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rfc:rfc8972



Internet Engineering Task Force (IETF) G. Mirsky Request for Comments: 8972 X. Min Updates: 8762 ZTE Corp. Category: Standards Track H. Nydell ISSN: 2070-1721 Accedian Networks

                                                              R. Foote
                                                                 Nokia
                                                           A. Masputra
                                                            Apple Inc.
                                                            E. Ruffini
                                                                OutSys
                                                          January 2021
   Simple Two-Way Active Measurement Protocol Optional Extensions

Abstract

 This document describes optional extensions to Simple Two-way Active
 Measurement Protocol (STAMP) that enable measurement of performance
 metrics.  The document also defines a STAMP Test Session Identifier
 and thus updates RFC 8762.

Status of This Memo

 This is an Internet Standards Track document.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Further information on
 Internet Standards is available in 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/rfc8972.

Copyright Notice

 Copyright (c) 2021 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.  Code Components extracted from this document must
 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
 2.  Conventions Used in This Document
   2.1.  Acronyms
   2.2.  Requirements Language
 3.  STAMP Test Session Identifier
 4.  TLV Extensions to STAMP
   4.1.  Extra Padding TLV
   4.2.  Location TLV
     4.2.1.  Location Sub-TLVs
     4.2.2.  Theory of Operation of Location TLV
   4.3.  Timestamp Information TLV
   4.4.  Class of Service TLV
   4.5.  Direct Measurement TLV
   4.6.  Access Report TLV
   4.7.  Follow-Up Telemetry TLV
   4.8.  HMAC TLV
 5.  IANA Considerations
   5.1.  STAMP TLV Types Subregistry
   5.2.  STAMP TLV Flags Subregistry
   5.3.  STAMP Sub-TLV Types Subregistry
   5.4.  STAMP Synchronization Sources Subregistry
   5.5.  STAMP Timestamping Methods Subregistry
   5.6.  STAMP Return Codes Subregistry
 6.  Security Considerations
 7.  References
   7.1.  Normative References
   7.2.  Informative References
 Acknowledgments
 Contributors
 Authors' Addresses

1. Introduction

 The Simple Two-way Active Measurement Protocol (STAMP) [RFC8762]
 defines the STAMP base functionalities.  This document specifies the
 use of optional extensions that use Type-Length-Value (TLV) encoding.
 Such extensions enhance the STAMP base functions, such as measurement
 of one-way and round-trip delay, latency, packet loss, packet
 duplication, and out-of-order delivery of test packets.  This
 specification defines optional STAMP extensions, their formats, and
 the theory of operation.  Also, a STAMP Test Session Identifier is
 defined as an update of the base STAMP specification [RFC8762].

2. Conventions Used in This Document

2.1. Acronyms

 BDS         BeiDou Navigation Satellite System
 BITS        Building Integrated Timing Supply
 CoS         Class of Service
 DSCP        Differentiated Services Code Point
 ECN         Explicit Congestion Notification
 GLONASS     Global Orbiting Navigation Satellite System
 GPS         Global Positioning System [GPS]
 HMAC        Hashed Message Authentication Code
 LORAN-C     Long Range Navigation System Version C
 MBZ         Must Be Zero
 NTP         Network Time Protocol [RFC5905]
 PMF         Performance Measurement Function
 PTP         Precision Time Protocol [IEEE.1588.2008]
 RP          Reverse Path
 SMI         Structure of Management Information
 SSID        STAMP Session Identifier
 SSU         Synchronization Supply Unit
 STAMP       Simple Two-way Active Measurement Protocol
 TLV         Type-Length-Value

2.2. 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.

