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Versions: (draft-koike-mpls-tp-temporal-hitless-psm) 00 01 02 03 04 05 06 07 08 09 10 11 12 13

Network Working Group                                    A. D'Alessandro
Internet-Draft                                            Telecom Italia
Intended status: Informational                              L. Andersson
Expires: September 9, 2017                           Huawei Technologies
                                                                 S. Ueno
                                                      NTT Communications
                                                                 K. Arai
                                                                Y. Koike
                                                                     NTT
                                                           March 8, 2017


         Requirements for hitless MPLS path segment monitoring
             draft-ietf-mpls-tp-temporal-hitless-psm-13.txt

Abstract

   One of the most important OAM capabilities for transport network
   operation is fault localisation.  An in-service, on-demand segment
   monitoring function of a transport path is indispensable,
   particularly when the service monitoring function is activated only
   between end points.  However, the current segment monitoring approach
   defined for MPLS (including the transport profile (MPLS-TP)) in RFC
   6371 "Operations, Administration, and Maintenance Framework for MPLS-
   Based Transport Networks" has drawbacks.  This document provides an
   analysis of the existing MPLS-TP OAM mechanisms for the path segment
   monitoring and provides requirements to guide the development of new
   OAM tools to support a Hitless Path Segment Monitoring (HPSM).

Status of This Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on September 9, 2017.






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Copyright Notice

   Copyright (c) 2017 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
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions used in this document . . . . . . . . . . . . . .   3
     2.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
     2.2.  Definitions . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Problem Statement . . . . . . . . . . . . . . . . . . . . . .   4
   4.  Requirements for Hitless Path Segment Monitoring  . . . . . .   7
     4.1.  Backward compatibility  . . . . . . . . . . . . . . . . .   7
     4.2.  Non-intrusive segment monitoring  . . . . . . . . . . . .   8
     4.3.  Multiple segments monitoring  . . . . . . . . . . . . . .   8
     4.4.  Single and multiple level monitoring  . . . . . . . . . .   8
     4.5.  HPSM and end-to-end proactive monitoring independence . .   9
     4.6.  Arbitrary segment monitoring  . . . . . . . . . . . . . .  10
     4.7.  Fault while HPSM is operational . . . . . . . . . . . . .  11
     4.8.  HPSM Manageability  . . . . . . . . . . . . . . . . . . .  12
     4.9.  Supported OAM functions . . . . . . . . . . . . . . . . .  13
   5.  Summary . . . . . . . . . . . . . . . . . . . . . . . . . . .  13
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  14
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  14
   8.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  14
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  14
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  14
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  15
     10.2.  Informative References . . . . . . . . . . . . . . . . .  15
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  15

1.  Introduction

   According to the MPLS-TP OAM requirements RFC 5860 [RFC5860],
   mechanisms MUST be available for alerting service providers of faults
   or defects that affects their services.  In addition, to ensure that
   faults or service degradation can be localized, operators need a



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   function to diagnose the detected problem.  Using end-to-end
   monitoring for this purpose is insufficient in that an operator will
   not be able to localize a fault or service degradation accurately.

   A segment monitoring function that can focus on a specific segment of
   a transport path and that can provide a detailed analysis is
   indispensable to promptly and accurately localize the fault.  A path
   segment monitoring function has been defined to perform this task for
   MPLS-TP.  However, as noted in the MPLS-TP OAM Framework RFC 6371
   [RFC6371], the current method for segment monitoring of a transport
   path has implications that hinder the usage in an operator network.

   This document, after elaborating on the problem statement for the
   path segment monitoring function as it is currently defined, provides
   requirements for an on-demand segment monitoring function without
   traffic distruption.  Further works are required to evaluate how
   proposed requirements match with current MPLS architecture and to
   identify possibile solutions.

2.  Conventions used in this document

   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 [RFC2119].

2.1.  Terminology

      ATM - Asynchronous Transfer Mode

      HPSM - Hitless Path Segment Monitoring

      LSP - Label Switched Path

      LSR - Label Switching Router

      ME - Maintenance Entity

      MEG - Maintenance Entity Group

      MEP - Maintenance Entity Group End Point

      MIP - Maintenance Entity Group Intermediate Point

      OTN - Optical Transport Network

      TCM - Tandem connection monitoring

      SPME - Sub-path Maintenance Element



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2.2.  Definitions

   None.

