| Internet-Draft | OAM Requirements for Enhanced DetNet | February 2025 |
| Yan, et al. | Expires 24 August 2025 | [Page] |
This document describes the specific requirements of the Operations, Administration, and Maintenance (OAM) for Enhanced DetNet, and analyzes the gaps with the existing OAM methods. It describes related OAM solutions considerations as well.¶
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The framework of OAM for DetNet has been specified in [RFC9551]. Aa per[RFC8655], DetNet functionality is divided into forwarding sub-layer and service sub-layer.[RFC9551]lists general functional requirements for DetNet OAM as well as functional requirements in each of the DetNet sub-layers of a DetNet domain. The IP and MPLS DetNet data plane have been defined respectively in[I-D.ietf-detnet-ip-oam]and[RFC9546].¶
The DetNet data plane enhancement requirements are described in [I-D.ietf-detnet-scaling-requirements] , which demands the enhancement based on the existing bounded latency mechanisms and the corresponding data plane. The data plane enhancement solutions such as ECQF[IEEE 802.1Qdv], Multi-CQF[I-D.dang-queuing-with-multiple-cyclic-buffers], TCQF[I-D.eckert-detnet-tcqf], CSQF[I-D.chen-detnet-sr-based-bounded-latency], TQF[I-D.peng-detnet-packet-timeslot-mechanism], C-SCORE[I-D.joung-detnet-stateless-fair-queuing], EDF[I-D.peng-detnet-deadline-based-forwarding], gLBF[I-D.eckert-detnet-glbf]have been proposed and discussed, with the criteria for classifying data plane solutions is provided in[I-D.ietf-detnet-dataplane-taxonomy]. These queuing mechanisms demand high precision to achieve deterministic latency especially as link speeds increase from 100Mbps to 1Gbps, 10Gbps, 100Gbps, or even higher. with the increasing of link speed from 100Mbps to 1Gbps, 10Gbps, 100Gbps, or even higher.¶
For DetNet OAM, it is essential to provide DetNet services with high precision in a large-scale network, ensuring OAM performance requirements are strictly met. Existing OAM methods including proactive and reactive techniques are insufficient to meet the monitoring and measurement requirements for Enhanced DetNet.¶
Based on the consideration above, this document describes the specific requirements of the OAM for Enhanced DetNet, and analyzes the gaps with the existing OAM methods, and describes related OAM solutions considerations.¶
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119].¶
This section presents the enhanced requirements for Enhanced DetNet OAM and analyzes the technical gaps when applying OAM technologies as per [RFC9551]in large-scale networks.¶
As per [I-D.ietf-detnet-scaling-requirements], deterministic networks can utilize higher-speed links. With the increasing data rates, the network scheduling cycle can be shortened, provided that the amount of application data transmitted at any given time remains unchanged. This requires more precise time control, in the order of microseconds or sub-microseconds. As per[RFC9551], the service protection provided by the DetNet Service sub-layer aims to mitigate network failures more rapidly than the expected response time of the DetNet Controller Plane. Therefore, the time accuracy of the DetNet OAM mechanism must meet or exceed the accuracy requirements specified in SLAs. For instance, if service delay measurements require microsecond-level precision, the OAM mechanism should support sub-microsecond precision to assess whether service delay and jitter performance comply with SLA requirements.¶
The precision of time measurements depends on both the time synchronization protocol utilized in the network and the specific location where timestamps are captured during the forwarding process. According to [I-D.ietf-detnet-scaling-requirements], , Enhanced DetNet, which targets large-scale networks, should accommodate time asynchrony, making the efficient one-way delay measurement critical. Furthermore, based on the assumption of time asynchrony, synchronization technologies leveraging network effects, especially in metropolitan area networks with spine-leaf topologies, provide solutions capable of achieving synchronization accuracy down to the microsecond level.¶
According to [I-D.ietf-detnet-scaling-requirements], large-scale networks are becoming increasingly complex to meet the growing demands for higher bandwidth, lower latency and jitter, customized traffic prioritization, and SLA-grade network resilience. A more complex network infrastructure requires deeper visibility into Enhanced DetNet. The OAM of Enhanced DetNet should be capable of analyzing network behavior at the packet level. Legacy network monitoring technologies are insufficient since they do not provide real-time and granular visibility required for such detailed analysis.¶
DetNet requires high reliability to meet the demands of service flows. However, detecting SLA violations on a per-packet basis presents significant challenges in large-scale networks with thousands of service flows. The feasibility of implementing per-packet monitoring with the OAM mechanism depends on device capabilities, including counter resources, CPU resources, and port speeds. For instance, if the processing time for forwarding packets at line speed is 10 nanoseconds per packet in in-situ OAM mode, the network processor chip must parse the OAM data fields for each packet within this time frame. Any delay exceeding 10 nanoseconds per packet would hinder the device's capability to forward packets at line speed..In large-scale networks with thousands of services, mainstream equipment currently operates at capacities typically in the range of a few thousand, making it challenging to implement per-packet OAM effectively.¶
In DetNet, due to the limited network scale, the impact of detection and response time on OAM performance is less noticeable. However, in large-scale networks, long-distance transmission increases latency and the presence of a large number of devices leads to a higher likelihood of network link failures. To achieve real-time monitoring and awareness of the network’s operating state, high-speed monitoring and rapid response are critical., ensuring that the services are not be interrupted for extended periods or that SLA violations do not occur.¶
The traditional detection methods relying on switching and notification are ineffective in detecting millisecond-level latency variations and low-probability packet loss issues., making it unsuitable for Enhanced DetNet, as follows:¶
OAM methods can be classified into three types according to [RFC7799]:¶
Hybrid OAM mode. At present, the two most popular in-band OAM technologies are the Alternate-Marking (coloring) Method [RFC8321]and In-situ Network Telemetry (INT)[RFC9197], , which are both hybrid OAM methods and offers solutions for achieving fate-sharing among test packets and service packets on the forwarding plane. Based on forwarding plane detection technologies utilizing coloring and INT, there are two main OAM solutions:¶
Based on the above analysis, there are two technical approaches for Enhanced DetNet OAM to meet the high-reliability requirements.¶
Traditional protection switching networks employ the following three types of protection methods, each with different response speeds:¶
For Enhanced DetNet, where OAM protection is best-effort and primarily focused on deploying protection switching mechanisms, traditional forwarding sub-layer OAM protection methods can be utilized:¶
Observability technologies introduce extra latency and are thus unsuitable for real-time OAM detection of online services.¶
PREF aims to guarantee forwarding sub-layer performance through service sub-layer functionality, employing multi-path packet duplication to mitigate the path-switching delay. According to [IEEE802.1CB]and[RFC8655], ensuring high reliability for time-sensitive services is challenging without the deployment of PREF. When the network supports PREF configuration, it inherently meets reliability requirements including constraints on packet loss rate and latency violation, thus eliminating the need for enhanced detection speed. Another key factor contributing to high reliability is the ability to provide protection at node level and link level rather than solely at the path level. The PREF mechanism requires each packet encapsulated with a unique flow-id and a sequence number to facilitate selective receiving.¶
While the network supports PREF can guarantee a packet loss rate as low as 0.0001%, it remains essential to proactively monitor the performance of each individual path to promptly detect path defects. This proactive approach helps prevent SLA violations such as link degradation to ensure stable transmission of service traffic under PREF protection.¶
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