3. STAMP Test Session Identifier

 The STAMP Session-Sender transmits test packets to the STAMP Session-
 Reflector.  The STAMP Session-Reflector receives the Session-Sender's
 packet and acts according to the configuration and optional control
 information communicated in the Session-Sender's test packet.  STAMP
 defines two different test packet formats: one for packets
 transmitted by the STAMP Session-Sender and one for packets
 transmitted by the STAMP Session-Reflector.  STAMP supports two
 modes: unauthenticated and authenticated.  Unauthenticated STAMP test
 packets are compatible on the wire with unauthenticated TWAMP-Test
 [RFC5357] packets.
 By default, STAMP uses symmetrical packets, i.e., the size of the
 packet transmitted by the Session-Reflector equals the size of the
 packet received by the Session-Reflector.
 A STAMP Session is identified by the 4-tuple (source and destination
 IP addresses, source and destination UDP port numbers).  A STAMP
 Session-Sender MAY generate a locally unique STAMP Session Identifier
 (SSID).  The SSID is a two-octet, non-zero unsigned integer.  The
 SSID generation policy is implementation specific.  [NUM-IDS-GEN]
 thoroughly analyzes common algorithms for identifier generation and
 their vulnerabilities.  For example, an implementation can use the
 algorithms described in Section 7.1 of [NUM-IDS-GEN].  An
 implementation MUST NOT assign the same identifier to different STAMP
 test sessions.  A Session-Sender MAY use the SSID to identify a STAMP
 test session.  If the SSID is used, it MUST be present in each test
 packet of the given test session.  In the unauthenticated mode, the
 SSID is located as displayed in Figure 1.
     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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        Sequence Number                        |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                          Timestamp                            |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |         Error Estimate        |             SSID              |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    |                                                               |
    |                         MBZ (28 octets)                       |
    |                                                               |
    |                                                               |
    |                                                               |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    ~                            TLVs                               ~
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     Figure 1: The Format of an Extended STAMP Session-Sender Test
                     Packet in Unauthenticated Mode
 An implementation of the STAMP Session-Reflector that supports this
 specification MUST identify a STAMP Session using the SSID in
 combination with elements of the usual 4-tuple for the session.
 Before a test session commences, a Session-Reflector MUST be
 provisioned with all the elements that identify the STAMP Session.  A
 STAMP Session-Reflector MUST discard non-matching STAMP test packets.
 The means of provisioning the STAMP Session identification is outside
 the scope of this specification.  A conforming implementation of a
 STAMP Session-Reflector MUST copy the SSID value from the received
 test packet and put it into the reflected packet, as displayed 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
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                        Sequence Number                        |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                          Timestamp                            |
  |                                                               |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |         Error Estimate        |           SSID                |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                          Receive Timestamp                    |
  |                                                               |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                 Session-Sender Sequence Number                |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                  Session-Sender Timestamp                     |
  |                                                               |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  | Session-Sender Error Estimate |           MBZ                 |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |Ses-Sender TTL |                   MBZ                         |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  ~                            TLVs                               ~
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    Figure 2: The Format of an Extended STAMP Session-Reflector Test
                     Packet in Unauthenticated Mode
 A STAMP Session-Reflector that does not support this specification
 will return the zeroed SSID field in the reflected STAMP test packet.
 The Session-Sender MAY stop the session if it receives a zeroed SSID
 field.  An implementation of a Session-Sender MUST support control of
 its behavior in such a scenario.  If the test session is not stopped,
 the Session-Sender can, for example, send a base STAMP packet
 [RFC8762] or continue transmitting STAMP test packets with the SSID.
 The location of the SSID field in the authenticated mode is shown in
 Figures 3 and 4.
   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
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                      Sequence Number                          |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                                                               |
  |                      MBZ (12 octets)                          |
  |                                                               |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                        Timestamp                              |
  |                                                               |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |        Error Estimate         |            SSID               |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  ~                                                               ~
  |                         MBZ (68 octets)                       |
  ~                                                               ~
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                                                               |
  |                       HMAC (16 octets)                        |
  |                                                               |
  |                                                               |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  ~                            TLVs                               ~
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     Figure 3: The Format of an Extended STAMP Session-Sender Test
                      Packet in Authenticated Mode
     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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        Sequence Number                        |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        MBZ (12 octets)                        |
    |                                                               |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                          Timestamp                            |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |         Error Estimate        |            SSID               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        MBZ (4 octets)                         |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        Receive Timestamp                      |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        MBZ (8 octets)                         |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                 Session-Sender Sequence Number                |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        MBZ (12 octets)                        |
    |                                                               |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                 Session-Sender Timestamp                      |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    | Session-Sender Error Estimate |                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               +
    |                        MBZ (6 octets)                         |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |Ses-Sender TTL |                                               |
    +-+-+-+-+-+-+-+-+                                               +
    |                                                               |
    |                        MBZ (15 octets)                        |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        HMAC (16 octets)                       |
    |                                                               |
    |                                                               |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    ~                            TLVs                               ~
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    Figure 4: The Format of an Extended STAMP Session-Reflector Test
                      Packet in Authenticated Mode

4. TLV Extensions to STAMP

 The Type-Length-Value (TLV) encoding scheme provides a flexible
 extension mechanism for optional informational elements.  TLV is an
 optional field in the STAMP test packet.  Multiple TLVs MAY be placed
 in a STAMP test packet.  Additional TLVs may be enclosed within a
 given TLV, subject to the semantics of the (outer) TLV in question.
 TLVs have a one-octet STAMP TLV Flags field, a one-octet Type field,
 and a two-octet Length field that is equal to the length of the Value
 field in octets.  If a Type value for a TLV or sub-TLV is in the
 range for Private Use [RFC8126], the length MUST be at least 4, and
 the first four octets MUST be that vendor's Structure of Management
 Information (SMI) Private Enterprise Code, as recorded in IANA's "SMI
 Network Management Private Enterprise Codes" subregistry, in network
 octet order.  The rest of the Value field is private to the vendor.
 The following sections describe the use of TLVs for STAMP that extend
 the STAMP capability beyond its base specification.
     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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |STAMP TLV Flags|     Type      |           Length              |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    ~                            Value                              ~
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
            Figure 5: TLV Format in a STAMP Extended Packet
 The fields are defined as follows:
 STAMP TLV Flags:  An eight-bit field.  The detailed format and
    interpretation of flags defined in this specification are below.
 Type:  A one-octet field that characterizes the interpretation of the
    Value field.  It is allocated by IANA, as specified in
    Section 5.1.
 Length:  A two-octet field equal to the length of the Value field in
    octets.
 Value:  A variable-length field.  Its interpretation and encoding are
    determined by the value of the Type field.
 All multi-byte fields in TLVs defined in this specification are in
 network byte order.
 The format of the STAMP TLV Flags is displayed in Figure 6, and the
 location of flags is defined in Section 5.2.
     0 1 2 3 4 5 6 7
    +-+-+-+-+-+-+-+-+
    |U|M|I|R|R|R|R|R|
    +-+-+-+-+-+-+-+-+
                    Figure 6: STAMP TLV Flags Format
 The fields are defined as follows:
 U (Unrecognized):  A one-bit flag.  A Session-Sender MUST set the U
    flag to 1 before transmitting an extended STAMP test packet.  A
    Session-Reflector MUST set the U flag to 1 if the Session-
    Reflector has not understood the TLV.  Otherwise, the Session-
    Reflector MUST set the U flag in the reflected packet to 0.
 M (Malformed):  A one-bit flag.  A Session-Sender MUST set the M flag
    to 0 before transmitting an extended STAMP test packet.  A
    Session-Reflector MUST set the M flag to 1 if the Session-
    Reflector determined the TLV is malformed, i.e., the Length field
    value is not valid for the particular type, or the remaining
    length of the extended STAMP packet is less than the size of the
    TLV.  Otherwise, the Session-Reflector MUST set the M flag in the
    reflected packet to 0.
 I (Integrity):  A one-bit flag.  A Session-Sender MUST set the I flag
    to 0 before transmitting an extended STAMP test packet.  A
    Session-Reflector MUST set the I flag to 1 if the STAMP extensions
    have failed HMAC verification (Section 4.8).  Otherwise, the
    Session-Reflector MUST set the I flag in the reflected packet to
    0.
 R:  Reserved flags for future use.  These flags MUST be zeroed on
    transmit and ignored on receipt.
 A STAMP node, whether Session-Sender or Session-Reflector, receiving
 a test packet MUST determine whether the packet is a base STAMP
 packet or whether it includes one or more TLVs.  The node MUST
 compare the value in the Length field of the UDP header and the
 length of the base STAMP test packet in the mode, unauthenticated or
 authenticated, based on the configuration of the particular STAMP
 test session.  If the difference between the two values is greater
 than the length of the UDP header, then the test packet includes one
 or more STAMP TLVs that immediately follow the base STAMP test
 packet.  A Session-Reflector that does not support STAMP extensions
 will not process but copy them into the reflected packet, as defined
 in Section 4.3 of [RFC8762].  A Session-Reflector that supports TLVs
 will indicate specific TLVs that it did not process by setting the U
 flag to 1 in those TLVs.
 A STAMP Session-Sender that has received a reflected STAMP test
 packet with extension TLVs MUST validate each TLV:
  • If the U flag is set, the STAMP system MUST skip the processing of

