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Versions: (draft-gandhi-spring-sr-mpls-pm) 00 01

SPRING Working Group                                      R. Gandhi, Ed.
Internet-Draft                                               C. Filsfils
Intended Status: Informational                       Cisco Systems, Inc.
Expires: November 16, 2019                                      D. Voyer
                                                             Bell Canada
                                                              S. Salsano
                                        Universita di Roma "Tor Vergata"
                                                            P. L. Ventre
                                                                    CNIT
                                                                 M. Chen
                                                                  Huawei
                                                            May 15, 2019


                      Performance Measurement for
              Segment Routing Networks with MPLS Data Plane
                 draft-gandhi-spring-rfc6374-srpm-mpls-01

Abstract

   RFC 6374 specifies protocol mechanisms to enable the efficient and
   accurate measurement of packet loss, one-way and two-way delay, as
   well as related metrics such as delay variation in MPLS networks
   using synthetic probe messages.  This document reviews how these
   mechanisms can be used for Performance Delay and Loss Measurements in
   Segment Routing (SR) networks with MPLS data plane (SR-MPLS), for
   both SR links and end-to-end SR Policies.  The Performance
   Measurements (PM) for SR links are used to compute extended Traffic
   Engineering (TE) metrics for delay and loss and can be advertised in
   the network using the routing protocol extensions.


Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
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   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."





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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
   (http://trustee.ietf.org/license-info) in effect on the date of
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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.



Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Conventions Used in This Document  . . . . . . . . . . . . . .  3
     2.1.  Abbreviations  . . . . . . . . . . . . . . . . . . . . . .  3
     2.2.  Reference Topology . . . . . . . . . . . . . . . . . . . .  4
   3.  Probe Query and Response Packets . . . . . . . . . . . . . . .  5
     3.1.  Probe Packet Header for SR-MPLS Policies . . . . . . . . .  5
     3.2.  Probe Packet Header for SR-MPLS Links  . . . . . . . . . .  6
     3.3.  Probe Response Message for SR-MPLS Links and Policies  . .  6
       3.3.1.  One-way Measurement Mode . . . . . . . . . . . . . . .  6
       3.3.2.  Two-way Measurement Mode . . . . . . . . . . . . . . .  7
         3.3.2.1.  Return Path TLV  . . . . . . . . . . . . . . . . .  7
       3.3.3.  Loopback Measurement Mode  . . . . . . . . . . . . . .  7
   4.  Performance Delay Measurement  . . . . . . . . . . . . . . . .  7
     4.1.  Delay Measurement Message Format . . . . . . . . . . . . .  7
     4.2.  Timestamps . . . . . . . . . . . . . . . . . . . . . . . .  8
   5.  Performance Loss Measurement . . . . . . . . . . . . . . . . .  8
     5.1.  Loss Measurement Message Format  . . . . . . . . . . . . .  9
       5.1.1.  Block Number TLV . . . . . . . . . . . . . . . . . . .  9
   6.  Performance Measurement for P2MP SR Policies . . . . . . . . .  9
   7.  ECMP for SR-MPLS Policies  . . . . . . . . . . . . . . . . . . 10
   8.  SR Link Extended TE Metrics Advertisements . . . . . . . . . . 10
   9.  Security Considerations  . . . . . . . . . . . . . . . . . . . 11
   10.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
   11.  References  . . . . . . . . . . . . . . . . . . . . . . . . . 11
     11.1.  Normative References  . . . . . . . . . . . . . . . . . . 11
     11.2.  Informative References  . . . . . . . . . . . . . . . . . 11
   Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . . . 14
   Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14



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1.  Introduction

   Service provider's ability to satisfy Service Level Agreements (SLAs)
   depend on the ability to measure and monitor performance metrics for
   packet loss and one-way and two-way delay, as well as related metrics
   such as delay variation.  The ability to monitor these performance
   metrics also provides operators with greater visibility into the
   performance characteristics of their networks, thereby facilitating
   planning, troubleshooting, and network performance evaluation.

