RE: Radiotap header for S1G captures and associated changes and other definitions

Hi all,

Thank you for your valuable comments.
For the NDP related questions, yes. Hardware and its firmware can =
capture whole NDP
and get the NDP indication value.
And 802.11ah defines frequency spectrum from 750-950MHz; 700 for China, =
800 for EU,
and 900 for others in general.

Best regards,
Aaron
-----Original Message-----
From: Richard Sharpe <[email protected]>=20
Sent: Tuesday, March 5, 2019 7:29 AM
To: Johannes Berg <[email protected]>
Cc: [email protected]; Ray Wang <rwang-+OaQ/[email protected]>; Tasheng Lin =
<tlin-+OaQ/[email protected]>; Aaron J. Lee <[email protected]>
Subject: Re: Radiotap header for S1G captures and associated changes and =
other definitions

On Tue, Mar 5, 2019 at 3:58 AM Johannes Berg <[email protected]> =
wrote:
>
> Hi Richard,
>
> > 1. Channel field:
> >
> > 3 new values for Mask: 0x0002 for 700 MHz, 0x0004 for 800 MHz and
> > 0x0008 for 900 MHz spectrum channels respectively.
>
> How much space do we have there btw? We're going to get 6-7 GHz=20
> channels soon ... perhaps we should just give up on this field and put =

> the actual frequency & bandwidth etc. somewhere? If we don't already =
...

Yes, although that is possibly a more general question. S1G will always =
be below 1GHz, I believe.

However, in general, I think we need a separate field that specifies the =
BW as a string, and probably even one per antenna.

> > NDP type:
> > 0x00: NDP Control frame
> > 0x01: NDP Management frame
> > 0x02-0xFF: Reserved
> >
> > NDP data:
> >
> > These are as defined in 802.11ah-2016 Section 9.9 except that the=20
> > top two bits of data[4] are:
> >
> > 0x00: 1MHz
> > 0x01: 2MHz
> > 0x02-0x03: Reserved
>
> Is it really worth packing this into the end? You could have lots of=20
> space in e.g. the data2 or NDP type fields (I guess, you reserved lots =

> of values there).
>
> > The S1G NPD format is essentially from section 9.9 of 802.11ah-2016=20
> > with some additional syntactic sugar:
> >
> > It is a 40-bit field.
>
> Not sure I understand this sentence. What's the syntactic sugar in=20
> being a 40-bit field?
>
> > In between, a 1MHz NDP CMAC frame contains 26 used bits and 13=20
> > unused bits. The used bits are defined in section 9.9 of=20
> > 802.11ah-2016. A 2MHz NDP CMAC frame contains 37 used bits and one=20
> > unused bit. Again, the used bits are defined in 802.11ah-2016.
>
> Right.
>
> However, these also come with a 1-bit "NDP indication", 4-bit CRC and=20
> 6- bit tail; perhaps it should be at least *possible* to capture those =

> too, even if nobody might do that right now? Then you'd need a total=20
> of 48 bits for this, afaict.
>
>
> I guess a more fundamental question would be whether we should treat=20
> these as metadata or payload. Obviously here we're treating them as=20
> metadata and saying (by way of the 0-length field) that there's no=20
> payload. But perhaps these *should* in fact be the payload instead,=20
> and not use the 0-length field at all?
>
> I really don't know the answer to that. It seems fairly obvious that=20
> this one is more convenient, and the format of those frames is very=20
> specific to the S1G things, and they couldn't really be used outside=20
> of S1G unlike the 802.11 header & frame. So I think I'm happy with=20
> this, just wanted to note this design decision explicitly.

I will clean up the others over the next few days, but yes, I went back =
and forward between having the NDP info be a separate payload versus =
placing it in the S1G header. Placing it in the S1G header is more =
convenient but will mean moving code around over what we currently have, =
however, that is relatively easy.

It is a matter of convenience.

A question for Aaron and the WFA folks, however, is: Is there utility =
capturing the NDP indication, or is that already captured in IS NDP =
above? Similarly, is it useful to capture the CRC and tail etc. Does the =
hardware give you access to these extra fields?

--
Regards,
Richard Sharpe
(=E4=BD=95=E4=BB=A5=E8=A7=A3=E6=86=82=EF=BC=9F=E5=94=AF=E6=9C=89=E6=9D=9C=
=E5=BA=B7=E3=80=82--=E6=9B=B9=E6=93=8D)(=E4=BC=A0=E8=AF=B4=E6=9D=9C=E5=BA=
=B7=E6=98=AF=E9=85=92=E7=9A=84=E5=8F=91=E6=98=8E=E8=80=85)