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Versions: 00

DetNet  Working Group                                          G. Mirsky
Internet-Draft                                                 ZTE Corp.
Intended status: Informational                              June 2, 2018
Expires: December 4, 2018


   Operations, Administration and Maintenance (OAM) for Deterministic
                           Networks (DetNet)
                       draft-mirsky-detnet-oam-00

Abstract

   This document lists functional requirements for Operations,
   Administration and Maintenance (OAM) toolset in Deterministic
   Networks (DetNet) and, using these requirements, and analyzes
   possible DetNet data plane solutions.

Status of This Memo

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

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   This Internet-Draft will expire on December 4, 2018.

Copyright Notice

   Copyright (c) 2018 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   described in the Simplified BSD License.



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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions used in this document . . . . . . . . . . . . . .   2
     2.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   2
     2.2.  Keywords  . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Requirements  . . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  DetNet Data Plane in Support of Active OAM  . . . . . . . . .   4
     4.1.  DetNet Active OAM Encapsulation . . . . . . . . . . . . .   6
     4.2.  DetNet PREF Interaction with Active OAM . . . . . . . . .   6
     4.3.  Alternative Encapsulation for DetNet  . . . . . . . . . .   7
   5.  Use of Hybrid OAM in DetNet . . . . . . . . . . . . . . . . .   8
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   8.  Acknowledgment  . . . . . . . . . . . . . . . . . . . . . . .   9
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   9
     9.2.  Informational References  . . . . . . . . . . . . . . . .  10
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

   [I-D.ietf-detnet-architecture] 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 to 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.

2.  Conventions used in this document

2.1.  Terminology

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




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   AC Associated Channel

   CW Control Word

   DetNet Deterministic Networks

   d-CW DetNet Control Word

   OAM: Operations, Administration and Maintenance

   PREF Packet Replication and Elimination Function

   PW Pseudowire

   RDI Remote Defect Indication

   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 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:

   1.   The listed requirements MUST be supported with any type of
        underlay network over which a DetNet domain can be realized.

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

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

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




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

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

   7.   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.

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

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

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

   11.  DetNet OAM MUST support performance measurement methods.

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

4.  DetNet Data Plane in Support of Active OAM

   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:





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

   The data plane encapsulation for DetNet specified in
   [I-D.ietf-detnet-dp-sol] has been analyzed in details in
   [I-D.bryant-detnet-mpls-dp] and [I-D.malis-detnet-ip-dp] for use in
   MPLS and IP networks respectively.  For the MPLS underlay network
   DetNet flows to be encapsulated analogous to pseudowires (PW) over
   MPLS packet switched network, as described in [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 packet sequencing information, e.g., value
   in the Sequence Number field of DetNet CW (d-CW).  The replication
   sub-function uses one of two options:

   o  use S-Label and d-CW information;

   o  use S-Label information.

   For data packets Figure 2 presents an example of PREF in DetNet
   domain regardless of how the replication sub-function realized in the
   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




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4.1.  DetNet Active OAM Encapsulation

   DetNet OAM, like PW OAM, uses PW Associated Channel Header defined in
   [RFC4385].  Figure 3 displays encapsulation of a DetNet active OAM
   packet.  Figure 4 displays format of the DetNet Associated Channel
   (AC).

       +---------------------------------+
       |                                 |
       |           DetNet  Flow          |
       |           OAM   Packet          |
       |                                 |
       +---------------------------------+ <--\
       |    DetNet Associated Channel    |    |
       +=================================+    +--> DetNet OAM data plane
       |             S-Label             |    |    MPLS encapsulation
       +---------------------------------+ <--/
       |           T-Label(s)            |
       +---------------------------------+
       |           Data-Link             |
       +---------------------------------+
       |           Physical              |
       +---------------------------------+


               Figure 3: DetNet PW OAM Packet Encapsulation


       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|0 0 0 0|0 0 0 0 0 0 0 0|         Channel Type          |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


             Figure 4: DetNet Associated Channel Header Format

4.2.  DetNet PREF Interaction with Active OAM

   Consider the scenario when EN1 injects DetNet active OAM packet with
   the same S-Label as the DetNet service reflected in Figure 2.  EN1 is
   the first node with the replication sub-function.  If the replication
   uses S-Label information and the sequencing information in d-CW (the
   first option), then EN1 will only forward the OAM packet without
   replicating it because OAM encapsulation doesn't include d-CW.  The
   path that active OAM packet traverses through the DetNet domain
   presented in Figure 5 with 'O'.  The figure clearly demonstrates that




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   the DetNet OAM packet does not traverse all the segments that are
   traversed by the DetNet data packet as displayed in Figure 2.