   [RFC6374] specifies protocol mechanisms to enable the efficient and
   accurate measurement of performance metrics in MPLS networks using
   probe messages.  The One-Way Active Measurement Protocol (OWAMP)
   defined in [RFC4656] and Two-Way Active Measurement Protocol (TWAMP)
   defined in [RFC5357] provide capabilities for the measurement of
   various performance metrics in IP networks.  However, mechanisms
   defined in [RFC6374] are more suitable for Segment Routing (SR) when
   using MPLS data plane (SR-MPLS).  [RFC6374] also supports IEEE 1588
   timestamps [IEEE1588] and "direct mode" Loss Measurement (LM), which
   are required in SR networks.

   [RFC7876] specifies the procedures to be used when sending and
   processing out-of-band performance measurement probe replies over an
   UDP return path when receiving RFC 6374 based probe queries.  These
   procedures can be used to send out-of-band PM replies for both
   SR-MPLS links and Policies [I-D.spring-segment-routing-policy] for
   one-way measurement.

   This document reviews how synthetic probe-based mechanisms defined in
   [RFC6374] can be used for Performance Delay and Loss Measurements in
   SR networks with MPLS data plane, for both SR links and end-to-end SR
   Policies.  The Performance Measurements (PM) for SR links are used to
   compute extended Traffic Engineering (TE) metrics for delay and loss
   and can be advertised in the network using the routing protocol
   extensions.


2.  Conventions Used in This Document

2.1.  Abbreviations

   ACH: Associated Channel Header.

   DM: Delay Measurement.

   ECMP: Equal Cost Multi-Path.

   G-ACh: Generic Associated Channel (G-ACh).



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   GAL: Generic Associated Channel (G-ACh) Label.

   LM: Loss Measurement.

   MPLS: Multiprotocol Label Switching.

   NTP: Network Time Protocol.

   PM: Performance Measurement.

   PSID: Path Segment Identifier.

   PTP: Precision Time Protocol.

   SID: Segment ID.

   SL: Segment List.

   SR: Segment Routing.

   SR-MPLS: Segment Routing with MPLS data plane.

   TC: Traffic Class.

   TE: Traffic Engineering.

   URO: UDP Return Object.



2.2.  Reference Topology

   In the reference topology shown in Figure 1, the querier node R1
   initiates a performance measurement probe query and the responder
   node R5 sends a probe response for the query message received.  The
   probe response is typically sent back to the querier node R1.  The
   nodes R1 and R5 may be directly connected via a link enabled with
   Segment Routing or there exists a Point-to-Point (P2P) SR Policy
   [I-D.spring-segment-routing-policy] on node R1 with destination to
   node R5.  In case of Point-to-Multipoint (P2MP), SR Policy
   originating from source node R1 may terminate on multiple destination
   leaf nodes [I-D.spring-sr-p2mp-policy].









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             +-------+        Query        +-------+
             |       | - - - - - - - - - ->|       |
             |   R1  |---------------------|   R5  |
             |       |<- - - - - - - - - - |       |
             +-------+       Response      +-------+

                   Figure 1: Reference Topology

   For delay and loss measurements, for both links and end-to-end SR
   Policies, no PM session is created on the responder node R5.  One-way
   delay and two-way delay measurements are defined in Section 2.4 of
   [RFC6374].  Transmit and Receive packet loss measurements are defined
   in Section 2.2 and Section 2.6 of [RFC6374].  One-way loss
   measurement provides receive packet loss whereas two-way loss
   measurement provides both transmit and receive packet loss.

   For Performance Measurement, synthetic probe query and response
   messages are used as following:

   o  For Delay Measurement, the probe messages are sent on the
      congruent path of the data traffic by the querier node, and are
      used to measure the delay experienced by the actual data traffic
      flowing on the links and SR Policies.

   o  For Loss Measurement, the probe messages are sent on the congruent
      path of the data traffic by the querier node, and are used to
      collect the receive traffic counters for the incoming link or
      incoming SID where the probe query messages are received at the
      responder node (incoming link or incoming SID used as the
      responder node has no PM session state present).

