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Versions: (draft-fang-mpls-tp-use-cases-and-design) 00 01 02 03 04 05 06 07 08 RFC 6965

   Network Working Group                                L. Fang, Ed.
   Internet Draft                                      Cisco Systems
   Intended status: Informational                           N. Bitar
   Expires: December 11, 2012                                Verizon
                                                            R. Zhang
                                                      Alcatel Lucent
                                                          M. DAIKOKU
                                                                KDDI
                                                              P. Pan
                                                            Infinera


                                                       June 11, 2012


                MPLS-TP Applicability; Use Cases and Design
              draft-ietf-mpls-tp-use-cases-and-design-02.txt

Abstract


   This document provides applicability, use case studies and network
   design considerations for Multiprotocol Label Switching Transport
   profile (MPLS-TP).

   In the recent years, MPLS-TP has emerged as the technology of choice
   for the new generation of packet transport. Many service providers
   (SPs) are working to replace the legacy transport technologies, e.g.
   SONET/SDH, TDM, and ATM technologies, with MPLS-TP for packet
   transport, in order to achieve higher efficiency, lower operational
   cost, while maintaining transport characteristics.

   The use cases for MPLS-TP include Metro Ethernet access and
   aggregation, Mobile backhaul, and packet optical transport. The
   design considerations discussed in this documents ranging from
   operational experience; standards compliance; technology maturity;
   end-to-end forwarding and OAM consistency; compatibility with
   IP/MPLS networks; multi-vendor interoperability; and optimization
   vs. simplicity design trade off discussion. The general design
   principle is to provide reliable, manageable, and scalable transport
   solutions.



Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with
   the provisions of BCP 78 and BCP 79.



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   This Internet-Draft will expire on December 11, 2012.


Copyright Notice


   Copyright (c) 2012 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   publication of this document.  Please review these documents
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Table of Contents

   1. Introduction ...................................................3
                                                                      3
   1.1.  Background and Motivation ...................................3
                                                                      3
   1.2.  Co-authors and contributors .................................3
                                                                      5
   2. Terminologies ..................................................5
                                                                      5
   3. Overview of MPLS-TP base functions .............................6
                                                                      6
   3.1.  MPLS-TP development principles ..............................6
                                                                      6
   3.2.  Data Plane ..................................................7
                                                                      7
   3.3.  Control Plane ...............................................7
                                                                      7
   3.4.  OAM .........................................................7
                                                                      7
   3.5.  Survivability ...............................................8
                                                                      8
   4. MPLS-TP Use Case Studies .......................................8
                                                                      8
   4.1.  Metro Access and Aggregation ...............................8
                                                                      8


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   4.2.  Packet Optical Transport ....................................9
                                                                      9
   4.3.  Mobile Backhaul ............................................10
                                                                     10
   5. Network Design Considerations .................................11
                                                                     11
   5.1.  IP/MPLS vs. MPLS-TP ........................................11
                                                                     11
   5.2.  Standards compliance .......................................11
                                                                     12
   5.3.  End-to-end MPLS OAM consistency ............................12
                                                                     13
   5.4.  PW Design considerations in MPLS-TP networks ...............13
                                                                     13
   5.5.  Proactive and event driven MPLS-TP OAM tools ...............13
                                                                     14
   5.6.  MPLS-TP and IP/MPLS Interworking considerations ............14
                                                                     14
   5.7.  Delay and delay variation ..................................14
                                                                     14
   5.8.  More on MPLS-TP Deployment Considerations ..................17
                                                                     17
   6. Security Considerations .......................................19
                                                                     19
   7. IANA Considerations ...........................................19
                                                                     19
   8. Normative References ..........................................19
                                                                     19
   9. Informative References ........................................19
                                                                     19
   10.  Author's Addresses...........................................20
                                                                     20


   Requirements Language

   Although this document is not a protocol specification, the key
   words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED",  "MAY", and "OPTIONAL" in
   this document are to be interpreted as described in RFC 2119 [RFC
   2119].


1. Introduction


   1.1. Background and Motivation

   This document provides case studies and network design
   considerations for Multiprotocol Label Switching Transport Profile
   (MPLS-TP).

   In recent years, the urgency for moving from traditional transport
   technologies, such as SONET/SDH, TDM/ATM, to new packet technologies
   has been rising. This is largely due to the tremendous success of
   data services, such as IPTV and IP Video for content downloading,
   streaming, and sharing; rapid growth of mobile services, especially
   smart phone applications; the continued growth of business VPNs and
   residential broadband. The end of live for many legacy TDM devices
   and the continuing network convergence effort are also key
   contributing factors for transport moving toward packet


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   technologies. After several years of heated debate on which packet
   technology to use, MPLS-TP has emerged as the next generation
   transport technology of choice for many service providers
   worldwide.

