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DetNet  Working Group                                          G. Mirsky
Internet-Draft                                                 ZTE Corp.
Intended status: Standards Track                                 M. Chen
Expires: January 9, 2021                                          Huawei
                                                            July 8, 2020


   Operations, Administration and Maintenance (OAM) for Deterministic
                 Networks (DetNet) with MPLS Data Plane
                     draft-ietf-detnet-mpls-oam-01

Abstract

   This document lists functional requirements for Operations,
   Administration, and Maintenance (OAM) toolset in Deterministic
   Networks (DetNet) and, using these requirements; defines format and
   use principals of the DetNet service Associated Channel over a DetNet
   network with the MPLS data plane..

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
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   This Internet-Draft will expire on January 9, 2021.

Copyright Notice

   Copyright (c) 2020 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   include Simplified BSD License text as described in Section 4.e of



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   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 and Acronyms  . . . . . . . . . . . . . . . .   3
     2.2.  Keywords  . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Requirements  . . . . . . . . . . . . . . . . . . . . . . . .   4
   4.  Active OAM for DetNet Networks with MPLS Data Plane . . . . .   5
     4.1.  DetNet Active OAM Encapsulation . . . . . . . . . . . . .   6
     4.2.  DetNet Replication, Elimination, and Ordering Sub-
           functions Interaction with Active OAM . . . . . . . . . .   8
   5.  Use of Hybrid OAM in DetNet . . . . . . . . . . . . . . . . .   9
   6.  OAM Interworking Models . . . . . . . . . . . . . . . . . . .   9
     6.1.  OAM of DetNet MPLS Interworking with OAM of TSN . . . . .   9
     6.2.  OAM of DetNet MPLS Interworking with OAM of DetNet IP . .  10
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  10
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  10
   9.  Acknowledgment  . . . . . . . . . . . . . . . . . . . . . . .  11
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  11
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  11
     10.2.  Informational References . . . . . . . . . . . . . . . .  12
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  13

1.  Introduction

   [RFC8655] introduces and explains Deterministic Networks (DetNet)
   architecture and how the Packet Replication and Elimination function
   (PREF) can be used to ensure low packet drop ratio in DetNet domain.

   Operations, Administration and Maintenance (OAM) protocols are used
   to detect, localize defects in the network, and monitor network
   performance.  Some OAM functions, e.g., failure detection, work in
   the network proactively, while others, e.g., defect localization,
   usually performed on-demand.  These tasks achieved by a combination
   of active and hybrid, as defined in [RFC7799], OAM methods.

   This document lists the functional requirements toward OAM for DetNet
   domain.  The list can further be used for gap analysis of available
   OAM tools to identify possible enhancements of existing or whether
   new OAM tools are required to support proactive and on-demand path
   monitoring and service validation.  Also, this document defines
   format and use principals of the DetNet service Associated Channel
   over a DetNet network with the MPLS data plane
   [I-D.ietf-detnet-mpls].




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2.  Conventions used in this document

2.1.  Terminology and Acronyms

   The term "DetNet OAM" used in this document interchangeably with
   longer version "set of OAM protocols, methods and tools for
   Deterministic Networks".

   CW Control Word

   DetNet Deterministic Networks

   d-ACH DetNet Associated Channel Header

   d-CW DetNet Control Word

   DNH DetNet Header

   GAL Generic Associated Channel Label

   G-ACh Generic Associated Channel

   OAM: Operations, Administration and Maintenance

   PREF Packet Replication and Elimination Function

   POF Packet Ordering Function

   PW Pseudowire

   RDI Remote Defect Indication

   E2E End-to-end

   CFM Connectivity Fault Management

   BFD Bidirectional Forwarding Detection

   TSN Time-Sensitive Network

   F-Label A Detnet "forwarding" label that identifies the LSP used to
   forward a DetNet flow across an MPLS PSN, e.g., a hop-by-hop label
   used between label switching routers (LSR).

   S-Label A DetNet "service" label that is used between DetNet nodes
   that implement also the DetNet service sub-layer functions.  An
   S-Label is also used to identify a DetNet flow at DetNet service sub-
   layer.



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   Underlay Network or Underlay Layer: The network that provides
   connectivity between the DetNet nodes.  MPLS network providing LSP
   connectivity between DetNet nodes is an example of the underlay
   layer.

   DetNet Node - a node that is an actor in the DetNet domain.  DetNet
   domain edge node and node that performs PREF within the domain are
   examples of DetNet node.

