Subject: RE: Comments on draft-ip-optical-framework-00.txt

From: Lee Thomas <[email-masked]>
Date: Mon, 03 Apr 2000 12:03:39 -0500

Curtis,

I took vacation all last week and am just now reading this thread so I
apologize for harkening back to old mail.  Having read through the week's
discussion of open, peer and overlays, I like your descriptions the best.
As Grenville pointed out, the overlay simply implies an independence and not
necessarily an assumption that the underlying is static.  I agree with your
comments that ATM PVC-based IP backbones are not built as full-mesh
networks.  I like having the static overlay model identified as this
reflects many current network implementations and I like the Signaled
Overlay Model as it describes a model that may be implemented as a new
network, or a Static Overlay network could be transitioned to a SOM.
Similarly, a SOM could be migrated to a Peer model network.  The options are
there and I think these three model descriptions relate well to current
implementations and a number of migration scenarios.

Lee

-----Original Message-----
From:	[email-masked] [mailto:[email-masked]] On Behalf Of Curtis
Villamizar
Sent:	Tuesday, March 28, 2000 9:19 AM
To:	Krishna Bala
Cc:	Jagan Shantigram; Jonathan Lang; [email-masked]; Khaled Elsayed;
[email-masked]; [email-masked]
Subject:	Re: Comments on draft-ip-optical-framework-00.txt

In message <00f801bf9843$888c2560$425cc697@tempest>, "Krishna Bala" writes:
> Jagan,
> Just to beat a dead horse .. the difference between the open model
> and the overlay is just that the overlay model typically suggests that
> there would be N^2 connectivity (i.e., every router, for instance, is
> statically connected to every other). In any case, the open model allows
> for fully dynamic operation. The overlay model suggests static operation
of
> the optical layer.
>
> As I see it there are only two architectures that are worth considering:
> 1. Peer
> 2. Open
>
> I agree with you that there is no need to add the "overlay" model to
> this list. The open model covers the static and the dynamic cases.
>
> Krishna

In terms of visibility into the optical layer and control over path
selection, the proposals on the talbe can be characterized as follows:

  1.  Static Overlay Model - paths endpoints are specified through a
      network management system though the paths may be laid out
      statically (by the NMS system) or dynamically (by the network
      elements).  This is similar to ATM PVCs and SPVCs.

      [Note: networks built using the overlay model need not provide a
      full mesh contrary to misinformation provided on this mailing
      list.  Today ATM PVC based IP backbones are often not built as
      full mesh networks to reduce the nuber of routing adjacencies.]

  2.  Signaled Overlay Model (aka "Open" model) - paths endpoints are
      specified through signaling via a UNI.  Paths must be laid out
      dynamically since they are specified by signaling.  This is
      similar to ATM SVCs.

  3.  Peer model - The network elements are provided enough
      information such that they MAY attempt to set up path in
      addition to specifying their endpoints.  Paths may be laid out
      by the optical elements if the edge LSR provides only a static
      hop.  Paths may be laid out by the LSR.  Paths may also be laid
      out statically by having the NMS system configure explicit paths
      on the LSR and have those paths signaled.

It was my understanding that the MPLS WG traffic engineering work was
motivated largely by major Internet service provider's experience with
ATM and was making an effort to avoid repeating the mistakes of the
ATMF and therfore (among other differences between ATM and MPLS) is
interested in the peer model.

Note - If the OIF wants to ignore the experience that the Internet
community has had with ATM and wants to ignore the feedback through
the IETF of people involved in building those networks and and build
IP routers with ATM interfaces that were constrained to make use of
the interfaces that the ATMF chose to provide (in some cases omiting
capabilities over the loud objections within IETF WGs such as IP over
ATM) then that is a matter for OIF.

If we are putting together a framework, then in addition to the
"static overlay model" and "peer model", a distinction should be made
and a separate "signaled overlay model" can be provided.  In the
interest of completelness the framework can point out that the OIF is
working on a UNI which is based on the signaled overlay model.

I prefer the term "signaled overlay model" over "open model" because
the former is descriptive and that latter seems motivated by the
desire to use the marketing buzzword "open" rather than provide a
descriptive term.

Some people had envisioned going directly from static overlay model to
peer model or going directly to the peer model with the understanding
that the LSR can still be configured with explicit paths from an NMS
as long as quantifying and signaling impairments remains slightly
beyond the state of the art and determining the impact of optical
impairments remains a black art.

Curtis

---

From: Juha Heinanen <[email-masked]>
Date: Tue, 4 Apr 2000 07:03:01 +0300 (EEST)

Lee Thomas writes:

 > I like having the static overlay model identified as this

opposite of static is not signaled but dynamic.  we do all of our ip/atm
overlays using signaled svcs between the routers, but the topology is
still static.  so better names would be static and dynamic overlays.

an example of dynamic overlays was documented as

ftp://lohi.eng.telia.fi/tmp/draft-ietf-ion-intra-area-unicast-01.txt

which unfortunately never got progressed because in the atm world it had
a dependency with the ospf ara option.  since signaling in mpls is based
on ip addresses, the ara thing is not anymore needed and i may respin
the i-d for mpls.

