EAP: Extensible Authentication Protocol. A framework authentication protocol used by 802.1X to provide network authentication. Authentication itself is delegated to sub-protocols called methods.

EIFS: Extended Inter-Frame Space. The longest of the four inter-frame spaces, the EIFS is used when there has been an error in transmission.

EIRP: Effective Isotropic Radiated Power. An antenna system will have a footprint over which the radio waves are distributed. The power inside the footprint is called the effective isotropic radiated power.

ERP: Effective Radiated Power. Used to describe the strength of radio waves transmitted by an antenna.

ESS: Extended Service Set. A logical collection of access points all tied together. Link-layer roaming is possible throughout an ESS, provided all the stations are configured to recognize each other.

ETSI: European Telecommunications Standards Institute. ETSI is a multinational standardization body with regulatory and standardization authority over much of Europe. GSM standardization took place under the auspices of ETSI. ETSI has taken the lead role in standardizing a wireless LAN technology competing with 802.11 called the High Performance Radio LAN (HIPERLAN).

FCC: Federal Communications Commission. The regulatory agency for the United States. The FCC Rules in Title 47 of the Code of Federal Regulations govern telecommunications in the United States. Wireless LANs must comply with Part 15 of the FCC rules, which are written specifically for RF devices.

FCS: Frame Check Sequence. A checksum appended to frames on IEEE 802 networks to detect corruption. If the receiver calculates a different FCS than the FCS in the frame, it is assumed to have been corrupted in transit and is discarded.

FH: Frequency Hopping. See FHSS.

FHSS: Frequency Hopping Spread Spectrum. A technique that uses a time-varying narrowband signal to spread RF energy over a wide band.

FIPS: Federal Information Processing Standard. Public standards used by nonmilitary agencies of the United States federal government and its contractors.

four-way handshake: The key exchange defined in 802.11i that expands a pairwise master key into the full key hierarchy. The 4-Way Handshake allows a supplicant and an authenticator to agree on dynamically derived encryption keys.

GFSK: Gaussian Frequency Shift Keying. A modulation technique that encodes data based on the frequency of the carrier signal during the symbol time. GFSK is relatively immune to analog noise because most analog noise is amplitude-modulated.

GMK: Group Master Key. The key used by an authenticator to derive the group transient key.

GTK: Group Transient Key. Derived from the group master key by combining with the group random number, the GTK is used to derive the group key hierarchy, which includes keys used to protect broadcast and multicast data.

HR/DSSS: High-Rate Direct-Sequence Spread Spectrum. The abbreviation for signals transmitted by 802.11b equipment. Although similar to the earlier 2-Mbps transmissions in many respects, advanced encoding enables a higher data rate.

IAPP: Inter-Access Point Protocol. The protocol used between access points to enable roaming. 802.11F specifies a standard IAPP, though it is not widely implemented.

IBSS: Independent Basic Service Set. An 802.11 network without an access point. Some vendors refer to IBSSs as ad hoc networks; see also ad hoc.

ICV: Integrity Check Value. The checksum calculated over a frame before encryption by WEP. The ICV is designed to protect a frame against tampering by allowing a receiver to detect alterations to the frame. Unfortunately, WEP uses a flawed algorithm to generate the ICV, which robs WEP of a great deal of tamper-resistance.

IEEE: Institute of Electrical and Electronics Engineers. The professional body that has standardized the ubiquitous IEEE 802 networks.

IR: Infrared. Light with a longer wavelength and lower frequency than visible red light. The wavelength of red light is approximately 700 nm.

ISI: Inter-Symbol Interference. Because of delays over multiple paths, transmitted symbols may interfere with each other and cause corruption. Guarding against ISI is a major consideration for wireless LANs, especially those based on OFDM.

ISM: Industrial, Scientific, and Medical. Part 15 of the FCC Rules sets aside certain frequency bands in the United States for use by unlicensed Industrial, Scientific, and Medical equipment. The 2.4-GHz ISM band was initially set aside for microwave ovens so that home users of microwave ovens would not be required to go through the burdensome FCC licensing process simply to reheat leftover food quickly. Because it is unlicensed, though, many devices operate in the band, including 802.11 wireless LANs.

ITU: International Telecommunications Union. The successor to the CCITT. Technically speaking, the ITU issues recommendations, not regulations or standards. However, many countries give ITU recommendations the force of law.

IV: Initialization Vector. Generally used as a term for exposed keying material in cryptographic headers; most often used with block ciphers. WEP exposes 24 bits of the secret key to the world in the frame header, even though WEP is based on a stream cipher.

LLC: Logical Link Control. An IEEE specification that allows further protocol multiplexing over Ethernet. 802.11 frames carry LLC-encapsulated data units.

KCK: The EAPOL Key Confirmation Key. This key, derived as part of the pairwise hierarchy, is used to create message integrity check values in the four-way handshake. It may also be referred to as the "key MIC key."

KEK: The EAPOL Key Encryption Key. This key, derived as part of the pairwise hierarchy, is used to encrypt keys sent through the 4-Way Handshake. It may also be used as the pairwise key itself.

MAC: Medium Access Control. The function in IEEE networks that arbitrates use of the network capacity and determines which stations are allowed to use the medium for transmission.

MIB: Management Information Base. An ASN specification of the operational and configuration parameters of a device; frequently used with SNMP or other network management systems.

MIC: Message Integrity Code. A hash value calculated over a set of protected data to guard against tampering. In most cryptographic systems, such a hash is called a Message Authentication Code (MAC). 802.11 uses the algorithm MIC to avoid confusion with the Medium Access Control layer.

Michael: The message integrity check algorithm specified as part of TKIP.

MIMO: Multiple-Input/Multiple-Output. An antenna configuration that uses more than one transmission antenna and more than one receiver antenna to transmit multiple data streams. MIMO antenna configurations are often described with the shorthand "YxZ," where Y and Z are integers, used to refer to the number of transmitter antennas and the number of receiver antennas, respectively.

MPDU: MAC Protocol Data Unit. A fancy name for frame. The MPDU does not, however, include PLCP headers.

MSDU: MAC Service Data Unit. The data accepted by the MAC for delivery to another MAC on the network. MSDUs are composed of higher-level data only. For example, an 802.11 management frame does not contain an MSDU.

NAV: Network Allocation Vector. The NAV is used to implement the virtual carrier sensing function. Stations will defer access to the medium if it is busy. For robustness, 802.11 includes two carrier-sensing functions. One is a physical function, which is based on energy thresholds, whether a station is decoding a legal 802.11 signal, and similar things that require a physical measurement. The second function is a virtual carrier sense, which is based on the NAV. Most frames include a nonzero number in the NAV field, which is used to ask all stations to politely defer from accessing the medium for a certain number of microseconds after the current frame is transmitted. Any receiving stations will process the NAV and defer access, which prevents collisions.

NIST: National Institute of Standards and Technology. The United States government agency responsible for setting technology standards for the federal government. NIST standards are used by most non-classified agencies and have been adopted by many other organizations throughout all types of government.

OFDM: Orthogonal Frequency Division Multiplexing. A technique that splits a wide frequency band into a number of narrow frequency bands and inverse multiplexes data across the subchannels. 802.11a and 802.11g are based on OFDM. 802.11n uses MIMO to transmit multiple OFDM data streams.

OSI: Open Systems Interconnection. A baroque compendium of networking standards that was never implemented because IP networks actually existed.