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rfc:rfc8592

Independent Submission R. Browne Request for Comments: 8592 A. Chilikin Category: Informational Intel ISSN: 2070-1721 T. Mizrahi

                                      Huawei Network.IO Innovation Lab
                                                              May 2019
              Key Performance Indicator (KPI) Stamping
                for the Network Service Header (NSH)

Abstract

 This document describes methods of carrying Key Performance
 Indicators (KPIs) using the Network Service Header (NSH).  These
 methods may be used, for example, to monitor latency and QoS marking
 to identify problems on some links or service functions.

Status of This Memo

 This document is not an Internet Standards Track specification; it is
 published for informational purposes.
 This is a contribution to the RFC Series, independently of any other
 RFC stream.  The RFC Editor has chosen to publish this document at
 its discretion and makes no statement about its value for
 implementation or deployment.  Documents approved for publication by
 the RFC Editor are not candidates for any level of Internet Standard;
 see Section 2 of RFC 7841.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 https://www.rfc-editor.org/info/rfc8592.

Copyright Notice

 Copyright (c) 2019 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.

Browne, et al. Informational [Page 1] RFC 8592 KPI Timestamping May 2019

Table of Contents

 1. Introduction ....................................................2
 2. Terminology .....................................................3
    2.1. Requirements Language ......................................3
    2.2. Definition of Terms ........................................3
         2.2.1. Terms Defined in This Document ......................4
    2.3. Abbreviations ..............................................5
 3. NSH KPI Stamping: An Overview ...................................6
    3.1. Prerequisites ..............................................7
    3.2. Operation ..................................................9
         3.2.1. Flow Selection ......................................9
         3.2.2. SCP Interface ......................................10
    3.3. Performance Considerations ................................11
 4. NSH KPI-Stamping Encapsulation .................................12
    4.1. KPI-Stamping Extended Encapsulation .......................13
         4.1.1. NSH Timestamping Encapsulation (Extended Mode) .....15
         4.1.2. NSH QoS-Stamping Encapsulation (Extended Mode) .....17
    4.2. KPI-Stamping Encapsulation (Detection Mode) ...............20
 5. Hybrid Models ..................................................22
    5.1. Targeted VNF Stamping .....................................23
 6. Fragmentation Considerations ...................................23
 7. Security Considerations ........................................24
 8. IANA Considerations ............................................24
 9. References .....................................................25
    9.1. Normative References ......................................25
    9.2. Informative References ....................................25
 Acknowledgments ...................................................27
 Contributors ......................................................27
 Authors' Addresses ................................................27

1. Introduction

 The Network Service Header (NSH), as defined by [RFC8300], specifies
 a method for steering traffic among an ordered set of Service
 Functions (SFs) using an extensible service header.  This allows for
 flexibility and programmability in the forwarding plane to invoke the
 appropriate SFs for specific flows.
 The NSH promises a compelling vista of operational flexibility.
 However, many service providers are concerned about service and
 configuration visibility.  This concern increases when considering
 that many service providers wish to run their networks seamlessly in
 "hybrid mode", whereby they wish to mix physical and virtual SFs and
 run services seamlessly between the two domains.

Browne, et al. Informational [Page 2] RFC 8592 KPI Timestamping May 2019

 This document describes generic methods to monitor and debug Service
 Function Chains (SFCs) in terms of latency and QoS marking of the
 flows within an SFC.  These are referred to as "detection mode" and
 "extended mode" and are explained in Section 4.
 The methods described in this document are compliant with hybrid
 architectures in which Virtual Network Functions (VNFs) and Physical
 Network Functions (PNFs) are freely mixed in the SFC.  These methods
 also provide flexibility for monitoring the performance and
 configuration of an entire chain or parts thereof as desired.  These
 methods are extensible to monitoring other Key Performance Indicators
 (KPIs).  Please refer to [RFC7665] for an architectural context for
 this document.
 The methods described in this document are not Operations,
 Administration, and Maintenance (OAM) protocols such as [Y.1731].  As
 such, they do not define new OAM packet types or operations.  Rather,
 they monitor the SFC's performance and configuration for subscriber
 payloads and indicate subscriber QoE rather than out-of-band
 infrastructure metrics.  This document differs from [In-Situ-OAM] in
 the sense that it is specifically tied to NSH operations and is not
 generic in nature.

2. Terminology

2.1. Requirements Language

 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
 "OPTIONAL" in this document are to be interpreted as described in
 BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
 capitals, as shown here.

2.2. Definition of Terms

 This section presents the main terms used in this document.  This
 document also makes use of the terms defined in [RFC7665] and
 [RFC8300].