                    O       O        O        O
      CE1----EN1--------R1-------R2-------R3--------EN2----CE2
               \                /                   /
                \         /----+                   /
                 +------R4------------------------+

              Figure 5: OAM in DetNet Data Plane Based on PW

   If the replication is based solely on S-Label (the second option),
   EN1 node will replicate the OAM packet accordingly.  The replicated
   packet will be processed by the replication function at R4.  As
   result, the same OAM packet will be forwarded and another copy
   injected into the network.  This case displayed in Figure 6.  The OAM
   packet does traverse all links and nodes that the DetNet data packet
   of the monitored flow traverses but the egress node EN2 receives
   multiple, three in this example, copies of the same packet because
   the elimination function cannot be applied to the DetNet active OAM
   packet.


                O          O         OO       OO
      CE1----EN1--------R1-------R2-------R3--------EN2----CE2
               \O              O/                  O/
                \        O/----+                   /
                 +------R4------------------------+
                          O


             Figure 6: Over-Replication of Active OAM Packets

4.3.  Alternative Encapsulation for DetNet

   Introduction of DetNet header, that includes all necessary
   characteristic information to efficiently, among other scenarios, use
   multipath underlay, perform PERF, as part of DetNet service layer
   encapsulation allows DetNet active OAM packets to be in-band with the
   monitored DetNet data flow.  Figure 7 presents the format of DetNet
   packet with MPLS encapsulation.









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        +---------------------------------+
        |                                 |
        |           DetNet Flow           |
        |          Payload or OAM         |
        |              Packet             |
        +---------------------------------+
        |          DetNet Header          |
        ~                                 ~
        |                                 |
        +=================================+
        |             S-Label             |
        +---------------------------------+
        |           T-Label(s)            |
        +---------------------------------+
        |           Data-Link             |
        +---------------------------------+
        |           Physical              |
        +---------------------------------+


    Figure 7: DetNet Packet with DetNet Header Encapsulation over MPLS
                                 Underlay

   Demultiplexing of type of the payload encapsulated in the DetNet
   packet achieved using a field that explicitly identifies, e.g., OAM,
   Ethernet, or IPvX.

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 value
   of a designated field in the packet encapsulation.  One example of
   such 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.  IANA Considerations

   This document does not propose any IANA consideration.  This section
   may be removed.




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7.  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.

8.  Acknowledgment

   TBD

9.  References

9.1.  Normative References

   [I-D.bryant-detnet-mpls-dp]
              Bryant, S. and M. Chen, "Operation of Deterministic
              Networks over MPLS", draft-bryant-detnet-mpls-dp-00 (work
              in progress), March 2018.

   [I-D.ietf-detnet-architecture]
              Finn, N., Thubert, P., Varga, B., and J. Farkas,
              "Deterministic Networking Architecture", draft-ietf-
              detnet-architecture-05 (work in progress), May 2018.

   [I-D.ietf-detnet-dp-sol]
              Korhonen, J., Andersson, L., Jiang, Y., Finn, N., Varga,
              B., Farkas, J., Bernardos, C., Mizrahi, T., and L. Berger,
              "DetNet Data Plane Encapsulation", draft-ietf-detnet-dp-
              sol-04 (work in progress), March 2018.

   [I-D.malis-detnet-ip-dp]
              Malis, A., Bryant, S., Chen, M., and B. Varga, "DetNet IP
              Encapsulation", draft-malis-detnet-ip-dp-00 (work in
              progress), March 2018.

   [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>.

   [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>.








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9.2.  Informational References

   [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>.

   [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>.

   [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>.

Author's Address

   Greg Mirsky
   ZTE Corp.

   Email: gregimirsky@gmail.com


















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