The purpose of a transport network is to provide a reliable aggregation and transport
infrastructure for any client traffic type. With the growth of packet-based services,
operators are transforming their network infrastructures while looking at reducing capital
and operational expenditures. In this context, a new technology is emerging: a transport
profile of Multi-Protocol Label Switching called MPLS-TP. MPLS-TP is currently under
development at the IETF in collaboration with ITU-T experts.
The goal of MPLS-TP is to provide connection-oriented transport for packet and TDM
services over optical networks leveraging the widely deployed MPLS technology. Key to
this effort is the definition and implementation of OAM and resiliency features to ensure
the capabilities needed for carrier-grade transport networks – scalable operations, high
availability, performance monitoring and multi-domain support.
MPLS-TP key characteristics are:
· It is strictly connection oriented
· It is client-agnostic (can carry L3, L2, L1 services)
· It is physical layer agnostic (can run over IEEE Ethernet PHYs, SONET/SDH
[G.783] and OTN [G.709],[G.872] using GFP [G.7041], WDM, etc.)
· It provides strong operations, administration and maintenance (OAM) functions
similar to those available in traditional optical transport networks (e.g.,
SONET/SDH, OTN); these OAM functions are an integral part of the MPLSTP
data plane and are independent from the control plane
· It provides several protection schemes at the data plane similar to those
available in traditional optical transport networks.
· It allows network provisioning via a centralized NMS and/or a distributed
control plane
· The GMPLS control plane is also applicable to the MPLS-TP client or server
layers and allows to use a common approach for management and control of
multi-layer transport networks
Current transport networks (e.g. SONET/SDH) are typically operated from a network
operation center (NOC) using a centralized network management system (NMS) that
communicates with the network elements (NEs) in the field via the telecommunications
management network (TMN, see ITU-T Recommendation M.3010 [M.3010]). The NMS
provides well-known FCAPS management functions which are: fault, configuration,
accounting, performance, and security management as defined in ITU-T
Recommendation M.3400 [M.3400]. Together with survivability functions such as
protection and restoration, availability figures of >99,999% have been achieved thanks
to the highly sophisticated OAM functions that are existing e.g. in SONET/SDH
transport networks. This well proven network management paradigm has been taken as
basis for the development of the new MPLS-TP packet transport network technology.
Moreover, MPLS-TP provides dynamic provisioning of MPLS-TP transport paths via a
control plane. The control plane is mainly used to provide restoration functions for
improved network survivability in the presence of failures and it facilitates end-to-end
path provisioning across network or operator domains. The operator has the choice to
enable the control plane or to operate the network in a traditional way without control
plane by means of an NMS. It shall be noted that the control plane does not make the
NMS obsolete – the NMS needs to configure the control plane and also needs to interact
with the control plane for connection management purposes.
History of MPLS-TP Standardization
MPLS-TP started as Transport-MPLS at the ITU-T (see G.81xx series of ITU-T
Recommendations), which was renamed to MPLS-TP based on the agreement that was
reached between the ITU-T and the IETF to produce a converged set of standards for
MPLS-TP.
MPLS Standardization Efforts at the ITU-T
Transport-MPLS (T-MPLS) was a standardization effort that was undertaken by the
ITU-T. It is a packet-based transport network that will provide a key evolution path for
next-generation networks reusing a profile of existing MPLS as defined by IETF and
complementing it with transport-oriented OAM and protection capabilities. T-MPLS
promises multi-service provisioning, multi-layer OAM and protection resulting in
optimized circuit and packet resource utilization.
ITU-T approved the first version of its packet transport recommendation called
Transport MPLS (T-MPLS) Architecture in 2006. By 2008, the technology had reached
the stage where some vendors started supporting T-MPLS in their optical transport
products. At the same time, the IETF was working on a new mechanism called Pseudo
Wire Emulation Edge-to-Edge (PWE3) that emulates the essential attributes of a service
such as ATM, TDM, Frame Relay or Ethernet over a Packet Switched Network (PSN),
which can be an MPLS network [RFC3916].
A Joint Working Group (JWT) was formed between the IETF and the ITU-T to achieve
mutual alignment of requirements and protocols.
MPLS-TP Standardization Efforts at the IETF
On the basis of the JWT activity, it was agreed that future standardization work will
focus on defining MPLS-Transport Profile (MPLS-TP) within the IETF using the same
functional requirements that drove the development of T-MPLS. When MPLS-TP RFCs
will have reached a technical maturity level comparable with the existing T-MPLS
Recommendations,, the ITU-T will align the latter with the MPLS-TP accomplishments
from the IETF.
Reference: MPLS-TP – The New Technology for Packet Transport Networks
Dieter Beller, Rolf Sperber
FS/O/PDL, FS/R/VP
Alcatel-Lucent Deutschland AG
Lorenzstraße 10
D-70435 Stuttgart
Dieter.Beller@alcatel-lucent.com
Rolf.Sperber@alcatel-lucent.de
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