The MPLS WG Archive

[Sid Chaudhuri <sc@tellium.com>]

The routers can't figure out the failure scenarios unless they know the SRGs
within the optical layer. For example, consider three routers A, B, C each
pair connected by an OC-48 via optical switches, two of which (AB and BC)
may share part of the way the same conduit and hence may fail in a single
event. Routers wouldn't know that unless we assume that each router
connected to the optical layer receives the SRG information from the optical
layer.  It's possible to do that if we assume two things: (1) All routers
and optical switches in a network share the same information - in other
words peer model, (2) SRG can be defined in so many different ways - sharing
same WDM, same fiber cable, same WDM, same conduit, same office.  It's
difficult for me to assume that standards can be erected to define this and
passed to the routers.  These are the types of things I would presume ISPs
would inquire before connecting their routers to the optical layer service
provider and then request via signaling the type of services (Gold, Silver,
Bronze, etc.) they need.  The ISPs would know based on the optical layer
restoration, SRG implementation etc. what these service levels mean in terms
of availability, protection switching time, etc.

Setting up diverse routes within an optical layer which implements the
concept of SRGs is really not so complex.  Request by routers to provide
diverse routes in the optical layer is already incorporated in the OIF UNI
spec.

Regards.

Sid

		-----Original Message-----
		From:	Jim Boyle [mailto:jboyle@Level3.com]
		Sent:	Monday, October 23, 2000 2:09 PM
		To:	Sid Chaudhuri
		Cc:	'Kireeti Kompella'; xuyg@lucent.com; yxue@UU.NET;
ip-optical@lists.bell-labs.com; mpls@UU.NET
		Subject:	RE: [IP-Optical] RE: Optical link bundling.
Was Re: DraftMinutes  From         Pittsburgh



		if the lambda's are unprotected (which is debatable), then
the routers can
		communicate amongst themselves and decide what are the
failure scenarios,
		and request more or less capacity based on that analysis.  

		A complex alternative is to support things like:

		a) "setup these two circuits in a diverse manner"
		b) same as (a) but over different UNIs, in fact in different
towns
		(e.g. setup nyc-sfo diverse from wdc-lax)
		c) "setup this circuit diverse from SRLG A,B,C" (which may
be infeasible
		if the circuit which those SRLGs were derived from preclude
a diverse
		route).

		As for path selection in general, a knowledge of the
underlying topology
		is probably necessary for most optimal path selection when
establishing
		lightpaths for non-direct traffic.

		This only makes sense in the 2001 timeframe to support one's
ISP over
		one's optical network.  An argument can be made that a good
OSS makes a
		lot of this level of integration unnecessary.  Inter-company
is a whole
		other issue.

		regards,

		Jim




		On Mon, 23 Oct 2000, Sid Chaudhuri wrote:

		> 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.  Based on its traffic flow a router only
needs to know between
		> which
		> two routers it needs to establish a new lightpath.  How
the lightpath is
		> routed in the
		> optical layer seems to me irrelevant to TE.
		> 
		> Sid Chaudhuri
		> 
		> 
		> 		-----Original Message-----
		> 		From:	Kireeti Kompella
[mailto:kireeti@juniper.net]
		> 		Sent:	Monday, October 23, 2000 11:43 AM
		> 		To:	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
		> 
		> 		Hi,
		> 
		> 		> > (router determines the explicit routes).

		> 		> 
		> 		> This point has been raised by several
folks. It really
		> confuses me. If the
		> 		> optical switches are equipped with path
calculation
		> ability, what's the benefit
		> 		> to bother router to determine the explicit
routes within
		> optical domain
		> 		> (assuming router can be smart enough to
handle all optical
		> network specific
		> 		> attributes and constrains) than just have
routers to
		> determine the end points of
		> 		> optical trails.
		> 
		> 		Why does this confuse you?  Routers may want
to determine
		> the exact
		> 		path that their LSPs take for a number of
reasons, including
		> TE and
		> 		protection.  If a router doesn't care where
its LSPs are
		> laid out,
		> 		it can install loose hops at the boundaries
of the optical
		> cloud.
		> 
		> 		Kireeti.
		>