3.  Problem Statement

   To monitor (and to protect and/or manage) MPLS-TP network segments a
   Sub-Path Maintenance Element (SPME) function has been defined in RFC
   5921 [RFC5921].  The SPME is defined between the edges of the segment
   of a transport path that needs to be monitored, protected, or
   managed.  SPME is created by stacking the shim header (MPLS header)
   according to RFC 3031 [RFC3031] and it is defined as the segment
   where the header is stacked.  OAM messages can be initiated at the
   edge of the SPME and sent to the peer edge of the SPME or to a MIP
   along the SPME by setting the TTL value of the label stack entry
   (LSE) and interface identifier value at the corresponding
   hierarchical LSP level in case of a per-node model.

   MPLS-TP segment monitoring should satisfy two network objectives
   according to section 3.8 of RFC 6371 [RFC6371]:

      (N1) The monitoring and maintenance of current transport paths has
      to be conducted in-service without traffic disruption.

      (N2) Segment monitoring must not modify the forwarding of the
      segment portion of the transport path.

      The SPME function that has been defined in RFC 5921 [RFC5921] has
      the following drawbacks:

      (P1) It increases network management complexity, because a new
      sublayer and new MEPs and MIPs have to be configured for the SPME.

      (P2) Original conditions of the path change.

      (P3) The client traffic over a transport path is disrupted if the
      SPME is configured on-demand.

   Problem (P1) is related to the management of each additional sub-
   layer required for segment monitoring in a MPLS-TP network.  When an
   SPME is applied to administer on-demand OAM functions in MPLS-TP
   networks, a rule for operationally differentiating those SPME will be
   required at least within an administrative domain.  This forces
   operators to implement at least an additional layer into the
   management systems that will only be used for on-demand path segment
   monitoring.  From the perspective of operation, increasing the number
   of managed layers and managed addresses/identifiers is not desirable
   in view of keeping the management systems as simple as possible.



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   Moreover, using the currently defined methods, on-demand setting of
   SPMEs causes problems (P2) and (P3) due to additional label stacking.

   Problem (P2) arises from the fact that MPLS exposed label value and
   MPLS frames length changes.  The monitoring function should monitor
   the status without changing any conditions of the targeted, to be
   monitored, segment or transport path.  Changing the settings of the
   original shim header should not be allowed because this change
   corresponds to creating a new segment of the original transport path
   that differs from the original one.  When the conditions of the path
   change, the measured values or observed data will also change and
   this may make the monitoring meaningless because the result of the
   measurement would no longer reflect the performance of the connection
   where the original fault or degradation occurred.  As an example,
   setting up an on-demand SPME will result in the LSRs within the
   monitoring segment only looking at the added (stacked) labels and not
   at the labels of the original LSP.  This means that problems stemming
   from incorrect (or unexpected) treatment of labels of the original
   LSP by the nodes within the monitored segment cannot be identified
   when setting up SPME.  This might include hardware problems during
   label look-up, mis-configuration, etc.  Therefore operators have to
   pay extra attention to correctly setting and checking the label
   values of the original LSP in the configuration.  Of course, the
   reverse of this situation is also possible, e.g., an incorrect or
   unexpected treatment of SPME labels can result in false detection of
   a fault where no problem existed originally.

   Figure 1 shows an example of SPME settings.  In the figure, "X" is
   the label value of the original path expected at the tail-end of node
   D.  "210" and "220" are label values allocated for SPME.  The label
   values of the original path are modified as well as the values of the
   stacked labels.  As shown in Figure 1, SPME changes both the length
   of MPLS frames and the label value(s).  In particular, performance
   monitoring measurements (e.g.  Delay Measurement and Packet Loss
   Measurement) are sensitive to these changes.  As an example,
   increasing the packet lenght may impact on packet loss due to MTU
   settings, modifying the label stack may introduce packet loss or it
   may fix packet loss depending on the configuration status so
   modifying network conditions.  Such changes influence packets delay
   too even if, from a practical point of view, it is likely that only a
   few services will experience a practical impact.