the TLV.

  • If the M flag is set, the STAMP system MUST stop processing the

remainder of the extended STAMP packet.

  • If the I flag is set, the STAMP system MUST discard all TLVs and

MUST stop processing the remainder of the extended STAMP packet.

  • If an implementation of a Session-Reflector does not recognize the

Type field value, it MUST include a copy of the TLV in the

    reflected STAMP packet.  The Session-Reflector MUST set the U flag
    to 1.  The Session-Reflector MUST skip the processing of the
    unrecognized TLV.
  • If a TLV is malformed, the processing of extension TLVs MUST be

stopped. The Session-Reflector MUST copy the remainder of the

    received extended STAMP packet into the reflected STAMP packet.
    The Session-Reflector MUST set the M flag to 1.

4.1. Extra Padding TLV

     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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |STAMP TLV Flags|      Type     |           Length              |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    ~                         Extra Padding                         ~
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                      Figure 7: Extra Padding TLV
 The fields are defined as follows:
 STAMP TLV Flags:  An eight-bit field.  Its format is presented in
    Figure 6.
 Type:  A one-octet field.  Value 1 has been allocated by IANA
    (Section 5.1).
 Length:  A two-octet field equal to the length of the Extra Padding
    field in octets.
 Extra Padding:  This field SHOULD be filled by a sequence of
    pseudorandom numbers.  The field MAY be filled with all zeros.  An
    implementation MUST control the content of the Extra Padding
    field.
 The Extra Padding TLV is similar to the Packet Padding field in a
 TWAMP-Test packet [RFC5357].  The use of the Extra Padding TLV is
 RECOMMENDED to perform a STAMP test using test packets that are
 larger than the base STAMP packet [RFC8762].  The length of the base
 STAMP packet is 44 octets in the unauthenticated mode or 112 octets
 in the authenticated mode.  The Extra Padding TLV MAY be present more
 than one time in an extended STAMP test packet.

4.2. Location TLV

 STAMP Session-Senders MAY include the variable-size Location TLV to
 query location information from the Session-Reflector.  The Session-
 Sender MUST NOT fill any information fields except for the STAMP TLV
 Flags, Type, and Length fields.  The Session-Reflector MUST verify
 that the TLV is well formed.  If it is not, the Session-Reflector
 follows the procedure defined in Section 4 for a malformed TLV.
     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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |STAMP TLV Flags|      Type     |           Length              |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |        Destination Port       |          Source Port          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    ~                         Sub-TLVs                              ~
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                         Figure 8: Location TLV
 The fields are defined as follows:
 STAMP TLV Flags:  An eight-bit field.  Its format is presented in
    Figure 6.
 Type:  A one-octet field.  Value 2 has been allocated by IANA
    (Section 5.1).
 Length:  A two-octet field equal to the length of the Value field in
    octets.
 Destination Port:  A two-octet UDP destination port number of the
    received STAMP packet.
 Source Port:  A two-octet UDP source port number of the received
    STAMP packet.
 Sub-TLVs:  A sequence of sub-TLVs, as defined further in this
    section.  The sub-TLVs are used by the Session-Sender to request
    location information with generic sub-TLV types, and the Session-
    Reflector responds with the corresponding more-specific sub-TLVs
    for the type of address (e.g., IPv4 or IPv6) used at the Session-
    Reflector.
 Note that all fields not filled by either a Session-Sender or
 Session-Reflector are transmitted with all bits set to zero.

