The MPLS WG Archive

["Paul Tasillo" <Paul.tasillo@tivoli.com>]

Thank you for the insight.
So if I understand correctly, there are three possible MPLS over ATM
schemes:
1. ATM-LSR: Here the the LSR (maybe all of the links) has a IP address and
participates in L3 routing protocols. MPLS controls signaling and assigns
VPI/VCIs in a meaningful way to create VC to next hops.
2. The ATM cloud has a mesh of PVC which MPLS uses as ptp links. This is
frame based not cell based. This is an overlay model where MPLS works on top
of CLIP or LANE? And the LSR still participate in L3 routing protocols? (as
well as ATM routing protocols being run).
3. the VCID case. Again an overlay model where there exists CLIP or LANE
except here MPLS coordinates with ATM signaling to create SVCs as needed. L3
& ATM routing protocols are run.

Is this correct? If so case 1 would seem to be the preferable solution in
order for MPLS to allow ATM to scale and to reduce configuration headaches.

-Paul
-----Original Message-----
From: owner-mpls@UU.NET [mailto:owner-mpls@UU.NET]On Behalf Of Jeremy
Lawrence
Sent: Wednesday, August 23, 2000 8:40 PM
To: Paul Tasillo
Cc: mpls@UU.NET
Subject: Re: FW: basic MPLS ATM question


At 17:54 08/23/2000 -0400, Paul Tasillo wrote:


>Hi-
>        In draft-ietf-mpls-ldp-applic-02.txt it says,
>
>  LDP, together with an IP routing plane and software to program ATM
>   switch or Frame Relay switch cross-connect tables, can implement IP
>   in a network of ATM and/or Frame Relay switches without requiring an
>   overlay or the use of ATM-specific or Frame Relay-specific addressing
>   or routing.
>
>In the absence of ATM/FR specific addressing or routing, what is being used
>for addressing? If the answer is IP, then am I safe in assuming that this
>requires each ATM switch to have an IP address?

Yes, in the same way that a router does, for the purposes of
participating in an IP routing protocol. (From the perspective
of an IP routing protocol, an ATM-LSR is indistinguishable from
a router.) The links may also have IP addresses.

>I understand the ATM
>switches will be participating in L3 routing protocols (BGP, OSPF, etc).
>
>Is there also an overlay MPLS model? Where MPLS make decisions on a frame
>basis rather then cell and uses ATM/FR specifc addressing and routing?

Aside from VCID (covered in another email), MPLS-enabled routers
can be connected by RFC 1483 (or whatever the latest RFC number is)
PVCs. This is like ordinary IP over ATM, except that it is
frame-based MPLS over ATM. The PVCs act like any other non-channelized
point-to-point link between frame-based LSRs.

Regards,

Jeremy Lawrence