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      (Before SPME settings)
       ---     ---     ---     ---     ---
      |   |   |   |   |   |   |   |   |   |
      |   |   |   |   |   |   |   |   |   |
       ---     ---     ---     ---     ---
        A--100--B--110--C--120--D--130--E  <= transport path
       MEP                             MEP

      (After SPME settings)
       ---     ---     ---     ---     ---
      |   |   |   |   |   |   |   |   |   |
      |   |   |   |   |   |   |   |   |   |
       ---     ---     ---     ---     ---
        A--100--B-----------X---D--130--E  <= transport path
       MEP                             MEP
                 210--C--220               <= SPME
               MEP'          MEP'


                      Figure 1: SPME settings example

   Problem (P3) can be avoided if the operator sets SPMEs in advance and
   maintains them until the end of life of a transport path.  But this
   does not support on-demand.  Furthermore SMPEs cannot be set
   arbitrarily because overlapping of path segments is limited to
   nesting relationships.  As a result, possible SPME configurations of
   segments of an original transport path are limited due to the
   characteristic of the SPME shown in Figure 1, even if SPMEs are pre-
   configured.

   Although the make-before-break procedure in the survivability
   document RFC 6372 [RFC6372]  supports configuration for monitoring
   according to the framework document RFC 5921 [RFC5921], without
   traffic distruption, the configuration of an SPME is not possible
   without violating network objective (N2).  These concerns are
   described in section 3.8 of RFC 6371 [RFC6371].

   Additionally, the make-before-break approach typically relies on a
   control plane and requires additional functionalities for a
   management system to properly support SPME creation and traffic
   switching from the original transport path to the SPME.

   As an example, the old and new transport resources (e.g.  LSP
   tunnels) might compete with each other for resources which they have
   in common.  Depending on availability of resources, this competition
   can cause admission control to prevent the new LSP tunnel from being
   established as this bandwidth accounting deviates from traditional
   (non control plane) management system operation.  While SPMEs can be



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   applied in any network context (single domain, multi domain, single
   carrier, multi carrier, etc.), the main applications are in inter-
   carrier or inter-domain segment monitoring where they are typically
   pre- configured or pre-instantiated.  SPME instantiates a
   hierarchical path (introducing MPLS label stacking) through which OAM
   packets can be sent.  The SPME monitoring function is also mainly
   important for protecting bundles of transport paths and carriers'
   carrier solutions within an administrative domain.

   The analogy for SPME in other transport technologies is Tandem
   Connection Monitoring (TCM), used in Optical Transport Networks (OTN)
   and Ethernet transport networks, which supports on-demand but does
   not affect the path.  For example in OTN, TCM allows the insertion
   and removal of performance monitoring overhead within the frame at
   intermediate points in the network.  It is done such that their
   insertion and removal do not change the conditions of the path.
   Though as the OAM overhead is part of the frame (designated overhead
   bytes), it is constrained to a pre-defined number of monitoring
   segments.

   To summarize: the problem statement is that the current sub-path
   maintenance based on a hierarchical LSP (SPME) is problematic for
   pre-configuration in terms of increasing the number of managed
   objects by layer stacking and identifiers/addresses.  An on-demand
   configuration of SPME is one of the possible approaches for
   minimizing the impact of these issues.  However, the current
   procedure is unfavourable because the on-demand configuration for
   monitoring changes the condition of the original monitored path.  To
   avoid or minimize the impact of the drawbacks discussed above, a more
   efficient approach is required for the operation of an MPLS-TP
   transport network.  A monitoring mechanism, named Hitless Path
   Segment Monitoring (HPSM), supporting on-demand path segment
   monitoring without traffic disruption is needed.

4.  Requirements for Hitless Path Segment Monitoring

   In the following sections, mandatory (M) and optional (O)
   requirements for the Hitless Path Segment Monitoring function are
   listed.

4.1.  Backward compatibility

   HPSM would be an additional OAM tool that would not replace SPME.  As
   such:

      (M1) HPSM MUST be compatible with the usage of SPME

      (O1) HPSM SHOULD be applicable at the SPME layer too



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      (M2) HPSM MUST support both the per-node and per-interface model
      as specified in RFC 6371 [RFC6371].

4.2.  Non-intrusive segment monitoring

   One of the major problems of legacy SPME highlighted in section 3 is
   that it may not monitor the original path and it could disrupt
   service traffic when set-up on demand.

      (M3) HPSM MUST NOT change the original conditions of transport
      path (e.g.  must not change the length of MPLS frames, the exposed
      label values, etc.)

