Private Automatic Branch Exchange

Telephone switch for use inside a corporation. PABX is the preferred term in Europe, while PBX is used in the United States.

Priority Access Control Enabled

A short fixed-length section of data, transmitted as a unit in an electronic communications network.

Networking method in which nodes share bandwidth with each other by sending packets.

Packet Assembler/Disassembler

Device used to connect simple devices (like character-mode terminals) that do not support the full functionality of a particular protocol to a network. PADs buffer data and assemble and disassemble packets sent to such end devices.

Password Authentication Protocol

Authentication protocol that allows PPP peers to authenticate one another. The remote router attempting to connect to the local router is required to send an authentication request. Unlike CHAP, PAP passes the password and host name or username in the clear (unencrypted). PAP does not itself prevent unauthorized access, but merely identifies the remote end. The router or access server then determines if that user is allowed access. PAP is supported only on PPP lines.

Palo Alto Research Centre

Research and development centre operated by XEROX. A number of widely-used technologies were originally conceived at PARC, including the first personal computers and LANs.

Process for checking the integrity of a character. A parity check involves appending a bit that makes the total number of binary 1 digits in a character or word (excluding the parity bit) either odd (for odd parity) or even (for even parity).

Layer 3 in the SNA architectural model. This layer performs sequencing services related to proper data reassembly. The path control layer is also responsible for routing. Corresponds roughly with the network layer of the OSI model.

Portion of a cell, frame, or packet that contains upper-layer information (data).

Private Branch Exchange

Digital or analogue telephone switchboard located on the subscriber premises and used to connect private and public telephone networks.

Printed Circuit Boards

A local bus standard for connecting peripherals to a personal computer. Within a computer, the bus is the transmission path on which signals and data transfers occur between the CPU, system memory, and attached devices such as a network card, sound card, or CD-ROM drive.

Protocol Control Information Control

Control information added to user data to comprise an OSI packet. The OSI equivalent of the term header.

Personal Computer Interface Bus

Pulse Code Modulation

Transmission of analogue information in digital form through sampling and encoding the samples with a fixed number of bits.

Personal Communications Number

A telephone number in a PCS which is permanently assigned to a subscriber regardless of the person's location or service provider. The PCN remains static even if the user changes handsets or phones.

Personal Communications Network

Mobile telephone networks that permit two-way communications over small, inexpensive handsets.

Peak Cell Rate

The maximum rate at which ATM cells can be transmitted across a virtual circuit, specified in cells per second and defined by the interval between the transmission of the last bit of one cell and the first bit of the next.

Personal Communications Services

Services for digital Radio Frequency (RF) equipment conveying both voice and data over wireless networks.

Port Concentrator Switch

Personal Digital Assistant

A portable organiser, increasingly with Internet access and e-mail functions.

Personal Digital Cellular

Plesiochronous Digital Hierarchy

The transmission technology for transmitting multiple channels of traffic from one point to another.

Public Data Network

Network operated either by a government (as in Europe) or by a private concern to provide computer communications to the public, usually for a fee. PDNs enable small organizations to create a WAN without all the equipment costs of long-distance circuits.

Protocol Data Unit

OSI term for packet

Protocol Data Unit

E.g., a 53-byte ATM cell

Maximum rate, in kilobits per second, at which a virtual circuit can transmit.

Collection of ATM nodes that share identical topological databases and exchange full link state information with each other. Peer groups are arranged hierarchically to prevent excessive PTSP traffic.

Privacy Enhanced Mail

Internet e-mail that provides confidentiality, authentication, and message integrity using various encryption methods. Not widely deployed in the Internet.

In SNA, a node that uses local addresses and is therefore not affected by changes to network addresses. Peripheral nodes require boundary function assistance from an adjacent subarea node.

The Conference of European Postal and Telecommunications administrations' general tariff principles study group.

Personal Handyphone Services

Physical Layer

One of two sublayers of the FDDI physical layer. (2) In ATM, the physical layer provides for the transmission of cells over a physical medium that connects two ATM devices. The PHY is comprised of two sublayers: PMD and TC.

The process of procuring, storing, and allocating physical hardware such as CTR, BTR, cards, NIU, etc.

Physics Network

Group of many DECnet-based physics research networks, including HEPnet.

Protocol Independent Multicast

Multicast routing architecture that allows the addition of IP multicast routing on existing IP networks. PIM is unicast routing protocol independent and can be operated in two modes: dense and sparse.

PIM Dense Mode

One of the two PIM operational modes. PIM dense mode is data-driven and resembles typical multicast routing protocols. Packets are forwarded on all outgoing interfaces until pruning and truncation occurs. In dense mode, receivers are densely populated, and it is assumed that the downstream networks want to receive and will probably use the datagrams that are forwarded to them. The cost of using dense mode is its default flooding behaviour.

PIM Sparse Mode

One of the two PIM operational modes. PIM sparse mode tries to constrain data distribution so that a minimal number of routers in the network receive it. Packets are sent only if they are explicitly requested at the RP (rendezvous point). In sparse mode, receivers are widely distributed, and the assumption is that downstream networks will not necessarily use the datagrams that are sent to them. The cost of using sparse mode is its reliance on the periodic refreshing of explicit join messages and its need for RPs.

P-doped Intrinsic N-doped

Packet Internet Groper

ICMP echo message and its reply. Often used in IP networks to test the reachability of a network device.

