vering management, technical and operational security measures. The last chapter in Part III addresses WLAN troubleshooting, and covers strategies for problem identification and diagnosis, as well as specific measures for the two most common categories of WLAN problems - connectivity and performance. CHAPTER Wireless LAN Standards The 802.11 WLAN Standards Origins and Evolution The development of wireless LAN standards by the IEEE began in the late 1980s, following the opening up of the three ISM radio bands for unlicensed use by the FCC in 1985, and reached a major milestone in 1997 with the approval and publication of the 802.11 standard. This standard, which initially specified modest data rates of 1 and 2 Mbps, has been enhanced over the years, the many revisions being denoted by the addition of a suffix letter to the original 802.11, as for example in 802.11a, b and g. The 802.11a and 802.11b extensions were ratified in July 1999, and 802.11b, offering data rates up to 11 Mbps, became the first standard with products to market under the Wi-Fi banner. The 802.11g specification was ratified in June 2003 and raised the PHY layer data rate to 54 Mbps, while offering a degree of interoperability with 802.11b equipment with which it shares the 2.4 GHz ISM band. Table 6-1 summarises the 802.11 standard's relentless march through the alphabet, with various revisions addressing issues such as security, local regulatory compliance and mesh networking, as well as other enhancements that will lift the PHY layer data rate to 600 Mbps. Overview of the Main Characteristics of 802.11 WLANs The 802.11 standards cover the PHY and MAC layer definition for local area wireless networking. As shown in Figure 6-1, the upper part of the Data Link layer (OSI Layer 2) is provided by Logical Link Control (LLC) Chapter Six Table 6-1: The IEEE 802.11 Standard Suite Standard Key features 802.11a High speed WLAN standard, supporting 54 Mbps data rate using OFDM modulation in the 5 GHz ISM band. 802.11b The original Wi-Fi standard, providi