Browne, et al. Informational [Page 3] RFC 8592 KPI Timestamping May 2019

2.2.1. Terms Defined in This Document

 First Stamping Node (FSN):  The first node along an SFC that stamps
    packets using KPI stamping.  The FSN matches each packet with a
    Stamping Controller (SC) flow based on (but not limited to) a
    stamping classification criterion such as transport 5-tuple
    coordinates.
 Last Stamping Node (LSN):  The last node along an SFC that stamps
    packets using KPI stamping.  From a forwarding point of view, the
    LSN removes the NSH and forwards the raw IP packet to the next
    hop.  From a control-plane point of view, the LSN reads all the
    metadata (MD) and exports it to a system performance statistics
    agent or repository.  The LSN should use the NSH Service Index
    (SI) to indicate if an SF was at the end of the chain.  The LSN
    may change the Service Path Identifier (SPI) to a preconfigured
    value so that the network underlay forwards the MD back directly
    to the KPI database (KPIDB) based on this value.
 Key Performance Indicator Database (KPIDB):  Denotes the external
    storage of MD for reporting, trend analysis, etc.
 KPI stamping:  The insertion of latency-related and/or QoS-related
    information into a packet using NSH MD.
 Flow ID:  A unique 16-bit identifier written into the header by the
    classifier.  This allows 65536 flows to be concurrently stamped on
    any given NSH service chain.
 QoS stamping:  The insertion of QoS-related information into a packet
    using NSH MD.
 Stamping Controller (SC):  The central logic that decides what
    packets to stamp and how to stamp them.  The SC instructs the
    classifier on how to build the parts of the NSH that are specific
    to KPI stamping.
 Stamping Control Plane (SCP):  The control plane between the FSN and
    the SC.

Browne, et al. Informational [Page 4] RFC 8592 KPI Timestamping May 2019

2.3. Abbreviations

 DEI         Drop Eligible Indicator
 DSCP        Differentiated Services Code Point
 FSN         First Stamping Node
 KPI         Key Performance Indicator
 KPIDB       Key Performance Indicator Database
 LSN         Last Stamping Node
 MD          Metadata
 NFV         Network Function Virtualization
 NSH         Network Service Header
 OAM         Operations, Administration, and Maintenance
 PCP         Priority Code Point
 PNF         Physical Network Function
 PNFN        Physical Network Function Node
 QoE         Quality of Experience
 QoS         Quality of Service
 RSP         Rendered Service Path
 SC          Stamping Controller
 SCL         Service Classifier
 SCP         Stamping Control Plane
 SF          Service Function
 SFC         Service Function Chain
 SI          Service Index
 SSI         Stamp Service Index

Browne, et al. Informational [Page 5] RFC 8592 KPI Timestamping May 2019

 TS          Timestamp
 VLAN        Virtual Local Area Network
 VNF         Virtual Network Function

3. NSH KPI Stamping: An Overview

 A typical KPI-stamping architecture is presented in Figure 1.
     Stamping
    Controller
       |                                                     KPIDB
       | SCP Interface                                        |
     ,---.             ,---.              ,---.              ,---.
    /     \           /     \            /     \            /     \
   (  SCL  )-------->(  SF1  )--------->(  SF2  )--------->(  SFn  )
    \ FSN /           \     /            \     /            \ LSN /
     `---'             `---'              `---'              `---'
              Figure 1: Logical Roles in NSH KPI Stamping
 The SC will be part of the SFC control-plane architecture, but it is
 described separately in this document for clarity.
 The SC is responsible for initiating start/stop stamp requests to the
 SCL or FSN and also for distributing the NSH-stamping policy into the
 service chain via the SCP interface.
 The FSN will typically be part of the SCL but is called out as a
 separate logical entity for clarity.
 The FSN is responsible for marking NSH MD fields; this tells nodes in
 the service chain how to behave in terms of stamping at the SF
 ingress, the SF egress, or both, or ignoring the stamp NSH MD
 completely.
 The FSN also writes the Reference Time value, a (possibly inaccurate)
 estimate of the current time of day, into the header, allowing the
 "SPI:Flow ID" performance to be compared to previous samples for
 offline analysis.
 The FSN should return an error to the SC if not synchronized to the
 current time of day and forward the packet along the service chain
 unchanged.  The code and format of the error are specific to the
 protocol used between the FSN and SC; these considerations are out of
 scope.

Browne, et al. Informational [Page 6] RFC 8592 KPI Timestamping May 2019

 SF1 and SF2 stamp the packets as dictated by the FSN and process the
 payload as per normal.
 Note 1: The exact location of the stamp creation may not be in the SF
         itself and may be applied by a hardware device -- for
         example, as discussed in Section 3.3.
 Note 2: Special cases exist where some of the SFs are NSH unaware.
         This is covered in Section 5.
 The LSN should strip the entire NSH and forward the raw packet to the
 IP next hop as per [RFC8300].  The LSN also exports NSH-stamping
 information to the KPIDB for offline analysis; the LSN may export the
 stamping information of either (1) all packets or (2) a subset based
 on packet sampling.
 In fully virtualized environments, the LSN is likely to be co-located
 with the SF that decrements the NSH SI to zero.  Corner cases exist
 where this is not the case; see Section 5.

3.1. Prerequisites

 Timestamping has its own set of prerequisites; however, these
 prerequisites are not required for QoS stamping.  In order to
 guarantee MD accuracy, all servers hosting VNFs should be
 synchronized from a centralized stable clock.  As it is assumed that
 PNFs do not timestamp (as this would involve a software change and a
 probable impact on throughput performance), there is no need for them
 to synchronize.  There are two possible levels of synchronization:
 Level A: Low-accuracy time-of-day synchronization, based on NTP
          [RFC5905].
 Level B: High-accuracy synchronization (typically on the order of
          microseconds), based on [IEEE1588].
 Each SF SHOULD have Level A synchronization and MAY have Level B
 synchronization.
 Level A requires each platform (including the SC) to synchronize its
 system real-time clock to an NTP server.  This is used to mark the MD
 in the chain, using the Reference Time field in the NSH KPI stamp
 header (Section 4.1).  This timestamp is inserted into the NSH by the
 first SF in the chain.  NTP accuracy can vary by several milliseconds
 between locations.  This is not an issue, as the Reference Time is
 merely being used as a time-of-day reference inserted into the KPIDB
 for performance monitoring and MD retrieval.

