[OLPC Networking] Mesh multicast support

[Trent Lloyd]

(also, we would want to make sure the network card is filtering out
multicast traffic the host doesn't want so the CPU doesn't need to
process data it doesn't need

This seems pretty standard on networking devices these days, just
thought I'd mention it because it "really matters" in the OLPC world :)

Trent

On Tue, Jan 23, 2007 at 12:24:17AM +0900, Trent Lloyd wrote:
> Hi Krishna,
> 
> On Mon, Jan 22, 2007 at 07:01:52AM -0800, Krishna Sankar (ksankar) wrote:
> > Good question. 
> > 
> > >From my limited knowledge, the mesh is more or less transparent - i.e.
> > the 802.11s routing protocols use mesh algorithms; but the routed
> > protocols, over the 802.11s, could be anything. 
> >
> > But this raises a good point - may be we want to restrict multicast by
> > partitioning the network to small domains as well as keep a lid on the
> > number of multicast messages. There is a finite possibility that
> > multicast could drain the resources if not contained properly. OTOH,
> > because of the underlying mesh topology, multicast might not be as
> > costly as it seems.
> 
> I actually not so much want to "restrict the domain of multicast" but
> make sure that multicast is only sent over the mesh where it is needed,
> there are existing protocols in place for sets of switches etc only to
> forward multicast down the ports they are asked for on.
> 
> > Trent, I assume you are exploring Avahi for OLPC. I did look into it and
> > looks like it should work without any problems; except the partitioning
> > aspect. (An waiting for my modules to actually test this) If the whole
> > network (or some big superset in a domain) is a giant mesh, while it is
> > good in terms of visibility of services, end points et al, it could
> > cause lots of routing overhead basically draining the power.
> 
> Avahi is part of it, but if every machine is running Avahi anyway then
> it's going to effectively be "broadcasted" anyway
> 
> I know Lennart Poeterring (the other major author of avahi) is looking
> into some modifications to the mDNS caching that exploits mesh
> specifics, i.e. if the network is too large to support mDNS over the
> entire mesh, only speak to those within a few hops of you on the mesh,
> etc, but this is a totally separate work...
> 
> I am actually thinking more in terms of wide-spread
> multicast use, if an application uses multicast, we don't want the whole
> mesh receiving its packets but only enough to get the message from end
> to end to each of the machines actually subscribing to that multicast
> IP, I think this would be quite usefull for multi-user applications.
> 
> Cheers,
> Trent
> 
> > 
> > Cheers
> > <k/>
> > 
> >  
> > 
> > > -----Original Message-----
> > > From: networking-bounces at laptop.org 
> > > [mailto:networking-bounces at laptop.org] On Behalf Of Trent Lloyd
> > > Sent: Monday, January 22, 2007 6:21 AM
> > > To: networking at laptop.org
> > > Subject: [OLPC Networking] Mesh multicast support
> > > 
> > > Howdy all,
> > > 
> > > I'd like to know what support the mesh wireless is going to 
> > > have for multicast, i.e. will it broadcast it, or will it 
> > > currently forward packets only to the right part of the mesh 
> > > using something similar to IGMP?
> > > 
> > > Cheers,
> > > Trent
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> > >