orckit-corrigent mpls-tp technical note 1212
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Technical NoteMPLS-TP
Jan. 2011
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Table of contents
Introduction 3
MPLS-TP Overview 4-5
The need for MPLS-TP 6MPLS-TP OAM 7-8
MPLS-TP Survivability 9
MPLS-TP control plane and management 10
Orckit-Corrigent MPLS-TP value proposition 11-12
Migration to MPLS-TP 13
Summary 14
List of figures
Figure #1: MPLS-TP evolution 6
Figure #2: CCM Flow 7
Figure #3: Orckit-Corrigent IP/MPLS and MPLS-TP interworking 12
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Introduction
The Multiprotocol Label Switching Transport Profile (MPLS -TP) is a packet
transport technology that leverages benefits from the existing MPLS
networking infrastructure, and improves the efficiency and effectiveness of
packet transport networks, while maintaining the mandatory Operation
Administration and Maintenance (OAM) capabilities of legacy SONET/SDH
networks.
This technical note provides information on MPLS-TP technologies andimplementation in Orckit-Corrigents Packet Transport Network (PTN)
solutions.
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MPLS-TP Overview
MPLS-TP is based on a subset of MPLS technologies with additionaltransport functionalities, as in traditional transport networks, making it a
reliable, scalable, and cost optimized packet-based transport technology.
MPLS-TP introduces additional transport functionalities such as
comprehensive OAM capabilities, survivability, data-plane/control-plane
separation, and static provisioning of bidirectional services. This is in addition
to well-accepted MPLS functionalities such as Quality of Service (QoS),
scalability, traffic engineering and Layer 2 packet forwarding. The result is the
ability to provide network operators with full control over their packet
networks.
MPLS-TP Functionalities
MPLS-TP includes the following main functionalities defined by Internet
Engineer Task Force (IETF) and International Telecommunications UnionTelecommunications Standardization Sector (ITU-T) standardization bodies
Bidirectional Label Switch Path (LSP)
o Transmit and receive traffic following the same path throughout
the network
Enhanced OAM tools
o Continuity Check (CC) for fast failure detection
o Alarm Indication Signal (AIS) for fault isolation
o Remote Defect Indication (RDI) for fault isolation
o Loopback (LB), similar to IP ping, for basic maintenance
o Loss/delay measurement for detection of performance
degradation
End-to-end Protection
o 1:1 bidirectional end-to-end protection scheme triggered by
OAM
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o Sub 50ms linear protection
o Pseudo wire (PW) and LSP protection
Control plane options
o Separation from the data plane
o Static or dynamic LSP configuration
MPLS-TP in the standardization bodies
The IETF and the ITU-T teams agreed to work together on the design of
MPLS-TP, in order to bring transport network requirements to the existing
MPLS technology.
The Joint Working Group (JWT) focuses on the following main categories
General requirements
OAM
Survivability
Network management
The JWT started their work in March 2008. The first draft was published in
July 2008 and the final agreement is expected at the end of 2011.
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The need for MPLS-TP
The increasing growth of packet-based traffic is driving the need for evolved
transport networks. The next generation transport technologies should
leverage the same benefits of legacy transport in terms of end-to-end
determinism, OAM, high availability, high reliability, and easy to use
management.
IP/MPLS
SONET/SDH
MPLS-TP
P a c k e t e f f i c i e n c y
T r a n s p o
r t r e l i a b i
l i t y
IP/MPLS
SONET/SDH
MPLS-TP
P a c k e t e f f i c i e n c y
T r a n s p o
r t r e l i a b i
l i t y
Figure #1: MPLS-TP evolution
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MPLS-TP OAM
MPLS-TP OAM provides the same OAM concepts and methods which areavailable in legacy transport networks, including
Fast failure detection
Alarm suppression
Remote defect indication
Protection switching
OAM packets are carried on Generic Associated channel (G-Ach).
OAM and data packets are carried on the same path, therefore enabling
simpler and faster monitoring of the PW and LSP layers.
MPLS-TP OAM introduces the functional components, Maintenance End
Point (MEP) and Maintenance Intermediate Point (MIP), which enable running
OAM packets between two end points, such as:
1. Continuity checks (CC) messages allowing fast detection of lost of
connectivity, as well as connection mis-configuration.
The CC messages are sent periodically by MEP and monitored for Loss Of
Continuity (LOC) by each MEP/MIP.
The transmission interval can be set to a minimum of 3.3 ms, allowing forvery fast-failure detection.
Figure #2: CCM Flow
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2. Delay and Loss Measurements (DM/LM) allowing the detection of
performance degradations.
3. Loopback (LB) messages allowing on-demand bidirectional diagnostic
test for connectivity check and failure localization.
4. Alarms suppress enabling fault localization while avoiding unnecessary
alarms propagation. AIS and RDI are sent to the remote sides in case of
LOC detection.
