WDS problems observed in today's testing

[Ricardo Carrano]

(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 <javier at cozybit.com> 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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