The MPLS WG Archive

[Shahram Davari <Shahram_Davari@pmc-sierra.com>]

Yakov,

> > It seems that you have confused the "layer above" with the 
> "layer below".
> > X over MPLS always requires a Shim header. 
> 
> First of all, in the case of ATM-LSRs the presence of the shim header
> strictly speaking is not mandatory. Second, even when the shim header
> is present with ATM-LSRs, the forwarding information used by 
> ATM-LSRs is 
> *not* in the shim header, but in VCI/VPI fields of the ATM 
> cell header.

There are two methods of doing MPLS over ATM:

1) Network interworking (tunneling): You require to have a meaningful shim header
2) Service interworking: You could translate the MPLS label to VPI/VCI and therefore
you may not use shim header. This is done in FR over ATM too.

So it all depends on what type of interworking are you talking about. It is the
nature of the service interworking that you translate to the transport technology.
That doesn't mean that MPLS or FR are not layers! 
 
> Finally, in GMPLS there is no shim header at all.
> 

In GMPLS you are only using MPLS control-plane. You are not doing X over MPLS
over Y. So this does not apply to your layering argument.\

-Shahram

> Yakov.
>