On Fri, 2005-02-04 at 13:25 -0500, Sven wrote: > thanks for the info - i have a few more questions/suggestions: > > if the card reports RSSI and i know MAX_RSSI, is the relative "signal > strength" then RSSI / MAX_RSSI (* 100)? if one wants to use that as the > reported "Link Quality" but for some reason do not want to use %, what > should one do? converting the RSSI #'s to dBm and using that to compute > a % is clearly wrong. IMHO some better guidelines as to what "Link > Quality" in WEXT should mean is desirable. borrowing definitions from > Joshua Bardwell in > http://www.connect802.com/download/techpubs/2004/you_believe_D100201.pdf, > from a practical point of view "Signal Quality," though desirable as > link quality, is probably not feasible to get a handle on with the > (current and future) drivers. next best is probably "Signal Strength" - > from the RSSI values. Or is SNR better as a measurement of link quality? > but that would require a better reporting of noise by the drivers (and > not just a hardcoding) .
RSSI is totally manufacturer dependent. AFAIK, Cisco uses a MAX_RSSI of 63 for the 340/350, Atheros uses something like 30, etc. It depends on how many voltage values the hardware can physically measure. So yes, you do get a sort of Link Quality % when you take RSSI / MAX_RSSI * 100. You can (and should) augment this value with things like the ipw2200 driver does, ie receive packet errors, link speed, etc. Converting RSSI to dBm and using that for link quality is actually pretty wrong. dBm is actually useful though, you can do some interesting things with it like 1) distance from transmitter (if you know detailed antenna and card characteristics), 2) signal power levels and noise levels, 3) more accurately test different antennas, etc. Its just not useful for getting a Link Quality % of any accuracy whatsoever, except when the Signal approaches the Noise you know your reception is starting to suck. So 4 points to take out of this: 1) Drivers SHOULD use subjective values for calculating Quality, but that value SHOULD include some sort of RSSI measurement in addition to whatever else (ie invalid packets, retransmit count, link speed, etc) 2) Drivers SHOULD set both current level (ie qual.qual, qual.level) and max level (max_qual.qual, max_qual.level) 3) Drivers SHOULD use same units for level & noise (ie, either RSSI or dBm) 4) Drivers SHOULD use dBm wherever they can, if they can. Dan _______________________________________________ NetworkManager-list mailing list NetworkManager-list@gnome.org http://mail.gnome.org/mailman/listinfo/networkmanager-list