detnet L. M. Contreras Internet-Draft Telefonica Intended status: Informational 2 November 2026 Expires: 6 May 2027 PREOF Observability and OAM Requirements draft-contreras-detnet-preof-oam-01 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. The requirements, metrics and rest of information are intended to be independent of the underlying DetNet data plane and may be realized using different management, telemetry, or OAM mechanisms. 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 https://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 6 May 2027. Contreras Expires 6 May 2027 [Page 1] Internet-Draft PREOF OAM November 2026 Copyright Notice Copyright (c) 2026 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 (https://trustee.ietf.org/ license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Operational Use Cases . . . . . . . . . . . . . . . . . . . . 3 4. PREOF Observable Events . . . . . . . . . . . . . . . . . . . 4 4.1. PREOF Observability . . . . . . . . . . . . . . . . . . . 4 4.2. Replication Events . . . . . . . . . . . . . . . . . . . 4 4.3. Duplicate Elimination Events . . . . . . . . . . . . . . 5 4.4. Reordering Events . . . . . . . . . . . . . . . . . . . . 5 4.5. Timeout Events . . . . . . . . . . . . . . . . . . . . . 6 4.6. Gap Detection Events . . . . . . . . . . . . . . . . . . 6 4.7. Late Arrival Events . . . . . . . . . . . . . . . . . . . 6 5. PREOF Operational Metrics . . . . . . . . . . . . . . . . . . 7 6. PREOF OAM Requirements . . . . . . . . . . . . . . . . . . . 7 7. Operational and Scalability Considerations . . . . . . . . . 8 8. Security Considerations . . . . . . . . . . . . . . . . . . . 8 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 10. Informative References . . . . . . . . . . . . . . . . . . . 8 Appendix A. Relevant Obervations per Operational Use Case . . . 9 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 9 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 9 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. Contreras Expires 6 May 2027 [Page 2] Internet-Draft PREOF OAM November 2026 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. Troubleshooting a PREOF-protected DetNet flow will require visibility into both the end-to-end deterministic reliable service performance and the operation of the PREOF functions involved in providing that service. The former is addressed by existing DetNet OAM mechanisms, while this document focuses on the latter. 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. An observation point may be associated with replication, elimination, sequencing, or other PREOF processing. Multiple observation points may exist along the processing path of a PREOF-protected flow. * 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. Contreras Expires 6 May 2027 [Page 3] Internet-Draft PREOF OAM November 2026 * 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. 4. PREOF Observable Events This section defines events of interest to be supported by PREOF- capable systems. 4.1. PREOF Observability PREOF observability is based on the information provided by logical observation points associated with PREOF processing functions. Depending on the implementation, observation points may be associated with replication, elimination, sequencing, or any other PREOF operations. Observations at the different PREOF functions may need to be correlated in order to determine the overall behavior of a protected DetNet flow. The correlation process may use flow information such as the flow identifier, sequence number, observation point identifier, and local timing information. An observable event does not imply that an implementation is required to generate or export an individual record for every packet. Implementations may expose the corresponding information through counters, aggregated statistics, event notifications, sampled observations, or any other mechanism. 4.2. Replication Events A replication event occurs whenever a packet is replicated and multiple copies are transmitted through distinct forwarding paths. Contreras Expires 6 May 2027 [Page 4] Internet-Draft PREOF OAM November 2026 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 4.3. 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 4.4. 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 Contreras Expires 6 May 2027 [Page 5] Internet-Draft PREOF OAM November 2026 * Reordering Depth * Holding Time * Buffer Occupancy 4.5. 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 4.6. 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 4.7. Late Arrival Events A late arrival event occurs when a packet arrives after PREOF processing has already concluded for the associated sequence number. Contreras Expires 6 May 2027 [Page 6] Internet-Draft PREOF OAM November 2026 5. PREOF Operational Metrics The PREOF operational metrics can provide aggregated information derived from the operation of distinct PREOF functions. Such operational metrics are intended to characterize PREOF behavior over a set of packets or an observation interval. Moreover, the metrics may be maintained per DetNet flow, per PREOF function, per observation point, or at another implementation-defined aggregation level. 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: A PREOF implementation MUST provide operational information sufficient to determine the activity of packet replication functions. * REQ-2: A PREOF implementation MUST provide operational information sufficient to determine the activity of duplicate elimination functions. * REQ-3: A PREOF implementation MUST support identification of PREOF packet discard reasons when such reasons are distinguishable by the implementation. * REQ-4: A PREOF implementation supporting packet ordering SHOULD expose information about ordering behavior, including buffer utilization or equivalent indicators. * REQ-5: PREOF observability mechanisms SHOULD support time correlation of observations when required for troubleshooting. Contreras Expires 6 May 2027 [Page 7] Internet-Draft PREOF OAM November 2026 * REQ-6: The information model defined for PREOF observability MUST NOT depend on a particular DetNet data-plane technology. * REQ-7: PREOF observations SHOULD support correlation between observation points acting on the same DetNet flow. * REQ-8: Implementations SHOULD provide aggregated counters or statistics for operational monitoring without requiring per-packet event export. * REQ-9: Implementations SHOULD provide mechanisms to limit the amount of PREOF observability information generated or exported. * REQ-10: The absence of an expected packet copy SHOULD be distinguishable, when possible, from the elimination of a duplicate copy. 7. Operational and Scalability Considerations PREOF may operate on DetNet flows with high packet rates. Reporting every PREOF processing event individually may result in a volume of operational information impractical in terms of collection. Implementations are expected to select an appropriate level of observability according to the operational objective. Continuous monitoring may rely primarily on counters and aggregated metrics, while detailed event information may be enabled selectively for troubleshooting or diagnostic purposes. 8. Security Considerations Operational information associated with PREOF operation may expose details about network topology, path diversity mechanisms, traffic patterns, and service protection strategies. Implementations MUST ensure that access to PREOF operational information is appropriately authenticated and authorized. 9. IANA Considerations This document has no IANA actions. 10. Informative References [RFC8655] Finn, N., Thubert, P., Varga, B., and J. Farkas, "Deterministic Networking Architecture", RFC 8655, DOI 10.17487/RFC8655, October 2019, . Contreras Expires 6 May 2027 [Page 8] Internet-Draft PREOF OAM November 2026 [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, . Appendix A. Relevant Obervations per Operational Use Case The following table summarizes the kind of observations that could be relevant per each of the operational use cases. +------------------------+---------------------------+----------------------------+ | Operational use case | Relevant observations | Relevant metrics | +------------------------+---------------------------+----------------------------+ | Duplicate elimination | Replication + elimination | Copies received / | | validation | | duplicates discarded | +------------------------+---------------------------+----------------------------+ | Protected-path analysis| Replication + elimination | Accepted copies / branch- | | | | related observations | +------------------------+---------------------------+----------------------------+ | Reordering optimization| Reordering + timeout | Buffer depth / holding time| | | | / timeout count | +------------------------+---------------------------+----------------------------+ | Packet-loss | Replication + gap + | Gaps / discards / | | troubleshooting | timeout + elimination | available copies | +------------------------+---------------------------+----------------------------+ | Reliability validation | Replication + elimination | Recovered packets / | | | | alternative-copy usage | +------------------------+---------------------------+----------------------------+ 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). Author's Address Luis M. Contreras Telefonica Ronda de la Comunicacion, s/n 28050 Madrid Spain Email: luismiguel.contrerasmurillo@telefonica.com Contreras Expires 6 May 2027 [Page 9]