Re: [Manet-dt] OLSRv2 NHDP comments

["Samita Chakrabarti" <[e-mail]>]

Hi Christopher,

On 6/8/06, Dearlove, Christopher (UK) <[e-mail]> wrote:
>
> > I am not quite
> > sure how it gets neighbor info from 2hops away since HELLO is
> > only for single hop.
>
> In order that node A and node B can establish that there is a
> symmetric link between them (and many protocols - including
> of course OLSR - need this) node A must advertise B's address
> in its HELLO message (and vice versa). Now node C, which also
> hears node A's HELLO message, hears node B's address in that
> message, and hence knows that node B is a two hop neighbour.
> So you get two hop information "for free" as part of the
> establishment of symmetric links. Of course there are some
> additional complexities, in particular associated with multiple
> interface nodes where things aren't quite free any more. But
> an important thing to note is that although multiple interfaces
> complicate matters, if you don't have any (in your network) you
> don't pay that. (Note that even if you are single interface
> yourself you must be able to cope with multiple interface neighbours
> or you will be noncompliant as you can break things if you just
> assume neighbours are not. We've seen this in OLSRv1.) And we have
> done quite a bit of work on reducing the cost when you do have
> them. (OLSRv1 had MID messages, OLSRv2 first had MA messages,
> then these were incorporated into TC messages, then we got rid
> of them altogether with a bit of extra information in HELLO
> messages in NHDP.) And multiple interfaces are important in
> that if you have them, they need to work.
>

Thanks for explaining.

> > Also, the protocol seems a bit
> > complex with symmetric, assymtetric times and interfaces - perhaps
> > it's because it needs to support OLSRv2.
> > I wonder whether it can be simplified to deal with only MANET
> interfaces?
>
> I'm not sure what you mean here. Supporting symmetric links is
> important to many protocols, and that's most of the complexity.
> (Obviously asymmetric links occur in a dynamic network as a
> step towards establishing the symmetry of a link, as well as
> some links actually being asymmetric at right now.)
>

I understand that supporting symmetric links is improtant.
I think I am confused with different terms (1-hop neighborhood, symmetric
1-hop and 2-hop neighborhood)  and trying to assemble
them together to draw the complete picture. I am also new to
OLSR.
> But the basic thing is, it may look complicated, but that's because it's
> (hopefully - if you think otherwise, let us know) fully specified in all
> details (or at least the next draft coming before the next cutoff will
> be, I hope). Getting that right, and allowing for all the ways people
> might
> do something unexpected that you need to handle, is where the pages come
> from.
>

Will wait for the new version.

> > I assume, 2 hop restriction is because of OLSRv2 support as the nodes
> > are assumed to be multi-interfaced. Without that, it might be simple
> to
> > go for only link-local discovery of  MANET nodes.
>
> As I note above, once you want symmetry, you get two hop information.
> But two hop information is important - it allows you to establish
> a means of optimised flooding, using MPRs by original design (in OLSR)
> but also other options. And all three MANET protocols that may use
> NHDP (OLSRv2, DYMO and SMF) want (as a future option in DYMO)
> optimised flooding. (Because they may not all use MPRs, these are
> not currently specified in NHDP, but left to protocols building on
> NHDP.)
>

Ok. Understood.

Thanks again for the helpful explanation.
-Samita

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