RE: [PWE3] PWE Service interworking

[Mark Seery <mark@mseery.com>]

Sasha,

--- Sasha Vainshtein <Sasha@AXERRA.com> wrote:
> Shahram, Mark and all,
> A couple of comments/questions.
> 
> 1. I agree with Shahram that the model he has
> proposed
>    is much simpler than one proposed by Mark in his
>    "explanation email". To me, this makes it
> preferable.

I agree, Shahram got it right (even mention one
letter.number standard), though curious about how he
sees PW playing in all this.

> 
> 2. My gut feeling is that:
>    a) This difference in approaches is exactly what 
>       the current PWE3 WG Charter defines as the 
>       rationale for the PWE3 work when it says:
>       <quote>
>       	The PSN can transport PDUs for multiple
> services, 
> 	      and the conversion/interworking functions per
> 		service pair are not needed.  
> 	<end quote>
>    b) It means (and has been correctly interpreted
> by many
>       people including, I think, Mark) that the
> Charter defines
>       "service interworking" out of scope for PWE3 -
> and for a good
>       reason.

MS=> See below as well as my response to Shahram

> 3. I am not sure if the term "X-to-MPLS service
> interworking" 
>    is applicable to Shahram's diagram. E.g., for
> PL=Ethernet I 
>    do not expect that the EXC bits in the MPLS encap
> will reflect 
>    DE/CLP markings of the containing FR/ATM-based
> AC. All the 
>    ETHoATM/ETHoFR-specific information will be
> simply discarded by the PEs!
>    (At least this is, IMO, what the current Ethernet
> encapsulation 
>    draft says:-). However, this does not affect the
> conclusions of (1) 
>    and (2) above in any way.
> 
> Did I miss something?
> 

MS=> No, you did not miss something. This is in
essence one of the concerns I was raising when I
previously asked whether encap authors had considered
the service interworking case - though clearly I had
not formulated or articulated my thoughts properly.
This is I think also the same as the concern which has
sometimes been articulated as "..every encap author
doing their work independent of the others.." i.e. no
generalized format for interworking encaps.

So it is one of those things like inter-AS work, it is
good to put it off because it helps you to break down
the problem, but it is bad to put to off because as a
result, you don't actuallt see the long-term problem
for what it is.

Mark
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