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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Contreras Expires 7 January 2027 [Page 1] Internet-Draft PREOF OAM July 2026 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. 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. Contreras Expires 7 January 2027 [Page 2] Internet-Draft PREOF OAM July 2026 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. Contreras Expires 7 January 2027 [Page 3] Internet-Draft PREOF OAM July 2026 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 Contreras Expires 7 January 2027 [Page 4] Internet-Draft PREOF OAM July 2026 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 Contreras Expires 7 January 2027 [Page 5] Internet-Draft PREOF OAM July 2026 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. Contreras Expires 7 January 2027 [Page 6] Internet-Draft PREOF OAM July 2026 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, . [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, . Author's Address Luis M. Contreras Telefonica Ronda de la Comunicacion, s/n 28050 Madrid Spain Email: luismiguel.contrerasmurillo@telefonica.com Contreras Expires 7 January 2027 [Page 7]