   The In-Situ Operations, Administration, and Maintenance (IOAM)
   mechanisms for SR-MPLS defined in [I-D.spring-ioam-sr-mpls] are used
   to carry PM information in-band as part of the data traffic, and are
   outside the scope of this document.


3.  Probe Query and Response Packets

3.1.  Probe Packet Header for SR-MPLS Policies

   As described in Section 2.9.1 of [RFC6374], MPLS PM probe query and
   response messages flow over the MPLS Generic Associated Channel
   (G-ACh).  A probe packet for an end-to-end measurement for SR Policy
   contains SR-MPLS label stack [I-D.spring-segment-routing-policy],
   with the G-ACh Label (GAL) at the bottom of the stack (with S=1).
   The GAL is followed by an Associated Channel Header (ACH), which
   identifies the message type, and the message payload following the



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   ACH as shown in Figure 2.

    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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                  Label(1)             | TC  |S|      TTL      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    .                                                               .
    .                                                               .
    .                                                               .
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                  Label(n)             | TC  |S|      TTL      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                  GAL (value 13)       | TC  |S|      TTL      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |0 0 0 1|Version|  Reserved     | GAL Channel Type              |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

     Figure 2: Probe Packet Header for an End-to-end SR-MPLS Policy

   The SR-MPLS label stack can be empty (as shown in Figure 3) to
   indicate Implicit NULL label case.

3.2.  Probe Packet Header for SR-MPLS Links

   As described in Section 2.9.1 of [RFC6374], MPLS PM probe query and
   response messages flow over the MPLS Generic Associated Channel
   (G-ACh).  A probe packet for SR-MPLS links contains G-ACh Label (GAL)
   (with S=1).  The GAL is followed by an Associated Channel Header
   (ACH), which identifies the message type, and the message payload
   following the ACH as shown in Figure 3.

    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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |             GAL (value 13)            | TC  |S|      TTL      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |0 0 0 1|Version|  Reserved     | GAL Channel Type              |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

           Figure 3: Probe Packet Header for an SR-MPLS Link


3.3.  Probe Response Message for SR-MPLS Links and Policies

3.3.1.  One-way Measurement Mode

   In one-way performance measurement mode [RFC7679], the PM querier



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   node can receive "out-of-band" probe replies by properly setting the
   UDP Return Object (URO) TLV in the probe query message.  The URO TLV
   (Type=131) is defined in [RFC7876] and includes the
   UDP-Destination-Port and IP Address.  In particular, if the querier
   sets its own IP address in the URO TLV, the probe response is sent
   back by the responder node to the querier node.  In addition, the
   "control code" in the probe query message is set to "out-of-band
   response requested".  The "Source Address" TLV (Type 130), and
   "Return Address" TLV (Type 1), if present in the probe query message,
   are not used to send probe response message.

3.3.2.  Two-way Measurement Mode

   In two-way performance measurement mode [RFC6374], when using a
   bidirectional path, the probe response message is sent back to the
   querier node on the congruent path of the data traffic on the reverse
   direction SR Link or SR Policy using a message with format similar to
   their probe query message.  In this case, the "control code" in the
   probe query message is set to "in-band response requested".

   A Path Segment Identifier (PSID) [I-D.spring-mpls-path-segment] of
   the forward SR-MPLS Policy can be used to find the reverse SR-MPLS
   Policy and to send back the probe response message for two-way
   measurement.

3.3.2.1.  Return Path TLV

   For two-way performance measurement, the querier node can request the
   responder node to send a response message back on a given reverse
   path (typically co-routed path for two-way measurement).  Return Path
   TLV defined in [I-D.spring-rfc6374-srpm-udp] can be used to carry
   reverse SR path information as part of the payload of the probe query
   message.