4.2.1. Location Sub-TLVs

 A sub-TLV in the Location TLV uses the format displayed in Figure 5.
 Handling of the U and M flags in the sub-TLV is as defined in
 Section 4.  The I flag MUST be set by a Session-Sender and Session-
 Reflector to 0 before transmission and its value ignored on receipt.
 The following types of sub-TLVs for the Location TLV are defined in
 this specification (Table 5 lists the Type values):
 Source MAC Address sub-TLV:  A 12-octet sub-TLV.  The Type value is
    1.  The value of the Length field MUST be equal to 8.  The Value
    field is an 8-octet MBZ field that MUST be zeroed on transmission
    and ignored on receipt.
 Source EUI-48 Address sub-TLV:  A 12-octet sub-TLV that includes the
    EUI-48 source MAC address.  The Type value is 2.  The value of the
    Length field MUST be equal to 8.
     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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        EUI-48  Address                        |
    +                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                               |            MBZ                |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      Figure 9: The Value Field of the Source EUI-48 Address Sub-TLV
    The Value field consists of the following fields (Figure 9):
    EUI-48 Address:  A six-octet field.
    MBZ:  A two-octet field.  It MUST be zeroed on transmission and
       ignored on receipt.
 Source EUI-64 Address sub-TLV:  A 12-octet sub-TLV that includes the
    EUI-64 source MAC address.  The Type value is 3.  The value of the
    Length field MUST be equal to 8.  The Value field consists of an
    eight-octet EUI-64 field.
 Destination IP Address sub-TLV:  A 20-octet sub-TLV.  The Type value
    is 4.  The value of the Length field MUST be equal to 16.  The
    Value field consists of a 16-octet MBZ field that MUST be zeroed
    on transmit and ignored on receipt.
 Destination IPv4 Address sub-TLV:  A 20-octet sub-TLV that includes
    the IPv4 destination address.  The Type value is 5.  The value of
    the Length field MUST be equal to 16.
     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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                         IPv4 Address                          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    ~                        MBZ (12 octets)                        ~
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
            Figure 10: IPv4 Address in a Sub-TLV's Value Field
    The Value field consists of the following fields (Figure 10):
    IPv4 Address:  A four-octet field.
    MBZ:  A 12-octet field.  It MUST be zeroed on transmit and ignored
       on receipt.
 Destination IPv6 Address sub-TLV:  A 20-octet sub-TLV that includes
    the IPv6 destination address.  The Type value is 6.  The value of
    the Length field MUST be equal to 16.  The Value field is a
    16-octet IPv6 Address field.
 Source IP Address sub-TLV:  A 20-octet sub-TLV.  The Type value is 7.
    The value of the Length field MUST be equal to 16.  The Value
    field is a 16-octet MBZ field that MUST be zeroed on transmit and
    ignored on receipt.
 Source IPv4 Address sub-TLV:  A 20-octet sub-TLV that includes the
    IPv4 source address.  The Type value is 8.  The value of the
    Length field MUST be equal to 16.  The Value field consists of the
    following fields (Figure 10):
    IPv4 Address:  A four-octet field.
    MBZ:  A 12-octet field.  It MUST be zeroed on transmit and ignored
       on receipt.
 Source IPv6 Address sub-TLV:  A 20-octet sub-TLV that includes the
    IPv6 source address.  The Type value is 9.  The value of the
    Length field MUST be equal to 16.  The Value field is a 16-octet
    IPv6 Address field.

4.2.2. Theory of Operation of Location TLV

 The Session-Reflector that received an extended STAMP packet with the
 Location TLV MUST include in the reflected packet the Location TLV
 with a length equal to the Location TLV length in the received
 packet.  Based on the local policy, the Session-Reflector MAY leave
 some fields unreported by filling them with zeroes.  An
 implementation of the stateful Session-Reflector MUST provide control
 for managing such policies.
 A Session-Sender MAY include the Source MAC Address sub-TLV in the
 Location TLV.  If the Session-Reflector receives the Location TLV
 that includes the Source MAC Address sub-TLV, it MUST include the
 Source EUI-48 Address sub-TLV if the source MAC address of the
 received extended test packet is in EUI-48 format.  And the Session-
 Reflector MUST copy the value of the source MAC address in the EUI-48
 field.  Otherwise, the Session-Reflector MUST use the Source EUI-64
 Address sub-TLV and MUST copy the value of the Source MAC Address
 from the received packet into the EUI-64 field.  If the received
 extended STAMP test packet does not have the Source MAC Address, the
 Session-Reflector MUST zero the EUI-64 field before transmitting the
 reflected packet.
 A Session-Sender MAY include the Destination IP Address sub-TLV in
 the Location TLV.  If the Session-Reflector receives the Location TLV
 that includes the Destination IP Address sub-TLV, it MUST include the
 Destination IPv4 Address sub-TLV if the source IP address of the
 received extended test packet is of the IPv4 address family.  And the
 Session-Reflector MUST copy the value of the destination IP address
 in the IPv4 Address field.  Otherwise, the Session-Reflector MUST use
 the Destination IPv6 Address sub-TLV and MUST copy the value of the
 destination IP address from the received packet into the IPv6 Address
 field.
 A Session-Sender MAY include the Source IP Address sub-TLV in the
 Location TLV.  If the Session-Reflector receives the Location TLV
 that includes the Source IP Address sub-TLV, it MUST include the
 Source IPv4 Address sub-TLV if the source IP address of the received
 extended test packet is of the IPv4 address family.  And the Session-
 Reflector MUST copy the value of the source IP address in the IPv4
 Address field.  Otherwise, the Session-Reflector MUST use the Source
 IPv6 Address sub-TLV and MUST copy the value of the source IP address
 from the received packet into the IPv6 Address field.
 The Location TLV MAY be used to determine the last-hop IP addresses,
 ports, and last-hop MAC address for STAMP packets.  The MAC address
 can indicate a path switch on the last hop.  The IP addresses and UDP
 ports will indicate if there is a NAT router on the path.  It allows
 the Session-Sender to identify the IP address of the Session-
 Reflector behind the NAT and detect changes in the NAT mapping that
 could result in sending the STAMP packets to the wrong Session-
 Reflector.

