre-allotted time, measured after receipt of dial tones (permanent signal condition), or that he/she has not dialed enough digits (partial dial condition). This is a signal to hang up and dial again.

Partially Dedicated Access
Partially Dedicated Access is a long distance carrier access method in which a non-local call is carried by the long distance carrier via a dedicated trunk facility for either the first or last part of the call's journey, and on the carrier's network for the middle part of the journey. It is also called "dedicated to switched", "switched to dedicated", "on-net to off-net" and "off-net to on-net".

Party Line
Party Line is a circuit assigned to serve two or more subscribers with discriminatory signaling for each station.

Pass Along Method
Pass Along Method is a signaling scheme. In Pass Along Method, signaling traffic (information) is sent along the signaling path of a previously established physical connection.

Patch Panel
Patch panel is a panel of network ports contained together, usually within a telecommunications closet, that connects incoming and outgoing lines of a LAN or other communication, electronic or electrical system. The patch panel allows easy access to all cable and ground line conductors. Conductor functions can be interchanged or checked rapidly for continuity, insulation, or quality of signal brought to the surface. Also, it provides easy access to output of surface panels.

PBX: Private Branch Exchange
Private Branch Exchange (PBX) is a small telephone switch owned by a company or organization. These organizations purchase PBX's to reduce the total number of telephone lines they need to lease from the telephone company. Without a PBX, a company will need to lease one telephone line for every employee with a telephone. With a PBX system, the company only needs to lease as many lines from the telephone company as the maximum number of employees that will be making outside calls at one time. This is usually around 10% of the number of extensions. In a PBX system, every telephone is wired to the PBX. When an employee takes the receiver off-hook and dials the outside access code (usually 9), the PBX connects the employee to an outside line.

PC: Peg Count
Peg Count (PC) refers to the measurement of the number of attempts to seize a server in a group of one or more servers.

PC: Point Code
Point Code (PC) refers a unique address code in telecommunication system that identifies a service provider within a signaling network.

PC: Protection Channel
Protection Channel(PC) is a standby, fully operational facility, providing diversity for one or several similar channels. When correctly implemented, it can result in improved availability or reliability of the channel, and of the circuits carried on each so protected channel.

Provisioning
Provisioning refers to the creation of an active subscriber account, or modification of parameters for an existing subscriber account. Provisioning of a subscriber account includes subscriber account registration and device activation.

PCM: Pulse-Code Modulation
Pulse-code Modulation (PCM) is a sampling technique for digitizing analog signals, especially voice/audio signals. It samples the analog signals 8000 times per second; each sample is represented by 8 bits for a total of 64 Kbps. There are two standards for coding the sample level. The Mu-law is used in North America and Japan while the A-law is used in Europe and most other countries.

PCS: Personal Communications Service
Personal Communications Service (PCS) is a network that provides personal, terminal and service mobility. PCS includes broadband and narrowband in the United States.

PCV: Path Coding Violation
Path Coding Violation (PCV) is an Error Event in the DS1/T1 interface. PCV error event is a frame synchronization bit error in the D4 and E1-noCRC formats, or a CRC error in the ESF and E1-CRC formats.

PDH: Plesiochronous Digital Hierarchy
Plesiochronous Digital Hierarchy (PDH) refers to a protocol that consists of signals that have relatively the same bit rates and characteristics, but they are not synchronized to a common timing source.

Peak Load
Peak Load refers to the traffic volume at the highest level during a given time period. It is usually expressed as the traffic volume during the highest one-hour period of the day (Busy Hour).

Permanent Calls
Permanent Calls are the private line calls used for fixed point-to-point calls, for connections between PBXs (E&M to E&M), or for remote telephone extensions (FXO to FXS).

Permanent Signal
Permanent Signal is a high steady tone. Permanent Signal is used to inform an operator or other maintenance employees making a verification test that the line is temporarily out of service. An intermittent ground may also be applied to the ring of the telephone systems left in the hold condition.

PH: Protocol Handler
Protocol Handler refers to a device with programs that provides communications services that enables a device to send data to other devices by transmitting and receiving data as specified by the communications protocol.

Phantom Circuit
Phantom Circuit is a third circuit derived from two physical circuits by means of repeating coils installed at the terminals of the physical (side) circuits.

Phase Distortion
Phase Distortion, also known as as Delay Distortion, is an unwanted modification of a transmitted signal caused by the non-uniform transmission of the different frequency components of the signal.

Phase Shift
Phase Shift refers to the situation in which the relative position in time between the clock and data signals of a transmission becomes unsynchronized. In systems using long cables at higher transmission speeds, slight variances in cable construction, temperature, and other factors can cause a phase shift, result in high error rates.

PIC Charges
PIC Charges refers to a charge by Local Exchange Carrier(LEC) for a customer to change the PIC (Primary Interexchange Carrier). It is often paid by the new Inter Exchange Carrier (IEC). If a LEC sends a PIC charge to a customer, the new IEC will typically credit the customer's account.