3.3.3.  Loopback Measurement Mode

   The Loopback measurement mode defined in Section 2.8 of [RFC6374] can
   be used to measure round-trip delay for a bidirectional SR Path.  The
   probe query messages in this case carries the reverse SR Path label
   stack as part of the MPLS header.  The GAL is still carried at the
   bottom of the label stack (with S=1).  The responder node does not
   process the PM probe messages and generate response messages.


4.  Performance Delay Measurement

4.1.  Delay Measurement Message Format




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   As defined in [RFC6374], MPLS DM probe query and response messages
   use Associated Channel Header (ACH) (value 0x000C for delay
   measurement) [RFC6374], which identifies the message type, and the
   message payload following the ACH.  For both SR links and end-to-end
   measurement for SR-MPLS Policies, the same MPLS DM ACH value is used.

   The DM message payload as defined in Section 3.2 of [RFC6374] is used
   for SR-MPLS delay measurement, for both SR links and end-to-end SR
   Policies.

4.2.  Timestamps

   The Section 3.4 of [RFC6374] defines timestamp format that can be
   used for delay measurement.  The IEEE 1588 Precision Time Protocol
   (PTP) timestamp format [IEEE1588] is used by default as described in
   Appendix A of [RFC6374], preferred with hardware support.  As an
   alternative, Network Time Protocol (NTP) timestamp format can also be
   used [RFC6374].

   Note that for one-way delay measurement mode, clock synchronization
   between the querier and responder nodes using the methods detailed in
   [RFC6374] is required.  The two-way delay measurement mode and
   loopback measurement mode do not require clock synchronization
   between the querier and responder nodes.


5.  Performance Loss Measurement

   The LM protocol can perform two distinct kinds of loss measurement as
   described in Section 2.9.8 of [RFC6374].

   o  In inferred mode, LM will measure the loss of specially generated
      test messages in order to infer the approximate data plane loss
      level.  Inferred mode LM provides only approximate loss
      accounting.

   o  In direct mode, LM will directly measure data plane packet loss.
      Direct mode LM provides perfect loss accounting, but may require
      hardware support.

   For both of these modes of LM, Path Segment Identifier (PSID)
   [I-D.spring-mpls-path-segment] is used for accounting received
   traffic on the egress node of the SR-MPLS Policy as shown in Figure
   4.  Different values of PSID can be used to measure packet loss per
   SR-MPLS Policy, per Candidate Path or per Segment List of the SR
   Policy.





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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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                  PSID                 | TC  |S|      TTL      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                  GAL (value 13)       | TC  |S|      TTL      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |0 0 0 1|Version|  Reserved     | GAL Channel Type              |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

        Figure 4: With Path Segment Identifier for SR-MPLS Policy


5.1.  Loss Measurement Message Format

   As defined in [RFC6374], MPLS LM probe query and response messages
   use Associated Channel Header (ACH) (value 0x000A for direct loss
   measurement or value 0x000B for inferred loss measurement), which
   identifies the message type, and the message payload following the
   ACH.  For both SR links and end-to-end measurement for SR-MPLS
   Policies, the same MPLS LM ACH value is used.

   The LM message payload as defined in Section 3.1 of [RFC6374] is used
   for SR-MPLS loss measurement, for both SR links and end-to-end SR
   Policies.

5.1.1.  Block Number TLV

   The Loss Measurement using Alternate-Marking method defined in
   [RFC8321] requires to identify the Block Number (or color) of the
   traffic counters carried by the probe query and response messages.
   Block Number TLV defined in [I-D.spring-rfc6374-srpm-udp] is used to
   carry Block Number for the traffic counters in the probe query and
   response messages for loss measurement.