      (M4) HPSM MUST support on-demand provisioning without traffic
      disruption.

4.3.  Multiple segments monitoring

   Along a transport path there may be the need to support
   simultaneously monitoring multiple segments

      (M5) HPSM MUST support configuration of multiple monitoring
      segments along a transport path.


      ---     ---     ---     ---     ---
     |   |   |   |   |   |   |   |   |   |
     | A |   | B |   | C |   | D |   | E |
      ---     ---     ---     ---     ---
      MEP                              MEP <= ME of a transport path
       *------* *----*  *--------------* <=three HPSM monit. instances



                 Figure 2: Multiple HPSM instances example

4.4.  Single and multiple level monitoring

   HPSM would apply mainly for on-demand diagnostic purposes.  With the
   currently defined approach, the most serious problem is that there is
   no way to locate the degraded segment of a path without changing the
   conditions of the original path.  Therefore, as a first step, a
   single level, single segment monitoring, not affecting the monitored
   path, is required for HPSM.  A combination of multi-level and
   simultaneous segments monitoring is the most powerful tool for
   accurately diagnosing the performance of a transport path.  However,
   in the field, a single level, multiple segments approach would be
   less complex for management and operations.



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      (M6) HPSM MUST support single-level segment monitoring

      (O2) HPSM MAY support multi-level segment monitoring.

   Figure 3 shows an example of multi-level HPSM.


      ---     ---     ---     ---     ---
     |   |   |   |   |   |   |   |   |   |
     | A |   | B |   | C |   | D |   | E |
      ---     ---     ---     ---     ---
      MEP                             MEP <= ME of a transport path
              *-----------------*         <=On-demand HPSM level 1
                *-------------*           <=On-demand HPSM level 2
                      *-*                 <=On-demand HPSM level 3


                    Figure 3: Multi-level HPSM example

4.5.  HPSM and end-to-end proactive monitoring independence

   There is a need for simultaneously using existing end-to-end
   proactive monitoring and on-demand path segment monitoring.
   Normally, the on-demand path segment monitoring is configured on a
   segment of a maintenance entity of a transport path.  In such an
   environment, on-demand single-level monitoring should be performed
   without disrupting the pro-active monitoring of the targeted end-to-
   end transport path to avoid affecting user traffic performance
   monitoring.

      (M7) HPSM MUST support the capability of being operated
      concurrently to, and independently of operated of the OAM function
      operated on the end-to-end path


     ---     ---     ---     ---     ---
    |   |   |   |   |   |   |   |   |   |
    | A |   | B |   | C |   | D |   | E |
     ---     ---     ---     ---     ---
     MEP                             MEP <= ME of a transport path
       +-----------------------------+   <= Pro-active end-to-end mon.
             *------------------*        <= On-demand HPSM


    Figure 4: Independence between proactive end-to-end monitoring and
                              on-demand HPSM





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4.6.  Arbitrary segment monitoring

   The main objective for on-demand segment monitoring is to diagnose
   the fault locations.  A possible realistic diagnostic procedure is to
   fix one end point of a segment at the MEP of the transport path under
   observation and change progressively the length of the segments.  It
   is therefore possible to monitoring step by step all the path with a
   granularity that depends on equipment implementations.  For example,
   Figure 5 shows the case where the granularity is at interface level
   (i.e. monitoring is at each input interface and output interface of
   each piece of equipment).


       ---     ---     ---     ---     ---
      |   |   |   |   |   |   |   |   |   |
      | A |   | B |   | C |   | D |   | E |
       ---     ---     ---     ---     ---
       MEP                             MEP <= ME of a transport path
         +-----------------------------+   <= Pro-active end-to-end mon.
         *-----*                           <= 1st on-demand HPSM
         *-------*                         <= 2nd on-demand HPSM
              |                                |
              |                                |
         *-----------------------*         <= 4th on-demand HPSM
         *-----------------------------*   <= 5th on-demand HPSM


    Figure 5: Localization of a defect by consecutive on-demand segment
                           monitoring procedure

   Another possible scenario is depicted in Figure 6.  In this case, the
   operator wants to diagnose a transport path starting at a transit
   node, because the end nodes (A and E) are located at customer sites
   and consist of small boxes supporting only a subset of OAM functions.
   In this case, where the source entities of the diagnostic packets are
   limited to the position of MEPs, on-demand segment monitoring will be
   ineffective because not all the segments can be diagnosed (e.g.
   segment monitoring HPSM 3 in Figure 6 is not available and it is not
   possible to determine the fault location exactly).

