Subject: [PWE3] Q12/15 Liaison to MPLS WG

From: Stewart Bryant <[email-masked]>
Date: Mon, 24 Apr 2006 11:52:15 +0100

Please can I draw the attention of the PWE3 WG to the
following Liaison addressed to the MPLS WG from ITU SG15.

This is being discussed on the MPLS and CCAMP lists
and Loa is co-ordinating a response. Response is due back
to ITU 17/May.

https://datatracker.ietf.org/public/liaison_detail.cgi?detail_id=207

G.8110.1 contains an appendix that discusses PWE3.

This contains a reference to

Internet Draft draft-pan-pwe3-over-sub-ip-01.txt (2005), Dry-Martini: 
Supporting Pseudo-wires in Sub-IP Access Networks.

which is an expired individual submission.

Is there any other feedback that the PWE3 WG needs to give?

Regards

Stewart

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From: "Yaakov Stein" <[email-masked]>
Date: Tue, 25 Apr 2006 17:55:42 +0200

Stewart, 

In general, as PWs are also CO in nature, the subset of MPLS defined by
SG15 is reasonable for PWE purposes (although the MPLS WG may have
problems
with the blocking of some of their favorite optimizations and the use of
Y.1711 OAM).

One issue that may affect us is the deprecating of PHP. This means
that PWs must always have at least one tunnel label. 

Since Appendix I of G.8110.1 is the part that directly influences PWE
work,
I gave it a good read. It seems to have a few problems:

*      The IETF PWE3 work group has developed an MPLS transport concept,
know as pseudowires.  
Well, I think that PWE3 has developed a method of transporting services
over many different PSNs,
one of which is MPLS.

*   PWE3 is intended to provide only the minimum necessary functionality
to emulate a wire with the 
   required degree of faithfulness for the given service definition.
I am not sure where that came from. AFAIK PWs try to maximize the
functionality
although realizing that the emulation may not be perfect. In such cases
we have
applicability statements detailing where they emulated service may
differ from the native one.

*   The PSN can be implemented by utilizing a MPLS label switched
network. 
I think they mean "An MPLS label switched network is an example of a
PSN."

*   A four octet Control Word is added to the MPLS payload field for
some encapsulations. 
The CW is defined in all encapsulations. Its use is optional in some
(most?).

*   The NSP function process the Control Word. 
Well, yes the NSP does handle the flags (when there are flags defined).
But the IWF handles the sequencing, FRG, etc.
So I think this statement is misleading (and grammatically faulty).

*   IETF has defined pseudowire encapsulations for Ethernet, Frame
Relay, ATM, PPP, PDH, and SDH. 
Suggest  PPP -> HDLC/PPP

*   ITU SG 13 has developed a series of recommendations for MPLS /
Client Network Interworking 
   for Ethernet (Y.1415), ATM (Cell Mode - Y.1411), ATM (Frame Mode -
Y.1412), and TDM (Y.1413). 
They missed X.86 (frame relay PW)!  Although developed by SG17, it is
now in SG13.

*   These recommendations are similar in concept to IETF PWE3. 
I think they are identical in concept (even in detail).

*  Figure 8
Why do they pick the semi-formal diagram when the same Recommendation
has a G.805 diagram too? They should show Figure 6-2 of Y.1415 instead.

*   The Forwarder function is called an Interworking Function (IWF) 
I am not sure that IWF and forwarder are the same.

*   Figure 9 Pseudowire Model
They show the PW as a trail with a T-MPLS trail termination function.
This termination is defined here as injecting Y.1710 OAM.
Do they expect us to use Y.1710 instead of VCCV?

*   Pseudowires can be switched by a Subnetwork Connection (SNC). 
   This creates in PWE3 terminology Multi-Segment Pseudowires (MS-PW) 
    as defined in the bibliography reference [1].
Bibliography reference [1] is RFC 3985. Sorry, 3985 doesn't define (or
even mention)
MS-PWs. They mean reference [2].

*   When the MPLS server layer is an SDH layer network, an SDH path
layer may be used 
   instead of the pseudowire PSN transport tunnel. This approach has
been called "dry martini" 
   as defined in the bibliography reference [2]. 
First, that's reference [3]. Second, this should be marked as "work in
progress".
Third, it is probably not a good idea to reference a dead individual
submission.
Fourth, in the ITU itself there is work going on regarding generic
client adaptations
for SDH that includes this work.

*   Pseudowires can be used as a packet transport mechanism for
emulating LAN Services 
   over a Transport MPLS network. Like in Virtual Private LAN Service
(VPLS) a full mesh of 
   T-MPLS trails (PW trails) is used to interconnect split-horizon ETH
Flow Domains.
They should reference Appendix I of Y.1415.

Y(J)S