2.2.  Keywords

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

3.  Requirements

   This section lists requirements for OAM in DetNet domain with MPLS
   data plane:

   1.   It MUST be possible to initiate DetNet OAM session from any
        DetNet node towards another DetNet node(s) within given domain.

   2.   It SHOULD be possible to initialize DetNet OAM session from a
        centralized controller.

   3.   DetNet OAM MUST support proactive and on-demand OAM monitoring
        and measurement methods.

   4.   DetNet OAM packets MUST be in-band, i.e., follow precisely the
        same path as DetNet data plane traffic.

   5.   DetNet OAM MUST support unidirectional OAM methods, continuity
        check, connectivity verification, and performance measurement.

   6.   DetNet OAM MUST support bi-directional OAM methods.  Such OAM
        methods MAY combine in-band monitoring or measurement in the
        forward direction and out-of-bound notification in the reverse
        direction, i.e., from egress to ingress end point of the OAM
        test session.

   7.   DetNet OAM MUST support proactive monitoring of a DetNet node
        availability in the given DetNet domain.

   8.   DetNet OAM MUST support Path Maximum Transmission Unit
        discovery.



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   9.   DetNet OAM MUST support Remote Defect Indication (RDI)
        notification to the DetNet node performing continuity checking.

   10.  DetNet OAM MUST support performance measurement methods.

   11.  DetNet OAM MAY support hybrid performance measurement methods.

   12.  DetNet OAM MUST support unidirectional performance measurement
        methods.  Calculated performance metrics MUST include but are
        not limited to throughput, packet loss, delay and delay
        variation metrics.  [RFC6374] provides excellent details on
        performance measurement and performance metrics.

   13.  DetNet OAM MUST support defect notification mechanism, like
        Alarm Indication Signal.  Any DetNet node in the given DetNet
        domain MAY originate a defect notification addressed to any
        subset of nodes within the domain.

   14.  DetNet OAM MUST support methods to enable survivability of the
        DetNet domain.  These recovery methods MAY use protection
        switching and restoration.

   15.  DetNet OAM MUST support the discovery of Packet Replication,
        Elimination, and Order preservation sub-functions locations in
        the domain.

   16.  DetNet OAM MUST support testing of Packet Replication,
        Elimination, and Order preservation sub-functions in the domain.

   17.  DetNet OAM MUST support monitoring any sub-set of paths
        traversed through the DetNet domain by the DetNet flow.

4.  Active OAM for DetNet Networks with MPLS Data Plane

   OAM protocols and mechanisms act within the data plane of the
   particular networking layer.  And thus it is critical that the data
   plane encapsulation supports OAM mechanisms in such a way to comply
   with the above-listed requirements.  One of such examples that
   require special consideration is requirement #5:

      DetNet OAM packets MUST be in-band, i.e., follow precisely the
      same path as DetNet data plane traffic both for unidirectional and
      bi-directional DetNet paths.

   The Det Net data plane encapsulation in transport network with MPLS
   encapsulation specified in [I-D.ietf-detnet-mpls].  For the MPLS
   underlay network, DetNet flows to be encapsulated analogous to
   pseudowires (PW) over MPLS packet switched network, as described in



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   [RFC3985], [RFC4385].  Generic PW MPLS Control Word (CW), defined in
   [RFC4385], for DetNet displayed in Figure 1.


        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |0 0 0 0|                Sequence Number                        |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                   Figure 1: DetNet Control Word Format

   PREF in the DetNet domain composed by a combination of nodes that
   perform replication and elimination sub-functions.  The elimination
   sub-function always uses the S-Label and packet sequencing
   information, e.g., the value in the Sequence Number field of DetNet
   CW (d-CW).  The replication sub-function uses the S-Label information
   only.  For data packets Figure 2 presents an example of PREF in
   DetNet domain.


         1111   11111111  111111   112212   112212     132213
      CE1----EN1--------R1-------R2-------R3--------EN2----CE2
               \2          22222/                 3 /
                \2222222  /----+                 3 /
                 +------R4------------------------+
                          333333333333333333333333


                  Figure 2: DetNet Data Plane Based on PW

4.1.  DetNet Active OAM Encapsulation

   DetNet OAM, like PW OAM, uses PW Associated Channel Header defined in
   [RFC4385].  Figure 3 displays the encapsulation of a DetNet MPLS
   [I-D.ietf-detnet-mpls] active OAM packet.