   MPLS-TP is based on MPLS technologies. MPLS-TP re-use a subset of
   MPLS base functions, such as MPLS data forwarding, Pseudo-wire
   encapsulation for circuit emulation, and GMPLS for LSP, tLDP for PW,
   as dynamic control plane options; MPLS-TP extended current MPLS OAM
   functions, such as BFD extension for Connectivity for proactive
   Connectivity Check (CC) and Connectivity Verification (CV), and
   Remote Defect Indication (RDI), LSP Ping Extension for on demand
   Connectivity Check (CC) and Connectivity Verification (CV), fault
   allocation, and remote integrity check. New tools are being defined
   for alarm suppression with Alarm Indication Signal (AIS), and
   trigger of switch over with Link Defect Indication (LDI).

   The goal is to take advantage of the maturity of MPLS technology,
   re-use the existing component when possible and extend the existing
   protocols or create new procedures/protocols when needed to fully
   satisfy the transport requirements.

   The general requirements of MPLS-TP are provided in MPLS-TP
   Requirements [RFC 5654], and the architectural framework are defined
   in MPLS-TP Framework [RFC 5921]. This document intent to provide the
   use case studies and design considerations from practical point of
   view based on Service Providers deployments plans and field
   implementations.

   The most common use cases for MPLS-TP include Metro access and
   aggregation, Mobile Backhaul, and Packet Optical Transport. MPLS-TP
   data plane architecture, path protection mechanisms, and OAM
   functionalities are used to support these deployment scenarios.
   As part of MPLS family, MPLS-TP complements today's IP/MPLS
   technologies; it closes the gaps in the traditional access and
   aggregation transport to enable end-to-end packet technology
   solutions in a cost efficient, reliable, and interoperable manner.

   The unified MPLS strategy, using MPLS from core to aggregation and
   access (e.g. IP/MPLS in the core, IP/MPLS or MPLS-TP in aggregation
   and access) appear to be very attractive to many SPs. It streamlines
   the operation, many help to reduce the overall complexity and
   improve end-to-end convergence. It leverages the MPLS experience,
   and enhances the ability to support revenue generating services.

   The design considerations discussed in this document are generic.
   While many design criteria are commonly apply to most of SPs, each
   individual SP may place the importance of one aspect over another

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   depending on the existing operational environment, what type of
   applications need to be supported, the design objectives, the cost
   constrain, and the network evolution plans.


   1.2. Co-authors and contributors

   Luyuan Fang, Cisco Systems
   Nabil Bitar, Verizon
   Raymond Zhang, Alcatel Lucent
   Masahiro DAIKOKU, KDDI
   Ping Pan, Infinera
   Mach(Guoyi) Chen, Huawei Technologies
   Dan Frost, Cisco Systems
   Kam Lee Yap, XO Communications
   Henry Yu, Time W Telecom
   Jian Ping Zhang, China Telecom, Shanghai
   Nurit Sprecher, Nokia Siemens Networks
   Lei Wang, Telenor



2. Terminologies

      AIS       Alarm Indication Signal
      APS       Automatic Protection Switching
      ATM       Asynchronous Transfer Mode
      BFD       Bidirectional Forwarding Detection
      CC        Continuity Check
      CE Customer Edge device
      CV        Connectivity Verification
      CM        Configuration Management
      DM        Packet delay measurement
      ECMP      Equal Cost Multi-path
      FM        Fault Management
      GAL       Generic Alert Label
      G-ACH     Generic Associated Channel
      GMPLS     Generalized Multi-Protocol Label Switching
      LB        Loopback
      LDP       Label Distribution Protocol
      LM        Packet loss measurement
      LSP       Label Switched Path
      LT        Link trace
      MEP       Maintenance End Point
      MIP       Maintenance Intermediate Point
      MP2MP     Multi-Point to Multi-Point connections
      MPLS      Multi-Protocol Label Switching
      MPLS-TP   MPLS transport profile

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      OAM       Operations, Administration, and Management
      P2P       Point to Multi-Point connections
      P2MP      Point to Point connections
      PE         Provider-Edge device
      PHP       Penultimate Hop Popping
      PM        Performance Management
      PW         Pseudowire
      RDI       Remote Defect Indication
      RSVP-TE   Resource Reservation Protocol with Traffic
                Engineering Extensions
      SLA       Service Level Agreement
      SNMP      Simple Network Management Protocol
      SONET     Synchronous Optical Network
      S-PE      Switching Provider Edge
      SRLG      Shared Risk Link Group
      SM-PW     Multi-Segment PW
      SS-PW     Signle-Segment PW
      TDM       Time Division Multiplexing
      TE         Traffic Engineering
      tLDP      target LDP
      TTL       Time-To-Live
      T-PE      Terminating Provider Edge
      VPN       Virtual Private Network



3. Overview of MPLS-TP base functions

   The section provides a summary view of MPLS-TP technology,
   especially in comparison to the base IP/MPLS technologies. For
   complete requirements and architecture definitions, please refer to
   [RFC 5654] and [RFC 5921].

