Techmahindra - MPLSTPWhitepaper

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© Tech Mahindra Limited 2010

MPLS Evolution: MPLSTransport ProfileAuthorAnkur Rawat,Sasindran M Prabhu14th May, 2010

Abstract:

In recent years, market forces in the telecommunication industry have been pulling from several directions. There is an emerging need for packet-oriented aggregation infrastructures complementing the traditional SONET/SDH transport solutions with equivalent operational characteristics. To serve the need, in 2006, ITU-T came up with MPLS based T-MPLS protocol, but due to compatibility issues with MPLS, T-MPLS was terminated at a very early age. In 2008, ITU-T joined hands with IETF to develop a protocol called MPLS-TP. This protocol was extension of T- MPLS with compatibility issues resolved.This paper provides an overview of MPLS-TP, differences between MPLS-TP and T-MPLS, OAM frame structure of MPLS-TP and market prospects of MPLS-TP. Also, this paper outlines Tech Mahindra’s approach towards this protocol.



© Tech Mahindra Limited 2010

Table of Contents

Introduction to MPLS, T-MPLS & MPLS-TP ..................................................................................... 1 Acronyms & Abbreviations ............................................................................................................... 3

MPLS-TP Characteristic features & Advantages ............................................................................. 4 OAM frame structure of MPLS-TP & T-MPLS .................................................................................. 5 Functions of Associated Channel (ACH) .......................................................................................... 6 Differences between T-MPLS and MPLS-TP ................................................................................... 7 Market Prospects .............................................................................................................................. 8 Summary .......................................................................................................................................... 9 Tech Mahindra’s Plan ..................................................................................................................... 10 References ..................................................................................................................................... 11



1 © Tech Mahindra Limited 2010

Introduction to MPLS, T-MPLS & MPLS-TP

Standardized by the IETF, IP/MPLS is a scalable, protocol designed to carry circuit and packettraffic over virtual circuits known as label switched paths (LSPs). Operating at an OSI layerbetween the traditional definitions of Layer 2 and Layer 3, IP/MPLS makes packet-forwardingdecisions based on the contents of the label.

Standardized by ITU-T, Transport MPLS (T-MPLS) is a new formulation of MPLS, designedspecifically for application in transport networks. It builds upon well known and widely deployedIP/MPLS technology. It offers a simpler implementation, where features not relevant toconnection-oriented applications are removed and critical transport functionality gaps areaddressed. Work to define T-MPLS was started by the ITU-T in February 2006. ITU-T ceasedwork on T-MPLS in December 2008, in favor of MPLS-TP standardization.

IETF raised concerns over compatibility of T-MPLS with the already established IP/MPLS. To

address these concerns, In February 2008, the ITU-T and IETF joined hands to form a JointWorking Committee (JWC). JWC came up with a technical solution called MPLS Transport Profile(MPLS-TP). On one hand, MPLS-TP uses a subset of MPLS standards where features that are notrequired in transport networks such as IP forwarding, penultimate hop popping (PHP), or equalcost multiple paths (ECMP) are not supported or made optional. On the other hand, MPLS-TPdefines extensions to existing MPLS standards and introduces established requirements fromtransport networks.

MPLS-TP has comprehensive set of OAM and protection features. OAM features help in fastdetection, localization, troubleshooting, SLA verification and performance monitoring.

Protection functionality allows the transport grade sub-50 ms recovery for both linear and ringapplication. By providing an expansive set of OAM, recovery tools and NMS-based operation,MPLS-TP enables more deterministic network operation which allows quick detection andcorrection for any SLA violation. It gives the network operators full control of their networks.

MPLS-TP has some optional features e.g., the control plane is optional and protocols such asOAM and protection are designed to operate fully without a control plane. Figure 1 and 2illustrates the set of overall functionalities of the MPLS-TP [3].

