Techmahindra - MPLSTPWhitepaper
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MPLS Evolution: MPLS Transport Profile Author Ankur Rawat, Sasindran M Prabhu 14th 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 TMPLS 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.
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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
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Introduction to MPLS, T-MPLS & MPLS-TP Standardized by the IETF, IP/MPLS is a scalable, protocol designed to carry circuit and packet traffic over virtual circuits known as label switched paths (LSPs). Operating at an OSI layer
between the traditional definitions of Layer 2 and Layer 3, IP/MPLS makes packet-forwarding decisions based on the contents of the label.
Standardized by ITU-T, Transport MPLS (T-MPLS) is a new formulation of MPLS, designed
specifically for application in transport networks. It builds upon well known and widely deployed IP/MPLS technology. It offers a simpler implementation, where features not relevant to
connection-oriented applications are removed and critical transport functionality gaps are
addressed. Work to define T-MPLS was started by the ITU-T in February 2006. ITU-T ceased work 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 Joint
Working 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 not required in transport networks such as IP forwarding, penultimate hop popping (PHP), or equal
cost multiple paths (ECMP) are not supported or made optional. On the other hand, MPLS-TP
defines extensions to existing MPLS standards and introduces established requirements from transport networks.
MPLS-TP has comprehensive set of OAM and protection features. OAM features help in fast detection, localization, troubleshooting, SLA verification and performance monitoring.
Protection functionality allows the transport grade sub-50 ms recovery for both linear and ring
application. By providing an expansive set of OAM, recovery tools and NMS-based operation, MPLS-TP enables more deterministic network operation which allows quick detection and
correction 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 as OAM and protection are designed to operate fully without a control plane. Figure 1 and 2 illustrates the set of overall functionalities of the MPLS-TP [3].
Figure 1: Basic functionalities of MPLS-TP
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MPLS-TP introduces features associated with transport networks (such as data plane-based OAM & protection switching, separation of control & data plane) and transport grade OAM
functions. These features facilitate the transition to a connection-oriented packet transport
network by providing efficient packet switching while allowing transport-grade operations [3].
Figure 2: Additional functionalities of MPLS-TP
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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 Hierarchy
TTL
Time to Live
TMP
T-MPLS Map
T-MPLS
Transport MPLS
VCCV
Virtual Circuit Connectivity Verification
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MPLS-TP Characteristic features & Advantages MPLS-TP promises key enhancements to MPLS, such as engineered point-to-point bi-directional label switched paths (LSPs) and end-to-end LSP protection facilities. These features will provide
benefits to Telecom Service Providers. Some of the key characteristics features & there benefits are 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 data plane 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 as data.
• Control plane is not mandatory for network operation. Provisioning (automated or manual) can be via network management system.
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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 the
Associated Channel (ACH) to identify the OAM frame. LSP ACH and PW ACH adopt the same
OAM mechanism. Figure 3 shows the OAM frame structure of T-MPLS. Figure 4 and Figure 5 show 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 between the two end points. This works as a powerful tool for fast detection of lost connectivity as well as 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 delay and loss measurements to detect performance degradations. MPLS-TP OAM supports the
control of the alarm escalation process using alarm suppression, thereby enabling faults to b quickly detected and isolated, while avoiding unnecessary alarm storms in the network.
Figure 5: OAM frame structure of MPLS-TP PW
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Functions of Associated Channel (ACH) In order to ensure proper operational control, MPLS-TP network elements exchange OAM
packets that strictly follow the same path as traffic data (OAM in the data plane), with a common set of tools running at each network level (PW, LSP, and section). OAM packets are carried using the 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 associated channel to monitor if the PW is available.
• Associated Channel is capable of carrying user traffic, OAM traffic & Management traffic. For example, 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.
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Differences between T-MPLS and MPLS-TP OAM header and the interpretation of different fields inside the header form the base for the set
of 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) to
indicate 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 Entity
Group Intermediate Point (MIP): TTL=MIP hops+1, and MIP processes the OAM frames with MEL=0 and TTL=2. MPLS-TP uses TTL in the LSP or PW label only.
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Market Prospects In the fixed-line network, the successful application of ADSL technology has brought a 2Mbps
bandwidth to the end user’s home. The increasing growth of broadband subscriber base results in huge demands for large bandwidth. Data traffic transferred through the provincial backbone transport network accounts for 90% of the total traffic. This indicates that the IP-based service bearing has become the development trend in the industry. The future service transport
network tends to be intelligent, highly integrated and broadband-enabled, which can be achieved by using the MPLS-IP technology.
Leading network operators such as British Telecom (BT), France Telecom (FT) and China Mobile have 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 actively
participating in and paying much attention to the development and testing of related products by 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 the R&D of the MPLS-TP technology and related standardization work. For example, ZTE has
implemented MPLS-TP related OAM and protection functions on its ZXR10 9000 and ZXCTN 6100/6200/6300 product series and successfully trialed them over the networks of operators
such as China Mobile and Telecom Malaysia. Huawei has launched the PTN 912/OSN 3900/1900 series, FiberHome the CiTRANS 660/620 series, UTStarcom the TN 725/705 series, AlcatelLucent 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 been
actively engaged in the research and planning of the MPLS-TP technology. This indicates that
MPLS-TP has promising prospects and will play a key role in the future packet transport network.
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Summary MPLS-TP represents an optimized combination of MPLS & transport networks, designed to carry packets. It provides an evolution path from SONET/SDH based networks to packet networks. It preserves the advantageous features of SONET/SDH like OAM & protection switching, thus
allowing the full end-to-end integration with existing MPLS infrastructure. By using MPLS-TP,
Service providers will have the manageability, stability, flexibility, scalability and deterministic performance 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), guaranteed frame delay, frame delay variation and packet loss ratio.
•
Capability to obtain different performance characteristics for key applications without requiring the use and expense of multiple networks.
•
Support for sub 50ms protection switching ensuring high availability.
•
Comprehensive OAM functionality.
© Tech Mahindra Limited 2010
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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 select
a few among these areas. •
MPLS-TP Data plane module
•
MPLS-TP Control plane module
•
MPLS-TP OAM module
•
MPLS-TP EMS/NMS module
Based on the opportunity from the vendors, we will be able to select among these activities:
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•
Requirement Analysis
•
Product Design & Development
•
Testing & Validation
•
Interoperability Testing
•
Network Design, Deployment & Maintenance for Telecom Service Providers.
© Tech Mahindra Limited 2010
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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