   3.1. MPLS-TP development principles

   The principles for MPLS-TP development are: meeting transport
   requirements; maintain transport characteristics; re-using the
   existing MPLS technologies wherever possible to avoid duplicate the
   effort; ensuring consistency and inter-operability of MPLS-TP and
   IP/MPLS networks; developing new tools as necessary to fully meet
   transport requirements.


   MPLS-TP Technologies include four major areas: Data Plane, Control
   Plane, OAM, and Survivability. The short summary is provided below.




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   3.2. Data Plane

   MPLS-TP re-used MPLS and PW architecture; and MPLS forwarding
   mechanism;

   MPLS-TP extended the LSP support from unidirectional to both bi-
   directional unidirectional support.

   MPLS-TP defined PHP as optional, disallowed ECMP and MP2MP, only P2P
   and P2MP are supported.


   3.3. Control Plane

   MPLS-TP allowed two control plane options:

   Static: Using NMS for static provisioning;
   Dynamic control plane for LSP: using GMPLS, OSPF-TE, RSVP-TE for
   full automation;
   Dymanic control plane for PW: using tLDP.
   ACH concept in PW is extended to G-ACh for MPLS-TP LSP to support
   in-band OAM.

   Both Static and dynamic control plane options must allow control
   plane, data plane, management plane separation.


   3.4. OAM

   OAM received most attention in MPLS-TP development; Many OAM
   functions require protocol extensions or new development to meet the
   transport requirements.

   1) Continuity Check (CC), Continuity Verification (CV), and Remote
   Integrity:
   - Proactive CC and CV: Extended BFD
   - On demand CC and CV: Extended LSP Ping
   - Proactive Remote Integrity: Extended BFD
   - On demand Remote Integrity: Extended LSP Ping

   2) Fault Management:
   - Fault Localization: Extended LSP Ping
   - Alarm Suppression: created AIS
   - Remote Defect Indication (RDI): Extended BFD
   - Lock reporting: Created Lock Instruct
   - Link defect Indication: Created LDI
   - Static PW defect indication: Use Static PW status


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   Performance Management:
   - Loss Management: Create MPLS-TP loss/delay measurement
   - Delay Measurement: Create MPLS-TP loss/delay measurement

   MPLS-TP OAM tool set overview can be found at [OAM Tool Set].

   3.5. Survivability

   - Deterministic path protection
   - Switch over within 50ms
   - 1:1, 1+1, 1:N protection
   - Linear protection
   - Ring protection
   - Shared Mesh Protection

   MPLS transport Profile Survivability Framework [RFC 6372] provides
   more details on the subject.

4. MPLS-TP Use Case Studies



   4.1. Metro Access and Aggregation

   The most common deployment cases observed in the field upto today is
   using MPLS-TP for Metro access and aggregation. Some SPs are
   building green field access and aggregation infrastructure, while
   others are upgrading/replacing the existing transport infrastructure
   with new packet technologies such as MPLS-TP.
   The access and aggregation networks today can be based on ATM, TDM,
   MSTP, or Ethernet technologies as later development.


   Some other SPs announced their plans for replacing their ATM or TDM
   aggregation networks with MPLS-TP technologies, simply because their
   ATM / TDM aggregation networks are no longer suited to support the
   rapid bandwidth growth, and they are expensive to maintain or may
   also be and impossible expand due to End of Sale and End of Life
   legacy equipments. Operators have to move forward with the next
   generation packet technology, the adoption of MPLS-TP in access and
   aggregation becomes a natural choice. The statistical muxing in
   MPLS-TP helps to achieve higher efficiency comparing with the time
   division scheme in the legacy technologies.

   The unified MPLS strategy, using MPLS from core to aggregation and
   access (e.g. IP/MPLS in the core, IP/MPLS or MPLS-TP in aggregation
   and access) appear to be very attractive to many SPs. It streamlines
   the operation, many help to reduce the overall complexity and

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   improve end-to-end convergence. It leverages the MPLS experience,
   and enhances the ability to support revenue generating services.

   The current requirements from the SPs for ATM/TDM aggregation
   replacement often include maintaining the current operational model,
   with the similar user experience in NMS, supports current access
   network (e.g. Ethernet, ADSL, ATM, STM, etc.), support the
   connections with the core networks, support the same operational
   feasibility even after migrating to MPLS-TP from ATM/TDM and
   services (OCN, IP-VPN, E-VLAN, Dedicated line, etc.). MPLS-TP
   currently defined in IETF are meeting these requirements to support
   a smooth transition.