Browne, et al. Informational [Page 7] RFC 8592 KPI Timestamping May 2019

 Level B synchronization requires each platform to be synchronized to
 a Primary Reference Clock (PRC) using the Precision Time Protocol
 (PTP) [IEEE1588].  A platform MAY also use Synchronous Ethernet
 [G.8261] [G.8262] [G.8264], allowing more accurate frequency
 synchronization.
 If an SF is not synchronized at the moment of timestamping, it should
 indicate its synchronization status in the NSH.  This is described in
 more detail in Section 4.
 By synchronizing the network in this way, the timestamping operation
 is independent of the current RSP.  Indeed, the timestamp MD can
 indicate where a chain has been moved due to a resource starvation
 event as indicated in Figure 2, between VNF3 and VNF4 at time B.
   Delay
    |                                  v
    |                           v
    |                                  x
    |                           x             x = Reference Time A
    |                    xv                   v = Reference Time B
    |             xv
    |      xv
    |______|______|______|______|______|_____
       VNF1    VNF2   VNF3   VNF4   VNF5
             Figure 2: Flow Performance in a Service Chain
 For QoS stamping, it is desired that the SCL or FSN be synchronized
 in order to provide a Reference Time for offline analysis, but this
 is not a hard requirement (they may be in holdover or free-run state,
 for example).  Other SFs in the service chain do not need to be
 synchronized for QoS-stamping operations, as described below.
 QoS stamping can be used to check the consistency of configuration
 across the entire chain or parts thereof.  By adding all potential
 Layer 2 and Layer 3 QoS fields into a QoS sum at the SF ingress or
 egress, this allows quick identification of QoS mismatches across
 multiple Layer 2 / Layer 3 fields, which otherwise is a manual,
 expert-led consuming process.

Browne, et al. Informational [Page 8] RFC 8592 KPI Timestamping May 2019

 |
 |
 |                                  xy
 |                           xy           x = ingress QoS sum
 |                    xv                  v = egress QoS sum
 |             xv                         y = egress QoS sum mismatch
 |      xv
 |______|______|______|______|______|_____
       SF1    SF2    SF3    SF4    SF5
           Figure 3: Flow QoS Consistency in a Service Chain
 Referring to Figure 3, x, v, and y are notional sum values of the QoS
 marking configuration of the flow within a given chain.  As the
 encapsulation of the flow can change from hop to hop in terms of VLAN
 header(s), MPLS labels, or DSCP(s), these values are used to compare
 the consistency of configuration from, for example, payload DSCP
 through overlay and underlay QoS settings in VLAN IEEE 802.1Q bits,
 MPLS bits, and infrastructure DSCPs.
 Figure 3 indicates that, at SF4 in the chain, the egress QoS marking
 is inconsistent.  That is, the ingress QoS settings do not match the
 egress.  The method described here will indicate which QoS field(s)
 is inconsistent and whether this is ingress (where the underlay has
 incorrectly marked and queued the packet) or egress (where the SF has
 incorrectly marked and queued the packet.
 Note that the SC must be aware of cases when an SF re-marks QoS
 fields deliberately and thus does not flag an issue for desired
 behavior.

3.2. Operation

 KPI-stamping detection mode uses MD Type 2 as defined in [RFC8300].
 This involves the SFC classifier stamping the flow at the chain
 ingress and no subsequent stamps being applied; rather, each upstream
 SF can compare its local condition with the ingress value and take
 appropriate action.  Therefore, detection mode is very efficient in
 terms of header size that does not grow after the classification.
 This is further explained in Section 4.2.

3.2.1. Flow Selection

 The SC should maintain a list of flows within each service chain to
 be monitored.  This flow table should be in the format "SPI:Flow ID".
 The SC should map these pairs to unique values presented as Flow IDs
 per service chain within the NSH TLV specified in this document (see
 Section 4).  The SC should instruct the FSN to initiate timestamping

Browne, et al. Informational [Page 9] RFC 8592 KPI Timestamping May 2019

 on flow table match.  The SC may also tell the classifier the
 duration of the timestamping operation, by either the number of
 packets in the flow or a certain time duration.
 In this way, the system can monitor the performance of all en-route
 traffic, an individual subscriber in a chain, or just a specific
 application or QoS class that is used in the network.
 The SC should write the list of monitored flows into the KPIDB for
 correlation of performance and configuration data.  Thus, when the
 KPIDB receives data from the LSN, it understands to which flow the
 data pertains.
 The association of a source IP address with a subscriber identity is
 outside the scope of this document and will vary by network
 application.  For example, the method of association of a source IP
 address with an International Mobile Subscriber Identity (IMSI) will
 be different from how a Customer Premises Equipment (CPE) entity with
 a Network Address Translation (NAT) function may be chained in an
 enterprise NFV application.

3.2.2. SCP Interface

 An SCP interface is required between the SC and the FSN or
 classifier.  This interface is used to:
 o  Query the SFC classifier for a list of active chains and flows.
 o  Communicate which chains and flows to stamp.  This can be a
    specific "SPI:Flow ID" combination or can include wildcards for
    monitoring subscribers across multiple chains or multiple flows
    within one chain.
 o  Instruct how the stamp should be applied (ingress, egress, both
    ingress and egress, or specific).
 o  Indicate when to stop stamping (after either a certain number of
    packets or a certain time duration).
 Typically, SCP timestamps flows for a certain duration for trend
 analysis but only stamps one packet of each QoS class in a chain
 periodically (perhaps once per day or after a network change).
 Therefore, timestamping is generally applied to a much larger set of
 packets than QoS stamping.
 The exact specification of SCP is left for further study.