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         +---------------------------------+
         |                                 |
         |         DetNet App-Flow         |
         |         Payload  Packet         |
         |                                 |
         +---------------------------------+ <--\
         | DetNet Associated Channel Header|    |
         +---------------------------------+    +--> DetNet active OAM
         |           S-Label               |    |    MPLS encapsulation
         +---------------------------------+    |
         |         [ F-Label(s) ]          |    |
         +---------------------------------+ <--/
         |           Data-Link             |
         +---------------------------------+
         |           Physical              |
         +---------------------------------+


    Figure 3: DetNet Active OAM Packet Encapsulation in MPLS Data Plane

   Figure 4 displays encapsulation of a test packet of an active DetNet
   OAM protocol in case of MPLS-over-UDP/IP
   [I-D.ietf-detnet-mpls-over-udp-ip].

         +---------------------------------+
         |                                 |
         |         DetNet App-Flow         |
         |         Payload  Packet         |
         |                                 |
         +---------------------------------+ <--\
         | DetNet Associated Channel Header|    |
         +---------------------------------+    +--> DetNet active OAM
         |             S-Label             |    |    MPLS encapsulation
         +---------------------------------+    |
         |          [ F-label(s) ]         |    |
         +---------------------------------+ <--+
         |           UDP Header            |    |
         +---------------------------------+    +--> DetNet data plane
         |           IP Header             |    |    IP encapsulation
         +---------------------------------+ <--/
         |           Data-Link             |
         +---------------------------------+
         |           Physical              |
         +---------------------------------+


   Figure 4: DetNet Active OAM Packet Encapsulation in MPLS-over-UDP/IP




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   Figure 5 displays the format of the DetNet Associated Channel Header
   (d-ACH).


       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |0 0 0 1|Version|Sequence Number|         Channel Type          |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


             Figure 5: DetNet Associated Channel Header Format

   The meanings of the fields in the d-ACH are:

      Bits 0..3 MUST be 0b0001.  This value of the first nibble allows
      the packet to be distinguished from an IP packet [RFC4928] and a
      DetNet data packet [I-D.ietf-detnet-mpls].

      Version: this is the version number of the d-ACH.  This
      specification defines version 0.

      Sequence Number: this is unsigned eight bits-long field.  The
      originating DetNet node MUST set the value of the Sequence Number
      field to a non-zero before packet being transmitted.  The
      originating node MUST monotonically increase the value of the
      Sequence Number field for the every next active OAM packet.

      Channel Type: the value of DetNet Associated Channel Type is one
      of values defined in the IANA PW Associated Channel Type registry.

   The DetNet flow, according to [I-D.ietf-detnet-mpls], is identified
   by the S-label that MUST be at the bottom of the stack.  Active OAM
   packet MUST have d-ACH immediately following the S-label.

4.2.  DetNet Replication, Elimination, and Ordering Sub-functions
      Interaction with Active OAM

   At the DetNet service layer, special functions MAY be applied to the
   particular DetNet flow - PREF to potentially lower packet loss,
   improve the probability of on-time packet delivery and Packet
   Ordering Function (POF) to ensure in-order packet delivery.  As data
   and the active OAM packets have the same Flow ID, S-label, sub-
   functions that rely on sequencing information in the DetNet service
   layer MUST process 28 MSBs of the d-ACH as the source of the
   sequencing information for the OAM packet.





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5.  Use of Hybrid OAM in DetNet

   Hybrid OAM methods are used in performance monitoring and defined in
   [RFC7799] as:

      Hybrid Methods are Methods of Measurement that use a combination
      of Active Methods and Passive Methods.

   A hybrid measurement method may produce metrics as close to passive,
   but it still alters something in a data packet even if that is the
   value of a designated field in the packet encapsulation.  One example
   of such a hybrid measurement method is the Alternate Marking method
   described in [RFC8321].  Reserving the field for the Alternate
   Marking method in the DetNet Header will enhance available to an
   operator set of DetNet OAM tools.

6.  OAM Interworking Models

   Interworking of two OAM domains that utilize different networking
   technology can be realized either by a peering or a tunneling model.
   In a peering model, OAM domains are within the corresponding network
   domain.  When using the peering model, state changes that are
   detected by a Fault Management OAM protocol can be mapped from one
   OAM domain into another or a notification, e.g., an alarm, can be
   sent to a central controller.  In the tunneling model of OAM
   interworking, usually, only one active OAM protocol is used.  Its
   test packets are tunneled through another domain along with the data
   flow, thus ensuring the fate sharing among test and data packets.

6.1.  OAM of DetNet MPLS Interworking with OAM of TSN

   Active DetNet OAM is required to provide the E2E fault management and
   performance monitoring for a DetNet flow.  Interworking of DetNet
   active OAM with MPLS data plane with the IEEE 802.1 Time-Sensitive
   Networking (TSN) domain based on [I-D.ietf-detnet-mpls-over-tsn].

