[CUWiN-Dev] Monitor mode with Atheros

[Jeongkeun Lee]

By any chance, the IEEE80211_RADIOTAP_TSFT type defined in
ieee80211_radiotap header has something to do with the tcpdump time stamp?

* IEEE80211_RADIOTAP_TSFT              u_int64_t       microseconds
 *
 *      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.

> -----Original Message-----
> From: cu-wireless-dev-bounces at lists.cuwireless.net [mailto:cu-wireless-
> dev-bounces at lists.cuwireless.net] On Behalf Of Jeongkeun Lee
> Sent: Wednesday, February 07, 2007 7:10 PM
> To: cu-wireless-dev at lists.cuwireless.net
> Subject: RE: [CUWiN-Dev] Monitor mode with Atheros
> 
> Dave,
> 
> My concern in using tcpdump to sniff packets is the timestamp precision.
> According to the following mailing list archive,
> http://www.tcpdump.org/lists/workers/2003/08/msg00411.html
> tcpdump time stamp imprecision includes time spent passing the packet
> through the networking code and the driver code, as well as, possibly,
> through the networking card.
> 
> But what I want is the hardware RX timestamp whose precision is in
> microsecond level. Reportedly (by some papers and madwifi mailing),
> Atheros
> card provides such precise timestamp of received packets for device
driver.
> It seems that calling ath_extend_tsf(ah, ds->ds_rxstat.rs_tstamp) returns
> the extended 64-bit timestamp from rx descriptor.
> 
> As I doubt that tcmdump timestamp is identical with the hardware RX
> timestamp, could you shed light on this? :)
> 
> I looked at ieee80211_radiotap header and relevant codes but still in
dark.
> 
> Thank you.
> -- Jeongkeun
> 
> > -----Original Message-----
> > From: cu-wireless-dev-bounces at lists.cuwireless.net [mailto:cu-wireless-
> > dev-bounces at lists.cuwireless.net] On Behalf Of David Young
> > Sent: Wednesday, February 07, 2007 2:36 PM
> > To: cu-wireless-dev at lists.cuwireless.net
> > Subject: Re: [CUWiN-Dev] Monitor mode with Atheros
> >
> > On Wed, Feb 07, 2007 at 02:21:56PM +0900, Jeongkeun Lee wrote:
> > > Hi Dave,
> > >
> > > I'd like to have a mesh node to operate as a packet sniffer. The
> sniffer
> > > will be placed right next to a sender and sniff out every packet
> > transmitted
> > > by the sender. We have written codes which read 64-bit hardware
> > timestamp of
> > > received packets in ath device driver, which is reported to the
> > application
> > > program (sniffer daemon).
> > >
> > > The sniffer does not have to transmit packets. But it has to hear
> every
> > > packet (from the sender) regardless of the destination address in the
> > > packet. Thus, the sniffer needs to operate in monitor mode, as I
> guessed.
> > > But it seems the device driver needs to be modified to support monitor
> > mode.
> > > Or there is another way to make a sniffer without using monitor mode?
> >
> > Promiscuous mode should be sufficient.  tcpdump puts an interface in
> > promiscuous mode by default.  In adhoc mode, have you tried 'tcpdump
> > -ne -y ieee802_11_radio -i ath0 -s 256 -w /tmp/capture-file.cap'?
> > That works for me.
> >
> > Dave
> >
> > > Thanks,
> > > -- Jeongkeun
> > >
> > > > You cannot transmit packets in monitor mode.  It is a receive-only
> > mode.
> > > > What are you trying to achieve?  I can probably suggest a different
> > way.
> > > >
> > > > Dave
> > > >
> > > > --
> > > > David Young             OJC Technologies
> > > > dyoung at ojctech.com      Urbana, IL * (217) 278-3933
> > > > _______________________________________________
> > > > CU-Wireless-Dev mailing list
> > > > CU-Wireless-Dev at lists.cuwireless.net
> > > > http://lists.chambana.net/cgi-bin/listinfo/cu-wireless-dev
> >
> > --
> > David Young             OJC Technologies
> > dyoung at ojctech.com      Urbana, IL * (217) 278-3933
> > _______________________________________________
> > CU-Wireless-Dev mailing list
> > CU-Wireless-Dev at lists.cuwireless.net
> > http://lists.chambana.net/cgi-bin/listinfo/cu-wireless-dev
> 
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