ich can penetrate walls and other nonmetal barriers. The total coverage area can be extended by connecting numer- ous WAPs. Roaming users are accommodated by handoffs between the WAPs. Fig- ure 15.4 shows an example of a WLAN. The applications for WLANs include low-cost installation, mobility, and sup- port for temporary arrangements. For example, retailers often reconfigure their displays within a store and reassign where the cash registers need to be, and the only rapid deployment solution is wireless. As another example, if a natural disas- ter such as a flood or an earthquake disables the existing wireline facilities, the only quick road to disaster recovery is wireless. Other applications include scenar- ios where there may be environmental hazards such as asbestos in the building, or where there is a desire or requirement to preserve a historic building containing marble walls or oak paneling where it would be a shame to destroy such richness with intrusive installation procedures. In each of these cases, wireless presents an elegant, fast, and low-cost solution to getting service in and running. The following sections describe a number of facets of WLANs: Wireless Fidelity (Wi-Fi) IEEE 802.11x standards WLAN security Chapter 15 WMANs, WLANs, and WPANs Internet CSU/DSU, Wired LAN Ethernet Switch Cable Modem, or Hub DSL Modem, etc. Router Wireless LANs 10/100/1,000Mbps Cable Links Figure 15.4 An example of a WLAN Voice over WLAN (VoWLAN) The integration of WLANs and cellular networks Mesh networks Wi-Fi The concept of readily available WLANs is being globally embraced. Many WLANs are being set up by grassroots groups that want to get on the Internet by sharing local connections. This opportunity is putting the grassroots networks on a collision course with cable companies and telecom carriers because it provides an opportunity for even an individual citizen to become a "telecom provider" to his or her neigh- bors. These new community wireless networks are based on Wi-Fi technology. Wi-Fi allows users to plug