The MPLS WG Archive

[Bala Rajagopalan <braja@tellium.com>]

There is one aspect missing in your description below. That is,
how routing information is passed between IP and optical
domains. Overlay models, static or otherwise, have no routing
protocol running between the two domains (IP and ATM or
in this case, IP and optical). The intent of the "open" model
(call it by another name if this isn't
suitable) is  to allow a
routing protocol to pass limited information between domains,
for example, reachability, and define standard signaling for
provisioning and (perhaps) restoration.

The real issue is to identify the service requirements at
the IP-optical interface. Currently, we see dynamic provisioning,
reachability determination and restoration as requirements.
None of these require passing detailed topology between
domains. If there are other specific operational requirements,
it'll be good to know about them.

regards,

Bala


Curtis Villamizar wrote:

> 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

--

Bala Rajagopalan
Tellium, Inc.
2 Crescent Place
P.O. Box 901
Oceanport, NJ 07757-0901
Tel: (732) 923-4237
Fax: (732) 923-9804
Email: braja@tellium.com