Re: [Mpls-interop] MPLS over MPLS-TP

Snipped, comment inline 

>1. What is the service provided by an MPLS-TP network?
>Is it (as described in some documents) the provision of 
>pseudowires over an MPLS transport network?
>Or is it the provision of services (including pseudowires) 
>over an MPLS transport network?
>
>AM> My preference is the latter - it should be more general than just
>the provisioning of pseudowires (even if we have IP and MPLS 
>pseudowires). A PW is an instance of a label in the stack, and 
>what can be transported over MPLS-TP shouldn't be limited to 
>just that instance.

JD:  I agree

>
>3. If there is demarcation as suggested in point 2, what is 
>the best way to provide demarcation?
>a. Encode as a PW with the end of stack set and a PW header 
>according to the appropriate PW encoding type.
>b. Simply use the end of stack bit to say that we have reached 
>the bottom of the MPLS-TP label stack.
>(The alternative clearly being that the label stack runs 
>through from the client label stack to the server label stack.)
>
>AM> I prefer b, for simplicity and generality of what can be carried
>over MPLS-TP. Thus we could have a label stack with two EOS bits set. 
>
>AM> Also, regarding the possible misconfiguration discussed in question
>2, this could happen with PW labels as easily as with non-PW 
>labels, so requiring PWs to be used with MPLS-TP is no 
>panacea. Rather, this sort of misconfiguration needs to be 
>detected using OAM and other MPLS-TP layer management mechanisms.

JD:  I agree with your point about PW labels, but doesn't the same point
apply to the label stack with two EOS bits?  Viz, having the EOS bit set
will not prevent an implementation from messing up the stack in
arbitrary and capricious ways.

Isn't another alternative to just have the MPLS TP network be completely
agnostic to the contents of its payloads, as a server layer is supposed
to be?
In that case, the payload could in fact be an MPLS payload with its own
stack.

>
>Cheers,
>Andy
>
>
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