   The green field network deployment is targeting using the state of
   art technology to build most stable, scalable, high quality, high
   efficiency networks to last for the next many years. IP/MPLS and
   MPLS-TP are both good choices, depending on the operational model.

   4.2. Packet Optical Transport

   Many SP's transport networks consist of both packet and optical
   portions. The transport operators are typically sensitive to network
   deployment cost and operation simplicity. MPLS-TP is therefore a
   natural fit in some of the transport networks, where the operators
   can utilize the MPLS-TP LSP's (including the ones statically
   provisioned) to manage user traffic as "circuits" in both packet and
   optical networks.
   Among other attributes, bandwidth management, protection/recovery
   and OAM are critical in Packet/Optical transport networks. In the
   context of MPLS-TP, each LSP is expected to be associated with a
   fixed amount of bandwidth in terms of bps and/or time-slots. OAM is
   to be performed on each individual LSP. For some of performance
   monitoring (PM) functions, the OAM mechanisms need to be able
   transmit and process OAM packets at very high frequency, as low as
   several msec's.

   Protection is another important element in transport networks.
   Typically, ring and linear protection can be readily applied in
   metro networks. However, as long-haul networks are sensitive to
   bandwidth cost and tend to have mesh-like topology, shared mesh
   protection is becoming increasing important.

   Packet optical deployment plans in some SPs cases are using MPLS-TP
   from long haul optical packet transport all the way to the
   aggregation and access.




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   4.3. Mobile Backhaul

   Wireless communication is one of the fastest growing areas in
   communication world wide. For some regions, the tremendous rapid
   mobile growth is fueled with lack of existing land-line and cable
   infrastructure. For other regions, the introduction of Smart phones
   quickly drove mobile data traffic to become the primary mobile
   bandwidth consumer, some SPs have already seen 85% of total mobile
   traffic are data traffic.

   MPLS-TP has been viewed as a suitable technology for Mobile
   backhaul.

   4.3.1. 2G and 3G Mobile Backhaul Support

   MPLS-TP is commonly viewed as a very good fit for 2G)/3G Mobile
   backhaul.

   2G (GSM/CDMA) and 3G (UMTS/HSPA/1xEVDO) Mobile Backhaul Networks are
   dominating mobile infrastructure today.

   The connectivity for 2G/3G networks are Point to point. The logical
   connections are hub-and-spoke. The physical construction of the
   networks can be star topology or ring topology. In the Radio Access
   Network (RAN), each mobile base station (BTS/Node B) is
   communicating with one Radio Controller (BSC/RNC) only. These
   connections are often statically set up.

   Hierarchical Aggregation Architecture / Centralized Architecture are
   often used for pre-aggregation and aggregation layers. Each
   aggregation networks inter-connects with multiple access networks.
   For example, single aggregation ring could aggregate traffic for 10
   access rings with total 100 base stations.

   The technology used today is largely ATM based. Mobile providers are
   replacing the ATM RAN infrastructure with newer packet technologies.
   IP RAN networks with IP/MPLS technologies are deployed today by many
   SPs with great success. MPLS-TP is another suitable choice for
   Mobile RAN. The P2P connection from base station to Radio Controller
   can be set statically to mimic the operation today in many RAN
   environments, in-band OAM and deterministic path protection would
   support the fast failure detection and switch over to satisfy the
   SLA agreement. Bidirectional LSP may help to simplify the
   provisioning process. The deterministic nature of MPLS-TP LSP set up
   can also help packet based synchronization to maintain predictable
   performance regarding packet delay and jitters.

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  4.3.2. LTE Mobile Backhaul

   One key difference between LTE and 2G/3G Mobile networks is that the
   logical connection in LTE is mesh while 2G/3G is P2P star
   connections.

   In LTE, the base stations eNB/BTS can communicate with multiple
   Network controllers (PSW/SGW or ASNGW), and each Radio element can
   communicate with each other for signal exchange and traffic offload
   to wireless or Wireline infrastructures.

   IP/MPLS may have a great advantage in any-to-any connectivity
   environment. The use of mature IP or L3VPN technologies is
   particularly common in the design of SP's LTE deployment plan.

   MPLS-TP can also bring advantages with the in-band OAM and path
   protection mechanism. MPLS-TP dynamic control-plane with GMPLS
   signaling may bring additional advantages in the mesh environment
   for real time adaptivities, dynamic topology changes, and network
   optimization.

