Re: [Autoconf] aspects of multi-hop wireless communication

Hello Breno,

Breno Jacinto wrote:
> - Should Mult-hop communications happen at the IP layer, really? I
> think that this decision was taken just because 802.11 b/g standard
> become popular and could not do multi-hop at layer 2. So, everyone
> thought, let's do it at layer 3, because it is possible to emulate
> multi-hop then.
>   

I think this is not an accurate reflection of the evolution of thought
on the subject.  At least for me, it was clear that one could easily
make a routing solution by revising RIP to get rid of poison reverse
and other hacks, so that we could have just the next-hop routing
as needed.  This was a very long time before 802.11.

Your word "should" is loaded.  IP is, I think, great at stitching together
links into a network.  They don't even have to be the same physical
media.  That's a major plus compared to layer 2 solutions.  Plus,
the same layer 3 solution works for a lot of different wireless physical
media.  That's better than blasting away with different solutions for
each different medium.

I just don't see what's wrong with it.

> - If multi-hopping is done at layer 2, isn't that a good thing? I
> mean, you can deal with problems specific to the link layer (including
> the aforementioned hidden node problem, or whatever
> next-popular-link-layer for multi-hop become available in the future)
> and make IP more neutral. I think that would conserve the initial aim
> of IP, which is simply to glue heterogeneous networks, not fixing a
> particular link-layer problem as it is being done with 802.11 b/g.
>   

There is no free lunch.  You are going to solve those problems at layer 3,
or you are going to solve them at layer 2.  And, even if the latter, you may
still have to worry about it at layer 3 unless you impose some very strong
regularity conditions (I'm still puzzling over truckloads of repeaters).

> - Now, if we could assume that multi-hop is done at layer 2; to layer
> 3 (such as IP), a broadcast should reach (be flooded to) everyone in
> the network. Now, IP sees the network as a single broadcast domain and
> issues in the "real" network should be dealt there. We may then shift
> to the problem of connecting multiple ad hoc networks at the IP layer,
> doing inter-domain routing etc.

There's that "should" again.  In fact, your very example of broadcast
disproves your point: what if the best broadcast used multiple media?

Regards,
Charlie P.

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