[Server-devel] Testing 200 XO's in two weeks time for Nepal's pilot

[Michail Bletsas]

server-devel-bounces at lists.laptop.org wrote on 03/03/2008 02:38:00 AM:


> Questions: 
> 
> 
> How many XO's can a single active antenna support? We only have two
> active antennas at the moment. 
The answer is always traffic depedent. Given the current status of the 
collaboration software on the XO and assuming that the school server's 
ejabberd works correctly (shutting off multicast traffic on the XOs), you 
should be able to put 30-40 laptops per "active antenna". 
You should always keep in mind that in "dense" deployments (classrooms), 
mesh is sub-optimal compared to standard access points (assuming that 
every XO can talk to the AP). That is because, you have all the path 
discovery control traffic overhead in mesh mode that you don't have in 
infrastructure mode.


> 
> Should we buy extra regular access points to back up our active
> antennas? Again, would love to know if particular AP is preferred and
> how many XO's one can support. I read in the devel list today that the
> WRT54G is not preferred. 
Yes, if you can afford them, APs will give you much better performance in 
schools. The issue with the stock firmware in the WRT54Gs is that it tries 
to establish WDS peer links with every other WDS capable node in the 
vicinity. So if you have a few of them in a school, you can end up with 
multiple WDS tunnels between them. Add to that the multicast traffic from 
the XOs and you end up with no spectrum at all, due to multicast/broadcast 
retransmissions.
The solution to that problem is to be able to turn off WDS. The stock 
Linksys firmware doesn't do it, however OpenWRT and its variants can do 
it.
So the answer to whether you should/can use WRT54Gx APs is "only if you 
can upgrade them to an OpenWRT variant".

We are working on HostAP support for the active antennas, so that for 
small schools, the school server is all that you need. In the meantime, 
APs with controllable WDS behavior are recommended.


> 
> We will have two pilot schools. One w/ 110 students and the other w/ 50
> students.
I would use 3 APs on the first and two on the second. In the future 2 and 
1 will suffice, however as of now we are wasting a lot of airtime in all 
layers of the network stack.


M.


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