   Since MPLS-TP is part of the MPLS family. Many component already
   shared by both IP/MPLS and MPLS-TP, the line can be further blurred
   by sharing more common features. For example, it is desirable for
   many SPs to introduce the in-band OAM developed for MPLS-TP back
   into IP/MPLS networks as an enhanced OAM option. Today's MPLS PW can
   also be set statically to be deterministic if preferred by the SPs
   without going through full MPLS-TP deployment.


  4.3.3. WiMAX Backhaul
   WiMAX Mobile backhaul shares the similar characteristics as LTE,
   with mesh connections rather than P2P, star logical connections.




5. Network Design Considerations

   5.1. IP/MPLS vs. MPLS-TP

   Questions one might hear: I have just built a new IP/MPLS network to
   support multi-services, including L2/L3 VPNs, Internet service,
   IPTV, etc. Now there is new MPLS-TP development in IETF. Do I need
   to move onto MPLS-TP technology to state current with technologies?



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   The answer is no. MPLS-TP is developed to meet the needs of
   traditional transport moving towards packet. It is designed to
   support the transport behavior coming with the long history. IP/MPLS
   and MPLS-TP both are state of art technologies. IP/MPLS support both
   transport (e.g. PW, RSVP-TE, etc.) and services (e.g L2/L3 VPNs,
   IPTV, Mobile RAN, etc.), MPLS-TP provides transport only. The new
   enhanced OAM features built in MPLS-TP should be share in both
   flavors through future implementation.

   Another common question: I need to evolve my ATM/TDM/SONET/SDH
   networks into new packet technologies, but my operational force is
   largely legacy transport, not familiar with new data technologies,
   and I want to maintain the same operational model for the time
   being, what should I do? The answer would be: MPLS-TP may be the
   best choice today for the transition.

   A few important factors need to be considered for IP/MPLS or MPLS-TP
   include:

   - Technology maturity (IP/MPLS is much more mature with 12 years
   development)
   - Operation experience (Work force experience, Union agreement, how
   easy to transition to a new technology? how much does it cost?)
   - Needs for Multi-service support on the same node (MPLS-TP provide
   transport only, does not replace many functions of IP/MPLS)
   - LTE, IPTV/Video distribution considerations (which path is the
   most viable for reaching the end goal with minimal cost? but it also
   meet the need of today's support)

   5.2. Standards compliance

   It is generally recognized by SPs that standards compliance are
   important for driving the cost down and product maturity up, multi-
   vendor interoperability, also important to meet the expectation of
   the business customers of SP's.

   MPLS-TP is a joint work between IETF and ITU-T. In April 2008, IETF
   and ITU-T jointly agreed to terminate T-MPLS and progress MPLS-TP as
   joint work [RFC 5317]. The transport requirements would be provided
   by ITU-T, the protocols would be developed in IETF.

   Today, majority of the core set of MPLS-TP protocol definitions are
   published as IETF RFCs already. It is important to deploy the
   solutions based on the standards definitions, in order to ensure the
   compatibility between MPLS-TP and IP/MPLS networks, and the
   interoperability among different equipment by different vendors.



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   Note that using non-standards, e.g. experimental code point is not
   recommended practice, it bares the risk of code-point collision, as
   indicated by [RFC 3692]: It can lead to interoperability problems
   when the chosen value collides with a different usage, as it someday
   surely will.


   5.3. End-to-end MPLS OAM consistency

   In the case Service Providers deploy end-to-end MPLS solution with
   the combination of dynamic IP/MPLS and static or dynamic MPLS-TP
   cross core, service edge, and aggregation/access networks, end-to-
   end MPLS OAM consistency becomes an essential requirements from many
   Service Provider. The end-to-end MPLS OAM can only be achieved
   through implementation of IETF MPLS-TP OAM definitions.


   5.4. PW Design considerations in MPLS-TP networks

   In general, PW works the same as in IP/MPLS network, both SS-PW and
   MS-PW are supported.

   For dynamic control plane, tLDP is used. For static provisioning is
   used, PW status is a new PW OAM feature for failure notification.

   In addition, both directions of a PW must be bound to the same
   transport bidirectional LSP.

   When multi-tier rings involved in the network topology, should S-PE
   be used or not? It is a design trade-off.

        . Pros for using S-PE
             .  Domain isolation, may facilitate trouble shooting
             .  the PW failure recovery may be quicker
        .  Cons for using S-PE
             .  Adds more complexity
             .  If the operation simplicity is the high priority, some
               SPs choose not to use S-PE, simply forming longer path
               across primary and secondary rings.

   Should PW protection for the same end points be considered? It is
   another design trade-off.

        . Pros for using PW protection
             .  PW is protected when both working and protect LSPs
               carrying the working PW fails as long as the protection
               PW is following a diverse LSP path from the one
               carrying the working PW.

