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Glossary Section "P" ( Definitions )

Guide -  Select first letter of word:
0-9 A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

packet The unit of data sent across a network. "Packet" is a generic term used to describe unit of data at all levels of the protocol stack, but it is most correctly used to describe application data units.

packet switching A communications paradigm in which packets (messages) are individually routed between hosts, with no previously established communication path.

PABX Private Automatie Branch Exchange. A telephone switch for use inside a corporation. It connects offices (internal extensions) with each other and provides access (typically by dialing an access number such as 9) to the public telephone network PABX is the preferred term in Europe, PBX is used in the USA.

PAMS Perceptual Analysis/Measurement System is a test method to send a reference signal through a telephony network and determine the quality. The scale is 1 to 5, with 5 being the best.

Packet Switch Node See PSN

Pause (IEEE 802.3xy) Pause signaling is an IEEE feature that temporarily  suspends data transmission between two devices in the event that one of the devices becomes overwhelmed. In the event that a device needs some time to clear network congestion, it will send out a pause signal to the other end device.

PBX Private Branch Exchange. (US terminology). The same as a PABX. See PABX

Peering A relationship between two or more small- or medium-sized ISPs in which the ISPs create a direct link between each other and agree to forward each other's packets directly across this link instead of using the standard Internet backbone.

Peering Point (Exchange Point) A public network exchange facility or Network Access Point (NAP) where Internet Service Providers (ISPs) can connect with one another in peering arrangements. The NAPs are a key component of the Internet backbone because the connections within them determine how traffic is routed. They are also the points of most Internet congestion.

PC Personal Computer

PCI Protocol Control Information. The protocol information added by an OSI entity to the service data unit passed down from the layer above, all together forming a Protocol Data Unit (PDU).

PEM Privacy Enhanced Mail. Internet e-mail which provides confidentiality, authentication and message integrity using various encryption methods. Not widely deployed in the Internet.

PGP Pretty Good Privacy. PGP provides confidentiality and authentication services for electronic mail and file storage applications. Developed by Phil Zimmermann and distributed for free on the Internet. Widely used by the Internet technical community. See DES, RSA

Phase Jitter The shifting of phase of one part of the frequency tone relative to an earlier part of the tone.

PDH Plesiochronous Digital Hierarchy

Physical Layer The OSI layer that provides the means to activate and use physical connections for bit transmission. In plain terms, the Physical Layer provides the procedures for transferring a single bit across a Physical Media.

physical media Any means in the physical world for transferring signals between OSI systems. Considered to be outside the OSI Model, and therefore sometimes referred to as "Layer 0."

PIM Protocol Independent Multicast. The emerging PIM protocols are intended to provide scaleable multicast routing across the internet. PIM routing protocols are independent on the mechanisms provided by any particular unicast routing protocol. Any PIM implementation depends upon the presence of a unicast routing protocol to provide routing table information and to adapt to topology changes.

ping Packet internet groper. A program used to test reach-ability of destinations by sending them an ICMP echo request and waiting for a reply.

PLC Power Line Communications is a method for transmitting data over electricity lines.

Plug A male connector

PM Performance Monitoring

PMR Professional Mobile Radio

PNNI Private Network-to-Network Interface. A routing information protocol that allows different vendors' ATM switches to be integrated in the same network. PNNI automatically and dynamically distributes routing information, enabling any switch to determine a path to any other switch.

PNO Public Network Operator. Usually a PTT of some sort.

POE Power over Ethernet

POP Point Of Presence.A site where there exists a collection of telecommunications equipment, usually digital leased lines and multi-protocol routers.

POP Post Office Protocol.A protocol for the exchange of e-mail using the mailbox paradigm. Mail is held by a server and downloaded/uploaded to the user's machine periodically. POP allows users to compose and reply to messages "off line" and queue them for delivery when connected to the POP server. Access to the server can be through a network connection or via a dialup line. A popular implementation of this paradigm is Eudora. See IMAP.

port The identifier (16-bit unsigned integer) used by Internet transport protocols to distinguish among multiple simultaneous connections to a single destination host. It can also refer to a physical port in a device such as an I/O port on a switch.

Port 80 is the standard port for Hyper-Text Transport Protocol which is used for transferring Web pages over the Internet.

POS Packet Over SONET or Point of Sale

POSI Promoting Conference for OSI Consists of executives from the six major Japanese computer manufacturers and Nippon Telephone and Telegraph. They set policies and commit resources to promote OSI.

POTS Plain Old Telephone System, what we consider to be the "normal" phone system, used with modems. Does not include leased lines or digital lines.

PPP Point-to-Point Protocol. The successor to SLIP, PPP provides router-to-router and host-to-network connections over both synchronous and asynchronous circuits. See SLIP.

PRA Primary Rate Access. Connects high-capacity CPE, such as PBXs, to the network. In the US, this is composed of twenty-three 64 kbps channels and one 64 kbps D-channel. Also known as Primary Rate Interface (PRI).

Presentation Layer The OSI layer that determines how Application information is represented (i.e., encoded) while in transit between two end systems.

PRI Primary Rate Interface

PRMD Private Management Domain. An X.400 Message Handling System private organization mail system.

Prospero A distributed directory service and file system that allows users to construct customized views of available resources while taking advantage of the structure imposed by others. See Gopher, WAIS, World-Wide Web.

protocol A formal description of messages to be exchanged and rules to be followed for two or more systems to exchange information.

Proxy The mechanism whereby one system "fronts for" another system in responding to protocol requests. Proxy systems are used in network management to avoid having to implement full protocol stacks in simple devices, such as modems.

proxy ARP The technique in which one machine, usually a router, answers ARP requests intended for another machine. By "Faking" its identity, the router accepts responsibility for routing packets to the "real" destination. Proxy ARP allows a site to use a single IP address with two physical networks. Subnetting would normally be a better solution.

pseudowire An emulation of a native service like T1 or T3 over a packet switched network (PSN) 

PSN Packet Switched Network  or Packet Switch Node. A dedicated computer whose purpose is to accept, route and forward packets in a packet switched network.

PSTN Public Switched Telephone Network

PTT Post, Telephone, Telegraph. Telecom companies.

PVC Permanent Virtual Circuit. There are two types, the Permanent Virtual Circuit and the Switched Virtual Circuit. A PVC is like a dedicated line between two points, most commonly associated with a packet switching network.

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