[Freedombox-discuss] [HacDC:Byzantium] Re: Serval Mesh Extenders

haxwithaxe me at haxwithaxe.net
Sat Jul 13 06:59:53 UTC 2013

On 07/12/2013 10:02 AM, Eugen Leitl wrote:
> ----- Forwarded message from John Gilmore <gnu at toad.com> -----
> Date: Thu, 11 Jul 2013 17:13:15 -0700
> From: John Gilmore <gnu at toad.com>
> To: Paul Gardner-Stephen <paul at servalproject.org>
> Cc: freedombox-discuss <freedombox-discuss at lists.alioth.debian.org>
> Subject: Re: [Freedombox-discuss] Serval Mesh Extenders
>> The idea is that it uses the UHF packet radio to mesh over greater
>> distances than is possible with Wi-Fi, the trade-off being lower bandwidth.
> PPS:  "Mesh doesn't scale over radio." is the 5-word summary of my
> experience. Merely making mesh work over wired connections is still
> a hard research problem that nobody has great solutions for.
mesh over wired networks is kinda silly. mesh over wireless is far more
useful and has been around for more than 20 years, and has gotten heavy
improvements since wifi has become popular.

if you expect every single device to be a mesh node in the same
collision domain within range of each other of course it won't work :P
in a weird way mesh doesn't scale _down_. if you have a one room mesh
with a chatty protocol it's going to talk itself into the ground like
the OLPC implemetation of the pre802.11s protocol. if you use the mesh
like a normal network is used (outside of classrooms and conferences) it
will generally work fine. if you have it spread across a large city and
to outlying islands of that city then it still works fine.
(see the Athens mesh, and Freifunk)
if you have a mesh infrastructure and non-mesh distribution at endpoints
you can use different collision domains for the mesh and user networks.
wifi sucks when there is no 100% clear line of sight (as in not your
rooftop antenna), end of story. UHF works better than wifi given a
partially obstructed line of sight (keeping in mind that is unobstructed
for that particular chunk of spectrum not physical objects ... which for
2.4GHz those are the same :P).
with slightly clear line of sight UHF can go miles. if you set the
device in a window that is enough for it to get signal through from the
inside to anything in a ~90deg cone of the window. it obviously isn't
ideal, but it's cheap and UHF-based extenders could be as good as a
similar system using only wifi, for much fewer units, and require less
people to collude or less unattended units strewn across a rural area.

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