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MPLS-TP Survivability
MPLS-TP provides similar protection switching mechanisms which are used inlegacy SONET/SDH transport networks, including
End to end linear protection for LSP, PW and Multi Segment PW (MS-
PW) layers
Protection State Coordination (PSC) mechanism to synchronize the
both ends on protection status and commands
Sub-50 ms protection in case of failure in the data plane (relying on
OAM messages transmission at 3.3 ms rate)
Manual protection commands e.g. manual switch, lockout, clear
Provides architecture of 1+1 and 1:1 protection schemes
Protection switching is triggered upon Signal Fail (i.e. LOC) or Signal
Degrade (SD) or manual commands
All these mechanisms provide enhanced LSP/PW/MS-PW end- to-end
protection, ensuring network reliability and high availability.
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MPLS-TP control plane and management
The control plane in MPLS-TP is the mechanism used for provisioningLSPs/PWs dynamically over the packet network. The control plane is optional
and separated from the data plane. A failure of the control plane will not
create any kind of data plane failure.
When no control plane is used, operators can set up LSPs and PWs statically
using a Network Management System (NMS), similar to the way it is done in
legacy transport networks, without IP or routing protocols.
In the dynamic approach, a control plane is used. LSPs and PWs creation is
done by Generalize MPLS (GMPLS) and Targeted Label Distribution Protocol
(T-LDP).
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Figure #3: Orckit-Corrigent IP/MPLS and MPLS-TP interworking
Together with the dual stacking of IP/MPLS and MPLS-TP, Orckit-Corrigent
CM-4000 offers a centralized NMS (CM-View) with a Path Computation
Element (PCE), Traffic Engineering Database (TED) and Call Admission
Control (CAC). This solution enables
Automatic provisioning of LSPs considering Traffic Engineering (TE)
properties such as Class of Service (CoS) and bandwidth
Understanding the relationship between network resources and LSPs
Creation of manual or automatic explicit route
Support of a disjointed path for LSP/PW protection
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Migration to MPLS-TP
Service providers who wish to deploy a new packet-based transport network
based on MPLS-TP technology are facing a dilemma of which technology to
use as a stepping stone until MPLS-TP will be ratified. Such intermediate step
should take into account the complexity and the cost of migrating at the end to
MPLS-TP. There are 2 options for such intermediate step:
1. T-MPLS technology
2. IP/MPLS Technology
In the first option, the T-MPLS which is a non-standard technology is
positioned as a stepping stone to MPLS-TP. The assumption is that since T-
MPLS is the basic of MPLS-TP, the migration in the future will only be a
software upgrade, but since the MPLS-TP standard still has a long way to go,
there is a risk that service providers will end up with a complicated and
expensive migration.
In the second approach, the service providers can choose the IP/MPLStechnology as a step towards the MPLS-TP, the IP/MPLS is field-proven and
a de-facto standard unlike T-MPLS.
In such approach the service providers will eliminate the risk of using a non-
standard technology and in addition they will have the ability to migrate only
part of their IP/MPLS network to MPLS-TP due to the interworking between
the 2 technologies.
Orckit-Corrigent CM-4000 products support both IP/MPLS and MPLS-TP
simultaneously making the migration process smooth and cost-efficient
enabling service providers to migrate to the standardized MPLS-TP by using a
software upgrade only and saving the cost of new hardware.
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Summary
MPLS-TP brings transport characteristics such as OAM, survivability and
management to the MPLS domain, while preserving its flexibility and
scalability.
Orckit-Corrigents CM-4000 PTN solutions support IP/MPLS and MPLS-TP
simultaneously, and by doing this enable the service provider a smooth
migration from IP/MPLS to MPLS-TP as well as interoperability between the
two technologies.
Orckit-Corrigent actively participates in the MPLS-TP standardization efforts
and its CM-4000 products already support MPLS-TP. The CM-4000 MPLS
and MPLS-TP interoperability was demonstrated at Carrier Ethernet World
Congress, Warsaw during September 2010.
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Acronyms
AIS Alarm Indication Signals
CAC Connection Admission Control
CC Continuity Check
CESoPSN Circuit Emulation Service over Packet SwitchingNetworks
G-Ach Generic Associated channel
GMPLS Generalize Multi Protocol Label Switching
IETF Internet Engineer Task Force
IP Internet Protocol
JWT Joint Working Group
LB Loopback
LM Loss Measurements
LOC Loss Of Continuity
LSP Label Switch Path
MEP Maintenance End Point
MPLS Multi Protocol Label Switching
MPLS-TP Multi Protocol Label Switching Transport Profile
NMS Network Management System
OAM Operation, Administration, Maintenance
PCE Path Computation Element
PSC Protection State Coordination
PTN Packet Transport Network
PW Pseudo wire
QoS Quality of Service
RDI Remote Defect Indications
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SD Signal Degrade
SDH Synchronous Digital Hierarchy
SONET Synchronous Optical Networking
TE Traffic Engineering
TED Traffic Engineering Database
T-LDP Targeted Label Distribution Protocol
TP Traffic Profile
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