The MPLS WG Archive

["John Strand" <jls@research.att.com>]

Hi Kireeti,
Comments in-line. Sorry about the MIME encoding ... when I get a
chance I'll check into my options.
John

John Strand
AT&T
Lightwave Networks Research Dept.
100 Schulz Drive, Room 4-212
Red Bank, N.J. 07701-7033
(732)345-3255
jls@research.att.com 

-----Original Message-----
From: Kireeti Kompella [mailto:kireeti@juniper.net]
Sent: Monday, October 23, 2000 4:25 PM
To: jls@research.att.com
Cc: ip-optical@lists.bell-labs.com; mpls@uu.net
Subject: RE: [IP-Optical] RE: Optical link bundling. Was Re:
DraftMinutes From Pittsburgh


Hi John,

> What's needed is a way for you to ask for a lightpath that's physically
> diverse from one or more other lightpaths, whether or not the other
> lightpaths have the same terminals as the new lightpath.

Yes, that is correct.

> This is done
> routinely at DS3 and (I think) OC-n levels today by PL services like
> AT&T's EDRO (Enhanced Diversity Routing Option).

Are you (or others) proposing the mechanisms to do this in the
UNI/GMPLS framework?

[JLS Comment] The Carrier Group requirements specify an interface that should
support the necessary information flow - in particular, specify that lambda
n+1 should be diverse from a specified list of existing lambdas. (At present it
doesnt explicitly say these existing lambdas can have different end points. I'm
going to try to get this fixed.) My OIF 2000.109 has additional specific requirements.

> The heuristics to simultaneously route a number of circuits simultaneously
> subject to diversity constraints essentially require zillions of calls
> to a Dijkstra algorithm and so don't seem to lend themselves to incorporation
> in the control plane.

In the IP world, I see the use for simultaneous set up of a small
number of disjoint paths, basically, a primary and one or more
backups for an LSP.  So, this may not be an issue.  What is the
requirement driving having lots of simultaneous diverse paths in
the telephony world?

[JLS Comment] Large single-customer PL networks. Frequently they have done their own
reliability analysis and come in with a matrix showing which circuits need to be diverse.
There are some examples in the OIF 2000.109 that give a little more information. For
another entirely different example consider a SONET ring: All edges of the ring must
be diverse.

> I'd be interested in hearing more about the drivers for your example. I would
> expect that if you want physical diversity you are setting up lightpaths that
> are going to be around for a while.

Yes, but as I said above, I visualize lots of LSPs, each requiring
two or three diverse paths, not hundreds of diverse paths.  So, this
should not be an issue.

[JLS Comment] I agree - sounds like you're at the easy end of this sort of problem.

> There's a book by Ramesh Bhandari that addresses some of the algorithm issues.
> I don't believe that the heuristics used for services like EDRO are in the
> public domain though.

More's the pity :-)

Kireeti.

PS. BTW, your mail replies are MIME encoded, even when they are
simple ASCII.