Subject: RE: MPLS and Optical network!!

From: Theimer Thomas <[email-masked]>
Date: Mon, 31 Jan 2000 17:13:51 +0100

> Where we should be going is to extend our signaling protocol so that we
> can
> automate traffic engineering for both the MPLS and optical planes.  This
> implies
> that the OXCs participate (possibly through a proxy) in the signaling
> protocols,
> that optical plane configuration information is carried in our IGPs, and
> that
> traffic engineering path computation also consider optical path
> establishment as
> well as LSP establishment.
> 
	[Theimer Thomas]  Why do you think that it's necessary for OXCs to
be in
	the same IGP routing domain as routers ? OXCs are not used for any
kind
	of hop-hop forwarding, so there is no immediate need for them to
share their
	topology information with routers.

	I would expect that initially the optical domain will have a control
plane that
	is independent from the layer 3 control plane of routers. Of course,
there is traffic
	engineering in the optical domain, and there is traffic engineering
in the layer 3 domain,
	but why do they have to be integrated ??? After all, the
granularities and LSP
	characteristics are completely different in both domains. In many
cases, both
	domains will also be operated by separate or even independent
organisations.

	That is not to say that both domains may use the same protocols and
principles 
	for signalling and routing (e.g. MPLS). Routers may even be able to
talk to OXCs
	and request additional optical trails. But that still doesn't
require an integrated IGP
	routing domain, that includes all routers and IXCs.

	Perhaps I'm missing something ?

	Thomas

---

From: Curtis Villamizar <[email-masked]>
Date: Mon, 31 Jan 2000 16:45:18 -0500

In message <3B59676F9ADBD211B5360060086E64EE45E7B4@MCHH237E>, Theimer Thomas wr
ites:
>    be in the same IGP routing domain as routers ? OXCs are not used
>    for any kind of hop-hop forwarding, so there is no immediate need
>    for them to share their topology information with routers.

The IP community has been down this road before with IP over ATM.
When you hear that MPLS is not just ATM all over again but with bigger
cells but rather a goal is to not make the same mistakes made in ATM,
the decoupling of IP from the underlying layer 2 was one of those
mistakes.

To make network routing scalable a full mesh is not a feasible
approach.  Beyond some size, routing hierarchy must be introduced,
meaning that routers are stategically placed within the topology.  In
this case traffic engineered paths may traverse more than one optical
domain or region.  An example is where regional or metro optical
domains exists and routers sit at the edge of these and are part of a
national (or larger) optical domain.  There may be a full mesh within
the higher level domain and there may be full meshes within each
regional optical domain.

The routers at these boeders may do OEO, buffering, and routing, or in
a vision in of all optical they may in effect splice lambdas between
domains, avoiding the OEO.

Even with that vision, connecting a few hundred routers together in an
optical full mesh (without putting full fledged routers in the middle)
has the problem of needing N-1 interfaces per router for a mesh of N
routers.

ISP networks have a core with order low 10s of core routers.  It is
feasible to terminate 10s of lambdas there to accommodate the core and
terminate lambdas to the high 10s of routers in the adjacent region.
As you can imagine some big routers are needed.

Altogether there are order 1000 access routers in the larger ISPs
(terminating order 10s of thousands of CPE routers plus racks of dial
equipment) so N and N-1 are big.  It is not feasible to terminate on
the order of 1000 lambdas on these access routers plus the IGP would
either be unstable or converge slowly.  The only way the order 1000
lambdas could be terminated cost effectively is if some form of
optical TDM worked.  If not, then big routers in the middle can't be
avoided.  (Of course, not that I want to see them avoided. :)

>    principles for signalling and routing (e.g. MPLS). Routers may even
>    be able to talk to OXCs and request additional optical trails. But
>    that still doesn't require an integrated IGP routing domain, that
>    includes all routers and IXCs.

The IGP provides feedback if the layout is at all dynamic.  If the
layout of active and backup paths is entirely done offline, then the
IGP still serves to reduce the number of IGP adjacencies and keep the
IGP flooding as efficient as it can be.  The optical paths serve as
"shortcuts" across the IGP.

>  	Perhaps I'm missing something ?

Perhaps not.  Or at least very little.

>  	Thomas

Curtis