      (M8) It SHALL be possible to provision HPSM on an arbitrary
      segment of a transport path.









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              ---     ---     ---
      ---    |   |   |   |   |   |    ---
     | A |   | B |   | C |   | D |   | E |
      ---     ---     ---     ---     ---
      MEP                             MEP <= ME of a transport path
        +-----------------------------+   <= Pro-active end-to-end mon.
        *-----*                           <= On-demand HPSM 1
              *-----------------------*   <= On-demand HPSM 2
              *---------*                 <= On-demand HPSM 3


            Figure 6: HPSM configuration at arbitrary segments

4.7.  Fault while HPSM is operational

   Node or link failures may occur while HPSM is active.  In this case,
   if no resiliency mechanism is set-up on the subtended transport path,
   there is no particular requirement for HPSM.  If the transport path
   is protected, the HPSM function should be terminated to avoid
   monitoring a new segment when a protection or restoration path is
   active.

      (M9) The HPSM SHOULD avoid monitoring an unintended segment when
      one or more failures occur

   The following examples are provided for clarification only and they
   are not intended to restrict any solution for meeting the
   requirements of HPSM.

   Protection scenario A is shown in figure 7.  In this scenario a
   working LSP and a protection LSP are set-up.  HPSM is activated
   between nodes A and E.  When a fault occurs between nodes B and C,
   the operation of HPSM is not affected by the protection switch and
   continues on the active LSP path.  As a result requirement (M9) is
   satisfied.
















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      A - B - C - D - E - F
        \               /
          G - H - I - L

      Where:
      - end-to-end LSP: A-B-C-D-E-F
      - working LSP:    A-B-C-D-E-F
      - protection LSP: A-G-H-I-L-F
      - HPSM:           A-E


                      Figure 7: Protection scenario A

   Protection scenario B is shown in figure 8.  The difference with
   scenario A is that only a portion of the transport path is protected.
   In this case, when a fault occurs between nodes B and C on the
   working sub-path B-C-D, traffic will be switched to protection sub-
   path B-G-H-D.  Assuming that OAM packet termination depends only on
   the TTL value of the MPLS label header, the target node of the HPSM
   changes from E to D due to the difference of hop counts between the
   working path route (A-B-C-D-E: 4 hops) and protection path route
   (A-B-G-H-D-E: 5 hops).  As a result requirement (M9) is not
   satisfied.


          A - B - C - D - E - F
                \     /
                 G - H

      - end-to-end LSP:      A-B-C-D-E-F
      - working sub-path:    B-C-D
      - protection sub-path: B-G-H-D
      - HPSM:                A-E


                      Figure 8: Protection scenario B

4.8.  HPSM Manageability

   From managing perspective, increasing the number of managed layers
   and managed addresses/identifiers is not desirable in view of keeping
   the management systems as simple as possible.

      (M10)HPSM SHOULD NOT be based on additional transport layers (e.g.
      hierarchical LSPs)






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      (M11) The same identifiers used for MIPs and/or MEPs SHOULD be
      applied to maintenance points for the HPSM when they are
      instantiated in the same place along a transport path.

      Anyway maintenance points for the HPSM may be different from MIPs
      and MEPs functional components as defined in the OAM framework
      document RFC 6371 [RFC6371].  Investigating potential solutions
      for satisfying proposed HPSM requirements might lead to propose
      new functional components that have to be backward compatible with
      MPLS architecture.  Solutions are outside the scope of this
      document.

4.9.  Supported OAM functions

   A maintenance point supporting the HPSM function has to be able to
   generate and inject OAM packets.  OAM functions that may be
   applicable for on-demand HPSM are basically the on-demand performance
   monitoring functions which are defined in the OAM framework document
   RFC 6371 [RFC6371].  The "on-demand" attribute is typically temporary
   for maintenance operation.

      (M12) HPSM MUST support Packet Loss and Packet Delay measurement.

   That because these functions are normally only supported at the end
   points of a transport path.  If a defect occurs, it might be quite
   hard to locate the defect or degradation point without using the
   segment monitoring function.  If an operator cannot locate or narrow
   down the cause of the fault, it is quite difficult to take prompt
   actions to solve the problem.

