PREOF Observability and OAM Requirements
draft-contreras-detnet-preof-oam-00

detnet                                                   L. M. Contreras
Internet-Draft                                                Telefonica
Intended status: Informational                               6 July 2026
Expires: 7 January 2027

                PREOF Observability and OAM Requirements
                  draft-contreras-detnet-preof-oam-00

Abstract

   Packet Replication, Elimination, and Ordering Functions (PREOF)
   enables highly reliable packet delivery through path redundancy and
   packet sequencing mechanisms in DetNet domains.

   Existing DetNet Operations, Administration, and Maintenance (OAM)
   specifications provide mechanisms for monitoring service
   connectivity, packet loss, delay, and overall service performance.
   However, they do not provide detailed operational visibility into the
   behavior of PREOF functions themselves.

   This document identifies operational observability gaps associated
   with PREOF, defines requirements for PREOF-specific OAM, and
   introduces a set of observable events and metrics to monitor,
   troubleshoot, and validate PREOF operation independently of the
   underlying DetNet data plane technology.

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Copyright Notice

   Copyright (c) 2026 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Operational Use Cases . . . . . . . . . . . . . . . . . . . .   3
   4.  PREOF Observable Events . . . . . . . . . . . . . . . . . . .   4
     4.1.  Replication Events  . . . . . . . . . . . . . . . . . . .   4
     4.2.  Duplicate Elimination Events  . . . . . . . . . . . . . .   4
     4.3.  Reordering Events . . . . . . . . . . . . . . . . . . . .   5
     4.4.  Timeout Events  . . . . . . . . . . . . . . . . . . . . .   5
     4.5.  Gap Detection Events  . . . . . . . . . . . . . . . . . .   5
     4.6.  Late Arrival Events . . . . . . . . . . . . . . . . . . .   6
   5.  PREOF Operational Metrics . . . . . . . . . . . . . . . . . .   6
   6.  PREOF OAM Requirements  . . . . . . . . . . . . . . . . . . .   6
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   7
   10. Informative References  . . . . . . . . . . . . . . . . . . .   7
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   Deterministic Networking (DetNet) introduces Packet Replication,
   Elimination, and Ordering Functions (PREOF) as a mechanism to improve
   service reliability and reduce packet loss in networks carrying
   deterministic flows.

   PREOF achieves these objectives by replicating packets across
   multiple paths, eliminating duplicate packets at convergence points,
   and restoring packet order whenever required.  These operations are
   fundamental to the reliability guarantees provided by DetNet
   networks.

   Current DetNet OAM specifications focus primarily on validating
   service connectivity and measuring service-level performance
   indicators such as packet delay, packet delay variation, and packet
   loss.  While these capabilities are necessary, they do not provide
   sufficient insight into the internal operation of PREOF functions.

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   This document addresses operational visibility requirements by
   identifying PREOF-specific observability and OAM requirements.

2.  Terminology

   The terminology defined in [RFC8655] and [RFC8938] applies.

   The following additional terms are defined for this document.

   *  PREOF Event: an observable action performed by a PREOF processing
      function.

   *  PREOF Observation Point: a logical location where PREOF
      operational information can be collected.

   *  PREOF Record: a collection of information describing the
      processing outcome associated with a packet or group of packets
      traversing a PREOF function.

3.  Operational Use Cases

   A number of use cases motivate the need of OAM capabilities related
   to PREOF functionality.

   *  Duplicate elimination validation, where an operator verifies that
      duplicate packets are correctly removed and that no duplicate
      packet reaches the destination.

   *  Protected path analysis, when PREOF observations can reveal how
      frequently each replicated path provides the packet copy
      ultimately selected by the elimination function.  This information
      can enable early detection of path degradation.

   *  Reordering buffer optimization, by observing reordering depth and
      packet holding times, which can assist operators in selecting
      appropriate buffer dimensions and timeout values.

   *  Packet loss troubleshooting, leveraging on PREOF observability to
      determine whether a packet was successfully replicated, eliminated
      as a duplicate, discarded due to timeout or to ordering
      constraints, etc.

