P

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Packet

A discrete packet of data which contains the addresses, and which is the basic transmission unit on an IP network. It can also be called a "datagram."

Packet Binary Convolutional Coding (PBCC)

A modulation/coding technique first developed by Texas Instrument for use in 802.11b networks as a means of doubling the signaling rate of the 11 Mbps standard to 22 Mbps while maintaining backward compatibility with legacy 802.11b 11 Mbps wireless equipment. In its simplest form, PBCC reduces packet overhead through the removal of extraneous information while optimizing transmission through the use of smaller data packets, thus cutting the response time in processing those packets, which in turn allows for a greater amount of data to be transmitted between networked devices. PBCC is an optional modulation technique for 802.11g.

PC Card

A term commonly used to refer to special card-like interface devices that are approximately the size of a credit card and can be plugged into a computing device's PCMCIA slot to add functionality to the computing device. For instance, PC Cards can add another hard disk, increase RAM, add modem capability or network interface card functionality, etc. The original Type I PC Card is 3.3mm thick, which is used mainly to add RAM. Type II cards are thicker (5.0mm) and often are used for modems and NICs (although they're also used to increase a computing device's RAM). Type III cards are much thicker (10.5mm) and often are used for hard disks and radio devices.

See also PCMCIA (Personal Computer Memory Card International Association).

See also PCMCIA Slot.

PCI (Peripheral Component Interconnect)

A mezzanine bus (a computer's electrical pathways along which signals are sent) standard developed by Intel Corporation. Most modern PCs include a PCI bus in addition to a more general ISA expansion bus.

PCMCIA (Personal Computer Memory Card International Association)

A trade association that establishes standards for expansion cards for portable computers. The PCMCIA's specifications for the PC card enable the computer industry to manufacture small cards (that resemble a credit card) for the purpose of adding RAM, modems, network interface cards, hard disks, and even radio devices (e.g. pagers and global positioning systems) to computing devices. Many people call PC cards by the longer name PCMCIA cards. The PCMCIA association, however, has trademarked the term "PC card," so that's the preferred usage.

See also PC Card.

PCMCIA Slot

Mostly found on the side of a laptop/notebook computer, the PCMCIA slot uses PC cards that fit into it for various Input/Output (I/O) functions such as networking.

PCF

See Point Coordination Function (PCF).

PCS

See Personal Communications Services (PCS).

PDA

See Personal Digital Assistant (PDA).

Personal Communications Services (PCS)

A mobile communications system interconnected with the PSTN. In Canada and the United States PCS spectrum has been allocated for use by public systems at the 2.0 GHz frequency range.

Personal Digital Assistant (PDA)

A handheld computer that combines personal organizer features with computing, telephone/fax, and networking capabilities. A PDA can also have cell phone and fax sender features.

Picocell

Describes a physically small communications coverage area (less than 0.5 km in diameter).

PHY

See Physical Layer.

Physical Layer

The Physical Layer is the lowest layer within the OSI Model. Commonly written as "PHY." Wi-Fi's Physical Layer is split into two parts. One is the the PLCP (Physical Layer Convergence Protocol) and the other is the PMD (Physical Medium Dependent) sublayer. The PMD takes care of the wireless encoding and the PLCP presents a common interface for higher-level drivers to write to as well as to provide carrier sense and CCA (Clear Channel Assessment), which is the signal that the MAC (Media Access Control) layer needs so it can determine whether the medium is currently in use.

See also OSI (Open System Interconnection) Model.

Physical Layer Convergence Protocol (PLCP)

Prepares MAC protocol data units (MPDUs) as instructed by the MAC Layer for transmission and delivers incoming frames to the MAC Layer.

Physical Medium Dependent (PMD)

Provides the actual transmission and reception of Physical Layer entities between two stations via the wireless medium.

Ping

A diagnostic test that sends a packet of data to another computer. The "pinged" computer then sends the packet back to the source computer. "Pinging" is commonly used to see if another computer on a LAN or across the Internet is up and running and how healthy are the pathways between the two.

Plain Old Telephone Service (POTS)

Standard wireline telephone service.

See also Public Switched Telephone Network (PSTN).

PLCP

See Physical Layer Convergence Protocol (PLCP).

PLCP Service Data Unit (PSDU)

This term refers to the contents of an 802.11 frame.

PMD

See Physical Medium Dependent (PMD).

Pocket PC

This term refers to Microsoft's mobile device platform that is based on the Windows CE operating system. The Pocket PC platform is used for standard PIM functionality, games and multimedia web browsing. The platform is capable of running custom enterprise applications built in Visual C++, Embedded Visual Basic, or .NET Compact Framework.

See also Windows CE.

Point Coordination Function (PCF)

An IEEE 802.11 mode that enables contention-free frame transfer based on a priority mechanism. Enables time-bounded services that support the transmission of voice and video.

Point-of-Presence (POP)

A physical location that provides an access point to the Internet. A POP can be either part of the facilities of a telecommunications provider that a service provider such as an Internet Service Provider (ISP) rents, or a separate location built and maintained by the service provider that houses servers, routers, ATM switches and digital/analog call aggregators.

Post Office Protocol (POP)

A protocol that retrieves email from a mail server. There are two versions of POP. The first, called POP2, became a standard in the 1980s and requires Simple Mail Transfer Protocol (SMTP) to send messages. The newer version, POP3, can be used with or without SMTP.

POP

This is a commonly used acronym for both Point-of-Presence and Post Office Protocol.

See also Point-of-Presence (POP).

See also Post Office Protocol (POP).

POTS

See Plain Old Telephone Service (POTS).

Protocol

A set of rules or standards designed to enable computers to connect with one another and to exchange information.

Proxy

A 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.

PSDU

See PLCP Service Data Unit (PSDU).

PSTN

See Public Switched Telephone Network (PSTN).

Public Switched Telephone Network (PSTN)

One of two common terms used to refer to the world's collection of interconnected voice-oriented public telephone networks, both commercial and government-owned. The other term that is often used to refer to this wired circuit-switched telephone network is "Plain Old Telephone Service" or "POTS."

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