high latency due to distant clients

[Petar Bogdanovic]

Hi,

for several years now, I've been running an ALIX-AP with a CM9 Atheros
5212 card.  The AP covers a whole house which has about 6 flats and the
average amount of active clients ranges from 10 to 15.

Recently I noticed high latency when pinging the AP itself which happens
when distant clients (who knows where around the house---could be inside
or outside) seem to cause "longs" (long on-chip tx retries) and/or
"xretries" (tx failed 'cuz too many retries).

The Rate, when talking to these distant clients, is usually below 11M
(sometimes as low as 1M) which is consistent with their low RSSI values
the AP is reporting.

With high latency I mean continuous bursts of 500-1000ms instead of
0.5ms so I wonder if this is normal.

The software is slightly out of date and athstats is not completely in
sync with the kernel i'm using (therefore its not reporting some values):

	# uname -a
	FreeBSD parrot.NGC004 8.1-RC2 FreeBSD 8.1-RC2 #2: Thu Aug 16 21:13:54 CEST 2012

	# athstats -i ath0
	athstats: ath0: Invalid argument
	athstats: ath0: Invalid argument
	3181606  data frames transmit
	45659    tx frames with an alternate rate
	568149   long on-chip tx retries
	19091    tx failed 'cuz too many retries
	0M       current transmit rate
	25       tx stopped 'cuz no xmit buffer
	20922    tx frames with no ack marked
	3039151  tx frames with short preamble
	362335   rx failed 'cuz of bad CRC
	1181     rx failed 'cuz of PHY err
	    315      OFDM restart
	    866      CCK restart
	2        TDMA slot timing updates
	-0/+0    TDMA slot adjust (usecs, smoothed)
	26135    TDMA tx failed 'cuz ACK required
	-74      rx noise floor
	3070927  tx frames through raw api
	6299685  fast frames received
	1328215  fast frames flushed from staging q
	20835    ANI decrease noise immunity
	6593     ANI increased spur immunity
	121582   ANI decrease spur immunity
	160      ANI decreased first step level
	2        cumulative OFDM phy error count
	2        RTS without CTS
	1360093  beacons received
	Antenna profile:

Any ideas on how to avoid that?  Of course I could buy better antennas
but it seems that, generally speaking, this shouldn't happen.

Thanks,

		Petar Bogdanovic