Subject: [Ospf-wireless-design] any consensus?

From: "Henderson, Thomas R" <[email-masked]>
Date: Tue, 25 Oct 2005 22:45:53 -0700

All,
It has been a while since we had any list activity-- basically, since
last IETF meeting.  Acee would like me to report on the design team at
the next IETF meeting.

As we announced, we at Boeing have studied the Ogier and Chandra drafts
carefully (and also Smart Peering by Abhay Roy), implemented both
approaches, conducted a number of simulations, and published our code
and report at:
http://hipserver.mct.phantomworks.org/ietf/ospf/

You can read the report for the details, but the essence of our
conclusion was that the MDR draft (at least the core CDS mechanism)
seemed better suited to OSPF than Overlapping Relays because of the
bi-directional nature of adjacencies, and the potential to leverage the
CDS to also do topology reduction.  The Smart Peering topology reduction
approach did not appear to offer as clean of a solution.  Overall, we
got quite good results from our implementation of MDR, and think that it
is a viable and productive extension to OSPF.  Because of this, we at
Boeing technically favor the Ogier draft.

On July 12, Emmanuel Baccelli from INRIA posted two reports:  MPR/CDS
stability, and on achieving partial topology in MPR-based solution.
These reports haven't generated much discussion, and we haven't had a
chance to look carefully at the CDS stability claims.  The partial
topology solutions recommended were to construct an MPR-CDS or to just
form adjacencies between MPRs and selectors, but because these
MPR/selector relationships are not symmetric, I am guessing that it will
result in many more adjacencies than the CDS approach.

I would like to be able to report to the WG one of two things:
i) "we have consensus on a core approach forward and it is <insert
consensus here>", or
ii) "we do not have consensus for the following reasons: <insert reasons
here>"

So maybe I should start by asking whether there is consensus on moving
forward on an Overlapping Relays core or an MDR core?  We have suggested
moving forward with the MDR core approach for the reasons outlined in
detail in our tech report.  Are the previous proponents of Overlapping
Relays in agreement, or should we have some discussion on the claims in
our report?

Tom

_______________________________________________
Ospf-wireless-design mailing list
[email-masked]
https://www1.ietf.org/mailman/listinfo/ospf-wireless-design

---

From: Emmanuel Baccelli <[email-masked]>
Date: Wed, 26 Oct 2005 12:48:17 +0200

>result in many more adjacencies than the CDS approach.

Hi all,

the trade-off in terms of partial topology is the following: if a CDS 
(i.e. MDR or MPR-CDS)
backbone is used to perform reduction in topology advertizement, the 
routes in the network
will suffer from a stretch factor that leads to a substantial amount of 
unnecessary retransmissions
(and hence overhead) in an ad hoc environment. We may decide to bear 
with this, but we can
also consider another approach based on MPRs that does not lead to any 
route stretch, but may
yield more ajacencies (if indeed routing has to happen over ajacencies). 
I think there is a
fine trade off that remains to be evaluated between taking a CDS or MPR 
as backbone to
compute the reduction in topology advertizement.

On the other hand, i am convinced that MPR flooding presents better 
properties than CDS
flooding, in an ad hoc environment (see the stability report we have issued
http://www.inria.fr/rrrt/rr-5609.html and experience gathered with MPRs 
in MANETs
over the years).

Therefore taking an approach based on MPR may be the best path, as it 
enables to
decouple the flooding optimization and the topology reduction schemes. 
This way,
the better properties of MPR flooding can be used, while topology 
reduction can
still be either based on:
(i) MPR-CDS adjacency, which will have the same adjacency properties than
     MDR-CDS topology reduction schemes (see the partial topology report we
     have issued http://www.inria.fr/rrrt/rr-5619.html ), or based on:
(ii) MPR-selector links/adjacency.

I guess my point is that the MDR approach should not be favoured for its 
topology
reduction abilities, since an MPR approach features at least as good 
topology reduction
abilities and a better flooding scheme.

Emmanuel