Band config through "setband" command does not reflect in "RF Bands" attribute of WPS-IE

[Jouni Malinen]

On Tue, Oct 13, 2015 at 05:20:23AM +0000, Shanbhag, Sandeep wrote:
> On the dual band capable device the default band setting is "Auto" in which case the "RF Bands" attribute indicates both bands "2.4 and 5 GHz ".
> Some devices like the latest mobile phones with Android version Lollipop provide an option for the end user to change the band settings.

Unfortunately, there does not seem to be any clear documentation (or
even consensus) on what exactly this setting does on Android. As an
example, setting 5 GHz only mode could be interpreted as not being able
to use P2P at all since P2P won't work without the social channels none
of which are defined for the 5 GHz band.. Still, some interpretation may
expect P2P to work but only allow 5 GHz operating channel to be
selected.

Similarly, it is not clear how permanent this configuration should be
considered and as such, it is not clear whether the RF Bands setting for
a WPS operation to enroll to a network should really be updated based on
a potentially very short lived constraint on the device that may get
removed shortly after running through the WPS operation.

IMHO, this select a band option should not be exposed at all in the UI.
If there is need to be able to force a specific band to be used, that
should really happen automatically whenever possible (i.e., no user
involvement) and if there is a user involvement needed for some special
cases, that should really be per network profile rather than a global
device parameter. As an example, I would not understand at all why this
design would be used to avoid roaming to congested 2.4 GHz band which
seems to be one of the use cases this is used for.. Surely the user
should not be forced to even know about this type of details and the
best network should be selected automatically.

> When such device uses the "setband" command to configure the supplicant, the changes only reflect in the channels used for scanning both in the case of STA and P2P but band setting does not reflect in the "RF Bands" attribute of the WPS-IE (Enrollee and P2P).
> For example, if the user selects "2.4 GHz only" only option the STA scanning or P2P discovery is done only in 2.4 GHz band, probe requests will be sent only in 2.4 GHz channels but the "RF Bands" would stills wrongly indicate both bands "2.4 and 5 GHz"
> 
> This option is a global option and when a particular band (2.4 or 5) is chosen it reduces the device from dual band to a single band device and hence the "RF Bands" attribute in WPS-IE of both standalone WPS-Enrollee and P2P should indicate the band setting.
> Supplicant requires a modification to reflect the band setting.

For P2P use cases, I don't see much, if any, point in using the WPS RF
Bands attribute; the P2P Channel list information should be used
instead.

For non-P2P WPS use cases, I would not change anything based on the
Android design. If there is a justifiable real work use cases for WPS
Enrollee to be able to indicate only a subset of RF Bands, I could
consider means for making this configurable, but I'm not convinced that
this should be bound to the setband parameter taken into account the
different interpretations on how user selecting a band should really
behave.

-- 
Jouni Malinen                                            PGP id EFC895FA