4.3. Timestamp Information TLV

 The STAMP Session-Sender MAY include the Timestamp Information TLV to
 request information from the Session-Reflector.  The Session-Sender
 MUST NOT fill any information fields except for STAMP TLV Flags,
 Type, and Length.  All other fields MUST be filled with zeroes.  The
 Session-Reflector MUST validate the Length value of the TLV.  If the
 value of the Length field is invalid, the Session-Reflector follows
 the procedure defined in Section 4 for a malformed TLV.
     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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |STAMP TLV Flags|      Type     |           Length              |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  Sync Src In  | Timestamp In  | Sync Src Out  | Timestamp Out |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    ~                    Optional sub-TLVs                          ~
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                  Figure 11: Timestamp Information TLV
 The fields are defined as follows:
 STAMP TLV Flags:  An eight-bit field.  Its format is presented in
    Figure 6.
 Type:  A one-octet field.  Value 3 has been allocated by IANA
    (Section 5.1).
 Length:  A two-octet field, set equal to the length of the Value
    field in octets (Figure 5).
 Sync Src In:  A one-octet field that characterizes the source of
    clock synchronization at the ingress of a Session-Reflector.
    There are several methods for synchronizing the clock, e.g., the
    Network Time Protocol (NTP) [RFC5905].  Table 7 lists the possible
    values.
 Timestamp In:  A one-octet field that characterizes the method by
    which the ingress of the Session-Reflector obtained the timestamp
    T2.  A timestamp may be obtained with hardware assistance via a
    software API from a local wall clock or from a remote clock (the
    latter is referred to as a "control plane").  Table 9 lists the
    possible values.
 Sync Src Out:  A one-octet field that characterizes the source of
    clock synchronization at the egress of the Session-Reflector.
    Table 7 lists the possible values.
 Timestamp Out:  A one-octet field that characterizes the method by
    which the egress of the Session-Reflector obtained the timestamp
    T3.  Table 9 lists the possible values.
 Optional sub-TLVs:  An optional variable-length field.

4.4. Class of Service TLV

 The STAMP Session-Sender MAY include a Class of Service (CoS) TLV in
 the STAMP test packet.  The format of the CoS TLV is presented in
 Figure 12.
     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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |STAMP TLV Flags|      Type     |           Length              |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |   DSCP1   |   DSCP2   |ECN| RP|          Reserved             |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                    Figure 12: Class of Service TLV
 The fields are defined as follows:
 STAMP TLV Flags:  An eight-bit field.  Its format is presented in
    Figure 6.
 Type:  A one-octet field.  Value 4 has been allocated by IANA
    (Section 5.1).
 Length:  A two-octet field, set equal to the value 4.
 DSCP1:  The Differentiated Services Code Point (DSCP) intended by the
    Session-Sender to be used as the DSCP value of the reflected test
    packet.
 DSCP2:  The received value in the DSCP field at the ingress of the
    Session-Reflector.
 ECN:  The received value in the ECN field at the ingress of the
    Session-Reflector.
 RP (Reverse Path):  A two-bit field.  A Session-Sender MUST set the
    value of the RP field to 0 on transmission.
 Reserved:  A 16-bit field that MUST be zeroed on transmission and
    ignored on receipt.
 A STAMP Session-Reflector that receives a test packet with the CoS
 TLV MUST include the CoS TLV in the reflected test packet.  Also, the
 Session-Reflector MUST copy the value of the DSCP and ECN fields of
 the IP header of the received STAMP test packet into the DSCP2 field
 in the reflected test packet.  Finally, the Session-Reflector MUST
 use the local policy to verify whether the CoS corresponding to the
 value of the DSCP1 field is permitted in the domain.  If it is, the
 Session-Reflector MUST set the DSCP field's value in the IP header of
 the reflected test packet equal to the value of the DSCP1 field of
 the received test packet.  Otherwise, the Session-Reflector MUST use
 the DSCP value of the received STAMP packet and set the value of the
 RP field to 1.  Upon receiving the reflected packet, if the value of
 the RP field is 0, the Session-Sender will save the DSCP and ECN
 values for analysis of the CoS in the reverse direction.  If the
 value of the RP field in the received reflected packet is 1, only CoS
 in the forward direction can be analyzed.
 Re-mapping of CoS can be used to provide multiple services (e.g., 2G,
 3G, LTE in mobile backhaul networks) over the same network.  But if
 it is misconfigured, then it is often difficult to diagnose the root
 cause of excessive packet drops of higher-level service while packet
 drops for lower service packets are at a normal level.  Using a CoS
 TLV in STAMP testing helps to troubleshoot the existing problem and
 also verify whether Diffserv policies are processing CoS as required
 by the configuration.

4.5. Direct Measurement TLV

 The Direct Measurement TLV enables collection of the number of in-
 profile packets, i.e., packets that form a specific data flow, that
 had been transmitted and received by the Session-Sender and Session-
 Reflector, respectively.  The definition of "in-profile packet" is
 outside the scope of this document and is left to the test operators
 to determine.
     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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |STAMP TLV Flags|      Type     |           Length              |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |              Session-Sender Tx counter  (S_TxC)               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |             Session-Reflector Rx counter  (R_RxC)             |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |             Session-Reflector Tx counter  (R_TxC)             |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                   Figure 13: Direct Measurement TLV
 The fields are defined as follows:
 STAMP TLV Flags:  An eight-bit field.  Its format is presented in
    Figure 6.
 Type:  A one-octet field.  Value 5 has been allocated by IANA
    (Section 5.1).
 Length:  A two-octet field equal to the length of the Value field in
    octets.  The Length field value MUST equal 12 octets.
 Session-Sender Tx counter (S_TxC):  A four-octet field.  The Session-
    Sender MUST set its value equal to the number of the transmitted
    in-profile packets.
 Session-Reflector Rx counter (R_RxC):  A four-octet field.  It MUST
    be zeroed by the Session-Sender on transmit and ignored by the
    Session-Reflector on receipt.  The Session-Reflector MUST fill it
    with the value of in-profile packets received.
 Session-Reflector Tx counter (R_TxC):  A four-octet field.  It MUST
    be zeroed by the Session-Sender and ignored by the Session-
    Reflector on receipt.  The Session-Reflector MUST fill it with the
    value of the transmitted in-profile packets.
 A Session-Sender MAY include the Direct Measurement TLV in a STAMP
 test packet.  If the received STAMP test packet includes the Direct
 Measurement TLV, the Session-Reflector MUST include it in the
 reflected test packet.  The Session-Reflector MUST copy the value
 from the S_TxC field of the received test packet into the same field
 of the reflected packet before its transmission.