Browne, et al. Informational [Page 10] RFC 8592 KPI Timestamping May 2019

3.3. Performance Considerations

 This document does not mandate a specific stamping implementation
 method; thus, NSH KPI stamping can be performed by either hardware
 mechanisms or software.
 If software-based stamping is used, applying and operating on the
 stamps themselves incur an additional small delay in the service
 chain.  However, it can be assumed that these additional delays are
 all relative for the flow in question.  This is only pertinent for
 timestamping mode, and not for QoS-stamping mode.  Thus, whilst the
 absolute timestamps may not be fully accurate for normal
 non-timestamped traffic, they can be assumed to be relative.
 It is assumed that the methods described in this document would only
 operate on a small percentage of user flows.
 The service provider may choose a flexible policy in the SC to
 timestamp a selection of a user plane every minute -- for example, to
 highlight any performance issues.  Alternatively, the LSN may
 selectively export a subset of the KPI stamps it receives, based on a
 predefined sampling method.  Of course, the SC can stress-test an
 individual flow or chain should a deeper analysis be required.  We
 can expect that this type of deep analysis will have an impact on the
 performance of the chain itself whilst under investigation.  This
 impact will be dependent on vendor implementations and is outside the
 scope of this document.
 For QoS stamping, the methods described here are even less intrusive,
 as typically packets are only QoS stamped periodically (perhaps once
 per day) to check service chain configuration per QoS class.

Browne, et al. Informational [Page 11] RFC 8592 KPI Timestamping May 2019

4. NSH KPI-Stamping Encapsulation

 KPI stamping uses NSH MD Type 0x2 for detection of anomalies and
 extended mode for root-cause analysis of KPI violations.  These are
 further explained in this section.
 The generic NSH MD Type 2 TLV for KPI stamping is shown below.
   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |Ver|O|U|    TTL    |   Length  |U|U|U|U|Type=2 | Next Protocol |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |          Service Path Identifier              | Service Index |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |        Metadata Class         |      Type     |U|    Length   |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |       Variable Length KPI Metadata header and TLV(s)          |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                Figure 4: Generic NSH KPI Encapsulation
 Relevant fields in the header that the FSN must implement are as
 follows:
 o  The O bit must not be set.
 o  The MD type must be set to 0x2.
 o  The Metadata Class must be set to a value from the experimental
    range 0xfff6 to 0xfffe according to an agreement by all parties to
    the experiment.
 o  Unassigned bits: All fields marked "U" are unassigned and
    available for future use [RFC8300].
 o  The Type field may have one of the following values; the content
    of the Variable Length KPI Metadata header and TLV(s) field
    depends on the Type value:
  • Type = 0x01 (Det): Detection
  • Type = 0x02 (TS): Timestamp Extended
  • Type = 0x03 (QoS): QoS stamp Extended
 The Type field determines the type of KPI-stamping format.  The
 supported formats are presented in the following subsections.

Browne, et al. Informational [Page 12] RFC 8592 KPI Timestamping May 2019

4.1. KPI-Stamping Extended Encapsulation

 The generic NSH MD Type 2 KPI-stamping header (extended mode) is
 shown in Figure 5.  This is the format for performance monitoring of
 service chain issues with respect to QoS configuration and latency.
   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |Ver|O|U|    TTL    |   Length  |U|U|U|U|Type=2 | Next Protocol |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |          Service Path Identifier              | Service Index |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Metadata Class        |     Type      |U|    Length   |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |           Variable Length KPI Configuration Header            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                  Variable Length KPI Value (LSN)              |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  \                                                               \
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                  Variable Length KPI Value (FSN)              |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
          Figure 5: Generic KPI Encapsulation (Extended Mode)
 As mentioned above, two types are defined under the experimental MD
 class to indicate the extended KPI MD: a timestamp type and a
 QoS-stamp type.
 The KPI Encapsulation Configuration Header format is shown below.
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |K|K|T|K|K|K|K|K|   Stamping SI |           Flow ID             |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                        Reference Time                         |
  |                                                               |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
           Figure 6: KPI Encapsulation Configuration Header

Browne, et al. Informational [Page 13] RFC 8592 KPI Timestamping May 2019

 The bits marked "K" are reserved for specific KPI type use and are
 described in the subsections below.
 The T bit should be set if Reference Time follows the KPI
 Encapsulation Configuration Header.
 The SSI (Stamping SI) contains the SI used for KPI stamping and is
 described in the subsections below.
 The Flow ID is a unique 16-bit identifier written into the header by
 the classifier.  This allows 65536 flows to be concurrently stamped
 on any given NSH service chain (SPI).  Flow IDs are not written by
 subsequent SFs in the chain.  The FSN may export monitored Flow IDs
 to the KPIDB for correlation.
 Reference Time is the wall clock of the FSN and may be used for
 historical comparison of SC performance.  If the FSN is not Level A
 synchronized (see Section 3.1), it should inform the SC over the SCP
 interface.  The Reference Time is represented in 64-bit NTP format
 [RFC5905], as presented in Figure 7:
   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                            Seconds                            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                            Fraction                           |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
           Figure 7: NTP 64-Bit Timestamp Format (RFC 5905)

