The MPLS WG Archive

["Krishna Bala" <kbala@tellium.com>]

Curtis,
I agree with most of your comments. Thanks for the clarification
on the Overlay Model also.
Yes, the "Signaled Overlay Model" is what I am calling the "Open Model".

Couple of Comments:
1. The OIF is not going to ignore the input of the internet community.
The fact that we (atleast Tellium and Sycamore .. I cannot comment for
the others) have stated clearly that they are going to use OSPF for routing
and MPLS for signaling at Layer 1! I think this suggests that we
are already in agreement with the IP community. We would like to
be a part of a multivendor IP Optical Network.
2. Regarding the marketing use of the term "Signaled Overlay Model"
versus the "Open Model". I am not sure how the term "Open" came to be used
among the "optics" community ... but it conveys the intent what we
are trying to accomplish, i.e., the interconnection of multiple network
elements and services to an Open optical layer that supports a multiplicity
of services (e.g. IP, Direct Wavelength, TDM, ATM.

Krishna Bala


> -----Original Message-----
> From: Curtis Villamizar [mailto:curtis@avici.com]
> Sent: Tuesday, March 28, 2000 10:19 AM
> To: Krishna Bala
> Cc: Jagan Shantigram; Jonathan Lang; curtis@avici.com; Khaled Elsayed;
> mpls@UU.NET; ip-optical@lists.research.bell-labs.com
> 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
>