WAP at a time. If a client goes out of range of one WAP, then associates with another while maintaining its wire- less configuration, the client is said to be roaming. WAPs may be standalone autonomous devices, or they may be lightweight devices that are controlled by a wireless LAN controller. Wireless LAN controllers are common in large deployments, since they allow central control of a large number of WAPs. An ad hoc wireless network is formed between two or more wireless endpoints. In this scenario, no WAP is involved and one node on the network may actually forward traffic destined for another node. Ham radio operators have been using a form of ad hoc wireless networking for decades, called packet radio networks. For the most part, en- terprises do not use ad hoc networks. Wireless Standards If you've ever dealt with wireless networking, you know that there is a dizzying array of standards and protocols out there. If you take a look at the IEEE docs, you'll discover that there are even more wireless standards with names like 802.11k (radio resource measurement enhancements), 802.11y (3,650-3,700 MHz operation in the US), and many others. The ones in wide use today are the ones we're all aware of: 802.11a/b/g/n, described as follows: 802.11a Based on the 802.11-1997 standard, this standard operates in the 5 GHz range with a surprising (to me, at least) maximum net data rate of 54 Mbps, though with error correction and other overhead, the usable rate is 20 Mbps or lower. 802.11a has a relatively short range when compared with 802.11b. 802.11b 802.11b is the wireless that most of us became familiar with when wireless became popular around the year 2000. Since it has a better range than 802.11a and was aggressively marketed by vendors, this became the de facto wireless standard for many years. Even today, most wireless access points support 802.11b. 802.11b operates in the 2.4 GHz band, and as such suffers from interference from many household items such as cordless phones, baby monitors, and microwave ovens. 80