SDK Resources > Redirection Library > Redirection and the Link Preference Feature

Redirection and the Link Preference Feature

In previous versions of Intel AMT since Release 2.5, when a redirection session was initiated over a wireless LAN interface (WLAN), Intel AMT took control of the WLAN (also known as “ME Preference”) for the duration of the session. This assured that the session would not be interrupted during a commanded power cycle or reboot. However, while the redirection session is active, the host OS has no access to the network. In some scenarios, this is not the desirable behavior. Release 6.0 adds a method for changing the link preference (AMT_EthernetPortSettings.SetLinkPreference). This method enables a console application to say either that the host should receive WLAN traffic while the host WLAN driver is active or the ME should receive all WLAN traffic even when the host driver is active.


If Intel AMT has not received a wireless profile or if none of the wireless profiles result in a successful connection, changing the link preference to ME will result in a loss of wireless connectivity. The ME will not give up control of the link until completion of the link preference timeout period. See Wireless Manageability

The Release 6.1 version of the redirection library, and later versions, allow a console application to control how Intel AMT will treat redirection sessions. The library sends the selected behavior when it initiates a redirection session. The application can choose between two behaviors (see IMR_SetOpt, used to set CLIENT_LINK_PREFERENCE_OPTION):

   The default behavior of previous versions: When a redirection session starts, the ME takes over the WLAN and does not release it until the session ends. During the session, Intel AMT ignores the AMT_EthernetPortSettings.SetLinkPreference method; therefore, a console cannot force Intel AMT to give up control of WLAN, and the link preference does not change, even if commanded to change.

   The new behavior that takes advantage of AMT_EthernetPortSettings.SetLinkPreference: The method determines the link preference and an application can command a change from Host preference to ME preference and back during a redirection session. Note that the default setting is Host link preference.

Examples of Usage

IT technicians may have multiple SOL sessions open on different platforms. They do not want to cut off the host user’s WLAN connectivity while they are dealing with different users.

A console may initiate an SOL session automatically before assigning the support session to a technician. Without this change, the user loses Host WLAN connectivity earlier than necessary.

Setting the Redirection Library Option

IMR_SetOpt and IMR_GetOpt allow setting the Intel AMT behavior. The choice applies to all sessions set up with the current client or with all clients set up in the future. The default value is the behavior of previous versions of the library. The option parameter is based on the CLIENT_LINK_PREFERENCE_OPTION enumeration. Set this option before opening a redirection session to a client.

Behavior of newer versions (Release 6.1and later) of the Redirection Library with Previous Releases

If the option is not changed, Intel AMT will assume ME preference for the duration of the session. If you attempt to change to the behavior of Intel AMT Release 6.0 and later releases opposite a version of Intel AMT that does not support it, the library will return an IMR_RES_CLIENT_INVALID_OPTION response, indicating that this function is not applicable to this version of Intel AMT.

Sample Sequence of Operations

Assume the Host WLAN driver is active. A possible sequence of operations would be:

1. Set the redirection option for a client to CONSOLE_LINK_PREFERENCE using the IMR_SetOpt method.

2. Set the link preference for the wireless LAN to Host by invoking AMT_EthernetPortSettings.SetLinkPreference.

3. Start an SOL session. The connection will be made via the Host driver as the wireless link preference and link control is with the Host.

4. Set the wireless LAN link preference to ME with a short timeout. Control will pass to the ME for the defined timeout period. This will assure that the ME has control of the link and the redirection session will be sustained during the reboot cycle.

5. Remotely command a platform reboot.

6. Control the client via the SOL session (performing Boot to BIOS, for example).

7. Once the client boots back to the operating system, control will return to the Host after the timeout expires.
It is likely that an open redirection session will close during a transfer of wireless LAN control from the ME to the Host. (SOL sessions have a better chance of not closing.) It will be necessary to reopen the session to continue it after the transfer completes.

See Also:

   A description of the link preference feature

   Managing Link Preference for a Session Connected Over a Wireless Interface (KVM)

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