Connectivity
W-USB can form true USB systems, formed by a host, devices and interconnection support. It implements the USB hub-spoke model, in which up to 127 wireless devices can form point-to-point links (spokes) with the host (the hub). The host controller is unique in the system and is usually embedded in a working computer, though it could be connected to it through a simple USB connection, possibly wireless as well. Such a topology is similar to a star network (but all communications are strictly point-to-point, never between devices).
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).
W-USB devices are categorized in the same way as traditional USB. Because of the existence of wire adapters, traditional USB hubs are not needed. A device supports one or more communication pipes to the host, and allocates endpoint 0 for the USB control pipe. Device type information is available through this pipe.
Connections with the host are created by means of an establishment message sent at some point. Both host and device can then proceed to authenticate using their unique keys; if the process succeeds, the host assigns a unique USB address to the device, after which the device becomes visible to the USB protocol. Because the connectivity model allows for on-the-fly, unannounced disconnection, connections must always remain active. Aside from host- or device-forced disconnections, long inactivity periods may trigger the same termination mechanisms.
In addition, W-USB hosts have other responsibilities which go beyond those of a wired host; namely, their MAC sublayer is responsible for supervising the suitability of device MAC layers. If needed, this requires assisting them in their beaconing duties and processing the beaconing data that could be sent to them. Furthermore, the UWB radio and associated bandwidth may be shared with other entities, and the host must make sure that the defined policies are satisfied; according to shared use (which may be coordinated to avoid interference) it will be able to offer full or partial functionality.
Read more about this topic: Certified Wireless USB