Wireshark-bugs: [Wireshark-bugs] [Bug 12558] Inconsistent VHT data rate
Date: Sun, 26 Jun 2016 20:39:27 +0000

Comment # 6 on bug 12558 from
(In reply to Guy Harris from comment #5)
> (In reply to Ashish Shukla from comment #0)
> >     VHT 20MHz MCS 9 1/2/3/4 stream data rate not displayed.
> >     Currently the other illegal MCSs e.g., 80MHz MCS6 when LDPC is not being
> > used are disaplyed as data rate values.
> 
> Then perhaps they should be fixed *not* to display them as data rate values.

I disagree, with LDPC enabled all of these are valid rates. The IEEE Std
802.11ac-2013 table 22-30 to 22-35 indicate these rates invalid assuming BCC
encoding.
The fact that these PPDUs are received on the sniffer, which is primarily used
as debugging tool, wireshark should be able to provide the data rate.

I don't think we would ever be able to see a frame without LDPC with invalid
rates even transmit side HW would not be able to support that.
Having said that IMHO it makes more sense to treat them consistently and also
allow people to use radiotap datarate filter consistently.

> 
> >     Also, VHT 20MHz 3x3 MCS9 is valid which as of now is not computed.
> 
> Yes, the only MCS 9 cases that are valid are NSS=3 and NSS=6, at least as I
> read IEEE Std 802.11ac-2013 tables 22-30 through 22-35.


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