PBCC: Packet Binary Convolution Coding. An alternative method of encoding data in 802.11b networks that has not been widely implemented. PBCC was also proposed for consideration for 20+ Mbps networks, but was rejected.

PC: Point Coordinator. A function in the access point responsible for central coordination of access to the radio medium during contention-free service.

PCF: Point Coordination Function. The set of rules that provides for centrally coordinated access to the medium by the access point.

PCMCIA: Personal Computer Memory Card International Association. An industry group that standardized the ubiquitous "PCMCIA card" form factor and made it possible to connect a wide variety of peripherals to notebook computers. 802.11 interfaces are available almost exclusively in the PCMCIA form factor. Also expanded humorously as People Who Can't Manage Computer Industry Acronyms because of its unwieldy length and pronunciation.

PDU: Protocol Data Unit. Layers communicate with each other using protocol data units. For example, the IP protocol data unit is the familiar IP packet. IP implementations communicate with each other using IP packets. See also service data unit.

PER: Packet Error Rate. Like the bit error rate, but measured as a fraction of packets with errors.

PHY: Common IEEE abbreviation for the physical layer.

physical-layer convergence procedure: The upper component of the PHY in 802.11 networks. Each PHY has its own PLCP, which provides auxiliary framing to the MAC.

PIFS: PCF Inter-Frame space. During contention-free service, any station is free to transmit if the medium is idle for the duration of one PCF inter-frame space.

PLCP:  Physical-Layer Convergence Procedure.

PMD: Physical Medium Dependent. The lower component of the PHY, responsible for transmitting RF signals to other 802.11 stations.

PMK: Pairwise Master Key. The root of all keying data between a supplicant and an authenticator. It may be derived from an EAP method during authentication, or supplied directly as a pre-shared key.

PPDU: PLCP Protocol Data Unit. The complete PLCP frame, including PLCP headers, MAC headers, the MAC data field, and the MAC and PLCP trailers.

PRF: Pseudo-Random Function. An 802.11i function that expands a small amount of data into a larger amount of data. The PRF is used most notably to expand master keys into key hierarchies.

PS: Power Save. Used as a generic prefix for power-saving operations in 802.11.

PSDU: PLCP Service Data Unit. The data the PLCP is responsible for delivering, i.e., one MAC frame with headers.

PSK - Phase Shift Keying: A method of transmitting data based on phase shifts in the transmitted carrier wave.

PSK - Pre-shared Key: In 802.11i, refers to the authentication method that depends on a statically configured authentication key that must be distributed manually. Also called WPA-PSK.

PTK: Pairwise Transient Key. Key derived from pairwise master key that includes keys used by encryption and integrity protocols, but also includes keys to distribute dynamic keys.

QPSK: Quadrature Phase Shift Keying. A modulation method that encodes bits as phase shifts. One of four phase shifts can be selected to encode two bits.

RA: Receiver Address. MAC address of the station that will receive the frame. The RA may also be the destination address of a frame, but not always. In infrastructure networks, for example, a frame destined for the distribution system is received by an access point

RADIUS: Remote Authenticated Dial-In User Service. A protocol used to authenticate dial-in users that has become more widely used because of 802.1X authentication. The most common type of authentication server used in 802.1X systems.

RC4: A proprietary cipher algorithm developed by RSA Data Security and licensed for a great deal of money. Also used as the basis for WEP and prevents open source WEP implementations from existing because of the fear of lawsuits by RSA.

RLAN: Radio LAN. A term used by European radio regulations to refer to any wireless network built on radio technology. Although 802.11 is the most popular, others do exist. One of the better known alternative radio network technologies is ETSI'S HIPERLAN.

RF: Radio Frequency. Used as an adjective to indicate that something pertains to the radio interface ("RF modulator," "RF energy," and so on).

RSN: Robust Security Network. A network that uses the security methods of 802.11i and does not provide any support for WEP.

RTS: Request to Send. The frame type used to begin the RTS-CTS clearing exchange. RTS frames are used when the frame that will be transmitted is larger than the RTS threshold.

SA: Source Address; as disinct from TA. Station that generated the frame. Different when frame originates on the distrbution system and goes to the wireless segment.

SDU:  Service Data Unit. When a protocol layer receives data from the next highest layer, it is sending a service data unit. For example, an IP service data unit can be composed of the data in the TCP segment plus the TCP header. Protocol layers access service data units, add the appropriate header, and push them down to the next layer. See also protocol data unit.

SFD: Start of Frame Delimiter. The component of the frame header that indicates when synchronization has concluded and the actual frame is about to start.

SIFS: Short Interframe Space. The shortest of the four interframe spaces. The SIFS is used between frames in an atomic frame exchange.

SSID: Service Set Identity. A string used to identify an extended service set. Typically, the SSID is a recognizable character string for the benefit of users.

SYNC: Short for Synchronize. Bits transmitted by the PLCP to allow senders and receivers to synchronize bit timers.

TA: Transmitter Address. Station that actually put the frame in the air. Often the access point in infrastructure networks.

TIM: Traffic Indication Map. A field transmitted in Beacon frames used to inform associated stations that the access point has buffered. Bits are used to indicate both buffered unicast frames for each associated station as well as the presence of buffered multicast frames.

TK: Temporal Key. 802.11i key hierarchies derive a temporal key to be used for authentication protocols. The temporal key is the main input to link-layer encryption protocols such as TKIP or CCMP.

TKIP: Temporal Key Integrity Protocol. One of the improved encryption protocols in 802.11i, TKIP uses the fundamental operations of WEP with new keying and integrity check mechanisms to offer additional security.

TPC: Transmit Power Control. A spectrum management service required by European regulations to ensure that 5 GHz radios avoid interfering with satellite services.

TSF: Timing Synchronization Function.

WEP: Wired Equivalent Privacy. Derided as Wiretap Equivalence Protocol by its critics. A standard for ciphering individual data frames. It was intended to provide minimal privacy and has succeeded in this respect. In August 2001, WEP was soundly defeated, and public code was released.

Wi-Fi: Wireless Fidelity. The Wi-Fi Alliance (formerly the Wireless Ethernet Compatibility Alliance) started the Wi-Fi ("wireless fidelity") certification program to test interoperability of 802.11 implementation. Originally, the term was applied to devices that complied with 802.11b (11-Mbps HR/DSSS). It now may include 802.11g and 802.11a interoperability, as well as WPA security.

WMM: Wi-Fi Multimedia. The Wi-Fi Alliance took a subset of the IEEE 802.11e WLAN QoS draft standard, and created the Wi-Fi Multimedia (WMM) specification. WMM provides Quality of Service (QoS) for wireless networks.

WPA and WPA2: Wi-Fi Protected Access. A security standard based on 802.11i draft 3. The Wi-Fi Alliance took 802.11i draft 3 and began certifying compliance with early TKIP implementations to accelerate adoption of 802.11 security protocols. WPA2 is based on the full ratified version of 802.11i.