Was anyone able to get a test with a different AP? We were only able to associate something like 20 laptops on Fri. Do we believe it should be 30 or more?
Kim On 3/1/08, Javier Cardona <[EMAIL PROTECTED]> wrote: > Kim, Michail, > > The conclusion to all of this is that we should not use WRT54G in > deployments, regardless of whether mesh is used or not (in fact, if we > *only* use mesh we don't have this problem as the AP ignores mesh > multicast traffic now). The WRT54G will forward multicast traffic to > all other APs in the vicinity that it identifies as peers using flawed > criteria (Lazy-WDS). Since the xo's generate a lot of multicast > traffic, that creates a risk of triggering the multicast storms that > we saw at OLPC. > > Javier > > PS. If we have no choice but to use that AP, then we should re-image > the AP with a distribution that allows turning WDS off. In Tomato > (http://www.polarcloud.com/tomato) this can be achieved via Basic -> > Wireless Mode = 'Access Point' and NOT 'Access Point + WDS' > > > On 3/1/08, Javier Cardona <[EMAIL PROTECTED]> wrote: > > Ricardo, > > > > > > > - The access point Javier mentions is the one I bought yesterday > (Linksys > > > WRT54G) > > > > > > Agreed, yes: > > 35 00:1d:7e:44:ce:6e Broadcast Beacon frame,SSID: "linksys" > > > > > > > - 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) > > > > > > Agreed. > > > > > > > - 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) > > > > > > Yes. Note that none of the WDS peers are xo's, as was the case in the > past. > > > > > > > It seems that the linksys is expecting acks for this wds frames (which > btw are mulcast frames). It is amazing. > > > > > > Well, even if the final destination is a multicast address, those WDS > > frames are unicast, and therefore acknowledged. What's troubling is > > that the WDS links are not torn down when the link quality is so poor. > > But we all know that Lazy-WDS is a flawed protocol. > > > > > > > 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. > > > > > > I don't have access to that capture. Maybe David? > > > > Javier > > > > > > > > > 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 > > > > 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. > > > > > > > > > > > > > > > > > > -- > > Javier Cardona > > cozybit Inc. > > > > > -- > Javier Cardona > cozybit Inc. > -- Sent from Gmail for mobile | mobile.google.com _______________________________________________ Devel mailing list [email protected] http://lists.laptop.org/listinfo/devel