   Other on-demand monitoring functions (e.g.  Delay Variation
   measurement) are desirable but not as necessary as the functions
   mentioned above.

      (O3) HPSM MAY support Packet Delay variation, Throughput
      measurement and other performance monitoring and fault management
      functions.

   Support of out-of-service on-demand performance management functions
   (e.g.  Throughput measurement) is not required for HPSM.

5.  Summary

   A new hitless path segment monitoring (HPSM) mechanism is required to
   provide on-demand segment monitoring without traffic disruption.  It
   shall meet the two network objectives described in section 3.8 of RFC
   6371 [RFC6371] and summarized in Section 3 of this document.




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   The mechanism should minimize the problems described in Section 3,
   i.e. (P1), (P2) and (P3).

   The solution for the on-demand segment monitoring without traffic
   disruption needs to cover both the per-node model and the per-
   interface model specified in RFC 6371 [RFC6371].

   The on-demand segment monitoring without traffic disruption solution
   needs to support on-demand Packet Loss Measurement and Packet Delay
   Measurement functions and optionally other performance monitoring and
   fault management functions (e.g.  Throughput measurement, Packet
   Delay variation measurement, Diagnostic test, etc.).

6.  Security Considerations

   Security is a significant requirement of MPLS Transport Profile.  The
   document provides a problem statement and requirements to guide the
   development of new OAM tools to support Hitless Path Segment
   Monitoring.  Such new tools must follow the security considerations
   provided in OAM Requirements for MPLS-TP in RFC5860 [RFC5860].

7.  IANA Considerations

   There are no requests for IANA actions in this document.

   Note to the RFC Editor - this section can be removed before
   publication.

8.  Contributors

   Manuel Paul

   Deutsche Telekom AG

   Email: manuel.paul@telekom.de

9.  Acknowledgements

   The authors would also like to thank Alexander Vainshtein, Dave
   Allan, Fei Zhang, Huub van Helvoort, Malcolm Betts, Italo Busi,
   Maarten Vissers, Jia He and Nurit Sprecher for their comments and
   enhancements to the text.

10.  References







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10.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC3031]  Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
              Label Switching Architecture", RFC 3031,
              DOI 10.17487/RFC3031, January 2001,
              <http://www.rfc-editor.org/info/rfc3031>.

   [RFC5860]  Vigoureux, M., Ed., Ward, D., Ed., and M. Betts, Ed.,
              "Requirements for Operations, Administration, and
              Maintenance (OAM) in MPLS Transport Networks", RFC 5860,
              DOI 10.17487/RFC5860, May 2010,
              <http://www.rfc-editor.org/info/rfc5860>.

10.2.  Informative References

   [RFC5921]  Bocci, M., Ed., Bryant, S., Ed., Frost, D., Ed., Levrau,
              L., and L. Berger, "A Framework for MPLS in Transport
              Networks", RFC 5921, DOI 10.17487/RFC5921, July 2010,
              <http://www.rfc-editor.org/info/rfc5921>.

   [RFC6371]  Busi, I., Ed. and D. Allan, Ed., "Operations,
              Administration, and Maintenance Framework for MPLS-Based
              Transport Networks", RFC 6371, DOI 10.17487/RFC6371,
              September 2011, <http://www.rfc-editor.org/info/rfc6371>.

   [RFC6372]  Sprecher, N., Ed. and A. Farrel, Ed., "MPLS Transport
              Profile (MPLS-TP) Survivability Framework", RFC 6372,
              DOI 10.17487/RFC6372, September 2011,
              <http://www.rfc-editor.org/info/rfc6372>.

Authors' Addresses

   Alessandro D'Alessandro
   Telecom Italia
   Via Reiss Romoli, 274
   Torino  10148
   Italy

   Email: alessandro.dalessandro@telecomitalia.it







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   Loa Andersson
   Huawei Technologies

   Email: loa@mail01.huawei.com


   Satoshi Ueno
   NTT Communications

   Email: satoshi.ueno@ntt.com


   Kaoru Arai
   NTT

   Email: arai.kaoru@lab.ntt.co.jp


   Yoshinori Koike
   NTT

   Email: y.koike@vcd.nttbiz.com





























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