[Olsr-users] Using multiple radio cards

[Juliusz Chroboczek]

> If you are using separate radio cards and separate channels would you just
> manually structure your "hybrid" network or is there any other intelligent
> options?

There are two separate issues here.

One is that of selecting the right radio to use when you have multiple
radios available.  The issue is non trivial, as the following well-known
example shows:


    A-------B=======S

The link between A and B is at 2.4GHz, while B and S are neighbours
twice: once at 2.4 and once at 5GHz.  In order to avoid interference,
B must choose the 5Gz link for going to S.  If B chooses the 2.4GHz
link, then in current routing protocols there's nothing A can do to
convince it to go through the 5GHz link.

This issue is known as the non-isotonicity of metrics including
a notion of route diversity.  It is an area of open research, and you
may want to search the archives for mentions of the MIC metric, which
is one promising approach.

The other issue, as you justly note, is that of automatically choosing
frequencies when you have tunable radios.  The approach chosen will
very much depend on whether your radios take seconds to retune (in
which case you will want to statically optimise your network), or
whether they can be retuned very quickly, with time constants on the
order of one packet time, in which case you will want to intelligently
hop between frequencies.  The latter approach needs some form of
link-layer support, and is present in the 802.11s drafts (but not, as
far as I know, in the extant implementations).

All of this is very interesting stuff, but there are no ready-made
answers yet.  You might want to research this on your own, and report
on this list.

Regards,

                                        Juliusz Chroboczek