   *  Reliability validation, using PREOF metrics allowing operators to
      quantify the actual benefit provided by replication and
      elimination mechanisms.

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4.  PREOF Observable Events

   This section defines events of interest to be supported by PREOF-
   capable systems.

4.1.  Replication Events

   A replication event occurs whenever a packet is replicated and
   multiple copies are transmitted through distinct forwarding paths.

   A replication event record is identified by the following
   information:

   *  Flow Identifier

   *  Sequence Number

   *  Timestamp

   *  Replication Point Identifier

   *  Number of Generated Copies

   *  List of Outgoing Branches

4.2.  Duplicate Elimination Events

   A duplicate elimination event occurs whenever multiple packet copies
   are received and duplicate copies are discarded.

   A duplicate elimination event is identified by the following
   information:

   *  Flow Identifier

   *  Sequence Number

   *  Timestamp

   *  Selected Copy

   *  Discarded Copies

   *  Elimination Reason

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4.3.  Reordering Events

   A reordering event occurs whenever packets are retained and released
   to restore sequence order.

   A reordering event is identified by the following information:

   *  Flow Identifier

   *  Expected Sequence Number

   *  Received Sequence Number

   *  Reordering Depth

   *  Holding Time

   *  Buffer Occupancy

4.4.  Timeout Events

   A timeout event occurs when packet reordering cannot be completed
   before expiration of a configured waiting interval.

   A timeout event is identified by the following information:

   *  Missing Sequence Number(s)

   *  Waiting Duration

   *  Timeout Threshold

   *  Action Performed

4.5.  Gap Detection Events

   A gap detection event occurs when a packet sequence discontinuity is
   identified.

   A gap event is identified by the following information:

   *  Flow Identifier

   *  Missing Sequence Number(s)

   *  Gap Size

   *  Detection Timestamp

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4.6.  Late Arrival Events

   A late arrival event occurs when a packet arrives after PREOF
   processing has already concluded for the associated sequence number.

5.  PREOF Operational Metrics

   The following PREOF operation metrics are relevant

   *  Replication Metrics, such as number of replicated packets.

   *  Elimination Metrics, as the number of duplicate packets received
      and duplicate packets discarded

   *  Reordering Metrics, like the number of reordered packets, the
      average reordering depth, the maximum reordering depth, the
      average holding time or the maximum hholding time

   *  Reliability Metrics, such as the number of recovered Packets

6.  PREOF OAM Requirements

   The following requirements are identified for the support of OAM
   associated to PREOF.

   REQ-1: PREOF implementations MUST expose counters associated with
   packet replication activities.

   REQ-2: PREOF implementations MUST expose counters associated with
   duplicate elimination.

   REQ-3: PREOF implementations MUST support identification of packet
   discard reasons.

   REQ-4: PREOF implementations SHOULD expose ordering buffer
   utilization statistics.

   REQ-5: PREOF implementations SHOULD support timestamped PREOF event
   reporting.

   REQ-6: PREOF observability mechanisms MUST operate independently from
   the underlying DetNet data plane technology.

7.  Security Considerations

   Operational information associated with PREOF operation may expose
   details about network topology, path diversity mechanisms, traffic
   patterns, and service protection strategies.

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   Implementations MUST ensure that access to PREOF operational
   information is appropriately authenticated and authorized.

8.  IANA Considerations

   This document has no IANA actions.

9.  Acknowledgements

   The work of L.M.  Contreras has been partially funded by the European
   Commission through the Horizon Europe SNS JU PRIME-6G project (GA
   101272485).

10.  Informative References

   [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>.

   [RFC8938]  Varga, B., Ed., Farkas, J., Berger, L., Malis, A., and S.
              Bryant, "Deterministic Networking (DetNet) Data Plane
              Framework", RFC 8938, DOI 10.17487/RFC8938, November 2020,
              <https://www.rfc-editor.org/info/rfc8938>.

Author's Address

   Luis M. Contreras
   Telefonica
   Ronda de la Comunicacion, s/n
   28050 Madrid
   Spain
   Email: luismiguel.contrerasmurillo@telefonica.com

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