6.  Performance Measurement for P2MP SR Policies

   The procedures for delay and loss measurement reviewed in this
   document for Point-to-Point (P2P) SR-MPLS Policies
   [I-D.spring-segment-routing-policy] are also equally applicable to
   the Point-to-Multipoint (P2MP) SR-MPLS Policies
   [I-D.spring-sr-p2mp-policy] as following:

   o  The querier root node sends probe query messages using the either
      Spray P2MP segment or TreeSID P2MP segment defined in
      [I-D.spring-sr-p2mp-policy] over the P2MP SR Policy as shown in
      Figure 5.



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   o  Each responder leaf node adds the "Source Address" TLV (Type 130)
      [RFC6374] with its IP address in the probe response messages.
      This TLV allows the querier root node to identify the responder
      leaf nodes of the P2MP SR Policy.

   o  The P2MP root node measures the end-to-end delay and loss
      performance for each P2MP leaf node.

    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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |              TreeSID OR Spray SID     | TC  |S|      TTL      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |              GAL (value 13)           | TC  |S|      TTL      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |0 0 0 1|Version|  Reserved     | GAL Channel Type              |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

        Figure 5: With P2MP Segment Identifier for SR-MPLS Policy


7.  ECMP for SR-MPLS Policies

   An SR Policy can have ECMPs between the source and transit nodes,
   between transit nodes and between transit and destination nodes.
   Usage of Anycast SID [RFC8402] by an SR Policy can result in ECMP
   paths via transit nodes part of that Anycast group.  The PM probe
   messages need to be sent to traverse different ECMP paths to measure
   performance delay of an SR Policy.

   Forwarding plane has various hashing functions available to forward
   packets on specific ECMP paths.  For SR-MPLS Policy, entropy label
   [RFC6790] can be used in PM probe messages to take advantage of the
   hashing function in forwarding plane to influence the ECMP path taken
   by them.


8.  SR Link Extended TE Metrics Advertisements

   The extended TE metrics for SR link delay and loss computed using the
   performance measurement procedures reviewed in this document can be
   advertised in the routing domain as follows:

   o  For OSPF, ISIS, and BGP-LS, protocol extensions defined in
      [RFC7471], [RFC8570], and [RFC8571] are used, respectively for
      advertising the extended TE link metrics in the network.

   o  The extended TE link delay metrics advertised are minimum-delay,



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      maximum-delay, average-delay, and delay-variance for one-way.

   o  The delay-variance metric is computed as specified in Section 4.2
      of [RFC5481].

   o  The one-way delay metrics can be computed using two-way delay
      measurement or round-trip delay measurement from loopback mode by
      dividing the measured delay values by 2.

   o  The extended TE link loss metric advertised is one-way percentage
      packet loss.


9.  Security Considerations

   This document reviews the procedures for performance delay and loss
   measurement for SR-MPLS networks, for both links and end-to-end SR
   Policies using the mechanisms defined in [RFC6374] and [RFC7876].
   This document does not introduce any additional security
   considerations other than those covered in [RFC6374], [RFC7471],
   [RFC8570], [RFC8571], and [RFC7876].


10.  IANA Considerations

   This document does not require any IANA actions.


11.  References

11.1.  Normative References

   [RFC6374]  Frost, D. and S. Bryant, "Packet Loss and Delay
              Measurement for MPLS networks', RFC 6374, September 2011.

   [RFC7876]  Bryant, S., Sivabalan, S., and Soni, S., "UDP Return Path
              for Packet Loss and Delay Measurement for MPLS Networks",
              RFC 7876, July 2016.

11.2.  Informative References

   [IEEE1588] IEEE, "1588-2008 IEEE Standard for a Precision Clock
              Synchronization Protocol for Networked Measurement and
              Control Systems", March 2008.

   [RFC4656]  Shalunov, S., Teitelbaum, B., Karp, A., Boote, J., and M.
              Zekauskas, "A One-way Active Measurement Protocol
              (OWAMP)", RFC 4656, September 2006.



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   [RFC5357]  Hedayat, K., Krzanowski, R., Morton, A., Yum, K., and J.
              Babiarz, "A Two-Way Active Measurement Protocol (TWAMP)",
              RFC 5357, October 2008.

