Subject: Support for Loop Free Convergence Drafts Moving forward

From: Greg Bernstein <[email-masked]>
Date: Tue, 30 May 2006 09:49:17 -0700

The three proposed working group drafts concerning loop free convergence:
(1) draft-bryant-shand-lf-applicability-01.txt
(2) draft-bryant-shand-lf-conv-frmwk-02.txt
(3) draft-francois-ordered-fib-01.txt
address a problem of increasing importance and I support these moving 
forward as working group drafts.

To amplify a bit the "applicability draft". Large carriers discovered 
that with reasonable measurement and optimization techniques that they 
could tune IGP (OSPF/IS-IS) link weights to achieve near MPLS like 
traffic engineering capabilities [Fortz00]. However changing too many 
link weights at a time is disruptive so further work was done [Fortz02] 
to minimize the number of weight changes that would be needed. But since 
any link change could be disruptive, practice has been to keep these to 
monthly [Fortz02] (or weekly updates), i.e., not even taking into 
account common day/night traffic changes.
In addition, when more "bandwidth" is needed than the current IP layer 
can provide we'd like to be able to use our newly agile (via GMPLS) 
WDM/SDH network to update our IP topology. Reference [Liu02] gives some 
algorithms for doing so with small incremental changes to the IP 
topology via the optical layer. As we move to offering guaranteed 
services (or classes of services) such techniques can be even more 
beneficial, however without good methods for suppressing transient 
routing loops (micro-loops) all would be of limited use due to their 
potentially disruptive nature (changing link wts, adding or deleting IP 
layer links).

References:

[Fortz00] B. Fortz and M. Thorup, "Internet traffic engineering by 
optimizing OSPF weights," /Proc. IEEE INFOCOM/, 2000, pp. 519 - 528, 
March 2000.

[Fortz02] Bernard Fortz and Mikkel Thorup Optimizing OSPF/IS--IS weights 
in a changing world, /IEEE Journal on Selected Areas in Communications/, 
vol. 20, no. 4, May 2002, pp. 756 – 767.

[Liu02] K. H. Liu, C. Liu, J. L. Pastor, A. Roy, and J. Y. Wei, 
"Performance and testbed study of topology reconfiguration in IP over 
optical networks," IEEE Trans. Communications, vol. COM-50, pp. 1662 - 
1679, October 2002.

Regards

Greg B.

-- 
===================================================
Dr Greg Bernstein, Grotto Networking (510) 573-2237

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