4.6. Access Report TLV

 A STAMP Session-Sender MAY include an Access Report TLV (Figure 14)
 to indicate changes to the access network status to the Session-
 Reflector.  The definition of an access network is outside the scope
 of this document.
      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |STAMP TLV Flags|     Type      |           Length              |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   ID  |  Resv |  Return Code  |          Reserved             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                      Figure 14: Access Report TLV
 The fields are defined as follows:
 STAMP TLV Flags:  An eight-bit field.  Its format is presented in
    Figure 6.
 Type:  A one-octet field.  Value 6 has been allocated by IANA
    (Section 5.1).
 Length:  A two-octet field, set equal to the value 4.
 ID (Access ID):  A four-bit field that identifies the access network,
    e.g., 3GPP (Radio Access Technologies specified by 3GPP) or non-
    3GPP (accesses that are not specified by 3GPP) [TS23501].  The
    value is one of the following:
    1:  3GPP Network
    2:  Non-3GPP Network
    All other values are invalid; a TLV that contains values other
    than '1' or '2' MUST be discarded.
 Resv:  A four-bit field that MUST be zeroed on transmission and
    ignored on receipt.
 Return Code:  A one-octet field that identifies the report signal,
    e.g., available or unavailable.  The value is supplied to the
    STAMP endpoint through some mechanism that is outside the scope of
    this document.  Section 5.6 lists the possible values.
 Reserved:  A two-octet field that MUST be zeroed on transmission and
    ignored on receipt.
 The STAMP Session-Sender that includes the Access Report TLV sets the
 value of the Access ID field according to the type of access network
 it reports on.  Also, the Session-Sender sets the value of the Return
 Code field to reflect the operational state of the access network.
 The mechanism to determine the state of the access network is outside
 the scope of this specification.  A STAMP Session-Reflector that
 received the test packet with the Access Report TLV MUST include the
 Access Report TLV in the reflected test packet.  The Session-
 Reflector MUST set the value of the Access ID and Return Code fields
 equal to the values of the corresponding fields from the test packet
 it has received.
 The Session-Sender MUST also arm a retransmission timer after sending
 a test packet that includes the Access Report TLV.  This timer MUST
 be disarmed upon reception of the reflected STAMP test packet that
 includes the Access Report TLV.  In the event the timer expires
 before such a packet is received, the Session-Sender MUST retransmit
 the STAMP test packet that contains the Access Report TLV.  This
 retransmission SHOULD be repeated up to four times before the
 procedure is aborted.  Setting the value for the retransmission timer
 is based on local policies and the network environment.  The default
 value of the retransmission timer for the Access Report TLV SHOULD be
 three seconds.  An implementation MUST provide control of the
 retransmission timer value and the number of retransmissions.
 The Access Report TLV is used by the Performance Measurement Function
 (PMF) components of the Access Steering, Switching, and Splitting
 feature for 5G networks [TS23501].  The PMF component in the User
 Equipment acts as the STAMP Session-Sender, and the PMF component in
 the User Plane Function acts as the STAMP Session-Reflector.

4.7. Follow-Up Telemetry TLV

 A Session-Reflector might be able to put only an "SW Local" (see
 Table 9) timestamp in the Follow-Up Timestamp field.  But the hosting
 system might provide a timestamp closer to the start of the actual
 packet transmission even though it is not possible to deliver the
 information to the Session-Sender in time for the packet itself.
 This timestamp might nevertheless be important for the Session-
 Sender, as it improves the accuracy of network delay measurement by
 minimizing the impact of egress queuing delays on the measurement.
 A STAMP Session-Sender MAY include the Follow-Up Telemetry TLV to
 request information from the Session-Reflector.  The Session-Sender
 MUST set the Follow-Up Telemetry Type and Length fields to their
 appropriate values.  The Sequence Number and Follow-Up Timestamp
 fields MUST be zeroed on transmission by the Session-Sender and
 ignored by the Session-Reflector upon receipt of the STAMP test
 packet that includes the Follow-Up Telemetry TLV.  The Session-
 Reflector MUST validate the Length value of the STAMP test packet.
 If the value of the Length field is invalid, the Session-Reflector
 MUST zero the Sequence Number and Follow-Up Timestamp fields and set
 the M flag in the STAMP TLV Flags field in the reflected packet.  If
 the Session-Reflector is in the stateless mode (defined in
 Section 4.2 of [RFC8762]), it MUST zero the Sequence Number and
 Follow-Up Timestamp fields.
      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |STAMP TLV Flags|      Type     |           Length              |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                        Sequence Number                        |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                      Follow-Up Timestamp                      |
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |  Timestamp M  |                     Reserved                  |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                   Figure 15: Follow-Up Telemetry TLV
 The fields are defined as follows:
 STAMP TLV Flags:  An eight-bit field.  Its format is presented in
    Figure 6.
 Type:  A one-octet field.  Value 7 has been allocated by IANA
    (Section 5.1).
 Length:  A two-octet field, set equal to the value 16 octets.
 Sequence Number:  A four-octet field indicating the sequence number
    of the last packet reflected in the same STAMP test session.
    Since the Session-Reflector runs in the stateful mode (defined in
    Section 4.2 of [RFC8762]), it is the Session-Reflector's Sequence
    Number of the previous reflected packet.
 Follow-Up Timestamp:  An eight-octet field, with the format indicated
    by the Z flag of the Error Estimate field of the STAMP base
    packet, which is contained in this reflected test packet
    transmitted by a Session-Reflector, as described in Section 4.2.1
    of [RFC8762].  It carries the timestamp when the reflected packet
    with the specified sequence number was sent.
 Timestamp M(ode):  A one-octet field that characterizes the method by
    which the entity that transmits a reflected STAMP packet obtained
    the Follow-Up Timestamp.  Table 9 lists the possible values.
 Reserved:  A three-octet field.  Its value MUST be zeroed on
    transmission and ignored on receipt.

