Re: [PATCH v3 3/3] mac80211: Add HT operation modes for IBSS

["Luis R. Rodriguez" <mcgrof@frijolero.org>]

On Tue, Sep 20, 2011 at 12:31 PM, Felix Fietkau <nbd@openwrt.org> wrote:
> On 2011-09-20 9:05 PM, Luis R. Rodriguez wrote:
>>
>> On Tue, Sep 20, 2011 at 11:46 AM, Felix Fietkau<nbd@openwrt.org>  wrote:
>>>
>>>  On 2011-09-20 8:38 PM, Luis R. Rodriguez wrote:
>>>>
>>>>  On Tue, Sep 20, 2011 at 11:21 AM, Felix Fietkau<nbd@openwrt.org>
>>>>  wrote:
>>>>>
>>>>>   On 2011-09-20 8:12 PM, Luis R. Rodriguez wrote:
>>>>>>
>>>>>>   On Tue, Sep 20, 2011 at 5:21 AM, Johannes Berg
>>>>>>   <johannes@sipsolutions.net>      wrote:
>>>>>>>
>>>>>>>    On Mon, 2011-09-19 at 17:46 +0200, Alexander Simon wrote:
>>>>>>>    That seems pretty complex too ...
>>>>>>>
>>>>>>>    I don't really know. As I said, I think I'd be happy with an
>>>>>>>    implementation that maybe doesn't fully implement everything as
>>>>>>> long
>>>>>>>  as
>>>>>>>    it considers the trade-offs.
>>>>>>
>>>>>>   The same questions come up with HT support and 802.11s, as per
>>>>>> Javier
>>>>>>   this is not really well spelled out in the spec. My recommendation
>>>>>> is
>>>>>>   to just support for now the most simple case and let us not entangle
>>>>>>   ourselves with the complexities of handling trying to merge
>>>>>> different
>>>>>>   setups. So only enable peering up for adhoc or mesh if and only if
>>>>>> the
>>>>>>   observed IE matches our own supported HT caps or target
>>>>>> configuration.
>>>>>>   If a legacy STA tries to peer up with an HT IBSS, this would simply
>>>>>> be
>>>>>>   rejected. We can leave off handling the change in configuration
>>>>>> later
>>>>>>   for userspace, but do not see this as being a requirement for
>>>>>>   supporting HT for IBSS or Mesh. The simpler the better, so long as
>>>>>> we
>>>>>>   simply respect the spec.
>>>>>
>>>>>   I disagree. That'll make it useless for real deployments, which are
>>>>>  often a
>>>>>   mix of HT and non-HT devices.
>>>>
>>>>  I'm not saying to not do it at all, I'm saying to start off with basic
>>>>  support *first* and *later* worry about the mixing.
>>>
>>>  Simply sticking with the configured HT opmode is also simple, but it's a
>>> lot
>>>  more practical.
>>
>> Just need to deal with the complexity, the complexity question is
>> where do we handle this, verifying it respects the standard, and
>> actually getting the work done. With AP mode of operation hostapd
>> already does all this for us so if we want to support IBSS and Mesh
>> without hostapd we'd need to figure out where to stuff this code. In
>> the long run this would need to be resolved for both IBSS and Mesh. We
>> can wait for all this work to get done or get a simple taste of basic
>> HT support for both modes by sticking to the supported HT mode based
>> on the observed beacons.
>
> HT capabilities are already handled properly, the main issue is handling the
> HT opmode. For that, the only important bit is whether we're using HT40+,
> HT40- or HT20. The code can easily just fall back to HT20 when the HT opmode
> of the peer is incompatible with the local HT opmode.

How about verifying that HT40 primary, secondary channel pair is
allowed per as IEEE 802.11n Annex J on each peer? In the AP case we do
this centrally, but for IBSS and Mesh, does each peer have to go on
and do the check? If each peer does the check, and change settings,
how do we go about changing the configuration of the established HT
configuration? Where will this code go? Currently this goes into
hostapd for APs.

  Luis