Subject: [Fwd: Re: [Ospf-manet] Re: Regarding MPR-OSPF]

From: Richard Ogier <[email-masked]>
Date: Sat, 24 Mar 2007 19:50:05 -0800

Emmanuel,

You did not respond to my question regarding your selection
of a synch router, which I posted on March 13 and am repeating
below.  I think my question is valid, so can you please respond?
This is important because your simulations assume that you can
always select a *single* router to be the synch router, which may
not be true in general.  As you know, the number of synch routers
affects overhead significantly in dense networks.

If Emmanuel does not respond, can someone else respond who either
agrees or disagrees with me?

Richard

Emmanuel Baccelli wrote:

> To clarify a point which you indicate that you missed concerning the 
> synch router: the willingness parameter influences a routers 
> forwarding ability only. If a synch router is outside the MANET, then 
> according to the I-D there exists a hybrid router which will 
> synchronise with its whole neighbourhood, thus fulfilling the synch role.

Emmanuel,

There still seems to be a problem when a router has multiple
MANET interfaces.  You define a hybrid router as follows.

Hybrid router  - a router which has OSPF interfaces of several types,
including the MANET type.

So a router with only MANET interfaces is not a hybrid router.
Consider a router A that has only one MANET interface, but has
only 1-hop neighbors and no 2-hop neighbors on this interface.
(I.e., Hellos received from neighbors on this interface advertise
only routers that are neighbors of router A itself.) As a result,
router A has no MPRs.  Assume it also has no MPR selectors.

A ----- B ===== C

Now suppose router A has a neighbor B which has two MANET
interfaces, one of which connects it to router A, and the other
of which connects it to router C, which is not a neighbor of A.
Assume router C has the largest RID and is therefore the synch router.
Therefore, since router A is not a synch router (nor a neighbor of a
synch router) and has no MPRs or MPR selectors, it has no adjacencies!

Therefore, it still looks like you need to select a synch router
for each MANET interface, or redefine a hybrid router to include
routers with multiple MANET interfaces.  Am I missing something?

Richard

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---

From: Emmanuel Baccelli <[email-masked]>
Date: Fri, 30 Mar 2007 09:08:50 +0200

Dear Richard,

see answer below

> routers with multiple MANET interfaces.  Am I missing something?

Yes. According to section 5.2.4. Hello packets contain a TLV that will:

"advertize the costs of links towards ALL its symmetric MANET neighbors. 
  If the router has several MANET interfaces, links to ALL the symmetric 
MANET neigbors over ALL the MANET interfaces of the router MUST have 
their costs listed."

Thus MPR selection algorithms take into account neighbors on multiple 
MANET interfaces, similar to the way OLSR works. Therefore in your 
example, A will select B as MPR, and will bring up an adjacency with B.

Emmanuel