Subject: RE: [PWE3] PWE3 VCCV breakout meeting

From: Sasha Vainshtein <[email-masked]>
Date: Thu, 4 Aug 2005 12:33:51 +0300

Scott, Carlos and all,
Please see a couple of brief comments inline below.
 
Regards,
                          Sasha

-----Original Message-----
From: Scott Wainner [mailto:[email-masked]]
Sent: Wednesday, August 03, 2005 11:29 PM
To: Carlos Pignataro
Cc: pwe3; Stewart Bryant
Subject: Re: [PWE3] PWE3 VCCV breakout meeting

Carlos Pignataro wrote:

Please find one question inline (that may have already come up and been

answered already).

Circa 8/3/2005 9:02 AM, Stewart Bryant said the following:

These are the minutes of the PWE3 VCCV breakout meeting

that took place at lunch time today.

Corrections from those present and comments from the

list on the proposed resolution are sought.

There were a number of other issues that were raised

at these meeting that were out of scope. Those

issues should be raised on the PWE3 list.

- Stewart

VCCV over IP/RTP Breakout Mtg 3 Aug 2005 @ 1240

===============================================

Present:

Stewart Bryant (Chair)

Bill Stor

Luca martini

Maria Alice

Matthew Bocci

Ron Cohen

Sasha Vainshtein

Scot Weiner

Skip Booth (By Phone)

Tim Frost

Tom Nadeau

Yaakov Stein

Proposals on the Table at Start of Meeting

==========================================

- never include RTP in VCCV

- use ACH

- note that RTP header always starts with 8

etc

or

change order of headers

Discussion

==========

Issue of need to interconnect ip & mpls PWs

Two cases what to do with L2TP and what to do

with UDP/IP

Could change L2TPv3 encap, but UDP problem

remains.

Proposal fix L2TP to be like MPLS and leave

UDP and live with the problems.

UDP has no signalling and is unlikely to be

used for stitching/switching.

Note needs to be added to switching draft

to say that UDP switching to MPLS/L2TP

currently out of scope.

Need to fix statement in VCCV saying that

sub-layer is REQUIRED.

Issue there is one implementation that uses

RTP then CW over L2TP. Needs backwards

compatibility mode.

Proposed Resolution for RTP and CW order for TDM PWs

====================================================

1) L2TP will use MPLS header ordering (i.e. L2TPv3/CW/RTP)

With this order, what is the benefit of hiding the CW presence (or

L2-Specific Sublayer) from the control protocol L2TPv3?

I don't think that was what is implied.  L2TPv3 control protocol would have
to specify that the
MPLS CW would be used for consistency.
[[Sasha]] IMHO this would require some additional capabilities for L2TPv3.
To the best of my recollection, today you can only signal:

*	whether L2-specific sub-layer is present (so that the L2TP switching
machine would be aware of its specific bits, e.g., S-bit)
*	whether sequencing based on the L2-specific  sub-layer is enabled.

It would seem that for TDM PWs over L2TPv3, defining a TDM-Specific

Sublayer with the same sequencing format as the MPLS CW would achieve

the same results, but also:

o Would free 6 bits from the CW for L2TPv3, since the Length is not

  needed in l2tpv3.

o Would allow identifying and intercepting VCCV messages by inspecting

  Bit 0 of the CW (the same way as described in VCCV draft for other

  L2TPv3 encaps) instead of the first nibble; this in turn:

  - Enables consistent vccv demux for L2TPv3 PWs

  - Frees up another 3 bits.

I think the intent was for L2TPv3 to NOT do any sequencing support for TDM.
In fact, the TDM
sequencing would be a function handled by a highler layer function.
[[Sasha]] Absolutely. Sequencing for  TDM pseudo-wires includes some highly
specific features that are hardly part of the generic L2TPv3.

While:

o Would retain consistent sequencing space.

o Would aware the control protocol of the existence of a CW (or

TDM-Specific Sublayer).

I still think we're talking about using the first bit of an L2SS (V-bit) to
identify the presence of a PW-AC or CW for TDMoL2TPv3 ...  
[[Sasha]] No, we are talking about always using MPLS-compliant Associated
Channel (marked with '0001' in the first nibble). 

Thanks,

--Carlos.

2) VCCV mux will use ACH

3) Main text will describe use of MPLS order.

4) Informational Appendix describing old mode RTP/CW order

   in TDM drafts that are affected.

5) Need new option in RTP AVP for new (MPLS) order IN L2TP

6) Change to VCCV draft to describe the above

7) Need to update TDMoIP, CESoPSN, SATOP to reflect the

   above.

8) SONET draft not affected.

9 In UDP/IP PWs VCCV will not use RTP - RTP header

  will be skipped by noting first nibble = 8.

Sasha noted that he needed to discuss the proposal with

his development team. Others present indicated support

for the proposal.

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---

From: Carlos Pignataro <[email-masked]>
Date: Thu, 04 Aug 2005 08:33:43 -0400

Sasha,

Please find two quick comments inline.

Circa 8/4/2005 5:33 AM, Sasha Vainshtein said the following:
>     *From:* Scott Wainner [mailto:[email-masked]]
>     *Sent:* Wednesday, August 03, 2005 11:29 PM
>     *To:* Carlos Pignataro
>     *Cc:* pwe3; Stewart Bryant
>     *Subject:* Re: [PWE3] PWE3 VCCV breakout meeting
> 
> 
> 
>     Carlos Pignataro wrote:
> 
>     I don't think that was what is implied.  L2TPv3 control protocol
>     would have to specify that the
>     [[Sasha]] IMHO this would require some additional capabilities for
>     L2TPv3. To the best of my recollection, today you can only signal:
> 
>         * whether L2-specific sub-layer is present (so that the
>           L2TP switching machine would be aware of its specific bits,
>           e.g., S-bit)
>     I think the intent was for L2TPv3 to NOT do any sequencing support
>     for TDM.  In fact, the TDM
>     [[Sasha]] *Absolutely*. Sequencing for  TDM pseudo-wires includes
>     some highly specific features that are hardly part of the generic
>     L2TPv3.
> 
>>While:
>     I still think we're talking about using the first bit of an L2SS
>     (V-bit) to identify the presence of a PW-AC or CW for TDMoL2TPv3 ... 
>     [[Sasha]] *No*, we are talking about always using MPLS-compliant
>     Associated Channel (marked with '0001' in the first nibble). 

That's what I was wondering. Why use an MPLS-compliant CW for L2TPv3,
since 2 fields of the CW are not applicable to L2TPv3 (i.e. Length and
"ECMP-avoidance discriminator")? Instead, TDMoL2TPv3 can include its
specific sequencing features/requirements in a TDM-Specific Sublayer
signaled using L2TPv3 control protocol. What would be the advantage of
not doing so and hiding the CW from L2TPv3?

Regards,

--Carlos.

-- 
--Carlos.
Escalation RTP - cisco Systems