Re: use of radiotap bit 14?

Hi all,
On 20/06/2008, at 6:56 AM, David Young wrote:

> On Thu, Jun 19, 2008 at 07:44:59PM +0200, Johannes Berg wrote:
>> Ok, I tried collecting all the information, and here's what I found  
>> so
>> far:
>>
>> http://www.radiotap.org/suggested-fields
>>
>> Bits 14, 15 and 16 are defined twice.
>>
>> Can we declare bits 14 through 18 reserved (i.e. may not be used) and
>> continue life at 19? Current parsers would have to be changed (the  
>> only
>> one I found is wireshark and internal ones like hostapd, Linux  
>> kernel)
>> to treat the presence of those bits to be an abort-condition and as  
>> an
>> error if there are any above them, current generators would have to  
>> stop
>> generating those fields over time and instead generate standardised
>> versions.
>>
>> For me, of course, it would be more comfortable to stick with RX/TX
>> flags in 14/15 and RTS retries in 16, but since it's not widely  
>> used in
>> Linux yet I can easily discard them.
>
> Johannes,
>
> I favor these assignments:
>
> 14 /RX flags
> 15 /TX flags
> 16 /RTS retries
> 17 /data retries
> 18 /XChannel

For what it's worth, back in March 2007 I spent some time making sure  
that madwifi used these bit assignments (minus XChannel, which I  
hadn't heard of back then). I took the NetBSD headers to be the  
"official" source of the Radiotap standard.

Previously we had been using the in-header FCS flag, which I got rid of.

So, madwifi has been using these bit assignments for some time now -  
hopefully one more reason to not change them :)

Cheers,

--
Scott Raynel
WAND Network Research Group
Department of Computer Science
University of Waikato
New Zealand