Liaison statement
T-MPLS Consented Recommendations

We apologize for not having sent a liaison regarding three consented Recommendations related to
T-MPLS. The intent of these Recommendations is not to change MPLS but rather to identify a
subset of existing MPLS necessary and sufficient to provide connection-oriented packet transport.
The approach to the work was to make a profile of the MPLS data plane functionalities defined in
IETF RFCs using the description of MPLS provided in G.8110 (which was approved last year).
The intended application of this profile is to provide a connection-oriented packet transport
network.
The focus of the three new recommendations is on the data plane aspects of T-MPLS. Control plane
aspects are currently for further study and the work on this subject is starting.
According to our work methodology the T-MPLS definitions are split into the three main
Recommendations that have been consented in February 2006:
*	G.8110.1 dealing with the T-MPLS Architecture
*	G.8112 dealing with T-MPLS interface specification
*	G.8121 dealing with T-MPLS equipment functional specification
A brief high-level introduction of the essential features and selected options for Transport MPLS
can be found in section 6/G.8110.1.
The objective of the work done by ITU-T SG15 was to define a way to use MPLS as a connection-
oriented packet-based transport solution for packet aware transport networks that can support both
packet and circuit (e.g. SDH, OTH or WDM) switching technologies under a common operation,
control and management paradigm. For this purpose T-MPLS deploys the MPLS frame format,
Client to MPLS mapping and MPLS to MPLS multiplexing and complements this with transport
network OAM (Y.1711), nested connection monitoring requiring the labels to be present up to the
final node in the network, protection switching (Y.1720/G.8131), transport network based control
and management planes, maintaining frame ordering and a restricted number of classes of
service/queues.
*	MPLS has many applications and it is desirable to identify a subset of MPLS technology that
provides the necessary and sufficient functionality for transport applications.
We have indicated below some of the options we have selected :-
*	In IETF RFCs the usage of PHP is optional. We decided not to use it in order to simplify OAM
procedures
*	In IETF RFCs the usage of merging is optional. We decided not to use it in order to simplify
OAM procedures and also because the relative lower number of LSPs to be supported is not
considered a major scaling issue
*	The usage of ECMP is optional. We decided not to use it in order to simplify OAM procedures
*	Leaving labels 16-31 for further study was seen as a no change because the label allocation on a
link is defined in IETF RFCs as a local matter for any MPLS device.
We are not expecting that the current version of the specification is going to create any
interoperability issue. We envisage two possible cases of interoperability:
1.	Interoperability between a T-MPLS box and an existing full-featured and fully configurable
MPLS box can be solved by configuring the MPLS box to use the same options selected by T-
MPLS (T-MPLS being a profile of MPLS this should be possible). In this case the link between
the two boxes is a T-MPLS link and in the scope of our Recommendations.
2.	Interoperability between a transport platform supporting T-MPLS and an existing MPLS box
that uses a different option selection than T-MPLS, should be solved by the transport platform.
In this case the link between the transport platform and the MPLS box is not a T-MPLS link and
therefore it is outside the scope of T-MPLS recommendations. We are looking for cooperation
with IETF to develop the detailed specification of this case.
Please find attached the text of the consented Recommendations.  Please note that some minor
modifications may be made to these draft Recommendations as a result of comments made during
the approval process
We will appreciate your comments and suggestions in relation to the initial scope of T-MPLS as a
packet transport network technology.
We are planning to review your comments during the next meeting that is planned in Kobe (Japan)
on 22-27 April 2006. Results of the comments will be included into our future work (e.g. corrigenda
or amendments) on T-MPLS Recommendations. Amendments of T-MPLS Recommendations are
already in our plan for the next SG15 plenary meeting in November 2006.We are looking forward
for future cooperation with you in T-MPLS data plane and control plane evolution.

Attachments: Consented Text of G.8110.1, G.8112, G.8121