From mboxrd@z Thu Jan 1 00:00:00 1970 From: Simon Barber Subject: Re: MCS field - STBC and Ness Date: Fri, 11 May 2012 09:44:20 -0700 Message-ID: <4FAD41E4.3090803@superduper.net> References: <4FAC5DE0.90708@superduper.net> <4FACBA13.9040509@neratec.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <4FACBA13.9040509-ASv44eHyqLVBDgjK7y7TUQ@public.gmane.org> Sender: radiotap-owner-sUITvd46vNxg9hUCZPvPmw@public.gmane.org To: Wojciech Dubowik Cc: radiotap-sUITvd46vNxg9hUCZPvPmw@public.gmane.org List-Id: radiotap@radiotap.org One possible solution would be to adopt your proposal to add a single bit STBC, but also add a second bit to the 'knows' byte - STBC2. If this second bit is set, then it indicates STBC=2. This would leave one remaining bit in the 'knows' byte, to indicate the presence of Ness information, and 2 bits in the 'flags' byte for 2 bits of Ness information. Copying the MCS definition from the radiotap.org website: The known field indicates which information is known: known definition 0x01 bandwidth 0x02 MCS index known (in mcs part of the field) 0x04 guard interval 0x08 HT format 0x10 FEC type 0x20 STBC - STBC is known 0x40 STBC2 - 2 STBC streams are present 0x80 Ness - Number of extra spatial streams is known The flags field is any combination of the following: flag definition 0x03 bandwidth - 0: 20, 1: 40, 2: 20L, 3: 20U 0x04 guard interval - 0: long GI, 1: short GI 0x08 HT format - 0: mixed, 1: greenfield 0x10 FEC type - 0: BCC, 1: LDPC 0x20 STBC - 0: no STBC streams, 1: 1 or 2 STBC streams (see STBC2) 0xc0 Ness - Number of extra spatial streams. Simon On Fri 11 May 2012 12:04:51 AM PDT, Wojciech Dubowik wrote: > Hello, > Atheros families 9002 and 9003 support only one STBC stream. I think I > have seen a Ralink chipset > which supports 2 stream at least on receive. I am not sure about > transmiter. > On Atheros you get STBC flag and two bits Ness field for received > packets but In the patch there is is only flag reading but you could > add Ness yourself it's only two bits left from the flag. > > Myself I have tested only one stream but I did it only by looking > whether other party is setting rx descriptor bit. I don't know how it > looks "in the air". I trust manufacturer;o) > > It's true that only one bit was allocated in wireshark extension. > Should have been two but it's a bit waste. My proposal wasn't accepted > but in the end I think it's ok becasue I have managed to get all info > in vendor namesapes where I can do what I want. > > Br, > Wojtek > >> >> I am writing a Wireshark extension to visualise 802.11 frames on a >> timeline. In order to do this I need to be able to calculate the >> duration from start of TX to end of TX for each frame. >> >> For 802.11n I need to know the number of HT-DLTF and HT-ELTF training >> symbols that are sent in the header - I have everything else needed >> to calculate the duration. Given the MCS and the STBC and the Ness >> (Number of extension spatial streams) I can calculate the number of >> training symbols. >> >> Both STBC and Ness are encoded in the HT-SIG transmitted at the start >> of each HT frame. >> >> The current proposal (or has it not yet been accepted?) for STBC >> allocates just 1 bit - but the STBC field can have values or 0, 1 or 2. >> >> Ness can be 0-3, so the remaining 2 bits could be allocated to Ness, >> but this does not solve the problem of how to encode the modes with 2 >> spatial streams and 2 additional streams for STBC. >> >> Does anyone know what current hardware supports - STBC values or >> 0,1,2? Ness values of 0-3? >> >> Any suggestions for how to convey these >> >> Simon >