Offhook - "The active condition of switched access or a telephone exchange service line. One digit of the dialed number. Stages work independently of each other, making the switch slow and inefficient. "

Offhook signaling state - A request from the telephone station set for access to the network. A set goes offhook when a caller picks up the handset.

Onhook - "An inactive phone ready to send or receive calls. Represented by having the phone on the cradle or the ""hang up"" position. "

Out of band - Transmission taking place external to allocated bandwidth. A video call with out-of-band audio requires a separate phone line for the audio.

Out-of-band signaling - Using a separate signaling channel for controlling a call.

Optical Fiber - (or "fiber optic") refers to the medium and the technology associated with the transmission of information as light pulses along a glass or plastic wire or fiber. 

Packet - The unit of data that is routed between an origin and a destination on the Internet or any other packet-switched network. 

Packet mode - Refers to switching of packets of information for different users by statistically multiplexing them over the same transmission facilities. ISDN packet mode capabilities are based on CCITT recommendation X.25 procedures.

Packet-Switched - The type of network in which relatively small units of data called packets are routed through a network based on the destination address contained within each packet. 

PAL - Phase Alternating Line. European television format. 720X576, 25 interlaced frames per second.

PBX - Private branch exchange.

PCI - Peripheral Component Interface. Bus interface technology for PC cards.

PCM - Pulse-code modulation. Sample-based coding technique.

PIP - Picture-in-picture ( a second smaller window inside the main screen).

Point of Presence (POP) - The IXC equivalent of a local phone company's central office. The POP is your long distance carrier's office inside your community. It is the place where the long distance lines and connects to the local phone company's lines.

Point to Point - Describing a circuit connecting two points directly with no intermediate nodes or computers ( although switching facilities could exists ). A type of connection that links two logical entities (i.e., phone-line circuit).

POTS - Plain Old Telephone System. Ordinary telephone lines that transmit information over twisted pair copper wires. Analog phone system that can carry frequencies from 300Hz - 3.4 kHz.

PPP - Point-to-point protocol. Allows for more efficient connections between ISPs and clients over modems.

PRI - Primary Rate Interface. 23X64 kbps (T1--US, Japan,etc.), 30X64 kbps (E1--Europe,China, etc.)

Protocol - A procedure for adding order to the exchange of data. A protocol is a specific set of rules, procedures, or conventions relating to the format and timing of data transmission between two devices.

PSN - Packet Switched Network (Internet, LAN).

PTZ - Pan-Tilt-Zoom. Camera functionality

PVC - (Permanent Virtual Circuit) is a software-defined logical connection in a frame relay network. 

Px64 - Alternative term used to refer to H.320 standard. Often used to specifically describe the video portion of H.320 (H.261). Px64 refers to an integer p times 64 kbps B channels.

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