Alliance ceased operations. In October 2009, the Bluetooth Special Interest Group dropped development of UWB as part of the alternative MAC/PHY, Bluetooth 3.0/High Speed technology. A small, but significant, number of former WiMedia members had not and would not sign up to the necessary agreements for the intellectual property transfer. The Bluetooth group then turned its attention from UWB to 60 GHz. On September 29, 2010, version 1.1 of the Wireless USB specification was announced. It delivered several backwards-compatible improvements: UWB upper band support for frequencies 6 GHz and above, improved power management and consumption, and support for NFC and proximity based association. Protocol architecture As mentioned, the USB model is preserved, and generally minor adjustments made to fit the specific needs of a wireless system. The changes are as follows, from top to bottom: The function layer only suffers minor changes to increase efficiency and support isochronism. The device layer includes wireless-oriented security and device management features. The bus layer does not change its functionality, but is substantially adapted for efficiency and security on wireless networks. Changes to USB The replacement of copper wires in the bus layer introduces ambiguity in the actual state of host-device connections and, even more importantly, potentially exposes communications fully to any other device within the propagation range, whereas they were reasonably secure over the wire. Hence an explicit secure relationship must be established. For this, the bus and device layers incorporate the necessary resources for use by the function layer. Every W-USB transmission is encrypted by the bus layer without impairing layer-to-layer horizontal communication. The bus follows a TDMA-based polling approach supervised by the host. A transfer is formed by three parts: token, data and handshake. For efficiency reasons, several tokens containing timing information for the devices can be grouped into one, thus forming transaction groups. Flow control and packet sizes are adjusted for power efficiency, while respecting the high-level pipe model of communication between source and destination. Even preserving the USB model typical error rates in wireless media require modifications in the mechanisms used to achieve said model: among others, data handshakes and buffering. UWB defines both PHY and MAC layers, which need to be integrated in the W-USB model. In particular, MAC is joined with the logical link control (LLC) sublayer to form the link layer, responsible for encryption/decryption, PHY error management and synchronization, while PHY itself covers the correctness of