On Wed, 2014-09-17 at 01:47 +0200, Steinar H. Gunderson wrote: > On Mon, Sep 08, 2014 at 10:53:20AM +0200, Johannes Berg wrote: > >> Linux already supports 802.11h, where the access point can tell the > >> client to reduce its transmission power. However, 802.11h is only > >> defined for 5 GHz, where the need for this is much smaller than on > >> 2.4 GHz. > >> > >> Cisco has their own solution, called DTPC (Dynamic Transmit Power > >> Control). Cisco APs on a controller sometimes but not always send > >> 802.11h; they always send DTPC, even on 2.4 GHz. This patch adds support > >> for parsing and honoring the DTPC IE in addition to the 802.11h > >> element (they do not always contain the same limits, so both must > >> be honored); the format is not documented, but very simple. > >> > >> Tested (on top of wireless.git and on 3.16.1) against a Cisco Aironet > >> 1142 joined to a Cisco 2504 WLC, by setting various transmit power > >> levels for the given access points and observing the results. > >> The Wireshark 802.11 dissector agrees with the interpretation of the > >> element, except for negative numbers, which seem to never happen > >> anyway. > > Applied both. > > I found what I believe is an edge case: What happens if the element suddenly > goes away from one beacon to another? Shouldn't there be a reset of the power > level and then a new call to __ieee80211_recalc_txpower()? > > (If so, I believe this bug was already present in the code before my first > patch, as I understand the existing logic.) I'm not sure it's worth worrying about, but if you want to write a patch I'd take it :) johannes -- 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
