Re: Public Release of Z-Wave G.9959 TAP Specification

[Denis Ovsienko via tcpdump-workers <tcpdump-workers () lists tcpdump org>]

> --- Begin Message ---
>
>
> From: Denis Ovsienko <denis () ovsienko info>
>
> Date: Mon, 5 Dec 2022 23:44:46 +0000
>
> On Mon, 5 Dec 2022 11:53:11 -0800
> Chris Brandson via tcpdump-workers <tcpdump-workers () lists tcpdump org>
> wrote:
>
> > Hello everyone,
> >
> > We are pleased to publish the draft Z-Wave G.9959 TAP Specification
> [...]
>
> Hello Chris.
>
> Thank you for preparing the document.  I am not familiar with the
> standard to make more substantial comments, but a few things seem to
> require some attention:
>
> * Page 7: "Length is a minimum of 4 octets and must be a multiple of 4.
>   The addition of new TLVs does not and must not require incrementing
>   the version number." -- this definition automatically creates a
>   problem space on the receiving/reading end of this encoding because
>   slightly more than 75% of all possible length values are invalid by
>   definition. The classic solution would be not to include the first 4
>   octets into the length, and to count in multiples of 4, this way any
>   length value would be valid, free of underflows and better consumable
>   by simple parsers such as BPF bytecode.
>
> * Page 8: "Z-Wave PHY Payload" -- is this the PPDU from Figure A.7 of
>   G.9959 2015/01, starting from "preamble sequence"?
>
> * Page 9: "length - number of octets for type in value field (not
>   including padding)" -- this definition looks better, but in the next
>   three TLV diagrams the length does include the T and the L.
>
> * Page 10: If the list of region code points is a copy/subset of an
>   external registry, it would help to give an exact reference.  Ditto
>   bit rate code points.  Clearly there is some relation with tables A.1
>   and A.2 from G.9959 2015/01.
>
> -- 
>     Denis Ovsienko
>
> --- End Message ---
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