The MPLS WG Archive

[David Charlap <david.charlap@marconi.com>]

Eric Rosen wrote:
> 
> Please note  that routers with ATM  cards are not  ATM switches.
> Therefore, routers with  ATM cards would not  be expected to use the
> encodings defined for ATM switches.  If two routers are connected to
> each other via an ATM VC, then of course they use the generic MPLS
> encapsulation when sending labeled packets over that VC, NOT the
> ATM-specific MPLS encapsulation.

Which deliberately makes the interface incompatible with an ATM switch
running MPLS code.

Why in the world would you want to use an ATM interface if it is
incompatible with ATM switches?

OK, so you can tunnel your LSP through an ATM VC.  But why would you
want to?  If you've got ATM, use it.  One of the big points about using
MPLS is to have one unified control plane - if you're going to run MPLS
through an ATM network that doesn't participat in MPLS, then you've just
put back the layer you were trying to get rid of.  Plus you've now added
the overhead of two redundant layers of encapsulation where only one is
necessary.

-- David