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        . Cons for using PW protection
             . Adds more complexity, some may choose not to use if
               protection against single point of failure is
               sufficient.


   5.5. Proactive and event driven MPLS-TP OAM tools

   MPLS-TP provide both proactive tools and event drive OAM Tools.

   E.g. in the proactive fashion, the BFD hellos can be sent every 3.3
   ms as its lowest interval, 3 missed hellos would be trigger the
   failure protection switch over. BFD sessions should be configured
   for both working and protecting LSPs.

   When Unidirectional Failure occurs, RDI will send the failure
   notification to the opposite direction to trigger both end switch
   over.

   In the reactive fashion, when there is a fiber cut for example, LDI
   message would be generated from the failure point and propagate to
   MEP to trigger immediate switch over from working to protect path.
   And AIS would propagate from MIP to MEP for alarm suppression.

   Should both proactive and event driven OAM tools be used? The answer
   is yes.

   Should BFD timers be set as low as possible? It depends on the
   applications. In many cases, it is not necessary. The lower the
   times are, the faster the detection time, and also the higher
   resource utilization. It is good to choose a balance point.



   5.6. MPLS-TP and IP/MPLS Interworking considerations

   Since IP/MPLS is largely deployment in most networks, MPLS-TP and
   IP/MPLS interworking is a reality.

   Typically, there is peer model and overlay model.

   The inter-connection can be simply VLAN, or PW, or could be MPLS-TE.
   A separate document is addressing the in the interworking issues,
   please refer to the descriptions in [Interworking].


   5.7. Delay and delay variation


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   Background/motivation: Telecommunication Carriers plan to replace
   the aging TDM Services (e.g. legacy VPN services) provided by Legacy
   TDM technologies/equipments to new VPN services provided by MPLS-TP
   technologies/equipments with minimal cost. The Carriers cannot allow
   any degradation of service quality, service operation Level, and
   service availability when migrating out of Legacy TDM
   technologies/equipments to MPLS-TP transport. The requirements from
   the customers of these carriers are the same before and after the
   migration.


  5.7.1. Network Delay

   From our recent observation, more and more Ethernet VPN customers
   becoming very sensitive to the network delay issues, especially the
   financial customers. Many of those customers has upgraded their
   systems in their Data Centers, e.g., their accounting systems.  Some
   of the customers built the special tuned up networks, i.e. Fiber
   channel networks, in their Data Centers, this tripped more strict
   delay requirements to the carriers.

   There are three types of network delay:

   1. Absolute Delay Time

   Absolute Delay Time here is the network delay within SLA contract.
   It means the customers have already accepted the value of the
   Absolute Delay Time as part of the contract before the Private Line
   Service is provisioned.

   2. Variation of Absolute Delay Time (without network configuration
   changes).

   The variation under discussion here is mainly induced by the
   buffering in network elements.

   Although there is no description of Variation of Absolute Delay Time
   on the contract, this has no practical impact on the customers who
   contract for the highest quality of services available. The
   bandwidth is guaranteed for those customers' traffic.

   3. Relative Delay Time

   Relative Delay Time is the difference of the Absolute Delay Time
   between using working and protect path.



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   Ideally, Carriers would prefer the Relative Delay Time to be zero,
   for the following technical reasons and network operation
   feasibility concerns.

   The following are the three technical reasons:

   Legacy throughput issue

   In the case that Relative Delay Time is increased between FC
   networks or TCP networks, the effective throughput is degraded.  The
   effective throughput, though it may be recovered after revert back
   to the original working path in revertive mode.

   On the other hand, in that case that Relative Delay Time is
   decreased between FC networks or TCP networks, buffering over flow
   may occur at receiving end due to receiving large number of busty
   packets.  As a consequence, effective throughput is degraded as
   well.  Moreover, if packet reordering is occurred due to RTT
   decrease, unnecessary packet resending is induced and effective
   throughput is also further degraded.  Therefore, management of
   Relative Delay Time is preferred, although this is known as the
   legacy TCP throughput issue.

   Locating Network Acceralators at CE

   In order to improve effective throughput between customer's FC
   networks over Ethernet private line service, some customer put "WAN
   Accelerator" to increase throughput value.  For example, some WAN
   Accelerators at receiving side may automatically send back "R_RDY"
   in order to avoid decreasing a number of BBcredit at sending side,
   and the other WAN Accelerators at sending side may have huge number
   of initial BB credit.

   When customer tunes up their CE by locating WAN Accelerator, for
   example, when Relative Delay Time is changes, there is a possibility
   that effective throughput is degraded.  This is because a lot of
   packet destruction may be occurred due to loss of synchronization,
   when change of Relative delay time induces packet reordering.  And,
   it is difficult to re-tune up their CE network element automatically
   when Relative Delay Time is changed, because only less than 50 ms
   network down detected at CE.

