RE: [PWE3] PWE Service interworking

["Mark Seery" <mark@mseery.com>]

Hi Zhi,

Imagine a network:

         |----------------------------|

               |----|-----|-----|      TE COS = Gold


CE1----PE1----P1----P2----P3----P4----PE1----CE2

There are two end-to-end OAMs that may be desireable in this network:

1) PE1--PE2 (the user plane for the LDP-LDP connection between PE1 and PE2)
2) P1-P4

If you take the layer between P1 and P4 and add a label, you do not reveal
the segments you obfiscate them by creating another "layer". The segments
P1-P2, P2-P3, and P3-P4 would ideally be treated via special segment OAMs,
and the end-to-end OAM between P1 and P4 would be handled by a different
type of OAM, and end-to-end OAM.

With PW, labels are used to represent attachment circuits (essentially as a
mux field), creating another Label push:

       |--------------------------------|

         |----------------------------|

               |----|-----|-----|


CE1----PE1----P1----P2----P3----P4----PE1----CE2

Creating another End-to-End OAM, the discussion then becomes what is the
termination points of this "layer". If you view PW as just a mux function,
and you create a mux field rather than pushing another label, then the
network looks like this:

 |---------------------------------------------|

         |----------------------------|

               |----|-----|-----|      TE COS = Gold


CE1----PE1----P1----P2----P3----P4----PE1----CE2

However, I suspect that the label push was used as automating the way a mux
indication is assigned to an attachment circuit. Perhaps an alternative
solution may have been to use signaling to indicate the relationship between
mux numbers and attachment circuits, and then use a mux field and not push a
label.

if you believe the OAM needs to flow to a different point in the PE system
because the PW logic is implemented in a different part of the system, then
you are back to this:

       |--------------------------------|

         |----------------------------|

               |----|-----|-----|


CE1----PE1----P1----P2----P3----P4----PE1----CE2

Which brings us back to the old conversations (described previously as
"useless" and "in-bred") about what is a layer.

Mark

-----Original Message-----
From: pwe3-admin@ietf.org [mailto:pwe3-admin@ietf.org]On Behalf Of Lin,
Zhi-Wei
Sent: Friday, June 06, 2003 5:52 AM
To: 'Shahram Davari'; 'Mark Seery'; Jack Pugaczewski
Cc: pwe3@ietf.org
Subject: RE: [PWE3] PWE Service interworking


Hi all,

Sorry to interrupt your very informative discussions, but I have a question.
In the case of the MPLS (which is our topic?) my understanding is that OAMs
are always end-to-end? "Segment" OAMs similar to ATM can be created for MPLS
simply by stacking a new MPLS header?

Thanks for any clarification
Zhi

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