Browne, et al. Informational [Page 14] RFC 8592 KPI Timestamping May 2019

4.1.1. NSH Timestamping Encapsulation (Extended Mode)

 The NSH timestamping extended encapsulation is shown below.
   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |Ver|O|C|U|U|U|U|U|U|   Length  |U|U|U|U|Type=2 |   NextProto   |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |          Service Path ID                      | Service Index |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |          Metadata Class         |  Type=TS(2) |U|     Len     |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |I|E|T|U|U|U|SSI|  Stamping SI  |           Flow ID             |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
  |              Reference Time (T bit is set)                    |
  |                                                               |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |I|E|U|U|U| SYN |  Stamping SI  |         Unassigned            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
  |            Ingress Timestamp (I bit is set) (LSN)             |
  |                                                               |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |             Egress Timestamp (E bit is set) (LSN)             |
  |                                                               |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  .                                                               .
  .                                                               .
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |I|E|U|U|U| SYN |  Stamping SI  |          Unassigned           |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
  |                 Ingress Timestamp (I bit is set) (FSN)        |
  |                                                               |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                 Egress Timestamp (E bit is set) (FSN)         |
  |                                                               |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
         Figure 8: NSH Timestamp Encapsulation (Extended Mode)
 The FSN KPI stamp MD starts with the Stamping Configuration Header.
 This header contains the I, E, and T bits, and the SSI.
 The I bit should be set if the Ingress stamp is requested.
 The E bit should be set if the Egress stamp is requested.

Browne, et al. Informational [Page 15] RFC 8592 KPI Timestamping May 2019

 The SSI field must be set to one of the following values:
 o  0x0: KPI stamp mode.  No SI is specified in the Stamping SI field.
 o  0x1: KPI stamp hybrid mode is selected.  The Stamping SI field
    contains the LSN SI.  This is used when PNFs or NSH-unaware SFs
    are used at the tail of the chain.  If SSI=0x1, then the value in
    the Type field informs the chain regarding which SF should act as
    the LSN.
 o  0x2: KPI stamp Specific mode is selected.  The Stamping SI field
    contains the targeted SI.  In this case, the Stamping SI field
    indicates which SF is to be stamped.  Both Ingress stamps and
    Egress stamps are performed when the SI=SSI in the chain.  For
    timestamping mode, the FSN will also apply the Reference Time and
    Ingress Timestamp.  This will indicate the delay along the entire
    service chain to the targeted SF.  This method may also be used as
    a light implementation to monitor end-to-end service chain
    performance whereby the targeted SF is the LSN.  This is not
    applicable to QoS-stamping mode.
 Each stamping node adds stamp MD that consists of the Stamping
 Reporting Header and timestamps.
 The E bit should be set if the Egress stamp is reported.
 The I bit should be set if the Ingress stamp is reported.
 With respect to timestamping mode, the SYN bits are an indication of
 the synchronization status of the node performing the timestamp and
 must be set to one of the following values:
 o  In synch: 0x00
 o  In holdover: 0x01
 o  In free run: 0x02
 o  Out of synch: 0x03
 If the platform hosting the SF is out of synch or in free run, no
 timestamp is applied by the node, and the packet is processed
 normally.

Browne, et al. Informational [Page 16] RFC 8592 KPI Timestamping May 2019

 If the FSN is out of synch or in free run, the timestamp request is
 rejected and is not propagated through the chain.  In such an event,
 the FSN should inform the SC over the SCP interface.  Similarly, if
 the KPIDB receives timestamps that are out of order (i.e., a
 timestamp of an "N+1" SF is prior to the timestamp of an "N" SF), it
 should notify the SC of this condition over the SCP interface.
 The outer SI value is copied into the stamp MD as the Stamping SI to
 help cater to hybrid chains that are a mix of VNFs and PNFs or
 through NSH-unaware SFs.  Thus, if a flow transits through a PNF or
 an NSH-unaware node, the delta in the inner SI between timestamps
 will indicate this.
 The Ingress Timestamp and Egress Timestamp are represented in 64-bit
 NTP format.  The corresponding bits (I and E) are reported in the
 Stamping Reporting Header of the node's MD.

4.1.2. NSH QoS-Stamping Encapsulation (Extended Mode)

 Packets have a variable QoS stack.  For example, the same payload IP
 can have a very different stack in the access part of the network
 than the core.  This is most apparent in mobile networks where, for
 example, in an access circuit we would have an infrastructure IP
 header (DSCP) composed of two layers -- one based on transport and
 the other based on IPsec -- in addition to multiple MPLS and VLAN
 tags.  The same packet, as it leaves the Packet Data Network (PDN)
 Gateway Gi egress interface, may be very much simplified in terms of
 overhead and related QoS fields.
 Because of this variability, we need to build extra meaning into the
 QoS headers.  They are not, for example, all PTP timestamps of a
 fixed length, as in the case of timestamping; rather, they are of
 variable lengths and types.  Also, they can be changed on the
 underlay at any time without the knowledge of the SFC system.
 Therefore, each SF must be able to ascertain and record its ingress
 and egress QoS configuration on the fly.