   Depending on the tuning up method, since Relative Delay Time affects
   effective throughput between customer's FC networks, management of
   Relative Delay Time is preferred.

   c) Use of synchronized replication system


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   Some strict customers, e.g. financial customers, implement
   "synchronized replication system" for all data back-up and load
   sharing.  Due to synchronized replication system, next data
   processing is conducted only after finishing the data saving to both
   primary and replication DC storage.  And some tuning function could
   be applied at Server Network to increase throughput to the
   replication DC and Client Network. Since Relative Delay Time affects
   effective throughput, management of Relative Delay Time is
   preferred.

   The following are the network operational feasibility issues.

   Some strict customers, e.g., financial customer, continuously
   checked the private line connectivity and absolute delay time at
   CEs.  When the absolute delay time is changed, that is Relative
   delay time is increased or decreased, the customer would complain.

   From network operational point of view, carrier want to minimize the
   number of customers complains, MPLS-TP LSP provisioning with zero
   Relative delay time is preferred and management of Relative Delay
   Time is preferred.

   Obviously, when the Relative Delay Time is increased, the customer
   would complain about the longer delay. When the Relative Delay Time
   is decreased, the customer expects to keep the lesser Absolute Delay
   Time condition and would complain why Carrier did not provide the
   best solution in the first place. Therefore, MPLS-TP LSP
   provisioning with zero Relative Delay Time is preferred and
   management of Relative Delay Time is preferred.

   More discussion will be added on how to manage the Relative delay
   time.



   5.8. More on MPLS-TP Deployment Considerations


   5.8.1. Network Modes Selection

   When considering deployment of MPLS-TP in the network, possibly
   couple of questions will come into mind, for example, where should
   the MPLS-TP be deployed? (e.g., access, aggregation or core
   network?) Should IP/MPLS be deployed with MPLS-TP simultaneously? If
   MPLS-TP and IP/MPLS is deployed in the same network, what is the
   relationship between MPLS-TP and IP/MPLS (e.g., peer or overlay?)
   and where is the demarcation between MPLS-TP domain and IP/MPLS

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   domain? The results for these questions depend on the real
   requirements on how MPLS-TP and IP/MPLS are used to provide
   services. For different services, there could be different choice.
   According to the combination of MPLS-TP and IP/MPLS, here are some
   typical network modes:

   Pure MPLS-TP as the transport connectivity (E2E MPLS-TP), this
   situation more happens when the network is a totally new constructed
   network. For example, a new constructed packet transport network for
   Mobile Backhaul, or migration from ATM/TDM transport network to
   packet based transport network.

   Pure IP/MPLS as transport connectivity (E2E IP/MPLS), this is the
   current practice for many deployed networks.
   MPLS-TP combines with IP/MPLS as the transport connectivity (Hybrid
   mode).

   Peer mode: some domains adopt MPLS-TP as the transport connectivity;
   other domains adopt IP/MPLS as the transport connectivity. MPLS-TP
   domains and IP/MPLS domains are interconnected to provide transport
   connectivity. Considering there are a lot of IP/MPLS deployments in
   the field, this mode may be the normal practice in the early stage
   of MPLS-TP deployment.

   Overlay mode:
   b-1: MPLS-TP as client of IP/MPLS, this is for the case where MPLS-
   TP domains are distributed and IP/MPLS do-main/network is used for
   the connection of the distributed MPLS-TP domains. For examples,
   there are some service providers who have no their own Backhaul
   network, they have to rent the Backhaul network that is IP/MPLS
   based from other service providers.

   b-2: IP/MPLS as client of MPLS-TP, this is for the case where
   transport network below the IP/MPLS network is a MPLS-TP based
   network, the MPLS-TP network provides transport connectivity for the
   IP/MPLS routers, the usage is analogous as today's ATM/TDM/SDH based
   transport network that are used for providing connectivity for
   IP/MPLS routers.


