On Wed, Sep 15, 2010 at 8:48 AM, Nick Kossifidis <mickflemm@xxxxxxxxx> wrote: > 2010/9/14 Jonathan Guerin <jonathan@xxxxxxxxxxxx>: >> Hi all, >> >> I have some behaviour I'm observing with some Atheros cards we use that >> doesn't seem to match what the initvals of ath5k are set up to. These are >> the cards I used: >> http://www.mini-box.com/s.nl/it.A/id.387/.f >> >> I have run a saturated iPerf flow on a conducted testbed with both stations >> being inside RF-shielding boxes. They are set to 802.11a mode, on channel 1. >> I then parse the trace, looking for ACK-DATA pairs, and calculating the time >> difference between them. From this, I remove the TX_TIME of the DATA frame, >> as well as a DIFS: >> >> ACK_TIMESTAMP + DIFS + CONTENTION_TIME + DATA_TX_TIME = DATA_TIMESTAMP >> >> which will leave me with the CONTENTION_TIME. Dividing this time by a >> SLOT_TIME will give me the slot which was chosen by the hardware. >> >> >> According to the driver, in ath5k.h: >> >> #define AR5K_TUNE_CWMIN 15 >> >> CWMIN is initialised to 15. >> >> The actual distribution of contention slots I'm observing resembles this: >> >> Slot Number,Count >> 0,1315 >> 1,1302 >> 2,1249 >> 3,1291 >> 4,1347 >> 5,1219 >> 6,1249 >> 7,0 >> 8,0 >> 9,0 >> <truncated> >> >> as well as 1360 frames which came in with a negative CONTENTION_TIME. >> >> Ignoring the fact that some frames are coming up with a negative >> CONTENTION_TIME (which potentially points to another problem), what is being >> observed here is that CW_MIN appears to start at 7, rather than the 15 which >> it should be. >> >> I'm just wondering if anyone would have any idea why this is occurring? >> >> Thanks, >> >> -- >> Jonathan Guerin >> > > What is your time refference ? Are the 2 stations synced to a point > you can have such great accuracy ? I'm capturing using a third-party station. I've had to use a Madwifi station, as ath5k throws a lot of spurious timestamps up, which make calculating this very, very difficult. > > > -- > GPG ID: 0xD21DB2DB > As you read this post global entropy rises. Have Fun ;-) > Nick > Thanks, -- Jonathan Guerin -- 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