4.8. HMAC TLV

 The STAMP authenticated mode protects the integrity of data collected
 in the STAMP base packet.  STAMP extensions are designed to provide
 valuable information about the condition of a network, and protecting
 the integrity of that data is also essential.  All authenticated
 STAMP base packets (per Sections 4.2.2 and 4.3.2 of [RFC8762])
 compatible with this specification MUST additionally authenticate the
 optional TLVs by including the keyed Hashed Message Authentication
 Code (HMAC) TLV, with the sole exception of when there is only one
 TLV present and it is the Extended Padding TLV.  The HMAC TLV MUST
 follow all TLVs included in a STAMP test packet except for the Extra
 Padding TLV.  If the HMAC TLV appears in any other position in a
 STAMP extended test packet, then the situation MUST be processed as
 HMAC verification failure, as defined below in this section.  The
 HMAC TLV MAY be used to protect the integrity of STAMP extensions in
 the STAMP unauthenticated mode.  An implementation of STAMP
 extensions MUST provide controls to enable the integrity protection
 of STAMP extensions in the STAMP unauthenticated mode.
     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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |STAMP TLV Flags|      Type     |             Length            |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    |                              HMAC                             |
    |                                                               |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                          Figure 16: HMAC TLV
 The fields are defined as follows:
 STAMP TLV Flags:  An eight-bit field.  Its format is presented in
    Figure 6.
 Type:  A one-octet field.  Value 8 has been allocated by IANA
    (Section 5.1).
 Length:  A two-octet field, set equal to the value 16 octets.
 HMAC:  A 16-octet field that carries the HMAC digest of the text of
    all preceding TLVs.
 As defined in [RFC8762], STAMP uses HMAC-SHA-256 truncated to 128
 bits (see [RFC4868]).  All considerations regarding using the key
 listed in Section 4.4 of [RFC8762] are fully applicable to the use of
 the HMAC TLV.  Key management and the mechanisms to distribute the
 HMAC key are outside the scope of this specification.  The HMAC TLV
 is anticipated to track updates in the base STAMP protocol [RFC8762],
 including the use of more advanced cryptographic algorithms.  HMAC is
 calculated as defined in [RFC2104] over text as the concatenation of
 the Sequence Number field of the base STAMP packet and all preceding
 TLVs.  The digest then MUST be truncated to 128 bits and written into
 the HMAC field.  If the HMAC TLV is present in the extended STAMP
 test packet, e.g., in the authenticated mode, HMAC MUST be verified
 before using any data in the included STAMP TLVs.  If HMAC
 verification by the Session-Reflector fails, then the Session-
 Reflector MUST stop processing the received extended STAMP test
 packet.  The Session-Reflector MUST copy the TLVs from the received
 STAMP test packet into the reflected packet.  The Session-Reflector
 MUST set the I flag in each TLV copied over into the reflected packet
 to 1 before transmitting the reflected test packet.  If the Session-
 Sender receives the extended STAMP test packet with I flag set to 1,
 then the Session-Sender MUST stop processing TLVs in the reflected
 test packet.  If HMAC verification by the Session-Sender fails, then
 the Session-Sender MUST stop processing TLVs in the reflected
 extended STAMP packet.

5. IANA Considerations

 IANA has created the following subregistries under the "Simple Two-
 way Active Measurement Protocol (STAMP) TLV Types" registry.

5.1. STAMP TLV Types Subregistry

 IANA has created the "STAMP TLV Types" subregistry.  The code points
 in this registry are allocated according to the registration
 procedures [RFC8126] described in Table 1.
                +===========+=========================+
                | Range     | Registration Procedures |
                +===========+=========================+
                | 1 - 175   |       IETF Review       |
                +-----------+-------------------------+
                | 176 - 239 | First Come First Served |
                +-----------+-------------------------+
                | 240 - 251 |     Experimental Use    |
                +-----------+-------------------------+
                | 252 - 254 |       Private Use       |
                +-----------+-------------------------+
                    Table 1: Registration Procedures
                  for the STAMP TLV Types Subregistry
 Per this document, IANA has allocated the following values in the
 "STAMP TLV Types" subregistry:
             +=======+=======================+===========+
             | Value |      Description      | Reference |
             +=======+=======================+===========+
             | 0     |        Reserved       | RFC 8972  |
             +-------+-----------------------+-----------+
             | 1     |     Extra Padding     | RFC 8972  |
             +-------+-----------------------+-----------+
             | 2     |        Location       | RFC 8972  |
             +-------+-----------------------+-----------+
             | 3     | Timestamp Information | RFC 8972  |
             +-------+-----------------------+-----------+
             | 4     |    Class of Service   | RFC 8972  |
             +-------+-----------------------+-----------+
             | 5     |   Direct Measurement  | RFC 8972  |
             +-------+-----------------------+-----------+
             | 6     |     Access Report     | RFC 8972  |
             +-------+-----------------------+-----------+
             | 7     |  Follow-Up Telemetry  | RFC 8972  |
             +-------+-----------------------+-----------+
             | 8     |          HMAC         | RFC 8972  |
             +-------+-----------------------+-----------+
             | 255   |        Reserved       | RFC 8972  |
             +-------+-----------------------+-----------+
                        Table 2: STAMP TLV Types

