From mboxrd@z Thu Jan 1 00:00:00 1970 From: Johannes Berg Subject: RE: Regarding A-MPDU status field Date: Wed, 09 Nov 2011 15:02:46 +0100 Message-ID: <1320847366.3845.72.camel@jlt3.sipsolutions.net> References: <21E1C3B49A18BA428D58607D5EEA5398BB2E90@nasanexd02b.na.qualcomm.com> <1320223343.3950.29.camel@jlt3.sipsolutions.net> <21E1C3B49A18BA428D58607D5EEA5398BB67FA@nasanexd02b.na.qualcomm.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <21E1C3B49A18BA428D58607D5EEA5398BB67FA-RqevaKtL5OWBP98+muIrrKRtKmQZhJ7pQQ4Iyu8u01E@public.gmane.org> Sender: radiotap-owner-sUITvd46vNxg9hUCZPvPmw@public.gmane.org To: "Rao, Krishna" Cc: "radiotap-sUITvd46vNxg9hUCZPvPmw@public.gmane.org" List-Id: radiotap@radiotap.org Hi, > > -- it might also be helpful to know the padding length before/after > (?) the packet for example. > We can add > 1) Padding length information > a) value of padding length after the MPDU, and > b) (debatable) total padding length before the subframe for the > special case of preceding delimiters with MPDU length zero used to > meet minimum MPDU start spacing requirements. All the octets of the > preceding 'zero delimiters' together form the pad, as I understand. > Note that this information might not be provided by some hardware. > If an MPDU (not 'zero delimiter') is actually present prior to the > current subframe for which radiotap info is being displayed, 1b) > should be zero for the current subframe. Post MPDU pad length > information for the prior MPDU would anyway be available (assuming the > containing subframe of the prior MPDU is not corrupted). So what I wanted here was to be able to reconstruct what happened on the air as precisely as possible. I don't think the length of the padding is actually needed -- it can be calculated after the fact since it is always 0-3 bytes up to a multiple of 4. The number of zero delimiters would be more interesting. I'm not sure how to deal with the corruption case. > Additionally: > 2) A bit to indicate if this is the last subframe in the A-MPDU. > Though there might be other ways to infer this information, having it > as an explicit field would provide convenience. That seems useful, although I'm not even sure how you would even know that it is the last one? > 3) A bit to indicate if the Delimiter CRC is in error. That's useful, but in that case are you even decoding the MPDU and passing it up? Also what if a zero delimiter has a bad CRC? Or what if it just got corrupted and you have to recover parsing? I'm not sure we can cover all these cases. > 4) (Debatable) Delimiter CRC value itself. I don't know if there is > any hardware which returns the actual value to software. Anyway, > having it as part of the field will allow platforms which do possess > the capability, to provide this information. It may come in handy for > some users. That seems a bit of a stretch, but it's only 8 bits so I wouldn't mind adding it. johannes