Re: [RFC] VHT fields

[Simon Barber <simon-vp0mx6+5gkqFX2APIN6yfw@public.gmane.org>]

I'm not very familar with 11ac - but does this information together 
with the packet data give you enough to calculate precisely the 
packet's duration in time? Are there any duration fields, as there are 
in 11n that might be useful?

Simon

On Fri 15 Jun 2012 01:15:26 AM PDT, Alwin Beukers wrote:
>> On Tue, 2012-06-12 at 15:05 +0000, Alwin Beukers wrote:
>>> Hi everyone,
>>>
>>> This is a proposal for adding support for 802.11ac. Four fields were
>> added to the suggested-fields section:
>>>
>>> http://www.radiotap.org/suggested-fields/SU_VHT
>>> http://www.radiotap.org/suggested-fields/MU_VHT
>>> http://www.radiotap.org/suggested-fields/GROUP_ID
>>> http://www.radiotap.org/suggested-fields/PARTIAL_AID
>>>
>>> A Wireshark patch for parsing SU_VHT, GROUP_ID and PARTIAL_AID is
>> attached.
>>
>> What's the reason for splitting it up?
>
> Johannes,
>
> The reason for splitting it up is to avoid extra overhead related to MU-MIMO
> when describing VHT SU PPDUs. The separation is based on the different PLCP
> header formats (VHT-SIG-A1/A2/B) for SU and MU PPDUs:
>
> SU PPDUs:
> - Only one NSTS, MCS and Coding field.
> - Partial AID identifies recipient
> - Group ID is always 0 (addressed to AP/mesh STA) or 63 (addressed to STA)
>
> MU PPDUs:
> - NSTS, MCS and Coding fields for up to four users
> - Partial AID is not applicable
> - Group ID is 1..62
>
> All fields common to both SU and MU are in the SU_VHT field. The MU_VHT field
> contains additional information for MU PPDUs. The GROUP_ID and PARTIAL_AID
> fields have varying value or applicability.
>
> So for SU PPDUs you would likely have SU_VHT and PARTIAL_AID fields, and maybe
> a GROUP_ID field (for SU the GROUP_ID field only provides direction info that
> could also be determined from PARTIAL_AID and/or MAC header).
> For MU PPDUs you would have SU_VHT (for the common fields as well as
> NSTS/MCS/Coding for the first user), MU_VHT (for NSTS/MCS/Coding for
> additional users), and GROUP_ID.
>
> By combining fields we can reduce complexity at the expense of some increased
> overhead, what are your thoughts on his? Also, I was wondering if we need all
> of the 'known' flags in SU_VHT. The MCS field (after which SU_VHT was modeled)
> also has these, but I don’t know the rationale behind them. Can one assume a
> driver has full access to the PLCP header and thus can fill in most of fields
> in the SU_VHT field?
>
> Thanks,
> Alwin
>
>> johannes
>>
>
>