Browne, et al. Informational [Page 17] RFC 8592 KPI Timestamping May 2019

 The suggested QoS Type (QT) and lengths are listed below.
  QoS Type  Value    Length    Comment
  ----------------------------------------------------------
  IVLAN     0x01     4 Bits    Ingress VLAN (PCP + DEI)
  EVLAN     0x02     4 Bits    Egress VLAN
  IQINQ     0x03     8 Bits    Ingress QinQ (2x (PCP + DEI))
  EQINQ     0x04     8 Bits    Egress QinQ
  IMPLS     0x05     3 Bits    Ingress Label
  EMPLS     0x06     3 Bits    Egress Label
  IMPLS     0x07     6 Bits    Two Ingress Labels (2x EXP)
  EMPLS     0x08     6 Bits    Two Egress Labels
  IDSCP     0x09     8 Bits    Ingress DSCP
  EDSCP     0x0A     8 Bits    Egress DSCP
 For stacked headers such as MPLS and 802.1ad, we extract the relevant
 QoS data from the header and insert it into one QoS value in order to
 be more efficient in terms of packet size.  Thus, for MPLS, we
 represent both experimental bits (EXP) fields in one QoS value, and
 both 802.1p priority and drop precedence in one QoS value, as
 indicated above.
 For stack types not listed here (for example, three or more MPLS
 tags), the SF would insert IMPLS/EMPLS several times, with each layer
 in the stack indicating EXP QoS for that layer.

Browne, et al. Informational [Page 18] RFC 8592 KPI Timestamping May 2019

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |Ver|O|C|U|U|U|U|U|U|   Length  |U|U|U|U|Type=2 | NextProto=0x0 |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |          Service Path ID                      | Service Index |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Metadata Class        |   Type=QoS(3) |U|     Len     |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |U|U|T|U|U|U|SSI|  Stamping SI  |           Flow ID             |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
  |              Reference Time (T bit is set)                    |
  |                                                               |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |U|U|U|U|U|U|U|U|  Stamping SI  |         Unassigned            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
  |   QT  |    QoS Value  |U|U|U|E|  QT   | QoS Value     |U|U|U|E|
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  .                                                               .
  .                                                               .
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |U|U|U|U|U|U|U|U|  Stamping SI  |          Unassigned           |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
  |   QT  |   QoS Value   |U|U|U|E|  QT   | QoS Value     |U|U|U|E|
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     Figure 9: NSH QoS Configuration Encapsulation (Extended Mode)
 The encapsulation in Figure 9 is very similar to the encapsulation
 detailed in Section 4.1.1, with the following exceptions:
 o  I and E bits are not required, as we wish to examine the full QoS
    stack at the ingress and egress at every SF.
 o  SYN status bits are not required.
 o  The QT and QoS values are as outlined in the list above.
 o  The E bit at the tail of each QoS context field indicates if this
    is the last egress QoS stamp for a given SF.  This should coincide
    with SI=0 at the LSN, whereby the packet is truncated, the NSH MD
    is sent to the KPIDB, and the subscriber's raw IP packet is
    forwarded to the underlay next hop.

Browne, et al. Informational [Page 19] RFC 8592 KPI Timestamping May 2019

 Note: It is possible to compress the frame structure to better
 utilize the header, but this would come at the expense of crossing
 byte boundaries.  For ease of implementation, and so that
 QoS stamping is applied on an extremely small subset of user-plane
 traffic, we believe that the above structure is a pragmatic
 compromise between header efficiency and ease of implementation.

4.2. KPI-Stamping Encapsulation (Detection Mode)

 The format of the NSH MD Type 2 KPI-stamping TLV (detection mode) is
 shown in Figure 10.
 This TLV is used for KPI anomaly detection.  Upon detecting a problem
 or an anomaly, it will be possible to enable the use of KPI-stamping
 extended encapsulations, which will provide more detailed analysis.
   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |Ver|O|U|    TTL    |   Length  |U|U|U|U|Type=2 | Next Protocol |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |          Service Path Identifier              | Service Index |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |        Metadata Class         | Type=Det(1)   |U|    Length   |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |   KPI Type    |      Stamping SI      |          Flow ID      |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                      Threshold KPI Value                      |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                       Ingress KPI stamp                       |
  |                                                               |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       Figure 10: Generic NSH KPI Encapsulation (Detection Mode)
 The following fields are defined in the KPIDB MD:
 o  KPI Type: This field determines the type of KPI stamp that is
    included in this MD.  If a receiver along the path does not
    understand the KPI type, it will pass the packet on transparently
    and will not drop it.  The supported values of KPI Type are:
  • 0x0: Timestamp
  • 0x1: QoS stamp

Browne, et al. Informational [Page 20] RFC 8592 KPI Timestamping May 2019

 o  Threshold KPI Value: In the first header, the SFC classifier may
    program a KPI threshold value.  This is a value that, when
    exceeded, requires the SF to insert the current SI value into the
    SI field.  The KPI type is the type of KPI stamp inserted into the
    header as per Figure 10.
 o  Stamping SI: This is the Service Identifier of the SF when the
    above threshold value is exceeded.
 o  Flow ID: The Flow ID is inserted into the header by the SFC
    classifier in order to correlate flow data in the KPIDB for
    offline analysis.
 o  Ingress KPI stamp: The last 8 octets are reserved for the
    KPI stamp.  This is the KPI value at the chain ingress at the SFC
    classifier.  Depending on the KPI type, the KPI stamp includes
    either a timestamp or a QoS stamp.  If the KPI type is Timestamp,
    then the Ingress KPI stamp field contains a timestamp in 64-bit
    NTP timestamp format.  If the KPI type is QoS stamp, then the
    format of the 64-bit Ingress KPI stamp is as follows.
   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |   QT  |    QoS Value  |              Unassigned               |
  +-+-+-+-+-+-+-+-+-+-+-+-+                                       +
  |                                                               |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
             Figure 11: QoS-Stamp Format (Detection Mode)
 As an example operation, let's say we are using KPI type 0x01
 (Timestamp).  When an SF (say SFn) receives the packet, it can
 compare the current local timestamp (it first checks that it is
 synchronized to the network's PRC) with the chain Ingress Timestamp
 to calculate the latency in the chain.  If this value exceeds the
 timestamp threshold, it then inserts its SI and returns the NSH to
 the KPIDB.  This effectively tells the system that at SFn the packet
 violated the KPI threshold.  Please refer to Figure 8 for the
 timestamp format.
 When this occurs, the SFC control-plane system would then invoke the
 KPI extended mode, which uses a more sophisticated (and intrusive)
 method to isolate the root cause of the KPI violation, as described
 below.