Figure 1: Basic functionalities of MPLS-TP






Acronyms & Abbreviations

ACH Associated Channel

APS Automatic Protection Switching

BoS Bottom of Stack

DCC Data Communication Channel

EXP Experimental

G-ACH Generic Associated Channel

IETF Internet Engineering Task Force

ITU-T International Telecommunication Union

LFU Label for You

LSP Label Switched Path

MAC Media Access Control

MCC Management Communication Channel

MEG Maintenance Entity Group

MEL Maintenance Entity Group Level

MEP Management End Point

MIP Management Intermediate Point

MPLS Multi Protocol Label Switching

MPLS-TP MPLS – Transport Profile

NMS Network Management System

OAM Operation, Administration and Maintenance

PW Psuedowire

SCC Signaling Communication Channel

SONET Synchronous Optical Network

SDH Synchronous Digital HierarchyTTL Time to Live

TMP T-MPLS Map

T-MPLS Transport MPLS

VCCV Virtual Circuit Connectivity Verification




MPLS-TP Characteristic features & Advantages

MPLS-TP promises key enhancements to MPLS, such as engineered point-to-point bi-directionallabel switched paths (LSPs) and end-to-end LSP protection facilities. These features will providebenefits to Telecom Service Providers. Some of the key characteristics features & there benefitsare mentioned below.

• Connection oriented protocol.• Meets functional requirements of service provider transport applications.• Interoperates with existing MPLS and pseudowire emulation edge-to-edge (PWE3) networks.

• Consistent with MPLS architecture and forwarding paradigm, using a subset of the MPLS dataplane and re-uses generic pseudowire (PW) and MPLS LSP constructs.

•

Enhanced OAM functionality.• OAM is able to trigger path recovery actions without control or management plane

interaction.• Packet forwarding is not required to operate or configure the data plane, or to support OAM,

and has no dependency on routing protocols.

• Allows bi-directional, congruent (share same path through network), point-to-point LSPs.

• Introduces the Generic Associated Channel, this channel can be used to send traffic as well asdata.

• Control plane is not mandatory for network operation. Provisioning (automated or manual)

can be via network management system.




OAM frame structure of MPLS-TP & T-MPLS

The OAM frame structure of MPLS-TP is different from that of T-MPLS. MPLS-TP uses theAssociated Channel (ACH) to identify the OAM frame. LSP ACH and PW ACH adopt the sameOAM mechanism. Figure 3 shows the OAM frame structure of T-MPLS. Figure 4 and Figure 5show the OAM frame structure of MPLS-TP LSP & PW respectively [1], [2].

Figure 3: OAM frame structure of T-MPLS

MPLS-TP introduces Management End Point (MEP) and Management Intermediate Point (MIP),which allows for continuity checks and connectivity verification messages propagated betweenthe two end points. This works as a powerful tool for fast detection of lost connectivity as wellas support for connection mis-configuration.

Figure 4: OAM frame structure of MPLS-TP LSP

MPLS-TP OAM supports monitoring of the SLAs using continuity check and connectivity

verification. In addition, it provides mechanism s for performance monitoring including delayand loss measurements to detect performance degradations. MPLS-TP OAM supports thecontrol of the alarm escalation process using alarm suppression, thereby enabling faults to bquickly detected and isolated, while avoiding unnecessary alarm storms in the network.

Figure 5: OAM frame structure of MPLS-TP PW




Functions of Associated Channel (ACH)

In order to ensure proper operational control, MPLS-TP network elements exchange OAMpackets that strictly follow the same path as traffic data (OAM in the data plane), with a commonset of tools running at each network level (PW, LSP, and section). OAM packets are carried usingthe Generic Associated Channel (G-ACh).

The functions of Associated Channel are listed below:• Associated Channel is a generic function. It can run over LSP as well as PW.• Associated Channel allows the operator to send any type of control traffic into a PW or LSP.

For example, Virtual Circuit Connectivity Verification (VCCV) may be sent over an associatedchannel to monitor if the PW is available.

• Associated Channel is capable of carrying user traffic, OAM traffic & Management traffic. Forexample, associated channel can also carry Automatic Protection Switching (APS)information and Data Communications Channel (DCC), Signaling Communication Channel(SCC), and Management Communication Channel (MCC) management traffic, etc.




Differences between T-MPLS and MPLS-TP

OAM header and the interpretation of different fields inside the header form the base for the setof differences between T-MPLS & MPLS-TP.

Some of the differences are listed below.• T-MPLS uses reserved “Label 14” as OAM identifier whereas MPLS-TP uses “Label 13” as OAM

identifier.

• T-MPLS uses the type of “+1” or “-1” values of MEL (Maintenance Entity Group Level) toindicate the nesting of OAM whereas MPLS-TP uses label stack to indicate nesting of OAM.

• MPLS-TP uses Time-to-Live (TTL) to trace the MIP path and monitor the loopback status ,while T-MPLS uses TTL in the OAM packet header label to identify Management EntityGroup Intermediate Point (MIP): TTL=MIP hops+1, and MIP processes the OAM frames withMEL=0 and TTL=2. MPLS-TP uses TTL in the LSP or PW label only.




