 working with unlicensed spectrum, as in building a large Wi-Fi grid. Unlicensed spectrum is good for campuses, but carriers prefer to use licensed spectrum, which they have control over. Load balancing-Mesh WAPs may need to practice load balancing to keep interference to a minimum, using 802.11a as the backhaul frequency while using 802.11b and 802.11g for client traffic. It is in the area of back- haul spectrum that WiMax is initially expected to be most important, as the backhaul link from the mesh network to the PSTN. (WiMax is dis- cussed in detail earlier in this chapter, in the section "IEEE 802.16 (WiMax).") However, finalized WiMax standards and widespread avail- ability of antennas and base stations at a reduced cost are not expected until 2007 at the earliest. When to Use Mesh Networks Enterprise users are likely to consider mesh networks when the cost and time to install are barriers to a wireless network, when site surveys cannot be done, when WAPs need to be moved frequently, and when client roaming is required (espe- cially if the application involves VoWLAN). Self-configuration, scalability, and self- healing are drivers in the enterprise user's selection of a network. As far as service providers go, mesh networks are indicated when Wi-Fi operators are seeking to extend the range of the Wi-Fi grid. With mesh networks, there is no Chapter 15 WMANs, WLANs, and WPANs need to provide individual backhaul connections for each and every WAP, as is generally required by regular Wi-Fi WAPs. Service providers also look to mesh net- works when a few nodes can be connected to the PSTN, allowing the others to pro- vide their own backhaul links to each other. In addition, mesh deployments are particularly useful in remote locations. Finally, service providers stand to play a major role in operating and managing networks built by city governments and municipalities. Municipalities across North America, Taiwan, and Australia already have mesh networks deployed, sometimes over well-financed objections by the local