To use the glossary, simply click below on the first letter of the term of interest:

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

P

P.800

Formerly known as P.80, an ITU-T recommendation regarding methods for the subjective determination of transmission quality and forms the basis of a wide range of subjective quality and intelligibility testing. These tests are offered by HEI.

P.830

This ITU-T recommendation covers subjective performance assessment of telephone-bandwidth and wideband digital codecs.

P.861

The objective quality measurement of telephone bandwidth (300Hz - 3400Hz) speech codecs is the topic of this ITU-T recommendation. The tests need to be applied with care as they produce valid results with only a limited range of codecs and test conditions. See PSQM below.

P.910

An ITU-T recommendation on the subjective assessment of video transmission quality for multimedia applications. Often, the criteria to be evaluated are determined using RISV or VIRIS.

P.920

An ITU-T recommendation regarding interactive test methods for the quality assessment of audio and visual communications, tests offered by HEI.

P.930

An ITU-T recommendation setting out the principles of a reference impairment system for use with subjective testing methods of the quality of various compressed video signals.

P802.9a

An IEEE standard providing the overview and architecture of: Integrated Services (IS) LAN: IEEE 802.9 Isochronous services with Carrier sense multiple access with collision detection (CSMA/CD) Media Access Control (MAC) service, the Iso-Ethernet standard. See also H.322.

Packet

A form of data transmission dividing the data information into many small packets, each including information such as source, destination, protocol and packet length. The concept is used for the Internet where transmission facilities are shared by many different users, with packets removed or added as appropriate at different locations.

PAD

Packet Assembler/Disassembler.

PAL

Phase Alternate Line, the European 625-line, 25-frame per second color-television standard.

PAM

Pulse Amplitude Modulation, a sampled analog signal which may exist as an intermediate step prior to the signal's coding and quantizing.

Passband

A range of frequencies passed by a device or network.

PBX

Private Branch eXchange. A telephony/data switching system, usually located on customer premises and belonging to the user. In contrast to Centrex which is largely located on the common carrier's premises. Some modern PBXs provide effective switched digital interfaces for operation of switched 64/56 Kbps and ISDN videoconferencing.

Some contemporary PBXs also provide VoIP encoding for VPN communications between an organization's offices.

PCB

Printed Circuit Board. An electronic assembly which is plugged into the main frame assembly of a complex electronic device or which may be used as the principle element of a simple electronic device.

PCM

Pulse Code Modulation, a basic form of digital modulation where an analog signal is sampled with each sample being quantized independently of the other samples.

PCS

Personal Communications Services.

PDA

Personal Digital Assistant.

PDU

Protocol Data Unit

PEL

Picture ELement.

Picture Element

The smallest discrete part of a video image, the size of which is controlled by the analog-to-digital conversion sampling process and subsequent other compression processes. The more picture elements per line, the higher the resolution of the image. To convert the number of H pixels to a close approximation of TV lines of resolution for the NTSC system, simply multiply the number of H pixels by 0.78. Furthermore, each 80 TV lines of resolution (NTSC) requires 1 MHz of analog bandwidth for transmission.

PID

Premises Interface Device, a filtering and splitter device for interfacing bidirectional cable systems and the customer.

PIP

Picture-In-Picture display. A video display mode in which a one-quarter- or smaller-size video image is superimposed over a full-screen video image. PIP is especially useful as a preview monitor for one-monitor videoconferencing installations and for TV receivers.

Pixel

Picture element.

POP

Point-Of-Presence, the common carrier physical location in a city, for example.

POTS

Jargon, Plain Old Telephone Service.

PPP

Point-to-Point Protocol, often used for Internet access.

PPTP

Point-to-Point Tunneling Protocol, a newer technology supporting multi-protocol virtual private networks (VPNs), letting remote user access to corporate networks securely across the Internet.

PRA

European name for ISDN PRI.

PRI

North American Primary-Rate Interface, 23B+D ISDN interface, made up of a 64 Kbps D-channel for signalling, and 23-B channels for data, each operating at 64 Kbps.

PSDN

Packet Switched Digital Network

PSQM

Perceptual Speech Quality Measurement. Using artificial speech, this test provides numeric values of approximate speech intelligibility including effects such as noise, coding errors, packet reordering, phase jitter, and excessive bit error rate. The value PSQM=0 signifies no impairment, while PSQM=6.5 is totally unusable. HEI offers these tests. See also P.861

PSTN

Public Switched Telephone Network

PTT

Posts, Telephone and Telegraph administration, international name for telephone companies.

Protection channel

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.

PVC

Permanent Virtual Circuit (frame relay use)

PWT

Personal Wireless Technology, the US version of DECT, operating between 1910 and 1920 MHz.

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