ical to USB 2.0, except for some enhancements to the isochronous data communication model to allow for the relative unreliability of the wireless PHY layer compared to a wired USB connection. Wireless USB Radio The wireless USB PHY layer is the Multiband OFDM Alliance (MBOA) UWB radio, operating across the 3.1 to 10.6 GHz frequency bands. Support for data rates of 53.3, 106.7 and 200 Mbps is mandatory for wireless USB devices, with additional rates up to 480 Mbps being optional for devices and mandatory for hosts. Support for bands 1 through 3 (Channel 1 - see Figure 10-4) is mandatory for all wireless USB implementations, with optional support for other band groups. All time-frequency codes (TFC) for each band group supported must also be supported (see the Section "Multiband UWB, p. 122"). Media Access Control Layer The WiMedia MAC has been specifically developed to address the shortcomings of previous MACs, such as pre-802.11e Wi-Fi and Chapter Ten Channel 1 Channel 2 Channel 3 Channel 4 Channel 5 10296 528 MHz wide bands Figure 10-4: WUSB MBOA Bands Bluetooth, in providing guaranteed quality of service for real time video and audio streaming applications, as well as robustness to changing network topology. The key design features of the WiMedia MAC are summarised in Table 10-10. MAC layer timing is defined within the superframe structure shown in Figure 10-5. Each 65 ms superframe is divided into 256 media access slots (MAS) each of 256 us duration. The leading MASs in each superframe are used as a beacon period, during which devices exchange information with the host on their capabilities and resource requirements. Devices can reserve one or more medium access slots using distributed reservation protocol (DRP) messages during the beacon period. This enables applications to guarantee media access for isochronous data streams. Table 10-10: WiMedia MAC Key Design Features Design feature Description Distributed network At the MAC level, responsibility for medium control is control shared by all devices, reducing