[OLPC Networking] Path discovery sanity

[Aaron Kaplan]

I see OLSR as a addition to the great 802.11s implementation of the XO.
IN general, layer 3 protocols have the added benefit of being  
device / wlan chip independant.
Of course that also has some drawbacks.

We are now thinking in OLSR.org to feed up layer 2 infos as "hints"  
to layer 3 and the metric calculations.

But in general, I agree with Javier... it really all depends on what  
you want. IMHO the best is to make two layers of networks:
one IGP and one EGP :))) for example: olsr inside and some other  
proto on the exterior. Or AODV inside the classroom and OLSR between  
schools.
That will greatly enhance scalability.

Anybody wants to help code a prefix trie for OLSR.org so that we can  
think about automatic prefix aggregation?

best,
a.


On May 13, 2008, at 9:12 PM, Javier Cardona wrote:

> Scott,
>
> On Tue, May 13, 2008 at 10:23 AM, C. Scott Ananian  
> <cscott at cscott.net> wrote:
>>  It may also be worth comparing to a pure proactive approach
>>  such as OLSR, which is also permitted under 802.11s and may scale
>>  further than HWMP.
>
> The draft defines an "extensibility framework" for path selection
> protocols, which allows the definition of vendor proprietary
> protocols.  But the only path selection protocol proposed for
> standarization is HWMP.
> OLSR was included in the past as an optional alternative to the
> mandatory HWMP, but it was removed last year.
> The group concluded that there were no usage scenarios in which OLSR
> would provide clear benefits over (the proactive part of) HWMP.
they might change their minds when they see how flexible the upcoming  
olsr v2 rfc is going to be.
:))

>
>> In contrast, the author of the HWMP protocol only expects it to  
>> scale to 50 nodes (see attached).
>
> The original HWMP specification (
> https://mentor.ieee.org/802.11/file/06/11-06-1778-01-000s-hwmp- 
> specification.doc
> ) does not specify a limit in the number of nodes.  Bahr takes the 32
> node
> limit from the 11s PAR
> (http://standards.ieee.org/board/nes/projects/802-11s.pdf) which is
> actually
> a design guideline and not a theoretical limit.  In fact, that limit
> probably comes from the medium
> access mechanism and not from the path selection protocol.
has anybody tried it - nope ! NOT in simulators please - but in real  
real big networks?
where the shared medium is not the limit because there are houses in  
between, distances are large, etc?

>
>>  A reactive approach is much more sensitive to the loss of a single
>>  packet during route-finding;
>
> That's just because the proactive approach transmits more redundant
> information.
actually it can be set to any speed (at least in olsr)

> The reactive approach can be made as "insensitive" by increasing  
> redundancy.
> The main trade-off between proactive and reactive methods is  
> latency vs.
> management overhead.
>
>>  Hybrid approaches (such as the one specified in
>>  802.11s but not actually implemented by OLPC) may combine the
>>  strengths of both.
>
> Yes.  Or the weaknesses.  It all depends how you tune it ;)
>

> Cheers,
>
> Javier
>
> -- 
> Javier Cardona
> cozybit Inc.
> _______________________________________________
> Networking mailing list
> Networking at lists.laptop.org
> http://lists.laptop.org/listinfo/networking
>

---
there's no place like 127.0.0.1