[Freedombox-discuss] mesh network [was: FreedomBox Testing 2012.0617 Image Published]
dave.taht at gmail.com
Mon Jun 18 14:16:34 UTC 2012
On Mon, Jun 18, 2012 at 2:19 AM, Yan Hetges <yan at exalot.com> wrote:
> first of all, i'd like to quickly introduce myself. My name is Yan, i
> like freedom and have been using Debian as my main desktop OS since woody
> and been playing with it on servers since the same time. I've also been
> actively deploying a wifi adhoc mesh network with OpenWrt and derivates
> since 2006 (it has ~15 nodes and covers an area of maybe 15 km^2).
> And i've been reading this list since late January...
I've also been working on mesh networks for a long time, with things
like OLPC, etc. I used google earth in a rather innovative way on my
last test deployment (since taken down) - zoom in below San Juan Del
using gps to locate places and height above ground to make estimates
of beam paths possible.
> On Sun, Jun 17, 2012 at 10:03:49PM -0400, Rick C. Hodgin wrote:
>> Hmmm... So, the Freedombox needs to use external infrastructure such as an ethernet or WiFi router?
> yes, freedombox wants to use the internet
>> I was thinking WiFi would connect all neighbors together on a WiFi mesh able to simultaneously transmit / receive to other Freedomboxes directly without a hub / router. Sort of an ad hoc Internet.
> it could theoretically connect all neighbours together and NOT
> simultaneously tx/rx because the wifi radio can only either or, not both
> at the same time. And that's the main issue, usable bandwidth gets less
> at each hop.
>> Is such a thing possible with WiFi?
> to a certain degree, and it might never be able to replace an
> infrastructure! Also, to connect neighbours without internet, they want
> to be pretty close to each other... like one in every appartment! That
> will then make so much noise that there might be no communication
> possible over more than 2-4 hops.
Two of the problems you mention here have recently been better solved
than in the past.
The first one semi-solved but could use more people to try the fixes
for is the "dense mesh problem", which is basically what you refer to
above. OLPC networks used to basically melt down over 1 hop, much less
due to that.
Babel implements "diversity routing" - what that is is that it tries
to choose a non-competing wifi channel for forwarding packets from one
box to another. this does of course mean you need two radios, on
different channels, for it to work. This holds great promise for
making mesh networks scale. Some info on that
The other one is that the codel work mentioned previously holds great
potential to help establish a congestion aware metric which could lead
to dynamic load balancing working semi-sanely across multiple paths.
We're not there yet tho, I'm not happy with any of the routing metrics
currently being used.
A useful abstraction for the dense mesh problem is the "four color
theorem" - which as a problem in topology is only solved in two
dimensions. Wireless is MUCH harder but it's obvious that more
than 4 are needed to scale well.
Also in terms of mesh networking conferences there are these wonderful
"battlemesh" sessions that occur periodically. They are like interop
used to be, only for wireless.
> Please don't understand me wrong, i
> LOVE the idea! Also, to make that work out of the box, without external
> antennas mounted on a roof, or the FBX mounted in a weatherproof box on
> top of a bamboo pole in a tall tree or something like that, is very
> unlikely. I suggest reading RFC 1925  espexially (5),(8) and (10).
> If you really want to integrate a self employing mesh function into
> FBX i'd recommend looking deeply into what R.O.B.I.N.  does.
Robin, catwoman, batman-adv, babel, etc are all interesting.
also 802.11s has small scale scaling properties. (32 nodes)
> Also, it would be very much appreciated and make group communication
> much easier if you (some of you) would consider reading and following
>  , especially 9. And/or RFC 1855 .
> Thank you everyone so much for all your work!
http://tools.ietf.org/html/rfc6126 Babel RFC
Recently some good work on securing babel, rip and related protocols was
announced on the babel lists...
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