Subject: [manet] Comments on draft-clausen-manet-ospf-dbx-00.txt

From: Richard Ogier <[email-masked]>
Date: Sun, 29 Feb 2004 22:10:52 -0800

To the authors of draft-clausen-manet-ospf-dbx-00.txt,

I have a few quick comments on the draft.
I'm not sure why you are focusing on OSPFv2.
The OSPF WG has decided to focus on OSPFv3, e.g.
http://peach.ease.lsoft.com/scripts/wa.exe?A2=ind0311&L=ospf&T=0&F=&S=&P=10149

Your scheme seems to imply that a prefix can be used to identify a set
of LSAs.  In OSPFv3, address and prefix information has been removed
from Router and Network LSAs (and moved to new LSA types), which express
topology information using 32-bit Router IDs. Router IDs need not be
related to addresses and need not have a common prefix.

So I am not sure exactly how your proposed scheme will apply to OSPFv3.
I'm not saying it can't be applied, only that it it does not
seem straighforward or natural. Have you thought about this?

However, as I have proposed in draft-ogier-manet-ospf-extension-00.txt,
I agree that the concept of Complete Sequence Numbers Packets (CSNP)
of IS-IS (or equivalently, periodic Database Description (DD) Packets),
can be used both for reliable flooding of LSAs and for database
exchange with new neighbors.

We all agree that it would generate too much overhead to have every
MANET node transmit a full set of DD or CSNP packets periodically.
You are proposing to reduce this overhead by using "prefix signatures"
(using CRC checksums). I am instead proposing to reduce this
overhead either by having only a few nodes (CDS nodes) transmit
these periodic messages, or (if MPRs are used) by having each node
transmit LS sequence numbers (or LSA headers) only for LSAs originating
from nodes u such that p(u) is an MPR selector, where p(u) is a
consistently chosen next hop to node u.

I am not sure which approach will perform better (but it probably
depends on the scenario and other aspects of the protocol).
Do you have any simulation results for you proposed scheme?

Regards,
Richard

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