Salut/avahi/meshview issues

[Sjoerd Simons]

On Wed, Jan 30, 2008 at 09:27:06AM -0500, Michail Bletsas wrote:
> Sjoerd Simons <sjoerd at luon.net> wrote on 01/30/2008 06:45:48 AM:
> 
> > 
> > Well both avahi and salut are quite capable. I'm not sure why it hassuch 
> a bad
> > reputation with you. Probably because your only seeing it in a very very
> > exterme network and because there seems to be a lot of FUD about mdns 
> going
> > around. MDNS definately isn't an optimal protocol for a mesh, but most 
> of the
> > issues in big rollouts are actually caused by the wireless firmware not 
> being
> > good enough to do actual multicast routing.
> > 
> > 
> Have you given any thought to the overhead (just in traffic - let's leave 
> memory out of the question right now) required to do what you call "actual 
> multicast routing" in the firmware? 

I did some research into mesh routing protocols before starting the salut muc
work. From the research papers i've seen, proper multicast routing seems
entirely viable. Traffic and memory overhead depend on the exact tradeoffs you
make and the protocols used. So i see no reason why this can't be done on
olpc's mesh network.

> We all understand how difficult is what we are trying to achieve. The
> firmware hasn't changed much since you started working on this project. So,
> let's drop the finger pointing and try to come up with realistic and
> implementable solutions.

As said, from my point of view, proper multicast routing is an entirely
realistic thing.

Note that nobody is claiming MDNS is particularely suited for mesh networks.
Because it's not. The reason why we used it, is that it was already used on the
olpc mesh even before salut came along and we just didn't have the resources to
do both a new presence protocol and a MUC protoocl. Also note that our muc
protocol uses multicast, the rationale for that was outlined when we originally
proposed telepathy.

Now the exact rationale doesn't matter much. The point is that we've always
been quite clear about the fact that we're heavily using multicast. And nobody
ever claimed that this was a bad/unrelistic thing (at some points there were
even interns at OLPC experimenting with reliable multicast on the mesh, so it
seems that even inside olpc multicast was regarded as a good thing). So we
always (maybe naievely) assume the mesh did/could do proper multicasting.

When we discovered the mesh did not do proper multicasting, we did tell various
people that this was going to be a bad thing. But apparently nobody ever seemed
to think this was a big deal untill recently.


So if you now want to say that multicast is not a viable solution and will
never be, because for some reason it's unrealistic with the current mesh
hardware. Please make this very very clear. Then at least we can throw more
then a year of development effort out of the window and redo things from
scratch.

> Yianni does testing, he doesn't care where specifically the problem is,
> all that he wants is to see something that works.

Well for good testing he should have least have an idea where the problems are
and what the issues involved are :) The scalability problem lies in the current
combination of the mesh implemenation and the mdns traffic, how exactly we're
going to solve that is still up for discussion.

  Sjoerd
-- 
Each of us bears his own Hell.
		-- Publius Vergilius Maro (Virgil)