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 09:53:04 -0700 Message-ID: <4FAD43F0.20807@superduper.net> References: <4FAC5DE0.90708@superduper.net> <4FACBA13.9040509@neratec.com> <4FAD41E4.3090803@superduper.net> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <4FAD41E4.3090803-vp0mx6+5gkqFX2APIN6yfw@public.gmane.org> Sender: radiotap-owner-sUITvd46vNxg9hUCZPvPmw@public.gmane.org To: Wojciech Dubowik Cc: radiotap-sUITvd46vNxg9hUCZPvPmw@public.gmane.org List-Id: radiotap@radiotap.org OK - perhaps a simpler/better suggestion would be for the STBC2 bit to just be the second bit of STBC information. Simon On Fri 11 May 2012 09:44:20 AM PDT, Simon Barber wrote: > 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 >>