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Glossary of broadband terminology: P

Packet: A sub-unit of a data stream; a grouping of information that includes a header (containing information like address destination) and, in most cases, user data.
Packet Switched Network: Network that does not establish a dedicated path through the network for the duration of a session, opting instead to transmit data in units called packets in a connectionless manner. Datastreams are broken into packets at the front end of a transmission, sent over the best available network connection, and then reassembled in their original order at the destination endpoint.
Packet Switching: A switching system that uses a physical communications connection only long enough to transit a data message; data messages are disassembled into packets and reassembled at the receiving end of the communication link. Packets may travel over many diverse communications links to get to the common endpoint. This is most often contrasted with circuit switching in data communications, where all data messages transmitted during a session are transmitted over the same path for the duration of the session. See also Circuit Switching.
Passband: A range of frequencies that has a non-zero lower limit and some upper limit.
Passive Optical Network: A fiber-based transmission network containing no active electronics.
Pay-Per-Play: See Pay-Per-View.
Pay-Per-View: In the cable television industry, the ability to view programming on a pay-per-play basis. See also Video on Demand.
Payload: That portion of a frame or cell that carries user traffic. It is effectively what remains in the frame or cell if you take out all headers or trailers.
Permanent Virtual Circuit: A term found in frame relay and ATM networkingi n which a virtual connection between two fixed endpoints is established through the network. See also Switched Virtual Circuit.
Plain Old Telephone Service: This term commonly refers to standard telephony, as in placing and receiving telephone calls.
Point Of Presence: A POP refers to a node of an ISP or other NSP. A POP is usually a network node.
Point-to-Point Protocol: A common, layer two protocol used with Internet protocols and services.
Point-to-Point Tunneling Protocol: A new technology for creating VPNs, developed jointly by Microsoft Corporation, US Robotics, and several remote access vendor companies, known collectively as the PPTP Forum. A VPN is a private network of computers that uses the public Internet to connect nodes. Because the Internet is essentially an open network, PPTP is used to ensure that messages transmitted from one VPN node to another are secure. With PPTP, users can dial in to their corporate network via the Internet.
Postal Telephone and Telegraph: Generic term for a provider of access services. A governmental agency in many countries.
POTS Splitter: A device that separates an xDSL communications stream into its POTS and data components, offering a standard POTS connection such as an RJ-11 jack in the US, and an Ethernet or ATM connection, such as an RJ-45 jack. See also Low Pass Filter, High Pass Filter.
Primary Rate Interface: This is an ISDN interface typically used by larger customers. This interface consists of a single 64 Kbps data (or"D") channel plus 23 or 30 bearer (or "B") channels for voice and/or data. Also known as Primary Rate Access, or PRA.
Private Line: See Dedicated Line.
Protocol Data Unit: A segment of data generated by a specific layer in a protocol stack; usually consists of a block of data from a higher layer (the Service Data Unit or SDU) encapsulated by the next lower layer with a header and trailer.
Public Branch Exchange: A private telephone network used within an enterprise. Users of the PBX share a certain number of outside lines for making telephone calls external to the PBX. Most medium-sized and larger companies use a PBX because it's much less expensive than connecting an external telephone line to every telephone in the organization. In addition, it's easier to call someone within a PBX because the number you need to dial is typically just three or four digits.
Public Utilities Commission: Each state's regulatory agency responsible for regulating intrastate communications.