   In the case of the peering model is used in the fault management OAM,
   then the node that borders both TSN and DetNet MPLS domains MUST
   support [RFC7023].  [RFC7023] specified the mapping of defect states
   between Ethernet Attachment Circuits (ACs) and associated Ethernet
   PWs that are part of an end-to-end (E2E) emulated Ethernet service.
   Requirements and mechanisms described in [RFC7023] are equally
   applicable to using the peering model to achieve E2E FM OAM over
   DetNet MPLS and TSN domains.  The Connectivity Fault Management (CFM)
   protocol [IEEE.CFM] or in [ITU.Y1731] can provide fast detection of a
   failure in the TSN segment of the DetNet service.  In the DetNet MPLS
   domain BFD (Bidirectional Forwarding Detection), specified in
   [RFC5880] and [RFC5885], can be used.  To provide E2E failure



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   detection, the TSN segment might be presented as a concatenated with
   the DetNet MPLS and the Section 6.8.17 [RFC5880] MAY be used to
   inform the upstream DetNet MPLS node of a failure of the TSN segment.
   Performance monitoring can be supported by [RFC6374] in the DetNet
   MPLS and [ITU.Y1731] in the TSN domains, respectively.  Performance
   objectives for each domain should refer to metrics that additive or
   be defined for each domain separately.

   The following considerations are to be realized when using the
   tunneling model of OAM interworking between DetNet MPLS and TSN
   domains:

   o  Active OAM test packet MUST be mapped to the same TSN Stream ID as
      the monitored DetNet flow.

   o  Active OAM test packets MUST be treated in the TSN domain based on
      its S-label and CoS marking (TC field value).

   Note that the tunneling model of the OAM interworking requires that
   the remote peer of the E2E OAM domain supports the active OAM
   protocol selected on the ingress endpoint.  For example, if BFD is
   used for proactive path continuity monitoring in the DetNet MPLS
   domain, a TSN endpoint of the DetNet service has also support BFD as
   defined in [RFC5885].

6.2.  OAM of DetNet MPLS Interworking with OAM of DetNet IP

   Interworking between active OAM segments in DetNet MPLS and DetNet IP
   domains can also be realized using either the peering or the
   tunneling model, as discussed in Section 6.1.  Using the same
   protocol, e.g., BFD, over both segments, simplifies the mapping of
   errors in the peering model.  To provide the performance monitoring
   over a DetNet IP domain STAMP [RFC8762] and its extensions
   [I-D.ietf-ippm-stamp-option-tlv] can be used.

7.  IANA Considerations

   TBA

8.  Security Considerations

   This document lists the OAM requirements for a DetNet domain and does
   not raise any security concerns or issues in addition to ones common
   to networking.  Additionally, security considerations discussed in
   DetNet specifications: [RFC8655], [I-D.ietf-detnet-security],
   [I-D.ietf-detnet-mpls] are applicable to this document.  Security
   concerns and issues related to MPLS OAM tools like LSP Ping
   [RFC8029], BFD over PW [RFC5885] also apply to this specification.



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9.  Acknowledgment

   Authors extend their appreciation to Pascal Thubert for his
   insightful comments and productive discussion that helped to improve
   the document.

10.  References

10.1.  Normative References

   [I-D.ietf-detnet-mpls]
              Varga, B., Farkas, J., Berger, L., Malis, A., Bryant, S.,
              and J. Korhonen, "DetNet Data Plane: MPLS", draft-ietf-
              detnet-mpls-08 (work in progress), July 2020.

   [I-D.ietf-detnet-mpls-over-tsn]
              Varga, B., Farkas, J., Malis, A., and S. Bryant, "DetNet
              Data Plane: MPLS over IEEE 802.1 Time Sensitive Networking
              (TSN)", draft-ietf-detnet-mpls-over-tsn-03 (work in
              progress), June 2020.

   [I-D.ietf-detnet-mpls-over-udp-ip]
              Varga, B., Farkas, J., Berger, L., Malis, A., and S.
              Bryant, "DetNet Data Plane: MPLS over UDP/IP", draft-ietf-
              detnet-mpls-over-udp-ip-06 (work in progress), May 2020.

