Liaison statement
Clarification on the intended scope of T-MPLS

Submission date 2006-05-04
From ITU-T SG 15 (Greg Jones)
To IETF MPLS WG, PWE3 WG (George Swallow, Loa Andersson, Stewart Bryant, Danny McPherson)
Cc Scott Bradner, Yoichi Maeda,,,
Response contact,
Technical contact,
Purpose For information
Attachments Clarification on the intended scope of T-MPLS (see this WinWord file for the diagrams)
Thank you for your informal feedback that has been provided on our
previous liaison statement on T-MPLS Consented Recommendations, we also
understand that you are in the process of developing a formal response.
 To assist you in providing your formal response we would like to
provide some additional clarifications on the intended application of
Our intention in developing the suite of T-MPLS Recommendations was to
define a packet based transport network technology.  The design
objectives of T-MPLS were:
a) Follow the principles of the transport network used in other ITU-T
defined transport technologies (e.g SDH, ATM, OTN).
b) To use the PDU and data plane processes defined by the IETF for
T-MPLS is not intended to duplicate the functionality already provided
The only client fully described in the current version of G.8110.1 is
point to point Ethernet Virtual Connection (EVC).  It was agreed to
revise the scope of the Recommendation and provide an appendix II
(attached) to reflect this.  Some other key points identified were:
•	The current version of G.8110.1 only defines the bearer plane and
only point to point trails are currently supported.  It should be noted
that version 2 of G.8110.1 will add point to multipoint trails.
•	Any interworking with client signals (e.g. MPLS, Ethernet) will be
client server i.e. any client OAM or control protocols will be tunneled
transparently across the T-MPLS layer network.
•	Interworking between a client control plane and a (yet to be
defined) T-MPLS control plane will be addressed as a part of the
control plane architecture work.
•	The T-MPLS network provides a single hop link to the client, it is
intended to offer a packet switched connection that has similar
operational characteristics to a SDH network providing a PDH link
connection, e.g. these connections must support the ability to activate
performance monitoring and fault management.  Any PM data or failures
will be reported to the transport operations center.
We also note your comments on the usage of the label space terminology.
 We will work to clarify and if necessary correct this in a future
We have also agreed to initiate work on the architecture of a control
plane for T-MPLS.  We will use the ASON architecture to provide a
framework to describe the problem that is to be addressed.  This does
not imply that we will specify an ASON control plane.  Once we have
refined our requirements we will communicate them to you for advice on
how they may be addressed.  If the requirements cannot be met by an
existing protocol suite we would like to work with you to develop the
appropriate enhancements.
We will be continuing our work on T-MPLS in particular the support of
other clients (e.g. IP/MPLS) at an interim meeting that is planned to
be held 19-23 June in Ottawa Canada.  We will also address any comments
that you provide in your planned liaison statement. Any urgent changes
may be included in an amendment or corrigendum that could be consented
in October 2006.  IETF experts are welcome to participate at this
meeting.  Please contact by May 31st 2006 if you
should wish to participate.
G.8110.1 draft Appendix II

Support of IP/MPLS LSR based networks by
T-MPLS networks supporting point-to-point EVC services
When two IP/MPLS LSRs are connected via e.g. 802.3 interfaces to a
T-MPLS network, the T-MPLS network can provide an EVC service between
these two LSRs (nodes LSR A and LSR B in Figure II-1) to establish an
IP/MPLS link between these LSRs. 
The IP/MPLS LSRs encapsulate their IP/MPLS packets into Ethernet frames
with or without VLAN Tag. These Ethernet frames are then transported
via 802.3 interfaces to the T-MPLS network edge (nodes X and Y). At the
T-MPLS network edge the Ethernet signal is treated either as an
all-to-one EVC service or as one or more EVC and/or bundled EVC
services of which the frames are mapped into one or more T-MPLS (PW)
trails and then transported through the T-MPLS network.
In this network scenario the IP/MPLS routing and control plane
adjacency is between LSR A and LSR B. The T-MPLS network elements do
not participate in the IP/MPLS routing and control plane. A signalling
session that requests PHP is between LSR A and LSR B (T-MPLS nodes X
and Y are not involved).
Figure II-1/G.8110.1 – IP/MPLS via EVC over T-MPLS network
The functional model for this scenario is described in Figure II-2. The
atomic functions in the figure are specified in Recommendations G.8021
and G.8121.The IP/MPLS signals are carried through an IP/MPLS link
between LSR A and LSR B supported by an ETH trail between LSR A and LSR
B. The ETH trail is carried through a serial-compound ETH link
supported by an ETY trail interconnecting LSR A with T-MPLS PE X, a
T-MPLS (PW) trail interconnecting T-MPLS PE X with T-MPLS PE Y and an
ETY trail interconnecting T-MPLS PE Y with LSR B.
<<Figure II-2/G.8110.1 – Functional Model for IP/MPLS via EVC over
T-MPLS network>> - see attachment