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IEEE 802.11 is a shared, Wireless Local Area Network (LAN) Standard including 80211b, 80211a, 80211g, 80211i (enhanced security), 80211h (spectrum and power control management) & 80211e (QoS - Quality of Service).

"The 802.11 Wireless LAN Standard defines Authentication and Encryption Services based on the Wired Equivalent Privacy (WEP) algorithm. The lack of a WEP Key Management Protocol is a principal limitation to providing 802.11 Security." www.Microsoft.com

Hence WPA - Wi-Fi Protected Access released in March 2003.

Physical Layer Terminologies:

A variety of radio transmission methods continuously changing frequencies or signal patterns.

1. FHSS - (Frequency Hopping Spread Spectrum):  Continuously changes center frequency of a conventional carrier several times per second according to a pseudo-random set of channels, while chirp spread spectrum changes the carrier frequency. Because a fixed frequency is not used, illegal monitoring of spread spectrum signals is extremely difficult, if not downright impossible depending on the particular method.
2. DSSS - (Direct Sequence Spread Spectrum): Used in CDMA, multiplies Data Bits by a very fast pseudo-random bit pattern (PN sequence) and "spreads" Data into a large coded stream taking full bandwidth of the channel. Used by the original IEEE 80211 Wireless Standard. 
3. OFDM -  (Orthogonal Frequency Division Multiplexing): This Spread Spectrum technique distributes data over a large number of carriers spaced apart at precise frequencies. This spacing provides the "orthogonality" in this technique thus preventing the demodulators from seeing frequencies other than their own.
4. CCK-OFDM - (Complementary Code Keying-Orthogonal Frequency Division Multiplexing): CCK works only in conjunction with the DSSS and not FHSS. CCK applies sophisticated mathematical formulas to the DSSS codes, permitting the codes to represent a greater volume of information per clock cycle. Technology by www.Intersil.com 
5. PBCC - (Packet Binary Convolutional Coding): Technology by www.Ti.com