Link Preference and Control

Link Preference/Control, added in Release 6.0, is only relevant for the wireless interface. The Link preference selection determines whether the wireless link is controlled by the host driver or by the Intel ME (the embedded Manageability Engine running the Intel AMT firmware):

   A Host link preference is defined as a behavior in which a link has host control as long as ME identifies a functional host driver over that link’s interface. Otherwise, ME takes control over that link – though this taking over is not guaranteed to be immediate. If ME has control and identifies that the host driver has resumed operation, ME relinquishes link control back to the host. Using host link preference, both host traffic and ME traffic are available (host traffic is only available if the host driver is functional). When the host has control, ME traffic is disconnected during resets and when the host driver is disabled (temporarily). This is the default setting.

   An ME link preference is defined as a behavior in which ME takes control of the link, regardless of host driver status. Note that with this preference, ME does not relinquish control to host. Also note that with this preference, the link survives host resets, host power-ups, and host driver disabling. The link is also guaranteed to survive power-down and power-cycle reset transitions in case those occur during a redirection session. Using ME link preference, only ME traffic is available.
The method AMT_EthernetPortSettings.SetLinkPreference has a timeout parameter. It determines how long to maintain an ME preference before attempting to return control to the Host.

Link Control and Power Packages

The ME will take control of the wireless link when the host is in a low power state only when Intel AMT is configured with a power package that supports ME operation during a host sleep state: either “Mobile: ON in S0; ME Wake in S3/AC, S4-S5/AC” on a mobile platform or “Desktop: ON in S0; ME Wake in S3, S4-S5” on a desktop platform equipped with a wireless interface. See List of Power Packages.


   The following sequence can lead to a condition where the host loses wireless connectivity:

The platform is configured for host link preference

The platform enters a sleep state (Sx)

The platform returns from a sleep state but waits for a login before allowing a wireless connection to complete.

In this case, especially if this is an unattended platform (no human operator present), there will be no wireless connectivity at all, including manageability connectivity to Intel AMT, and no way to recover from the situation until a human logs in.

A solution to this issue is to configure single sign-on (SSO) wireless profiles that will complete the wireless connection without the need for a user to enter a password. This is the recommended approach. See for a Signle Sign-On sample. describes how to configure a wireless profile for, among other things, SSO.

   For the wired interface, both host and ME traffic are always available, and the link survives resets and disabling the host driver.


See Also:

   Set/Get Link Preference and Control

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