Subject: Re: MPLS and Optical network!!

From: Danny McPherson <[email-masked]>
Date: Fri, 28 Jan 2000 22:42:23 -0700

> Yes, but to connect each of 80 routers to each of 80 others takes (if I
> remember the equation right) (N * (N-1))/2 total connections, or over 3000
> virtual links. And the number gets much bigger very quickly (e.g. 100 takes
> almost 5000 - it *is* an exponential).

and then came hierarchy and spatial reuse.

> Now, depending on the exact topology of the connectivity mesh of fibers and
> OXC switches between them, some of those virtual links can be carried on the
> same wavelength, since no parts of the paths of the two (or more) of them will
> be congruent (and exactly how many depends on the topology). So that will
> reduce the total number of wavelength you need to provide all N^2 (roughly)
> virtual links. Still, it's going to be a significant number.

Ahh, and this would require some type of intelligent connection management and 
calculations to setup the required protect path, _when it's required.
 
> In other words, modelling (at the internetwork layer) an OXC substrate as a
> giant Ethernet, where every device connected to it can talk directl to every
> other device connected to it, doesn't really work as the OXC substrate gets
> larger.

Nesting of lightpaths, that's interesting.  I think spatial reuse of 
wavelengths will have to suffice for now, though, as suggested above, 
providing shared-path protection for backup connections would certainly be 
more capacity efficient than dedicated-path protection alone.  Though this 
would require a bit of engineering in order to ensure complete diversity of 
wavelengths sharing a path, and assume accommodation of only a single failure 
.. unless some [more intelligent mechanism] were able to accommodate multiple 
failures, if alternative routes/capacity were available.
 
> (Which is sort of related to one of my favourite rants, about why you really
> want to have route selection at the internetwork layer only, but let's skip
> that rathole.)

The proposal(s) I've seen only deal with "automation" of connection management 
for lightpath (no opto-electronic conversions) and optical signal termination. 
 It's done today, just offline, and arguably, less efficiently.

-danny

---

From: "Metz, E.T." <[email-masked]>
Date: Mon, 31 Jan 2000 17:45:51 +0100

>> I would expect that initially the optical domain will have a control
plane that is 
>> independent from the layer 3 control plane of routers. 

This would mean going back to a situation similar to the IP/ATM overlay
model. I think eventually multiple control planes will/can run on an OXC
depending on the situation. If the OXC is deployed in an all-IP network I
see no use for other control planes than IP (or MPLS for that matter). If
the OXC is multi-purpose, multiple control planes may run on it.

>> 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. 

If both serve the same purpose, I think they should be integrated. You could
also integrate e.g. IP and ATM traffic engineering, but I haven't seen much
of that. Doing it right the first time has some clear advantages ...
(assuming there is a need of course). 

>> In many cases, both domains will also be operated by separate or even
independent 
>> organisations.

Not necessarily true in all situations, large providers may want to deploy
very large IP backbones on a wholly owned infrastructure.

>> 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.

Now I'm confused, this seems to be the opposite of the statements above ...
both domains use the same principles and protocols, but they are not
integrated ???

cheers,
	Eduard

>> Perhaps I'm missing something ?

>> Thomas

---

From: Theimer Thomas <[email-masked]>
Date: Mon, 31 Jan 2000 18:31:54 +0100

> (assuming there is a need of course). 
	[Theimer Thomas]  What are the advantages ? Why do we have to make
	things more complex than they need to be (at least initially) ? I
can see a
	lot of benefits in separating the two domains, in terms of fault
isolation and
	scalability. You would need at least one additional level of
hierarchy in the
	IGP domain if you integrate both domains, and that would probably
export
	only an abstracted view of the optical domain anyway. So why don't
we
	solve the optical intradomain problem first, and then think about
possible
	extensions, rather than trying to solve everything at once.

> both domains use the same principles and protocols, but they are not
	[Theimer Thomas] That is exactly my point. Routers should talk
	to routers, and OXCs should talk to OXCs. They may both talk some
dialect
	of MPLS, but they can be in different and independent domains.
Everyone
	just seems to imply that a fully integrated control plane model is
the only
	desirable option. I don't think so, and I am still looking for
arguments why
	a fully integrated model is needed at all. Perhaps a data centric IP
only
	network might be such an example where it makes sense.

	Thomas