Where a radio frequency local area network ( LAN) may cover a 50,000 to 1,000,000 square-foot facility, a radio frequency wide area network (WAN) can cover entire geographical regions. With radio frequency WANs, network operations are managed by vendors (ARDIS and RAM Mobile Data are two operators offering nationally networked RFDC support), and users rent air time for monthly fees. Terminals require special WAN radio modems, and data is transmitted via satellite networks with coverage in nearly all of North America.