[OLPC-AU] limits on ad-hoc connections

[Sridhar Dhanapalan]

On 8 February 2012 23:23, Martin Langhoff <martin.langhoff at gmail.com> wrote:
> On Wed, Feb 8, 2012 at 6:16 AM, Sridhar Dhanapalan
> <sridhar at laptop.org.au> wrote:
>> Ad-hoc connections only scale to a limited number of participants
>> before problems begin to occur.
>
> The technically correct answer is "it depends". And it is true, it
> depends on a ton of factors.
>
> As a rule of thumb, I've seen it work for groups of 5~6 units,
> physically close and without interference sources or reflective
> materials. I would not aim higher than that -- 5~6 units in a channel.
> You have 3 channels, so 3 groups of 5~6 units.

Great, that's what I was thinking.


> To clarify: keep any other laptops and cordless phones in the vicinity
> _off_, to allow these 18 users to work. In practice, it won't work in
> a school, but if you invite a few schoolmates home after school, or in
> the park, you're fine.
>
> No warranties expressed or implied. There's a long laundry list of
> things that can interfere, and make things not fine.
>
> For example, professional TV cameras from that friendly news crew
> transmit in the 2.4GHz band. That battery pack feeds a powerful
> antenna to get the signal back to the van that has the uplink, and it
> paves over consumer-grade wifi.
>
> So don't count in wifi (of any kind!) to work for a demo or
> show-and-tell when you get TV coverage at a school :-)

Interesting - definitely worth knowing!


>> Can we impose a hard limit on the number of clients to prevent too
>> many XOs connecting to a single ad-hoc session?
>
> As James says... unfortunately no.

This is possible on many wireless access points. Why isn't it possible
on the XO's ad-hoc?

Is it because WAPs do it by limiting DHCP leases, whereas ad-hoc uses
link-local?



Sridhar Dhanapalan
Engineering Manager
One Laptop per Child Australia