the host does not respond to the re-connect attempts, the device must then transition to the UnConnected state and can then begin connect attempts.

When the device knows that the host is asleep and has enabled the device to perform Remote Wakeup, the device should wait at least a TrustTimeout (the host required ‘polling’ rate) before assuming the host has disappeared.

When a Sleeping device returns to the Awake state, it begins looking for MMCs from its host on the same PHY channel it last saw MMCs from its host. It searches for MMCs via an open scan. Similar to above, if it cannot locate the correct MMC for 500 milliseconds, it should begin looking for its host on other PHY channels. See Section 4.16.2.2 for details on behavioral requirements for Remote Wake.

4.15Security Mechanisms

The security mechanisms described in this specification are implemented using the security mechanisms of the MAC Layer. This section describes the mapping between Wireless USB security concepts and MAC Layer security concepts see reference [3]. Refer to Section 6 for complete security details.

Wireless USB hosts and devices operate in MAC Layer Security Mode 1. This mode allows Wireless USB devices to connect using Wireless USB Control requests encapsulated in MAC Layer data frames.

A device receives a group key from the host at the completion of a successful 4-way handshake. However, a device must be able to receive MMCs from the host in order to locate the host and start the 4-way handshake. A device is permitted to successfully receive secured MMCs if it is not yet in possession of the valid group key. When the device receives a group key from the host, it should begin validation of the MMCs as described for the MAC Layer.

4.15.1Connection Lifetime

Wireless USB requires that data communications must occur frequently enough to keep the trust relationship intact. If a host does not receive any authenticated packets from a device or a device does not receive any authenticated packets from its host for a TrustTimeout period, the host (or device) must force a re-authentication (i.e. 4-way handshake) before resumption of normal data communications. The duration of TrustTimeout is four

(4) seconds.

4.15.2Host Security Considerations

4.15.2.1CHID Selection

Devices use the CHID field of a connection context to locate a host. To insure uniqueness in the presence of multiple hosts, a host should develop its CHID value from other values that supply uniqueness, such as the host’s EUI-64 address.

4.15.2.2CDID Selection

CDID values should be derived using the PseudoRandom Function PRF-128. This is described in Section 6.2.10.1

4.16Wireless USB Power Management

Wireless USB provides mechanisms that allow hosts and devices to opportunistically and explicitly control their power consumption. Because Wireless USB protocol is TDMA-based, hosts and devices know exactly when their radios do not need to be transmitting or receiving and can take steps to conserve power during these times. Other mechanisms allow hosts and devices to turn off their radios for longer periods of time. The sections below cover power management mechanisms available for devices and for hosts and define the interactions between the two.

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