In order to allow common wired USB devices to be connected, the specification defines "device wire adapters". Likewise, hosts connect to W-USB systems through use of a "host wire adapter". Even though the physical layer is based on Ultra-WideBand, W-USB devices have a fully compliant USB interface. The physical layer may support a wide range of transfer rates, of which three are defined as mandatorily supported: 53.3, 106.7 and 200 Mbit/s, all other possible UWB rates being optional for devices (hosts must support them all).