From mboxrd@z Thu Jan 1 00:00:00 1970 From: Johannes Berg Subject: RE: [RFC] VHT fields Date: Fri, 15 Jun 2012 10:29:51 +0200 Message-ID: <1339748991.4512.12.camel@jlt3.sipsolutions.net> References: Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Return-path: In-Reply-To: Sender: radiotap-owner-sUITvd46vNxg9hUCZPvPmw@public.gmane.org To: Alwin Beukers Cc: "radiotap-sUITvd46vNxg9hUCZPvPmw@public.gmane.org" List-Id: radiotap@radiotap.org On Fri, 2012-06-15 at 08:15 +0000, Alwin Beukers wrote: > The reason for splitting it up is to avoid extra overhead related to MU= -MIMO=20 > when describing VHT SU PPDUs. The separation is based on the different = PLCP=20 > header formats (VHT-SIG-A1/A2/B) for SU and MU PPDUs: >=20 > 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 S= TA) >=20 > MU PPDUs: > - NSTS, MCS and Coding fields for up to four users > - Partial AID is not applicable > - Group ID is 1..62 >=20 > All fields common to both SU and MU are in the SU_VHT field. The MU_VHT= field=20 > contains additional information for MU PPDUs. The GROUP_ID and PARTIAL_= AID > fields have varying value or applicability. Ok, makes sense. > So for SU PPDUs you would likely have SU_VHT and PARTIAL_AID fields, an= d maybe > a GROUP_ID field (for SU the GROUP_ID field only provides direction inf= o that > could also be determined from PARTIAL_AID and/or MAC header). Right. I haven't looked into all these details of 11ac (yet) > For MU PPDUs you would have SU_VHT (for the common fields as well as=20 > NSTS/MCS/Coding for the first user), MU_VHT (for NSTS/MCS/Coding for > additional users), and GROUP_ID. >=20 > By combining fields we can reduce complexity at the expense of some inc= reased > overhead, what are your thoughts on his?=20 I don't really care much either way -- was mostly curious why you were splitting it up so much. I have a feeling though that the group ID would be useful to always have, even if it's just 0/63 in the SU case, to make it easier on filtering? > Also, I was wondering if we need all > of the 'known' flags in SU_VHT. The MCS field (after which SU_VHT was m= odeled) > also has these, but I don=E2=80=99t 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? I know that's usually the case for your devices, but it isn't typically the case for all the random devices out there ... so I think we should have the known flags to not run into a situation later where a device has to lie. johannes