Browne, et al. Informational [Page 21] RFC 8592 KPI Timestamping May 2019

 Note: Whilst detection mode is a valuable tool for latency actions,
 the authors feel that building the logic into the KPI system for QoS
 configuration is not justified.  As QoS stamping is done infrequently
 and on a tiny percentage of the user plane, it is more practical to
 use extended mode only for service chain QoS verification.

5. Hybrid Models

 A hybrid chain may be defined as a chain whereby there is a mix of
 NSH-aware and NSH-unaware SFs.
 Figure 12 shows an example of a hybrid chain with a PNF in the
 middle.
    Stamping
   Controller
       |                                                      KPIDB
       | SCP Interface                                        |
     ,---.             ,---.              ,---.              ,---.
    /     \           /     \            /     \            /     \
   (  SCL  )-------->(  SF1  )--------->(  SF2  )--------->(  SFn  )
    \ FSN /           \     /            \ PNF1/            \ LSN /
     `---'             `---'              `---'              `---'
              Figure 12: Hybrid Chain with PNF in Middle
 In this example, the FSN begins its operation and sets the SI to 3.
 SF1 decrements the SI to 2 and passes the packet to an SFC proxy
 (not shown).
 The SFC proxy strips the NSH and passes the packet to the PNF.  On
 receipt back from the PNF, the proxy decrements the SI and passes the
 packet to the LSN with SI=1.
 After the LSN processes the traffic, it knows from the SI value that
 it is the last node in the chain, and it exports the entire NSH and
 all MD to the KPIDB.  The payload is forwarded to the next hop on the
 underlay minus the NSH.  The stamping information packet may be given
 a new SPI to act as a homing tag to transport the stamp data back to
 the KPIDB.

Browne, et al. Informational [Page 22] RFC 8592 KPI Timestamping May 2019

 Figure 13 shows an example of a hybrid chain with a PNF at the end.
   Stamping
  Controller
      |                                                      KPIDB
      | SCP Interface                                        |
    ,---.             ,---.              ,---.              ,---.
   /     \           /     \            /     \            /     \
  (  SCL  )-------->(  SF1  )--------->(  SF2  )--------->(  PNFN )
   \ FSN /           \     /            \ LSN /            \     /
    `---'             `---'              `---'              `---'
                Figure 13: Hybrid Chain with PNF at End
 In this example, the FSN begins its operation and sets the SI to 3.
 The SSI field is set to 0x1, and the type is set to 1.  Thus, when
 SF2 receives the packet with SI=1, it understands that it is expected
 to take on the role of the LSN, as it is the last NSH-aware node in
 the chain.

5.1. Targeted VNF Stamping

 For the majority of flows within the service chain, stamps (Ingress
 stamps, Egress stamps, or both) will be carried out at each hop until
 the SI decrements to zero and the NSH and stamp MD are exported to
 the KPIDB.  However, the need to just test a particular VNF may exist
 (perhaps after a scale-out operation, software upgrade, or underlay
 change, for example).  In this case, the FSN should mark the NSH as
 follows:
 o  The SSI field is set to 0x2.
 o  Type is set to the expected SI at the SF in question.
 o  When the outer SI is equal to the SSI, stamps are applied at the
    SF ingress and egress, and the NSH and MD are exported to the
    KPIDB.

6. Fragmentation Considerations

 The methods described in this document do not support fragmentation.
 The SC should return an error should a stamping request from an
 external system exceed MTU limits and require fragmentation.
 Depending on the length of the payload and the type of KPI stamp and
 chain length, this will vary for each packet.

Browne, et al. Informational [Page 23] RFC 8592 KPI Timestamping May 2019

 In most service provider architectures, we would expect SI << 10,
 which may include some PNFs in the chain that do not add overhead.
 Thus, for typical Internet Mix (IMIX) packet sizes [RFC6985], we
 expect to be able to perform timestamping on the vast majority of
 flows without fragmentation.  Thus, the classifier can apply a simple
 rule that only allows KPI stamping on packet sizes less than 1200
 bytes, for example.