   [RFC5481]  Morton, A. and B. Claise, "Packet Delay Variation
              Applicability Statement", RFC 5481, March 2009.

   [RFC6790]  Kompella, K., Drake, J., Amante, S., Henderickx, W., and
              L. Yong, "The Use of Entropy Labels in MPLS Forwarding",
              RFC 6790, November 2012.

   [RFC7679]  Almes, G., et al., "A One-Way Delay Metric for IP
              Performance Metrics (IPPM)', RFC 7679, January 2016.

   [RFC7471]  Giacalone, S., et al., "OSPF Traffic Engineering (TE)
              Metric Extensions", RFC 7471, March 2015.

   [RFC8321]  Fioccola, G. Ed., "Alternate-Marking Method for Passive
              and Hybrid Performance Monitoring", RFC 8321, January
              2018.

   [RFC8402]  Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
              Decraene, B., Litkowski, S., and R. Shakir, "Segment
              Routing Architecture", RFC 8402, July 2018.

   [RFC8570]  Ginsberg, L. Ed., et al., "IS-IS Traffic Engineering (TE)
              Metric Extensions",  RFC 8570, March 2019.

   [RFC8571]  Ginsberg, L. Ed., et al., "BGP - Link State (BGP-LS)
              Advertisement of IGP Traffic Engineering Performance
              Metric Extensions", RFC 8571, March 2019.

   [I-D.spring-segment-routing-policy]  Filsfils, C., et al., "Segment
              Routing Policy Architecture",
              draft-ietf-spring-segment-routing-policy, work in
              progress.

   [I-D.spring-sr-p2mp-policy]  Voyer, D. Ed., et al., "SR Replication
              Policy for P2MP Service Delivery",
              draft-voyer-spring-sr-p2mp-policy, work in progress.

   [I-D.spring-mpls-path-segment]  Cheng, W., et al., "Path Segment in
              MPLS Based Segment Routing Network",
              draft-ietf-spring-mpls-path-segment, work in progress.

   [I-D.spring-rfc6374-srpm-udp]  Gandhi, R. Ed., et al., "Performance
              Measurement Using UDP Path for Segment Routing Networks",
              draft-gandhi-spring-rfc6374-srpm-udp, work in progress.



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   [I-D.spring-ioam-sr-mpls]  Gandhi, R. Ed., et al., "Segment Routing
              with MPLS Data Plane Encapsulation for In-situ OAM Data",
              draft-gandhi-spring-ioam-sr-mpls, work in progress.
















































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Acknowledgments

   The authors would like to thank Thierry Couture for various
   discussions on the use-cases for the performance measurement in
   segment routing networks.  The authors would like to thank Greg
   Mirsky for providing many useful comments and suggestions.  The
   authors would also like to thank Stewart Bryant and Rajiv Asati for
   their review comments.


Contributors

   Sagar Soni
   Cisco Systems, Inc.
   Email: sagsoni@cisco.com


   Patrick Khordoc
   Cisco Systems, Inc.
   Email: pkhordoc@cisco.com


   Zafar Ali
   Cisco Systems, Inc.
   Email: zali@cisco.com



Authors' Addresses

   Rakesh Gandhi (editor)
   Cisco Systems, Inc.
   Canada
   Email: rgandhi@cisco.com


   Clarence Filsfils
   Cisco Systems, Inc.
   Email: cfilsfil@cisco.com


   Daniel Voyer
   Bell Canada
   Email: daniel.voyer@bell.ca


   Stefano Salsano
   Universita di Roma "Tor Vergata"



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   Italy
   Email: stefano.salsano@uniroma2.it


   Pier Luigi Ventre
   CNIT
   Italy
   Email: pierluigi.ventre@cnit.it


   Mach(Guoyi) Chen
   Huawei
   Email: mach.chen@huawei.com






































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