Subject: RE: [PWE3] draft-ietf-pwe3-cw-04.txt

From: "Yaakov Stein" <[email-masked]>
Date: Wed, 15 Jun 2005 17:07:05 +0200

Carlos, 

For two years I tried to get the WG to agree on a single control word.
But everyone told me that there was no good reason for a single CW,
that there were already deployments with other CWs, 
that changing hardware would be too expensive etc.
At the IETF 55 meeting, when I pointed out that we had three different
CWs
and suggested choosing a single one, I was hooted off the stage.

Then it was "discovered" that forwarding devices of a certain
manufacture
needed the initial nibble to be zero for non-IP MPLS payloads. 
Amazingly this strong architectural argument changed everyone's minds
overnight.
Miraculously, it became possible for all non-compliant CWs to be
changed,
and the problem of existing deployments disappeared.

However, this miracle cure was only needed for MPLS CWs.
By this time it was already completely clear that PWE3 was responsible 
only for MPLS PWs, and that the l2tpext WG worked independently 
on similar problems but with different techniques.

That's why the CW draft specifically says that L2TPv3 has its own
mechanisms.
I would be very happy if l2tpext would adopt our CW, putting the length
and framentation where we have it. It would be nice for there to be a
single
draft on ATM PWs over MPLS and L2TPv3, on TDM PWs, etc.
I would also be happy if there were a single PW signaling protocol,
and a single OAM mechanism.

But it is not going to happen - not because of the architectural reasons
that Neil points out, but simply because there are two WGs,
each of which has to keep itself busy.

So until someone suggests really unifying the work,
let's leave all mention of L2TP CWs out of our draft,
and let's hope that l2tpext leaves mention of our formats out of
their's.

Y(J)S

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From: Carlos Pignataro <[email-masked]>
Date: Wed, 15 Jun 2005 11:28:41 -0400

Yaakov,

Please see inline.

> That's why the CW draft specifically says that L2TPv3 has its own

This is the core of what I'm trying to understand. Quoting, the CW draft
says: "L2TPv3 [RFC3931] has its own mechanisms for providing this
associated channel". What mechanisms? The only one that seems to exist
for L2TPv3 is the one specified in VCCV Section 7, a PWE3 WG draft.

> and framentation where we have it.

Interestingly enough, the Fragmentation and VCCV drafts (PWE3 WG) define
those bits for L2TPv3 encapsulation (bits in the L2-specific Sublayer).

> It would be nice for there to be a
> single

Is there a technical reason for not considering this suggestion? It
should be good to avoid duplication of efforts when there's not much
divergence, specially when two pwe3 drafts define bits in the "L2TPv3
L2-Specific Sublayer".

Regards,

--Carlos.

-- 
--Carlos.
Escalation RTP - cisco Systems