radio frequencies and Ethernet signals on cabled networks. An access point has similar functions to base stations in cellular net- works. Access points for the residential market also include routers and switches with ports to which Ethernet cables can be connected. The router functionality aggregates traffic and sends it to the Internet via dial-up, Digital Subscriber Line (DSL), and cable modems. Access points for corporations are more expensive and feature-rich than those sold to residential customers. Some contain security capabilities, such as intrusion detec- tion, the ability to detect hacker attacks, and Quality of Service (QoS) needed for voice and video. There are also robust access points for outdoor locations that are made to withstand harsh environmental conditions. Cabling and Electrical Requirements In a similar manner to cellular networks, Wi-Fi networks require wired connections to switches, controllers and data centers, and electricity for access points. Access points in organizations are connected to the LAN via a data jack and, from there, an unshielded twisted-pair (UTP) copper wire connection to the local wiring closet. Electrical and cabling requirements represent an often overlooked cost in implementing WLANs. The power each access point requires can be located remotely in wiring closets on each floor or locally by nearby electrical outlets. For local power, new outlets might be needed. Mobile and Wi-Fi Networks WLAN Controllers For the most part, WLANs in small and midsize organizations have controllers that manage access points and monitor the network. Until recently, all Wi-Fi traffic was routed through these centralized controllers. The controllers were part of core switches or separate devices. If they are part of separate devices, they sit between the wireless and wired parts of networks. They act as gateways to the network, allowing access to only certain users. They often allow access to particular applications on a per-user basis. In addition, centralized controllers authenticate 