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From: David Young <dyoung-e+AXbWqSrlAAvxtiuMwx3w@public.gmane.org>
To: "radiotap-sUITvd46vNxg9hUCZPvPmw@public.gmane.org"
	<radiotap-sUITvd46vNxg9hUCZPvPmw@public.gmane.org>
Subject: Re: TSFT
Date: Sat, 17 Nov 2012 00:48:49 -0600
Message-ID: <20121117064848.GO21779@pixotech.com> (raw)
In-Reply-To: <50A72E17.6070207-vp0mx6+5gkqFX2APIN6yfw@public.gmane.org>

On Fri, Nov 16, 2012 at 10:26:31PM -0800, Simon Barber wrote:
> This is the current definition of TSFT:
> 
> "Value in microseconds of the MAC's 64-bit 802.11 Time
> Synchronization Function timer when the first bit of the MPDU
> arrived at the MAC. For received frames only."
> 
> My experience with TSFT is with Atheros cards, which record the
> timestamp at the end of the frame, not the start.

Interesting.  Is it consistent across the whole Atheros product line?

> Furthermore for DSSS/CCK the definition above is reasonable, but for
> OFDM and HT (802.11n) the SIGNAL field (part of the PLCP header, not
> part of the MPDU) is part of the first data symbol. It would be much
> clearer to change the definition to state that the timestamp is at
> the start of this first SIGNAL/data symbol. Any objections to doing
> this, or preference to change the reference point to a different
> part of the frame?
> 
> In my wireshark patch I've added options to interpret TSFT as the
> start of end of the frame.

I think we need 1) a methodology for an author to identify their
device's reference point so that they can calibrate their driver to the
standard and/or 2) a radiotap datum that identifies the reference point
in use or 3) something entirely different.

Dave

-- 
David Young
dyoung-e+AXbWqSrlAAvxtiuMwx3w@public.gmane.org    Urbana, IL    (217) 721-9981

  parent reply index

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-11-17  6:26 TSFT Simon Barber
     [not found] ` <50A72E17.6070207-vp0mx6+5gkqFX2APIN6yfw@public.gmane.org>
2012-11-17  6:48   ` David Young [this message]
     [not found]     ` <20121117064848.GO21779-Gq8g4XVd89tWk0Htik3J/w@public.gmane.org>
2012-11-17  8:45       ` TSFT Johannes Berg
     [not found]         ` <1353141950.9543.3.camel-8Nb76shvtaUJvtFkdXX2HixXY32XiHfO@public.gmane.org>
2012-11-17 17:46           ` TSFT David Young
     [not found]             ` <20121117174600.GQ21779-Gq8g4XVd89tWk0Htik3J/w@public.gmane.org>
2012-11-17 18:43               ` TSFT Johannes Berg
2012-11-17 18:56               ` TSFT Guy Harris
2012-11-17 23:26   ` TSFT Thomas Pedersen
2012-11-18  7:20     ` TSFT Simon Barber
     [not found]       ` <50A88C3D.5030809-vp0mx6+5gkqFX2APIN6yfw@public.gmane.org>
2012-11-18 11:07         ` TSFT Johannes Berg
     [not found]           ` <1353236845.9649.6.camel-8Nb76shvtaUJvtFkdXX2HixXY32XiHfO@public.gmane.org>
2012-11-20 22:43             ` TSFT Simon Barber
     [not found]               ` <50AC0791.3040005-vp0mx6+5gkqFX2APIN6yfw@public.gmane.org>
2012-11-21 10:42                 ` TSFT Johannes Berg

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