Market Prospects

In the fixed-line network, the successful application of ADSL technology has brought a 2Mbpsbandwidth to the end user’s home. The increasing growth of broadband subscriber base resultsin huge demands for large bandwidth. Data traffic transferred through the provincial backbonetransport network accounts for 90% of the total traffic. This indicates that the IP-based servicebearing has become the development trend in the industry. The future service transportnetwork tends to be intelligent, highly integrated and broadband-enabled, which can beachieved by using the MPLS-IP technology.

Leading network operators such as British Telecom (BT), France Telecom (FT) and China Mobilehave been actively participating in the MPLS-TP standardization and have planned to use the

MPLS-TP technology for service transport and mobile data backhaul. They have been activelyparticipating in and paying much attention to the development and testing of related productsby telecom equipment manufacturers.

Leading telecom equipment manufacturers, such as Alcatel-Lucent, Cisco, Nortel, Nokia-Siemens, Ericsson, ZTE, Huawei, FiberHome, UTStarcom, etc., have been actively involved in theR&D of the MPLS-TP technology and related standardization work. For example, ZTE hasimplemented MPLS-TP related OAM and protection functions on its ZXR10 9000 and ZXCTN6100/6200/6300 product series and successfully trialed them over the networks of operatorssuch as China Mobile and Telecom Malaysia. Huawei has launched the PTN 912/OSN 3900/1900series, FiberHome the CiTRANS 660/620 series, UTStarcom the TN 725/705 series, Alcatel-Lucent the 1850 TSS 320/40/5 series and Ericsson the OMS 2430/2450 series.

On all accounts, both telecom equipment manufacturers and network operators have beenactively engaged in the research and planning of the MPLS-TP technology. This indicates thatMPLS-TP has promising prospects and will play a key role in the future packet transportnetwork.




Summary

MPLS-TP represents an optimized combination of MPLS & transport networks, designed to carrypackets. It provides an evolution path from SONET/SDH based networks to packet networks. Itpreserves the advantageous features of SONET/SDH like OAM & protection switching, thusallowing the full end-to-end integration with existing MPLS infrastructure. By using MPLS-TP,Service providers will have the manageability, stability, flexibility, scalability and deterministicperformance in there network from edge to edge.

With MPLS-TP, Service Providers will enjoy all of the following benefits.• Carrier grade, multi vendor, IETF/ITU-T standardized Common packet transport

network.• Fully integrated IP and transport platform for next-generation common access and

transport solution.

• Support for end to end QoS, strict Committed Information Rate (CIR), guaranteedframe delay, frame delay variation and packet loss ratio.

• Capability to obtain different performance characteristics for key applicationswithout requiring the use and expense of multiple networks.

• Support for sub 50ms protection switching ensuring high availability.• Comprehensive OAM functionality.




Tech Mahindra’s Plan

Based on the Capabilities in MPLS, Optical Networks (SONET/SDH) and other data-communication technologies, Tech Mahindra will be able to contribute in the following areas.Based on the market potential and the opportunities from the vendors, we will be able to selecta few among these areas.

• MPLS-TP Data plane module

• MPLS-TP Control plane module

• MPLS-TP OAM module

• MPLS-TP EMS/NMS moduleBased on the opportunity from the vendors, we will be able to select among these activities:

• Requirement Analysis

• Product Design & Development

• Testing & Validation• Interoperability Testing• Network Design, Deployment & Maintenance for Telecom Service Providers.



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References

1. http://wwwen.zte.com.cn/endata/magazine/ztecommunications/2009year/no1/articles/200903/t20090319_170886.html

2. http://www.ietf.org/MPLS-TP_overview-22.pdf

3. “MPLS-TP: The Key Enabler of Converged Packet Transport Networks” -Whitepaper by

Alcatel-Lucent.

4. http://www.faqs.org/rfcs/rfc5317.html

5. http://www.cisco.com/en/US/technologies/tk436/tk428/white_paper_c11-562013.pdf

6. http://tools.ietf.org/pdf/draft-ietf-mpls-tp-oam-framework-06.pdf

7. http://en.wikipedia.org/wiki/T-MPLS

8. http://en.wikipedia.org/wiki/MPLS-TP

9. http://www.dfn.de/fileadmin/3Beratung/DFN-Forum2/118.pdf

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Techmahindra - MPLSTPWhitepaper