mechanisms tied to mesh: "under a tree" collab

[Benjamin M. Schwartz]

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John Gilmore wrote:
| [I posted bug #8524 re lease activation not working on AP's.]
|
| Another mechanism that only works on Mesh is sharing "under a tree".
|
| It's perfectly feasible for four or five kids with laptops, all
| sitting under a tree, to share over ad-hoc 802.11 mode.  They don't
| need a mesh that forwards packets; they can all hear each other on the
| radio just fine.

I'm not quite so certain.  I wouldn't venture to predict how TCP behaves
over a pure ad-hoc 802.11b network in the face of congestion, signal
nulls, etc.  I think an experiment is in order...

| OLPC's collaboration infrastructure doesn't support this -- or if some
| underlying layer does, there's no UI for it.  There's no way for the
| user to tell the laptop, "Talk to other nearby laptops -- without the
| mesh, without an access point".

I think there is, somewhere in the command line, a way to set TTL=0 or
similar, but that's certainly far from a nice GUI toggle.

| Future hardware might well want to discard the complicated and
| power-hungry mesh option, since we really aren't using it anyway,
| except for lease activation and this "under a tree" scenario.  That
| would give us lots more choices on future WiFi hardware.

It's a little more complex than that.  My sense is that many OLPC
developers would ideally like a relatively thin, generic 802.11 chip and a
relatively generic, low-power processor to go with it, so that the main
CPU can shut down, and critical network services can run on the
coprocessor.  The best architecture I can imagine is to run the Cerebro
mesh routing and presence algorithms on that coprocessor.  Cerebro's
performance in tests on XO's has been amazing to me, so far.

|  If we fix
| collab to work in ad-hoc mode under a tree, and when two or more
| machines are plugged-together via Ethernet without a server,

The wired-ethernet case is already working, and has been for a year or
more.  Drop Sugar onto two Thinkpads connected to the same subnet, and
they will instantly find each other over Avahi, etc.  If it's a wireless
network, or if you have XOs with ethernet dongles, they'll also see any
XO's that are also connected to that AP.  (Actually, Sugar will also find
any nearby Macs running Avahi, but doesn't quite know what to do with them.)

| then not
| only will our future products have that choice, but also, our collab
| stuff will be MUCH easier to drop into ordinary Linux distros and
| applications.

"Our collab stuff" is essentially Telepathy, which is a freedesktop.org
project that originated separately from OLPC.  The Telepathy gtk chat
client Empathy may soon be Gnome's default IM client.  Sugar is already
available as a package for Fedora, Debian, and Ubuntu, with working collab
out of the box over the internet, ethernet, or wireless AP.  I don't know
what happens if you configure Network Manager for ad-hoc mode before
launching Sugar.

Also, open80211s is now in the mainline linux kernel (as of 2.6.26). This
is a pure-software implementation that will work on a wide variety of
existing hardware, and should interoperate cleanly with the XO mesh.  In
short, I'm not convinced that the mesh network approach is a real
liability for Sugar on non-XO hardware.

- --Ben
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