Network association algorithm

Jim Gettys jg at
Wed May 2 08:01:05 EDT 2007

On Wed, 2007-05-02 at 07:27 -0400, Walter Bender wrote:
> Wad,
> Thanks for writing this up. A few additional comments:
> (1) We need to characterize the amount of time necessary at each step
> and--at some point--tune the algorithms. For example, we probably
> don't want to wait 30 seconds for each attempt at DHCP.
> (2) We need to expose the status at all steps in the UI. We also
> probably want to enable the child to jump into the flow at different
> points from the UI, such as going directly to search for AP or forcing
> back to the search for a school server.
> (3) We need to determine the most efficient way to know if the state
> of the mesh has changed such that we should reenter the process. E.g.,
> what if you move away from the school server and you had been an MPP.
> Now you have to look for an MPP... There are many anomalous cases we
> need to consider.
> (4) It was proposed that we dedicate one of the LEDs to indicate a AP
> connection and the other to indicate an MPP connection.

We talked to Javier last night about the change in use of the LED's; he
was on the call and is now aware of our discussion.
> One thing we didn't discuss at all and is probably something we don't
> do for the time being is some sort of gain control. If we have a
> crowded classroom, I assume it would be better to turn down the volume
> on the radios so that everyone is not shouting, but just quietly
> talking to their neighbors. Maybe we want to add an outer loop to the
> whole thing where you start off whispering and gradually crank up the
> volume until you have a connect?

Startup time is an issue: if you whisper, you are less likely to get
associated. Startup doesn't happen that often; rather, I suspect we
might be better off by shouting, and then crank gain down in use.
                                 - Jim

> -walter
> On 5/1/07, John Watlington <wad at> wrote:
> >
> > Dan,
> >    I'm pretty sure that the attached flowchart documents the network
> > association algorithm developed in today's meeting.
> >
> > There are four end conditions, in rough order of desirability:
> > 1. The XO finds an established MPP (w. DHCP), and uses it for
> > internet access.
> > 2. The XO finds an AP, and becomes an ad-hoc MPP (no DHCP)
> > 3. The XO finds an ad-hoc MPP (no DHCP), and uses it for internet access
> > 4. The XO finds no AP nor MPP, and becomes a mesh node on channel 1
> > w. no internet access
> >
> > It has already been pointed out that for optimum performance, we will
> > eventually want to
> > randomly prefer end condition 3 over condition 2.
> >
> > Cheers,
> > wad
> >
> >
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> >
> >
> >
Jim Gettys
One Laptop Per Child

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