On Thu, Jan 10, 2008 at 12:50:58AM +0100, Johannes Berg wrote: > What's the meaning of these defines? > > #define CHAN_UTIL_HDR_LONG (202 * CHAN_UTIL_PER_USEC) > #define CHAN_UTIL_HDR_SHORT (40 * CHAN_UTIL_PER_USEC) > > I can't figure out what the values 202 and 40 are. Hmm.. I thought I had filtered out the channel use estimation code from the original release since I did not see much use for this and the values were not exactly valid in many cases.. ;-). This code is almost five years old and maybe not so surprisingly, I don't remember the exact details anymore.. Since these are use as "hdrtime", I would assume they were derived using following calculation: CHAN_UTIL_HDR_LONG: assume 802.11b with long preamble: aSIFSTime (10 usec) + aPreambleLength (144 usec) + aPLCPHeaderLength (48 usec) = 202 usec CHAN_UTIL_HDR_SHORT: assume OFDM: aSIFSTime (+ signal ext in case of 802.11g; 16 usec) + preamble (16 usec) + signal (4 usec) = 36 usec; add one symbol time (4 usec) for some reason (or a sign of someone not knowing how to add small numbers together.. ;-), I don't remember anymore and cannot figure out this without wasting way too much time..) > And probably related, what does it mean for a bitrate to be an "ERP > rate"? Does that just mean it's an OFDM bitrate? That would be any rate using Extended Rate PHY (ERP; 802.11 Clause 19). This is not necessarily OFDM (it could also be using PBCC modulation). In practice, I would expect the kernel side implementation to use this in anything PHY related as ERP-OFDM (i.e., it may not support optional PBCC rates). The association and beacon/probe processing may be more generic to any ERP rate. I don't think ERP-PBCC is very commonly used, so this may be more on the theoretical side.. -- Jouni Malinen PGP id EFC895FA - 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
