The MPLS WG Archive

["valerie le faucheur" <valerie.lefaucheur@algety.com>]

Kireeti,

Some followup discussions in line.

Regards,
Angela

-----Original Message-----
From: owner-mpls@UU.NET [mailto:owner-mpls@UU.NET]On Behalf Of Kireeti
Kompella
Sent: Monday, October 23, 2000 1:58 PM
To: kireeti@juniper.net; sc@tellium.com; xuyg@lucent.com; yxue@UU.NET
Cc: ip-optical@lists.bell-labs.com; mpls@UU.NET
Subject: RE: [IP-Optical] RE: Optical link bundling. Was Re:
DraftMinutes From Pittsburgh


> I don't see why TE and protection require the routers to specify explicit
> routes.
> The routers can simply specify to the optical layer what type of optical
> layer protection
> it requires.

Suppose router A wants to get to router B, and wants to take two
different ingress and egress points in the optical domain, X->Y
for the primary LSP, and W->Z for the backup.  A does not require
optical protection for the X->Y path, nor for the W->Z path.  A
*does* require that the X->Y path and the W->Z path do not share
common links.  How is this to be done?

If A did the full path computation, this is simplicity itself.

[AC] I think you have a good point here. I also heard the same kind if
reasoning (i.e., have a layer-3 like protection switching) for supporting
the peer model. But after discussing with others, it seems that overlay
model should be able to provide the same capability. Normally, the primary
LSP X->Y is set up first, and becomes a forwarding adjacency (FA) according
to your LSP Hierarchy draft. Then the associated information of the FA X->Y
including its exact path and SRLG information should be propagated via IGP
extensions, same as with any other link in the network. Thus if router A
sends a request to OXC W to set up a backup lightpath from W->Z to be
diversely router from the existing FA X->Y, OXC W should already have the
right information to perform proper routing.

Comparing with the peer model solution where routers need to know all the
SRLG information of the optical domain as well as all relevant physical
impairments in the optical signal in the case of transparent optical
network, it is still not clear to me which one is simpler.

I think it is very good to have this kind of technical discussion openly on
the list. Hope others can provide more technical and business (after all
carriers need to pay for these features) evidences for the need of each
model. Some other reasoning I heard includes that peer model can improve the
IGP scalability in terms of the number of neighbors a router needs to peer
with. But since large ISPs today seem to cope well with the IGP scalability
today, I don't see why the problem will get significant worst when optical
networks come into play.

Regards,

Angela

BTW, the draft John Strand mentioned on the list earlier should be at
http://search.ietf.org/internet-drafts/draft-chiu-strand-unique-olcp-00.txt
with all lower cases.
A new version will be out in a few weeks before the deadline since we are
still working on a few details and editing.




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