ta demands in met- ropolitan areas. They are additionally attractive for carriers that have not upgraded to LTE, and carriers such as AT&T, which has expertise in managing and implementing hot zones. Another strategy for hot zone maintenance is to use the vendor organization that built the hot zones to manage them. Wireless Internet Service Providers A Wireless Local-Area Network (WLAN) hotspot is a public area where people with Wi-Fi-equipped laptops, tablet computers, and handsets can access the Internet. The Wi-Fi hotspot business is multilayered and includes aggregators, cellular providers, and companies that supply "back office" services such as billing, roaming, and secure access to corporate networks from hotspots. Hotspot operators are also referred to as Wireless Internet Service Providers (WISPs). The largest hotspot operator in the United States is AT&T Wi-Fi Services (for- merly Wayport before AT&T purchased it in 2008). AT&T Wi-Fi Services is an aggre- gator. Aggregators install hardware and Internet access for hotspot services and resell it to other providers who provide billing, marketing, and customer service to end users. AT&T offers free Wi-Fi access directly to its own subscribers as well as on a whole- sale basis to other providers. These providers in turn offer it to their own customers. T-Mobile USA also owns an extensive number of hot spots. It offers the service at no charge to its subscribers. SATELLITES Geosynchronous satellites orbit 22,300 miles above the Earth's surface. Because of this distance, each satellite can beam signals to a very large area; therefore, less equip- ment is required for coverage. This makes satellite service attractive for rural and dif- ficult-to-cable areas. Satellites Satellite Networks Satellite networks are composed of a hub, the satellites themselves, and receiving dish antennas. Receiving antennas also are called ground stations. Receivers on antennas convert Radio Frequency (RF) signals to electrical signals. The transmitter on the antenna converts elect