Private Integrated Services Network Exchange

A PBX or key system which, in a BRI voice application, uses QSIG signalling.

Public Key Cryptology

Provides asymmetric encryption of confidential messages and transactions, authenticates the origin of such data, and guarantees data integrity.

Public Key Cryptography Standards

Set of intervendor standard protocols for making possible secure information exchange on the Internet using a public key infrastructure. Standards include RSA encryption, password-based encryption, extended certificate syntax, and cryptographic message syntax for S/MIME.

Public Key Infrastructure

A system that enables users of a public network to exchange data securely and privately through the use of a public and private cryptographic key pair that is obtained and shared through a trusted authority. Provides for a digital certificate that can identify an individual or an organization and director services that can store and, when necessary, revoke the certificates. The comprehensive architecture includes key management, the registration authority, certificate authority, and various administrative tool sets.

Private Line, Automatic Ringdown

Leased voice circuit that connects two single endpoints together. When either telephone handset is taken off-hook, the remote telephone automatically rings.

Physical Layer Convergence Procedure

Specification that maps ATM cells into physical media, such as T3 or E3, and defines certain management information.

Physical Layer Interface Module

Public Land Mobile Network

Packet Level Protocol

Network layer protocol in the X.25 protocol stack.

PNNI Link State Packets

Physical Medium Dependent

Sublayer of the FDDI physical layer that interfaces directly with the physical medium and performs the most basic bit transmission functions of the network.

Point-to-Multipoint

Private Network Node Interface

ATM Forum specification for signalling to establish point-to-point and point-to-multipoint connections across an ATM network. The protocol is based on the ATM Forum UNI specification with additional mechanisms for source routing, crankback, and alternate routing of call setup requests.

Public Network Operator

Packet Over E3/T3

One of two fundamental connection types. In ATM, a point-to-multipoint connection is a unidirectional connection in which a single source end-system (known as a root node) connects to multiple destination end-systems (known as leaves).

A connection with only two endpoints; a communications line connected directly from one point to one other point as opposed to multi-point lines.

One of two fundamental connection types. In ATM, a point-to-point connection can be a unidirectional or bidirectional connection between two ATM end-systems.

Usage/network parameter control

Routing scheme that forwards packets to specific interfaces based on user-configured policies. Such policies might specify that traffic sent from a particular network should be forwarded out one interface, while all other traffic should be forwarded out another interface.

Path Overhead

Alarm indication and quality control within SDI network

Passive Optical Network

Post Office Protocol

Protocol that client e-mail applications use to retrieve mail from a mail server.

Point of Presence

In OSS, a physical location where an interexchange carrier installed equipment to interconnect with an LEC (local exchange carrier).

Packet over Sonet

Promoting Conference for OSI

Group of executives from the six major Japanese computer manufacturers and Nippon Telephone and Telegraph that sets policies and commits resources to promote OSI.

Plain Old Telephone System

Point-to-Point Protocol

Successor to SLIP that provides router-to-router and host-to-network connections over synchronous and asynchronous circuits.

Equipment which makes simultaneous calls to the numbers in a database, then as "live" answers are received, callers are instantly transferred to a Formus representative. Eliminates wasted time due to busy signals, rings-but no answer, operator intercepts because of disconnected numbers, answering machines, etc.

This description of services and interfaces offered to integrated services digital network customers is not capitalised. In Europe, the primary rate interface operates at 2.048 megabits per second and has 30 64-kilobit-per-second B, or bearer channels, and one 64 kbps D, or signalling, channel. The North American equivalent operates at 1.544 megabits per second and has 23 64-kbps B channels and one 64-kbps signalling channel.

Private Management Domain

Programmable Read-Only Memory

ROM that can be programmed using special equipment. PROMs can be programmed only once.

Set of related communications protocols that operate together and, as a group, address communication at some or all of the seven layers of the OSI reference model. Not every protocol stack covers each layer of the model, and often a single protocol in the stack will address a number of layers at once. TCP/IP is a typical protocol stack.

Processes associated with establishing customer service.

The mechanism whereby one system acts for another system in responding to protocol requests.

Packet Switch Exchange

Packet Switched Network

Network that uses packet-switching technology for data transfer.

Personal Software Products

Public Switched Telephone Network

General term referring to the variety of telephone networks and services in place worldwide.

Payload Type Indentifier

3-bit descriptor in the ATM cell header indicating the type of payload that the cell contains. Payload types include user and management cells; one combination indicates that the cell is the last cell of an AAL5 frame.

Plesiochronous Transmission

Term describing digital signals that are sourced from different clocks of comparable accuracy and stability.

PNNI Topology State Element

Collection of PNNI information that is flooded among all logical nodes within a peer group.

PNNI Topology State Packet

Type of PNNI routing packet used to exchange reachability and resource information among ATM switches to ensure that a connection request is routed to the destination along a path that has a high probability of meeting the requested QoS. Typically, PTSPs include bidirectional information about the transit behaviour of particular nodes (based on entry and exit ports) and current internal state.

Postal Telephone and Telegraph

Permanent Virtual Circuit

A connection in a connection-oriented network which is established through configuration, rather than dynamically.

Private Virtual Network

Permanent Virtual Path

Virtual path that consists of PVCs.

Permanent Virtual Path Tunneling

Method of linking two private ATM networks across a public network using a virtual path. The public network transparently trunks the entire collection of virtual channels in the virtual path between the two private networks.