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

   [RFC7023]  Mohan, D., Ed., Bitar, N., Ed., Sajassi, A., Ed., DeLord,
              S., Niger, P., and R. Qiu, "MPLS and Ethernet Operations,
              Administration, and Maintenance (OAM) Interworking",
              RFC 7023, DOI 10.17487/RFC7023, October 2013,
              <https://www.rfc-editor.org/info/rfc7023>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8655]  Finn, N., Thubert, P., Varga, B., and J. Farkas,
              "Deterministic Networking Architecture", RFC 8655,
              DOI 10.17487/RFC8655, October 2019,
              <https://www.rfc-editor.org/info/rfc8655>.






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10.2.  Informational References

   [I-D.ietf-detnet-security]
              Mizrahi, T. and E. Grossman, "Deterministic Networking
              (DetNet) Security Considerations", draft-ietf-detnet-
              security-10 (work in progress), May 2020.

   [I-D.ietf-ippm-stamp-option-tlv]
              Mirsky, G., Min, X., Nydell, H., Foote, R., Masputra, A.,
              and E. Ruffini, "Simple Two-way Active Measurement
              Protocol Optional Extensions", draft-ietf-ippm-stamp-
              option-tlv-06 (work in progress), June 2020.

   [IEEE.CFM]
              IEEE, "Connectivity Fault Management clause of IEEE
              802.1Q", IEEE 802.1Q, 2013.

   [ITU.Y1731]
              ITU-T, "OAM functions and mechanisms for Ethernet based
              Networks", ITU-T Recommendation G.8013/Y.1731, November
              2013.

   [RFC3985]  Bryant, S., Ed. and P. Pate, Ed., "Pseudo Wire Emulation
              Edge-to-Edge (PWE3) Architecture", RFC 3985,
              DOI 10.17487/RFC3985, March 2005,
              <https://www.rfc-editor.org/info/rfc3985>.

   [RFC4385]  Bryant, S., Swallow, G., Martini, L., and D. McPherson,
              "Pseudowire Emulation Edge-to-Edge (PWE3) Control Word for
              Use over an MPLS PSN", RFC 4385, DOI 10.17487/RFC4385,
              February 2006, <https://www.rfc-editor.org/info/rfc4385>.

   [RFC4928]  Swallow, G., Bryant, S., and L. Andersson, "Avoiding Equal
              Cost Multipath Treatment in MPLS Networks", BCP 128,
              RFC 4928, DOI 10.17487/RFC4928, June 2007,
              <https://www.rfc-editor.org/info/rfc4928>.

   [RFC5880]  Katz, D. and D. Ward, "Bidirectional Forwarding Detection
              (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010,
              <https://www.rfc-editor.org/info/rfc5880>.

   [RFC5885]  Nadeau, T., Ed. and C. Pignataro, Ed., "Bidirectional
              Forwarding Detection (BFD) for the Pseudowire Virtual
              Circuit Connectivity Verification (VCCV)", RFC 5885,
              DOI 10.17487/RFC5885, June 2010,
              <https://www.rfc-editor.org/info/rfc5885>.





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   [RFC6374]  Frost, D. and S. Bryant, "Packet Loss and Delay
              Measurement for MPLS Networks", RFC 6374,
              DOI 10.17487/RFC6374, September 2011,
              <https://www.rfc-editor.org/info/rfc6374>.

   [RFC7799]  Morton, A., "Active and Passive Metrics and Methods (with
              Hybrid Types In-Between)", RFC 7799, DOI 10.17487/RFC7799,
              May 2016, <https://www.rfc-editor.org/info/rfc7799>.

   [RFC8029]  Kompella, K., Swallow, G., Pignataro, C., Ed., Kumar, N.,
              Aldrin, S., and M. Chen, "Detecting Multiprotocol Label
              Switched (MPLS) Data-Plane Failures", RFC 8029,
              DOI 10.17487/RFC8029, March 2017,
              <https://www.rfc-editor.org/info/rfc8029>.

   [RFC8321]  Fioccola, G., Ed., Capello, A., Cociglio, M., Castaldelli,
              L., Chen, M., Zheng, L., Mirsky, G., and T. Mizrahi,
              "Alternate-Marking Method for Passive and Hybrid
              Performance Monitoring", RFC 8321, DOI 10.17487/RFC8321,
              January 2018, <https://www.rfc-editor.org/info/rfc8321>.

   [RFC8762]  Mirsky, G., Jun, G., Nydell, H., and R. Foote, "Simple
              Two-Way Active Measurement Protocol", RFC 8762,
              DOI 10.17487/RFC8762, March 2020,
              <https://www.rfc-editor.org/info/rfc8762>.

Authors' Addresses

   Greg Mirsky
   ZTE Corp.

   Email: gregimirsky@gmail.com


   Mach(Guoyi) Chen
   Huawei

   Email: mach.chen@huawei.com













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