7. Security Considerations

 The security considerations for the NSH in general are discussed in
 [RFC8300].
 In-band timestamping, as defined in this document, can be used as a
 means for network reconnaissance.  By passively eavesdropping on
 timestamped traffic, an attacker can gather information about network
 delays and performance bottlenecks.
 The NSH timestamp is intended to be used by various applications to
 monitor network performance and to detect anomalies.  Thus, a
 man-in-the-middle attacker can maliciously modify timestamps in order
 to attack applications that use the timestamp values.  For example,
 an attacker could manipulate the SFC classifier operation, such that
 it forwards traffic through "better-behaved" chains.  Furthermore, if
 timestamping is performed on a fraction of the traffic, an attacker
 can selectively induce synthetic delay only to timestamped packets
 and can systematically trigger measurement errors.
 Similarly, if an attacker can modify QoS stamps, erroneous values may
 be imported into the KPIDB, resulting in further misconfiguration and
 subscriber QoE impairment.
 An attacker that gains access to the SCP can enable timestamping and
 QoS stamping for all subscriber flows, thereby causing performance
 bottlenecks, fragmentation, or outages.
 As discussed in previous sections, NSH timestamping relies on an
 underlying time synchronization protocol.  Thus, by attacking the
 time protocol, an attacker can potentially compromise the integrity
 of the NSH timestamp.  A detailed discussion about the threats
 against time protocols and how to mitigate them is presented in
 [RFC7384].

8. IANA Considerations

 This document has no IANA actions.

Browne, et al. Informational [Page 24] RFC 8592 KPI Timestamping May 2019

9. References

9.1. Normative References

 [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119,
            DOI 10.17487/RFC2119, March 1997,
            <https://www.rfc-editor.org/info/rfc2119>.
 [RFC7665]  Halpern, J., Ed. and C. Pignataro, Ed., "Service Function
            Chaining (SFC) Architecture", RFC 7665,
            DOI 10.17487/RFC7665, October 2015,
            <https://www.rfc-editor.org/info/rfc7665>.
 [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in
            RFC 2119 Key Words", BCP 14, RFC 8174,
            DOI 10.17487/RFC8174, May 2017,
            <https://www.rfc-editor.org/info/rfc8174>.
 [RFC8300]  Quinn, P., Ed., Elzur, U., Ed., and C. Pignataro, Ed.,
            "Network Service Header (NSH)", RFC 8300,
            DOI 10.17487/RFC8300, January 2018,
            <https://www.rfc-editor.org/info/rfc8300>.

9.2. Informative References

 [IEEE1588]
            IEEE, "IEEE Standard for a Precision Clock Synchronization
            Protocol for Networked Measurement and Control Systems",
            IEEE Standard 1588,
            <https://standards.ieee.org/standard/1588-2008.html>.
 [RFC5905]  Mills, D., Martin, J., Ed., Burbank, J., and W. Kasch,
            "Network Time Protocol Version 4: Protocol and Algorithms
            Specification", RFC 5905, DOI 10.17487/RFC5905, June 2010,
            <https://www.rfc-editor.org/info/rfc5905>.
 [RFC7384]  Mizrahi, T., "Security Requirements of Time Protocols in
            Packet Switched Networks", RFC 7384, DOI 10.17487/RFC7384,
            October 2014, <https://www.rfc-editor.org/info/rfc7384>.
 [RFC6985]  Morton, A., "IMIX Genome: Specification of Variable Packet
            Sizes for Additional Testing", RFC 6985,
            DOI 10.17487/RFC6985, July 2013,
            <https://www.rfc-editor.org/info/rfc6985>.

Browne, et al. Informational [Page 25] RFC 8592 KPI Timestamping May 2019

 [Y.1731]   ITU-T Recommendation G.8013/Y.1731, "Operations,
            administration and maintenance (OAM) functions and
            mechanisms for Ethernet-based networks", August 2015,
            <https://www.itu.int/rec/T-REC-G.8013/en>.
 [G.8261]   ITU-T Recommendation G.8261/Y.1361, "Timing and
            synchronization aspects in packet networks", August 2013,
            <https://www.itu.int/rec/T-REC-G.8261>.
 [G.8262]   ITU-T Recommendation G.8262/Y.1362, "Timing
            characteristics of a synchronous Ethernet equipment slave
            clock", November 2018,
            <https://www.itu.int/rec/T-REC-G.8262>.
 [G.8264]   ITU-T Recommendation G.8264/Y.1364, "Distribution of
            timing information through packet networks", August 2017,
            <https://www.itu.int/rec/T-REC-G.8264>.
 [In-Situ-OAM]
            Brockners, F., Bhandari, S., Pignataro, C., Gredler, H.,
            Leddy, J., Youell, S., Mizrahi, T., Mozes, D., Lapukhov,
            P., Chang, R., Bernier, D., and J. Lemon, "Data Fields for
            In-situ OAM", Work in Progress,
            draft-ietf-ippm-ioam-data-05, March 2019.

Browne, et al. Informational [Page 26] RFC 8592 KPI Timestamping May 2019

Acknowledgments

 The authors gratefully acknowledge Mohamed Boucadair, Martin
 Vigoureux, and Adrian Farrel for their thorough reviews and helpful
 comments.

Contributors

 This document originated as draft-browne-sfc-nsh-timestamp-00; the
 following people were coauthors of that draft.  We would like to
 thank them and recognize them for their contributions.
 Yoram Moses
 Technion
 Email: moses@ee.technion.ac.il
 Brendan Ryan
 Intel Corporation
 Email: brendan.ryan@intel.com

Authors' Addresses

 Rory Browne
 Intel
 Dromore House
 Shannon
 Co. Clare
 Ireland
 Email: rorybrowne@yahoo.com
 Andrey Chilikin
 Intel
 Dromore House
 Shannon
 Co. Clare
 Ireland
 Email: andrey.chilikin@intel.com
 Tal Mizrahi
 Huawei Network.IO Innovation Lab
 Israel
 Email: tal.mizrahi.phd@gmail.com

Browne, et al. Informational [Page 27]

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