[Olsr-dev] OLSR on OLPC?

[Henning Rogge]

On Thu, Jun 5, 2008 at 6:12 PM, C. Scott Ananian <(spam-protected)> wrote:
> On Thu, Jun 5, 2008 at 10:42 AM, Aaron Kaplan <(spam-protected)> wrote:
> There are a number of possible solutions:
>  a) use all 3 non-overlapping 802.11bg channels (and somehow bridge
> between them)
This is done in Freifunk nets by connecting multiple WLAN routers with
an ethernet bridge.
We have plans for some radio channel aware routing for the future.

>  b) detect the dense scenario and dial down the tx power to reduce
> interference (at the cost of introducing multi-hop paths)
Dangerous because you might loose the link to some far away nodes. But
could be interesting to experiment with.

>  c) deploy some of the windowed media access protocols so ensure that
> access to the airwaves remains "fair" even as available bandwidth
> decreases
Difficult because of the not completely overlapping wlan zones of the
different routers.

>  d) fall back to fancy APs and centralized media access coordination.
> This stuff is in the 802.11 standards, but is not widely implemented.

As soon as we have a firmware that has Adhoc-Mode, Station-Mode and
AP-Mode we could do something like this. Detect too large
neighborhoods and force some nodes to go back to station mode, use the
rest to keep the OLSR net going. Difficult to do without multiple
channels to do this.

> tc?  could you expand that acronym for me?
TC = Topology Control (Message)
one of the four OLSR message types.

> Hmm.  I think our front-end and antennas are tuned for b/g, but the
> chipset it technically capable of a.  And there are 12-24 extra
> channels in a.  That may be worth looking into.  If we can get
> (conservatively) 25 users per channel using the standard 802.11 media
> access mechanisms, we could reasonably scale up to 700 users within
> radio "sight" of each other.  That sounds very attractive for dense
> schools.
If you do a multichannel-network, you need some nodes with at least two radios.

>> There is no other magic extension to the MAC afaik. Except some hacks to
>> keep it from splitting into different BSSID cells .
>
> Could you elaborate?
Many older WLAN-drivers had a bug that splitted large Adhoc-Networks.
I heared it was fixed in recent madwifi drivers and the new mac80211
driver package.

Henning

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