-- juha

---

From: Lee Thomas <[email-masked]>
Date: Tue, 04 Apr 2000 09:19:18 -0500

Juha,

> still static.  so better names would be static and dynamic overlays.

I agree.

-- juha

---

From: Curtis Villamizar <[email-masked]>
Date: Tue, 04 Apr 2000 10:56:16 -0400

> on ip addresses, the ara thing is not anymore needed and i may respin

We are splitting hairs but please recall that there were three cases:

  static
  signaled
  peer

One could argue that the latter two are dynamic and that the peer
model is just a bit more dynamic that the signaled model.  The PVC
style is certainly the most static.

Since the first two have limited or no visibility into the underlying
topology they are overlay.

Juha may have added a fourth case.  The following table might help.

   router's topology  type of
   visibility         path setup      model name           example

    configured*        none            static overlay       ATM-PVC
    configured*        endpoint        signaled overlay     ATM-SVC
    endpoints          endpoint        dynamic overlay      MPLS-loose
    full               full path       peer                 MPLS-strict

   *configured here means endpoints only are configured in the router.

The model Juha proposed is a slight improvement over the pure ATM SVC
model in that the endpoints to the ATM are advertised for the purpose
of making ATM call setups.  This model seems similar to the use of
MPLS with a single loose hop in the explicit route.  It is similar in
that the ingress knows about the endpoint through signaling rather
than configuration but leaves it to the next (signaling) hop (which
would be an optical device) to figure out how to get there.  If the
ingress had enough information to compute the path, we'd have the peer
model and the ingress would use strict hops in the explicit route.

It wouldn't hurt to add the distinction that Juha has pointed out and
adapt the term "dynamic overlay" that he suggested.  I hope this
terminology is clear.  We seem to have some growing consensus on these
model names.

Curtis

---

From: Bala Rajagopalan <[email-masked]>
Date: Tue, 04 Apr 2000 13:01:06 -0400

Curtis:

The dynamic overlay, as suggested, is somewhat close to the intent
of what we were calling "open". However, we need to clarify a few things.
First is the routing interaction between IP and optical domains.
I'm not sure what you mean
by "endpoints" in the dynamic overlay case. If you mean ATM endpoints,
then the so-called "open" model is different.
As Heinrich pointed out in an
earlier email, the addressing
is the same in IP and optical domains.  In the "open" model
scenario, there could be routing exchange between the domains
(e.g., BGP), so there
is really no need to know about optical endpoints corresponding
to destinations in the IP domain (but as in the dynamic overlay
case, the optical network will take care of routing within).
Second, a distinction has to
be made between control and data planes. Even if you use
the peer model with full exchange of topology etc in the control
plane, the
connectivity between routers in the data plane is over a pipe in the optical
domain. That is, the interior nodes in the optical
domain cannot see the IP data or LSPs, and data plane
connectivity is still overlay. The establishment
of the pipes and management of pipe bandwidth will
be similar in each of signalled, dynamic or peer models. Specifically,
the end routers are solely responsible for setting up and managing
the pipe bandwidth. So, it's perhaps useful to just focus on
interface functional requirements (including routing) and not
worry too much about the terminology.

Regards,

Bala

--

Bala Rajagopalan
Tellium, Inc.
2 Crescent Place
P.O. Box 901
Oceanport, NJ 07757-0901
Tel: (732) 923-4237
Fax: (732) 923-9804
Email: [email-masked]

---

From: Curtis Villamizar <[email-masked]>
Date: Tue, 04 Apr 2000 19:24:39 -0400

In message <[email-masked]>, Bala Rajagopalan writes:
> Curtis:
> 
> ... So, it's perhaps useful to just focus on

The OIF can continue to work on the "open" model and they can, just
like the ATMF before them, ignore issues (like IP routing) that are
critical to building IP networks if that is what they are inclined to
do.  Is so, the outcome may be no more useful than the ATMF vision of
a big global ATM network with IP routers and host around the perimeter
finding the right path by magic (or by NHRP which doesn't work).

In the IETF (not the OIF) we may need terminology to describe a set of
proposals that involve using MPLS over optical.  If so, the terms
below might be appropriate and descriptive and cover the set of
(reasonably sane) proposals that have been discussed.

btw- By endpoints I do mean endpoints of an ATM VC or endpoints of a
PSC in the terminology used in draft-kompella-mpls-optical-00.txt.
This does not imply endpoints on the Internet (a pair of hosts) or
even customer ingress or egress, just boundaries of an optical region
which could be a traffic engineered optical backbone or a traffic
engineered regional or metropolitan area that makes up part of a
provider's network.

Curtis

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