   5.8.2. Provisioning Modes Selection

   As stated in MPLS-TP requirements [RFC 5654], MPLS-TP network MUST
   be possible to work without using Control Plane. And this does not
   mean that MPLS-TP network has no control plane. Instead, operators
   could deploy their MPLS-TP with static provisioning (e.g., CLI, NMS
   etc.), dynamic control plane signaling (e.g., OSPF-TE/ISIS-TE,
   GMPLS, LDP, RSVP-TE etc.), or combination of static and dynamic
   provisioning (Hybrid mode). Each mode has its own pros and cons and
   how to determine the right mode for a specific network mainly

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   depends on the operators' preference. For the operators who are used
   to operate traditional transport network and familiar with the
   Transport-Centric operational model (e.g., NMS configuration without
   control plane) may prefer static provisioning mode. The dynamic
   provisioning mode is more suitable for the operators who are
   familiar with the operation and maintenance of IP/MPLS network where
   a fully dynamic control plane is used. The hybrid mode may be used
   when parts of the network are provisioned with static way and the
   other parts are controlled by dynamic signaling. For example, for
   big SP, the network is operated and maintained by several different
   departments who prefer to different modes, thus they could adopt
   this hybrid mode to support both static and dynamic modes hence to
   satisfy different requirements. Another example is that static
   provisioning mode is suitable for some parts of the network and
   dynamic provisioning mode is suitable for other parts of the
   networks (e.g., static for access network, dynamic for metro
   aggregate and core network).

6. Security Considerations

   General security considerations for MPLS and GMPLS networks are
   addressed in Security Framework for MPLS and GMPLS Networks[RFC 5920].
   General MPLS-TP security considerations are described in MPLS-TP
   Security Framework [MPLS-TP Sec FW]. No new security issues in this
   document.

7. IANA Considerations

   This document contains no new IANA considerations.

8. Normative References

   [RFC 5317]: Joint Working Team (JWT) Report on MPLS Architectural
   Considerations for a Transport Profile, Feb. 2009.

   [RFC 5654], Niven-Jenkins, B., et al, "MPLS-TP Requirements," RFC
   5654, September 2009.

9. Informative References
   [RFC 2119] Bradner, S., "Key words for use in RFCs to Indicate
   Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC 3692] T. Narten, "Assigning Experimental and Testing Numbers
   Considered Useful", RFC 3692, Jan. 2004.

   [RFC 5921] Bocci, M., ED.,  Bryant, S., ED., et al., Frost, D. ED.,
   Levrau, L., Berger., L., "A Framework for MPLS in Transport," July
   2010.

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   [RFC 5920] Fang, L., ED., et al, "Security Framework for MPLS and
   GMPLS Networks," July 2010.

   [RFC 6372] Sprecher, N., Ferrel, A., MPLS transport Profile
   Survivability Framework [RFC 6372], September 2011.

   [OAM Tool Set] Sprecher, N., Fang, L., "An Overview of the OAM Tool
   Set for MPLS Based Transport Networks,", draft-ietf-mpls-to-oam-
   analysis-09.txt, April 2012, work in progress.

   [Interworking] Martinotti, R., et al., "Interworking between MPLS-TP
   and IP/MPLS," draft-martinotti-mpls-tp-interworking-02.txt, June
   2011.

   [MPLS-TP Sec FW] Fang, L. ED., et al., "MPLS-TP Security Framework,"
   draft-ietf-mpls-tp-security-framework-03.txt, March 2012.


10.     Author's Addresses

   Luyuan Fang
   Cisco Systems, Inc.
   111 Wood Ave. South
   Iselin, NJ 08830
   USA
   Email: lufang@cisco.com

   Nabil Bitar
   Verizon
   40 Sylvan Road
   Waltham, MA 02145
   USA
   Email: nabil.bitar@verizon.com

   Raymond Zhang
   Alcatel-Lucent
   701 Middlefield Road
   Mountain View, CA 94043
   Email: raymond.zhang@alcatel-lucent.com

   Masahiro DAIKOKU
   KDDI corporation
   3-11-11.Iidabashi, Chiyodaku, Tokyo
   Japan
   Email: ms-daikoku@kddi.com


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   Kam Lee Yap
   XO Communications
   13865 Sunrise Valley Drive,
   Herndon, VA 20171
   Email: klyap@xo.com

   Dan Frost
   Cisco Systems, Inc.
   Email:danfrost@cisco.com

   Henry Yu
   TW Telecom
   10475 Park Meadow Dr.
   Littleton, CO 80124
   Email: henry.yu@twtelecom.com

   Jian Ping Zhang   China Telecom, Shanghai
   Room 3402, 211 Shi Ji Da Dao
   Pu Dong District, Shanghai
   China   Email: zhangjp@shtel.com.cn

   Lei Wang
   Telenor
   Telenor Norway
   Office Snaroyveien
   1331 Fornedbu
   Email: Lai.wang@telenor.com

   Mach(Guoyi) Chen
   Huawei Technologies Co., Ltd.
   No. 3 Xinxi Road
   Shangdi Information Industry Base
   Hai-Dian District, Beijing 100085
   China
   Email: mach@huawei.com

   Nurit Sprecher
   Nokia Siemens Networks
   3 Hanagar St. Neve Ne'eman B
   Hod Hasharon, 45241
   Israel
   Email: nurit.sprecher@nsn.com







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