Subject: [Mpls-interop] MPLS-TP Alert mechanism and existing MPLS OAM alert mechanisms

From: Rahul Aggarwal <[email-masked]>
Date: Fri, 30 May 2008 17:10:05 -0700 (PDT)

Hi All,

While discussing the MPLS TP Alert label draft, the issue of the
applicability of the MPLS TP Alert label to "traditional" MPLS
environments came up. I want to step back for a bit to discuss this in a
wider context.  Hence this email.

The MPLS TP Alert label + G-ACH provide a generic control
channel for MPLS LSPs. This control channel can be used for OAM and for
other purposes.

Now there are *existing* MPLS mechanisms that provide a control channel
for MPLS LSP OAM. These consist of TTL expiration, router alert MPLS label
etc along with an assumed IP encapsulation for the OAM packets.

We need to spell out:

a) Can the MPLS TP Alert label + G-ACH based control channel apply to
"traditional" MPLS environments ?

If yes, when does it apply to those environments ? What is the preferred
MPLS OAM technique in the traditional environments ?

b) Can the G-ACH based control channel be used in conjunction with an
existing MPLS OAM alert mechanism e.g. TTL expiration ? Can this be
done for the MPLS-TP ? Can this be done in "traditional" environments
? (Note that this might be sufficient for MPLS-TP if the LSP has more than
a single label stack and there is no PHP.)

Once we figure this out, the different pieces will need to be folded in
the overall architecture, G-ACH draft and TP Alert label draft.

Answering the above is necessary as the mechanisms we are putting in place
for MPLS-TP are generic in nature and may not apply to MPLS-TP alone
going forward.

rahul
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