On Tuesday, October 23, 2012 08:58:39 PM David H. Lynch Jr. wrote: >> On Sunday, October 21, 2012 09:58:18 PM David H. Lynch Jr. wrote: >>> I am looking for an easy means to determine the characteristics of a >>> transmitted packet. >>> Particularly whether it is HT20/HT40-/HT40+ I have used a variety of >>> sniffers, airodump, wireshark, ... and I can not seem to find anything >>> that will tell me what I am after - or I do not know how to use them. >>differentiating between HT40+ and HT40- will be difficult to do with >>just one standard wifi device (should be possible with two though). >> >>If you use mac80211, have you setup your monitor channel by adding >>the HT20/HT40+/HT40- flag? >># iw dev wlanX set channel 1 HT40+ (or HT40-/HT20) > > This is setting up to send on channel 1 HT40+ correct ? yes, I hope so. > >As for retrieving the information: > >If a HT20/HT40 frame was received, it should have a radiotap > >IEEE80211_RADIOTAP_MCS header element (on the monitor interface dump). > >In this element should provide the MCS and flags for > > - BW40 (if false => HT20, if true => HT40+ or HT40- depending > > on the channel configuration) > > - Short GI > > - Greenfield flag > > - (LDPC) > > Wireshark appears to handle RadioTap - I am seeing lots of other flags > etc. but not BW40. It depends on the version. Here's a screenshot from wireshark 1.8.2: <http://imageshack.us/f/703/mcsinfo.png/> >> But I don't know if any of this information is parsed by any of the >> current tools (depends on the version I guess). At least for wireshark >> you can always look at the raw hex dump of the package, so it should >> be there! The definitions of what RADIOTAP_MCS bit means what are in: >> <include/net/ieee80211_radiotap.h> > > Googling Radiotap produces lots of comments that suggest that Radiotap > headers - send and receive are not necescarily complete or accurate from > device to device - is that a reasonable conclusion ? Most mac80211 driver should report rx'ed MCS information. At least ath9k, ath9k_htc, brcmsmac, carl9170, iwlagn, iwllegacy, mwl8k, rt2800*, rtl8192* do. What might not work is: injecting frames with MCS rates [no code in ieee80211_parse_tx_radiotap for that?]... So maybe the issue is indeed at the other end? Regards, Chr -- To unsubscribe from this list: send the line "unsubscribe linux-wireless" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
