P Terms

P-picture: Prediction-coded picture: An MPEG term to describe a picture that is coded using motion compensated prediction from the past reference picture.

Packet: A packet consists of a header followed by a number of continuous bytes from an elementary data stream.

Packet Data: Contiguous bytes of data from an elementary stream present in a packet.

Packet Header: The data structure used to convey information about the elementary stream data contained in the packet data.

Packet Switching: A type of data communications in which small defined blocks of data, called packets, are independently transmitted from point to point between source and destination, and reassembled into proper sequence at the destination.

PAL: Phase Alternation Line: A TV color broadcast standard used in Western Europe, Latin America, Great Britain, South Africa, and Australia; PAL uses 625 scan lines with a 25 frame'50 field per second rate. PAL is not compatible with NTSC.

Pay or Premium: Movies, sports, and other programming for which a TV subscriber pays a monthly Programming service charge over and above the basic programming fee.

PBX: Private branch exchange.

PCI bus: Peripheral Component Interconnect bus provides increased data transmission within a PC on par with the speed and capability of new microprocessors. PCI has multi-platform support from Intel, Apple and DEC. It differs from the VL bus by being a concurrent processing bus that allows five devices to be on the bus vs. two for VL bus. Eventually PCI bus will provide plug and play capability with self configuration when a new card is added.

PCMCIA: Personal Computer Memory Card International Association The association that promotes standard for plug in PC cards. These cards may add memory or functionality such as a fax, modem or LAN connection to a PC.

PCS: Personal communications services. Newly developed wireless communication services (intended for use by light weight portable telephone devices).

Pel: Picture element, same as pixel

Pipe: General term to indicate any type of fixed transmission media such as twisted pair, coax or fiber.

Pixel: Picture Element: 1.) The smallest unit of picture information on imagers, scanners, printers, displays, images, or graphic files.

2.) The basic picture element of a computer screen or graphics sensing array, such as a CCD; the smallest dot a computer can create.

3.) The individual "picture elements" on a picture tube or display device.

PON: Passive optical network: Fiber in the loop technology for splitting the signal strength of a laser transmitter to serve multiple photodetector receivers

POP: Point of presence: Long distance company switching centers which connect to LEC networks.

POTS: Plain old telephone service.

PPV: Pay-per-view: A usage-based fee structure in which the user is charged a price for individual programs requested.

Prediction: (audio) The use of a predictor to provide an estimate of the sub-band sample in one channel from the sub-band samples in other channels.

Prediction: (video) The use of a predictor to provide an estimate of the pel value or data element currently being decoded.

Prediction Error: The difference between the actual value of a pel or data element and its predictor.

Preset Bus: The switcher bus that selects the video that will appear next on-line or on-air.

Profile: A defined sub-set of the syntax of MPEG specification

Program Bus: The switcher bus that selects the on-line or on-air output signal.

Progressive Scan: A process in which each line in a frame is scanned in sequential order from top to bottom.

Protocol: An agreement on formats and procedures between elements of a system to facilitate their interoperability and interaction.

PSN: Packet Switched Network: Self routing system in which each packet contains its address. SONET, FDDI, and A~ are all PSN implementations

PSTN: Public Switched Telephone Network.

Psychoacoustic Model: A mathematical model of the masking behavior of the human auditory system.

PTTA: Post Telephone and Telegraph Authority.

PUC: Public Utility Commission: State agency that has regulatory authority of phone and utility companies.

PVC: Permanent virtual circuit: Path for routing data packets from one point to another point (often using ATM).