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 ? -- GPG ID: 0xD21DB2DB As you read this post global entropy rises. Have Fun ;-) Nick -- 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
