[Babel-users] Roaming at layer 3

[Mitar]

Hi!

Of course it can be solved with multiple radios, but that costs more.
Also, even having two radios (2 and 5 GHz) for example is in fact not
enough this days because you want AP to be on two bands as well, again
on separate 5 GHz channels to not interfere with each other. Many
clients can now use 5 GHz and to offload the 2.4 GHz spectrum we
should be using that fact.

I am trying to explain that we have a problem that we have competing needs:

- for end-users we have a need that they should roam in houses/spaces
and not have interference between APs, so the best would be to have
each AP on a separate channels to other devices, using wired
connections, ideally if there they are on the same switch, they should
just connect directly, otherwise over the VPN tunnel via servers
- for mesh operation you would need nodes to be on the same channel so
that they can communicate to each other, so those who do not have
Internet uplink, can still connect to the rest of the network

Now, the issue is that these two things are conflicting. But I think
we should try to find a solution.

So one option I see is that we have all nodes using different
channels, to maximize the use of the spectrum, on both 2.4 and 5 GHz.
They create both AP and ad-hoc networks, but they do not care that
ad-hoc links are not established because they have an uplink. In the
case that a node does not have an uplink, then it scans the
surroundings and if it finds our mesh ad-hoc network, it chooses the
same channel and connects with ad-hoc network to that one AP. Now, the
question is to what if there are multiple nodes around, which channel
this uplink-less node should pick and when it should switch it to
another channel. (The same problem in fact have the APs with uplinks
as well, but they could at least communicate with each other and
decide which channel one should pick.) One more problem is what
happens if multiple nodes lose uplinks. Then it could happen that half
of them pick one channel and another the other channel and then you
have a split.

The other option I see is to have a centralized node planing system.
When a user registers a new node they tell if the node will have an
uplink or not. If it will have, then the system allocates to the node
a channel which interferes the least.  If it will not have, then user
can pick which closest neighboor the node should connect to and
central system selects the channel so that the link is possible. This
second approach has a benefit that also backbone connections could be
done through the same system.


Mitar

On Sun, Aug 9, 2015 at 8:25 PM, Juliusz Chroboczek
<jch at pps.univ-paris-diderot.fr> wrote:
>> Your understanding is correct. And, as you said, I also think that the
>> issue can only be solved by having multiple radios on a node.
>
> I see now.  And agreed about multiple radios.
>
> -- Juliusz
>
>
>
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