1. Introduction

This section preserves the RFC text for IPFIX delay performance metric export, including On-Path Telemetry, OAM nodes, Flow Records, performance metric IDs 27-30, IPFIX Information Elements 530-533, IANA registrations, operational guidance, and encoding examples.

Original RFC Text

1.  Introduction

   Network operators usually maintain statistical views of delay across
   their networks to support diagnostics and performance analysis.
   These views assist in identifying the location, extent, and potential
   causes of abnormal delay affecting specific customer traffic or
   services.  To achieve this, delay-related metrics need to be reported
   from devices covering both data and control planes.  Further, in
   order to understand which customers are affected, delay-related
   metrics need to be reported in the context of the customer data
   plane.  This correlation enables the detection of changes in
   forwarding paths, such as updated intermediate hops or interfaces,
   and of the resulting impact on delay experienced by customer traffic.

   Delay measurements in the network are computed using an On-Path
   Telemetry protocol, which inserts metadata into the data-plane packet
   when entering the monitored domain [RFC9232].  To compute delay
   measurements, the On-Path Telemetry protocol inserts a timestamp
   reference when entering the OAM encapsulating node.  Implementation
   examples are In situ Operations, Administration, and Maintenance
   (IOAM) [RFC9197] or Enhanced Alternate Marking [ENH-ALT-MARKING].

   Two modes of On-Path Telemetry are generally recognized: passport
   mode, in which only the OAM header decapsulating node of the OAM
   domain reports metrics; and postcard mode, in which OAM header
   transit nodes also export On-Path Telemetry data.  Both modes enable
   exposure of per-hop performance metrics, including delay
   accumulation.  The approach defined in this document is primarily
   applicable to postcard mode.

   To enable the export of the delay-related metrics via IPFIX
   [RFC7011], this document defines four new IPFIX Information Elements
   (IEs), exposing the On-Path delay on OAM header transit and
   decapsulating nodes, following the principles of postcard mode.

   This enables the computation of delay metrics (minimum, maximum, and
   mean) directly on the OAM header transit and decapsulating node,
   allowing aggregation within the Flow Record.

   As these IEs represent performance metrics, they are also registered
   in the IANA "Performance Metrics Registry" [IANA-PERF-METRIC] in
   accordance with [RFC8911].