    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.

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    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.

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       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].

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    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.

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    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

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       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.

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       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.

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       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.

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       |
       |
       |                                  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

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       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.

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    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.

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    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.

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    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

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       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)

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    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.

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       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.

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       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.

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       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.

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         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.

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       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

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       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.

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       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.

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       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.

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       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.

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    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>.

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    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.

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    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

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