(last version was incomplete): Just to add that:
- The access point Javier mentions is the one I bought yesterday (Linksys WRT54G) - Most of this traffic is retransmission (3606): (wlan.fc.ds == 3 and wlan.sa[0-2] == 00:17:C4 and wlan.ta[4-5] == ce:6e) && (wlan.fc.retry == 1) - It is also interesting to detect other wds peers this AP identified (one is 00:0b:85:53:27:50 and got 1066 of these frames). ((wlan.fc.ds == 3 and wlan.sa[0-2] == 00:17:C4 and wlan.ta[4-5] == ce:6e)) && (wlan.ra == 00:0b:85:53:27:50) It seems that the linksys is expecting acks for this wds frames (which btw are mulcast frames). It is amazing. I believe we should compare this with the previous capture from the Netgear AP, just to confirm that this is (again) specific to WDS issues on the Linksys. -- RC On Sat, Mar 1, 2008 at 5:23 AM, Javier Cardona <[EMAIL PROTECTED]> wrote: > Michail, Chris, > > > This afternoon I captured some traffic while Chris was running tests > for Peru. The test setup consisted on ~25 laptops associated to a > WRT54 access point. When the laptops were on, associated and (not > sure about this) idle, we observed a high volume of wireless traffic. > The spectrum analyzer showed close to 50% duty cycle utilization of > the channel. > We also observed that a few xo's could not associate, and some seemed to > intermittently lose and recover association. > > Turning off the WRT54 (and therefore stopping all the infra traffic) > freed up most of the bandwidth on that channel. > > In my 50 second capture (taken before turning off the AP) we observe: > > Total traffic: 15081 frames (100%) > All WDS traffic (1): 6023 frames ( 40%) > WDS, xo is source addr (2): 4343 frames ( 29%) > (96% of the above xmitted at 1 Mbps (3) and 100% sent by a single AP(4)) > > Compare that with > > xo originated infra frames (5): 401 frames ( 3%) > (77% of the above xmitted at rates higher than 2 Mbps (6)) > > What does all this mean? > > 1. Multicast traffic gets replicated and retransmitted. > 2. The ratio of original frames to AP generated multicast > retransmissions is 1:11 > 3. Taking into account the data rates this means that for 1 airtime > unit used to transmit useful traffic, over 200 units are wasted > transmitting useless WDS traffic. > 4. All this is done by a single Cisco AP, MAC: 00:1e:7e:44:ce:6e > > Michail, is that one of OLPC APs? > Chris, we should see a big improvement if we can disable that > "feature" on the AP... or put it under water. > > I've posted my capture here: > > http://dev.laptop.org/~javier/captures/cisco-wds-traffic-around-xo-testbed.cap<http://dev.laptop.org/%7Ejavier/captures/cisco-wds-traffic-around-xo-testbed.cap> > in case someone wants to double check my analysis (Ricardo?). > > Cheers, > > Javier > > (1) wlan.fc.ds == 3 > (2) wlan.fc.ds == 3 and wlan.sa[0-2] == 00:17:C4 > (3) wlan.fc.ds == 3 and wlan.sa[0-2] == 00:17:C4 and radiotap.datarate == > 0x2 > (4) wlan.fc.ds == 3 and wlan.sa[0-2] == 00:17:C4 and wlan.ta[4-5] == ce:6e > (5) wlan.fc.ds == 1 and wlan.sa[0-2] == 00:17:C4 > (6) wlan.fc.ds == 1 and wlan.sa[0-2] == 00:17:C4 and radiotap.datarate > 4 > > -- > Javier Cardona > cozybit Inc. >
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