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From: Krishna Chaitanya <chaitanya.mgit@gmail.com>
To: Johannes Berg <johannes@sipsolutions.net>
Cc: Guy Harris <guy@alum.mit.edu>,
	"radiotap@netbsd.org" <radiotap@netbsd.org>,
	Simon Barber <simon@superduper.net>,
	Richard Sharpe <realrichardsharpe@gmail.com>,
	linux-wireless <linux-wireless@vger.kernel.org>,
	Maya Erez <merez@codeaurora.org>,
	wil6210@qti.qualcomm.com
Subject: Re: Correct radiotap header for 802.11ad
Date: Wed, 11 Dec 2019 15:09:19 +0530
Message-ID: <CABPxzY+0v-Rb-GWkL-iwCfefzhFE5AiGBh2xxV_U_OC0Q+eoVQ@mail.gmail.com> (raw)
In-Reply-To: <4cf0c2a4a2d1cd92dff4f1a791d74523e446cf01.camel@sipsolutions.net>

On Wed, Dec 11, 2019 at 2:02 PM Johannes Berg <johannes@sipsolutions.net> wrote:
>
> ++ for the DMG discussion
>
> On Tue, 2019-12-10 at 15:51 -0800, Guy Harris wrote:
> > On Sep 17, 2015, at 9:37 AM, Johannes Berg <johannes@sipsolutions.net> wrote:
>
> Reviving an old thread :-)
>
> > > Not being familiar with DMG, I can't really comment on this.
> > >
> > > It does sound like we need *some* new field though, be it either a DMG
> > > field or a PLCP SIGNAL field, or perhaps even both.
> > >
> > > Going back to the original thread though, I think using the MCS field
> > > is quite wrong.
> >
> > But a presumably-Linux system does appear to use it; see Wireshark bug
> >
> >       https://bugs.wireshark.org/bugzilla/show_bug.cgi?id=16272
> >
> > For now, I'll throw a hack into Wireshark to treat a signal >= 60 GHz
> > as meaning 11ad,
>
> I don't think that's quite right - you'll need to do something like >=
> 56 GHz.
>
> > but, again, should there be additional fields for 11ad?
>
> I would think so.
>
> On the one hand I think (and looking at the spec seems to confirm this)
> that basically DMG uses an MCS index. Now, the MCS radiotap field was
> designed for HT and has a lot of things that are not applicable (GI,
> STBC, etc.)
>
> OTOH, there are DMG-specific things that probably ought to be captured
> by a proper sniffer, like the PPDU type, training length, etc. Also,
> there's the thing with the "Extended SC MCS Indication field", which
> really also ought to be captured.
>
> Sadly, the only Linux implementation didn't bother adjusting any of this
> even in the Linux general stack (and I didn't pay enough attention to it
> at the beginning), so even the rate reporting to userspace is just the
> MCS index. This might actually be sufficient for the current uses
> (there's a conversion function to bandwidth too), though it doesn't seem
> quite applicable to the whole spec.
>
> For both the Linux userspace reporting and radiotap then, this
> completely ignores the existence of the MCSes 9.1 and 12.1-12.6, which
> cannot be captured in either format right now. Maybe the extended SC
> MCSes are just not used by equipment in the field?
>
They are used. Unfortunately, Linux-wireless doesn't have native support for DMG
wil6210 and our driver has to workaround by using HT IE's
(ieee80211_supported_band).
>
>
> In any case, to capture DMG properly I'd say we need a new radiotap
> field with at least
>  * (base) MCS
>  * Extended SC MCS bit
> and it should probably optionally cover the other possible fields as
> well
>  * Scrambler Initialization
>  * Length (?)
>  * Additional PPDU bit
>  * PPDU type bit
>  * Training Length
>  * Beam Tracking Request
>  * Last RSSI
>  * Turnaround
yes, we definitely need this, there are some additional fields in
11ay, but I guess that
discussion is for another time.



  reply index

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-08-22 19:41 Richard Sharpe
     [not found] ` <CACyXjPzq-ePB1ux6wi_Rv3onPKXomcJcm15XJwA51u0E4W2txw-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2015-08-22 20:59   ` Guy Harris
     [not found]     ` <38F46E1D-1C4A-48DC-A906-9522006E8474-FrUbXkNCsVf2fBVCVOL8/A@public.gmane.org>
2015-08-22 22:06       ` Richard Sharpe
     [not found]         ` <CACyXjPx81fh_jeQSUjE-_w8NQ_Jr-ajmnVWSopfzcLPOWoGmGg-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2015-08-22 22:24           ` Guy Harris
2015-08-22 23:34       ` Guy Harris
     [not found]         ` <1606812C-649C-4C06-ABE0-AE2F4474BCD0-FrUbXkNCsVf2fBVCVOL8/A@public.gmane.org>
2015-08-24  7:40           ` Johannes Berg
     [not found]             ` <1440402013.3735.1.camel-cdvu00un1VgdHxzADdlk8Q@public.gmane.org>
2015-08-24 16:21               ` Richard Sharpe
     [not found]                 ` <CACyXjPwSZPV+U_=zQpDBpeBnhMntzEFhyJnBOw3-N8qPfyHc1A-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2015-08-24 16:28                   ` Johannes Berg
2015-08-26 22:59                   ` Simon Barber
     [not found]                     ` <55DE44EB.6080603-vp0mx6+5gkqFX2APIN6yfw@public.gmane.org>
2015-08-27  1:17                       ` Guy Harris
     [not found]                         ` <126B842D-05EA-4510-BC9B-DB1A4AABEC12-FrUbXkNCsVf2fBVCVOL8/A@public.gmane.org>
2015-09-10 18:25                           ` Guy Harris
     [not found]                             ` <1135A126-6A5A-4C84-A52D-13C0387609CC-FrUbXkNCsVf2fBVCVOL8/A@public.gmane.org>
2015-09-17 16:37                               ` Johannes Berg
2019-12-10 23:51                                 ` Guy Harris
2019-12-11  8:32                                   ` Johannes Berg
2019-12-11  9:39                                     ` Krishna Chaitanya [this message]
2019-12-11 12:57                                       ` Johannes Berg
2019-12-11 13:20                                         ` Krishna Chaitanya
2019-12-20 21:56                                     ` Guy Harris
2015-09-17 16:32                       ` Johannes Berg
2015-08-26 22:56       ` Simon Barber

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