Subject: Traffic Engineering Question

From: Manish Gupta <[email-masked]>
Date: Thu, 9 Sep 1999 12:21:22 -0400 (EDT)

Hi

I am wondering that how various LSRs in a network will build their
"Resource Attribute Availability Database" ( Requirements for Traffic Engg
over MPLS ,Internet Draft, page 25), are there any extensions to current
IGP/EGP protocols to distribute this information to various LSRs or any
other nmechanism to distribute this information is proposed and if so how
this information will be kept up-to-date at all LSRs as and when resources
are allocated and de-allocated. Furthermore, if such information is
somehow (I dont know yet how) kept at each LSR and maintained uptodate by
some mechanism, are we going to use some algorithm like simulated
annealing to map these virtual topologies to underlying physical
topologies (in the CR-LDP Process) or we have any standard mechanism for
this mapping. 

Thanks
Manish

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From: [email-masked] (Daniel Awduche)
Date: Thu, 9 Sep 1999 13:43:57 -0400 (EDT)

The general requirements for distribution of additional topology state
information to support traffic engineering using IGPs are stated in
"IGP Requirements for Traffic Engineering with MPLS"
(draft-li-mpls-igp-te-00.txt

These requirements are specialized to IS-IS (by adding new TLVs) in
"IS-IS extensions for Traffic Engineering"
(draft-ietf-isis-traffic-01.txt)

and to OSPF (by using Rob Coltun's Opaque LSA) in "Traffic Engineering
Extensions to OSPF," (draft-katz-yeung-ospf-traffic-00.txt).

The issue of how to "map these virtual topologies to [the] underlying
physical topologies," is the general problem with which
constraint-based routing is concerned. At this time, no standard
mechanisms/algorithms exist for path selection using constraint-based
routing. Simulated annealing is certainly one class of heuristics that
may be applicable to constraint-based routing and similar
computationally difficult problems.  Whether simulated annealing can
be implemented online at reasonable cost remains to be seen. There are
certainly simpler algorithms. The literature abounds with such
heuristics, some useful, others mere theoretical curiosities...

Cheers,
/Dan

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From: Tony Li <[email-masked]>
Date: Thu, 09 Sep 1999 11:40:55 -0700

> heuristics, some useful, others mere theoretical curiosities...

It should be pointed out that there need not be any standardized (in the IETF
sense) algorithm for performing this function.  As architected, each LSR is
responsible for mapping its LSPs onto the physical topology using whatever
computational methods it deems approproate.  Such methods may vary from domain
to domain.

An approach that I expect to see widely deployed will be a centralized
computation of an optimal mapping, resulting in configuration information for
LSRs that are distrubted using normal configuration mechanisms.  As such, there
are no new protocol issues involved, and no new standards that need to be
written in this area.

Regards,
Tony