PIC Freeze
PIC Freeze refers to an option that customers can choose to prevent unauthorized changes to their chosen Primary Long Distance Carrier

PIC Request
PIC Request is a request record sent to a Local Exchange Carrier (LEC) asking for an ANI (Automatic Number Identification) to be activated, deactivated or changed in some way.

PIC Response
PIC Response is a response record sent by a Local Exchange Carrier (LEC), corresponding to a previous PIC Request, with a response code that indicates whether the request was performed.

PIC: Point In Call
Point In Call (PIC) refers to the phase or position within a call. Examples of PIC are Answered, Long Duration, Released, and so on.

PIC: Primary Interexchange Carrier
Primary Interexchange Carrier (PIC) refers to the long distance company that is automatically accessed when a customer dials 1+.

PICC: Pre-Subscribed Inter-Exchange Carrier Charge
Pre-subscribed Inter-exchange Carrier Charge is the charge that long distance companies pay to local telephone companies to help them recover the costs of providing the telephone wires, underground conduit, telephone poles, and other facilities that link each telephone customer to the telephone network. A long distance company pays this charge for each residential and business telephone line presubscribed to that long distance company. There is no tax due on PICC charges paid from one telecommunications vendor to another. However, if a retail consumer or business has not selected a long distance company, the local telephone company may bill the consumer or business for the Presubscribed Interexchange Carrier Charge. If the PICC charge is billed to the retail customer, it is subject to sales tax.

Pilot Signal
Pilot signal, in telecommunication, is a signal usually in single frequency, transmitted over a communications system for supervisory, control, equalization, continuity, synchronization, or reference purposes.

PINX: Private INtegrated Services Network eXchange
Private INtegrated services network eXchange(PINX) is a PBX or key system which, in a BRI voice application, uses QSIG signaling.

PLAR: Private Line, Automatic Ringdown
Private Line, Automatic Ringdown (PLAR) is a leased voice circuit that connects two single endpoints together. When either telephone handset is taken off-hook, the remote telephone automatically rings.

Plar-Opx
Plar-Opx specifies a PLAR Off-Premises eXtension connection. Using this option, the local voice port provides a local response before the remote voice port receives an answer. On FXO interfaces, the voice port will not answer until the remote side answers.

Plesiochronous
Plesiochronous is the term used in telecommunication signal hierarchy. Plesiochronous comes from a combination of Greek words: (1) "Plesio" meaning "close", "near", or "almost the same"; and (2) "synchronous" meaning "happening at the same time", "occurring together", "simultaneous", or "having the same period between occurrences". In telecommunications, Plesiochronous is used to describe any two signals that have the same "nominal rate", but do not originate from the same (identical) timing (clock) source.

PNP: Private Numbering Plan
Private Numbering Plan (PNP) is the telephone numbering plan that defines the format of telephone numbers to be used within a private telephone system. The Private Numbering Plan number normally consists of at least 3 digits, excluding "112".

POH: Path Overhead
Path Overhead (POH) refers to overhead accessed, generated and processed by path-terminating equipment; POH includes 9 bytes of STS POH and, when the frame is VT-structured, 5 bytes of VT (Virtual Tributary) POH.

Polling
Polling is an access method in which a primary network device inquires, in an orderly fashion, whether secondaries have data to transmit. The inquiry occurs in the form of a message to each secondary that gives the secondary the right to transmit. In telecommunications, polling is a long distance carrier access method in which a non-local call is carried by the long distance carrier via a dedicated trunk facility for either the first or last part of the call's journey, and on the carrier's network for the middle part of the journey.

PON: Passive Optic Network
Passive Optical Network (PON) refers to a group of ITU-T and IEEE standard technologies, which enable fiber as the first mile (or last mile) to the customer premises. A PON consists of a central office node Optical Line Termination (OLT) at the service providers office and a number of Optical Network Units (ONUs) near end users, and the fibers and splitters between them, called the optical distribution network (ODN). The OLT provides the interface between the PON and the backbone network, while the ONT provides the service interface to the end user. PON is a converged infrastructure that can carry multiple services such as voice (plain old telephony service or voice over IP), data, video, and/or telemetry, in that all of these services are converted and encapsulated in a single packet type for transmission over the PON fiber.

POP: Point Of Presence
Point Of Presence (POP) is the physical access location interface between a local exchange carrier and an Interexchange Carrier fiber network. The point to which the telephone company terminates a subscriber's circuit for long distance services or leased line communications.

Post-Dial Delay
Post-dial Delay is the time interval between "end of dialing" by the customer and the reception (by the same customer) of the call progress signaling generated by the exchange serving this customer. The call progressing signals can be the dial tone, a recorded announcement, or the abandon of the call.

POTS Dial Peer
POTS Dial Peer refers to the dial peer connected via a traditional telephony network (POTS). POTS peers point to a particular voice port on a voice network device.

POTS: Plain Old Telephone Service
Plain Old Telephone Service (POTS) is the standard, analog telephone service which remains the basic form of residential and small business telephone service nearly everywhere in the world. Plain Old Telephone Service was originally known as the Post Office Telephone Service in many countries. It has been available almost since the introduction of the telephone system in the late 19th century, mostly unchanged to the normal user since then despite the introduction of electronic telephone exchanges into the public switched telephone network since the middle of the 20th century.

PPS: Pulses Per Second
Pulses Per Second (PPS) refers to the number of pulses per second and the number of dial pulses per second. It is used as a type of measure in telecommunication and many other applications such as in clock oscillator discipline.

PRC: Primary Reference Source
Primary Reference Source(PRC) refers to a telecommunication equipment that provides a timing signal whose long-term accuracy is maintained very well with verification to UTC (Coordinated Universal Time), and whose timing signal may be used as the basis of reference for the control of other clocks within a network. The Primary Reference Source may generate a timing signal completely autonomous of other references, in which case cesium beam technology is suitable. Alternatively, the primary reference source may not be a completely autonomous implementation, in which case it may employ direct control from normal UTC-derived frequency and time services.

Preemption Tone
Preemption Tone is one of the telephone system audible tones that provides to both parties of a connection that is preempted by a priority call from the AUTOVON network. Preemption Tone is 440 Hz and 620 Hz at -18 dBm0/frequency steady for anywhere from three to fifteen seconds.

Presubscription
Presubscription refers to a BOC (Bell Operating Company) tariff service that permits each customer served from an equal access EO switching system to automatically route, without the use of access codes, all the customer's interLATA communications to one IC of the customer's choice. The customer may also gain access to other ICs using the appropriate carrier access code, e.g., 10XX.

PRI: Primary Rate Interface
Primary Rate Interface (PRI) is an ISDN interface for primary rate access, which consists of a single 64-kbps D channel plus 23 (T1) or 30 (E1) B channels for voice or data. PRI intended for larger users, such as business users. The other ISDN interface is the Basic Rate Interface (BRI), which is for homes and small businesses.

Primary Path
Primary Path refers to the preferred route from one switched node to another.

Priority Audible Ring
Priority Audible Ring Tone is one of the telephone system audible tones that replaces normal audible ring for priority calls within the AUTOVON network. Priority Audible Ring is 440 Hz and 480 Hz at -16 dBm0/frequency on for 1.65 seconds and off for .35 seconds.

Private Line
Private Line is a telecommunication service that involves dedicated circuits with private switching arrangements, and/or predefined transmission paths, whether virtual or physical. The purpose of Private Line is to provide communications between specific interested points.

Proceed To Send Tone
Proceed to Send Tone is a steady tone with 480 Hz at -22 dBm0/frequency. It informs the operator that an overseas sender has been seized and the address information (KP-CC-CC-ST) should be transmitted.

Proctor Test Set
Proctor Test Set is a tool used by Telco personnel to diagnose problems with phone lines.

Property Surcharge
Property Surcharge is 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 package.

Provisioning Software
Provisioning software refers to the software in telecommunication system which configures and records the hardware and software for specific telecommunication services when additions or changes are needed in the network and its elements. It optimizes the use of network elements and available network routes.

PSTN: Public Switched Telephone Network
The Public Switched Telephone Network (PSTN) is a circuit-switched network that is used primarily for voice communications worldwide, with hundreds of millions subscribers. Originally a network of fixed-line analog telephone systems, the PSTN is now almost entirely digital and provides mobile as well as fixed telephone services.

PTE: Path Terminating Equipment
Path Terminating Equipment (PTE) refers to a SONET element that terminates a SONET/SDH (Synchronous Digital Hierarchy) path.

PTS: Public Telephone Service
Public Telephone Service (PTS), sometimes called plain old telephone service (POTS), is the ordinary telephone service in which a customer has a connection to a central office and can be connected to any other customer of the service.

PTT: Post, Telephone, and Telegraph
Post, Telephone, and Telegraph(PTT) are the government agency that provides telephone services. PTTs exist in most areas outside North America and provide both local and long-distance telephone services.

Pulse Link Repeater
Pulse link repeater is a device in telecommunications that interface concatenated E&M (Ear & Mouth) signal paths.

Pulsing
Pulsing is the part of signaling that forwards the destination code required to route a call. In telephony, the transmission of address information to a switching office is via pulses (i.e., signals) that originate from the user's equipment. An examples of pulsing methods is DTMF (dual-tone multifrequency). Rotary dialing is another example in which DC (Direct Current) pulses are generated by a rotary dial.

Push Button Dialing
Push Button Dialing is the use of buttons on a telephone rather than a rotary dial to address a telephone message to a terminal point on the network. Push button dialing usually enlists two-tone signaling. In AT&T's terminology, the registered trademark "TouchTone" is used.

Push-to-Talk Operation
Push-to-talk operation refers to the method of communication over a speech circuit in which the talker is required to keep a switch operated while talking. Push-to-talk operation can be found in a telephone system or two-way radio systems.

PVC: Permanent Virtual Connection
Permanent Virtual Connection(PVC) is the term that describes that path data takes through a virtual network. PVCs are an integral component of many circuits and connections to the Internet.