5.2. STAMP TLV Flags Subregistry

 IANA has created the "STAMP TLV Flags" subregistry.  The registration
 procedure is "IETF Review" [RFC8126].  The flags are 8 bits.  Per
 this document, IANA has allocated the following bit positions in the
 "STAMP TLV Flags" subregistry.
    +==============+========+========================+===========+
    | Bit position | Symbol |      Description       | Reference |
    +==============+========+========================+===========+
    |      0       |   U    |    Unrecognized TLV    |  RFC 8972 |
    +--------------+--------+------------------------+-----------+
    |      1       |   M    |     Malformed TLV      |  RFC 8972 |
    +--------------+--------+------------------------+-----------+
    |      2       |   I    | Integrity check failed |  RFC 8972 |
    +--------------+--------+------------------------+-----------+
                       Table 3: STAMP TLV Flags

5.3. STAMP Sub-TLV Types Subregistry

 IANA has created the "STAMP Sub-TLV Types" subregistry.  The code
 points in this registry are allocated according to the registration
 procedures [RFC8126] described in Table 4.
                +===========+=========================+
                |   Range   | Registration Procedures |
                +===========+=========================+
                | 1 - 175   |       IETF Review       |
                +-----------+-------------------------+
                | 176 - 239 | First Come First Served |
                +-----------+-------------------------+
                | 240 - 251 |     Experimental Use    |
                +-----------+-------------------------+
                | 252 - 254 |       Private Use       |
                +-----------+-------------------------+
                    Table 4: Registration Procedures
                      for the STAMP Sub-TLV Types
                              Subregistry
 Per this document, IANA has allocated the following values in the
 "STAMP Sub-TLV Types" subregistry:
      +=======+==========================+==========+===========+
      | Value |       Description        | TLV Used | Reference |
      +=======+==========================+==========+===========+
      | 0     |         Reserved         |          | RFC 8972  |
      +-------+--------------------------+----------+-----------+
      | 1     |    Source MAC Address    | Location | RFC 8972  |
      +-------+--------------------------+----------+-----------+
      | 2     |  Source EUI-48 Address   | Location | RFC 8972  |
      +-------+--------------------------+----------+-----------+
      | 3     |  Source EUI-64 Address   | Location | RFC 8972  |
      +-------+--------------------------+----------+-----------+
      | 4     |  Destination IP Address  | Location | RFC 8972  |
      +-------+--------------------------+----------+-----------+
      | 5     | Destination IPv4 Address | Location | RFC 8972  |
      +-------+--------------------------+----------+-----------+
      | 6     | Destination IPv6 Address | Location | RFC 8972  |
      +-------+--------------------------+----------+-----------+
      | 7     |    Source IP Address     | Location | RFC 8972  |
      +-------+--------------------------+----------+-----------+
      | 8     |   Source IPv4 Address    | Location | RFC 8972  |
      +-------+--------------------------+----------+-----------+
      | 9     |   Source IPv6 Address    | Location | RFC 8972  |
      +-------+--------------------------+----------+-----------+
      | 255   |         Reserved         |          | RFC 8972  |
      +-------+--------------------------+----------+-----------+
                      Table 5: STAMP Sub-TLV Types

5.4. STAMP Synchronization Sources Subregistry

 IANA has created the "STAMP Synchronization Sources" subregistry.
 The code points in this registry are allocated according to the
 registration procedures [RFC8126] described in Table 6.
                +===========+=========================+
                | Range     | Registration Procedures |
                +===========+=========================+
                | 1 - 127   |       IETF Review       |
                +-----------+-------------------------+
                | 128 - 239 | First Come First Served |
                +-----------+-------------------------+
                | 240 - 249 |     Experimental Use    |
                +-----------+-------------------------+
                | 250 - 254 |       Private Use       |
                +-----------+-------------------------+
                    Table 6: Registration Procedures
                     for the STAMP Synchronization
                          Sources Subregistry
 Per this document, IANA has allocated the following values in the
 "STAMP Synchronization Sources" subregistry:
        +=======+=================================+===========+
        | Value |           Description           | Reference |
        +=======+=================================+===========+
        | 0     |             Reserved            | RFC 8972  |
        +-------+---------------------------------+-----------+
        | 1     |               NTP               | RFC 8972  |
        +-------+---------------------------------+-----------+
        | 2     |               PTP               | RFC 8972  |
        +-------+---------------------------------+-----------+
        | 3     |             SSU/BITS            | RFC 8972  |
        +-------+---------------------------------+-----------+
        | 4     | GPS/GLONASS/LORAN-C/BDS/Galileo | RFC 8972  |
        +-------+---------------------------------+-----------+
        | 5     |        Local free-running       | RFC 8972  |
        +-------+---------------------------------+-----------+
        | 255   |             Reserved            | RFC 8972  |
        +-------+---------------------------------+-----------+
                 Table 7: STAMP Synchronization Sources

5.5. STAMP Timestamping Methods Subregistry

 IANA has created the "STAMP Timestamping Methods" subregistry.  The
 code points in this registry are allocated according to the
 registration procedures [RFC8126] described in Table 8.
                +===========+=========================+
                | Range     | Registration Procedures |
                +===========+=========================+
                | 1 - 127   |       IETF Review       |
                +-----------+-------------------------+
                | 128 - 239 | First Come First Served |
                +-----------+-------------------------+
                | 240 - 249 |     Experimental Use    |
                +-----------+-------------------------+
                | 250 - 254 |       Private Use       |
                +-----------+-------------------------+
                    Table 8: Registration Procedures
                   for the STAMP Timestamping Methods
                              Subregistry
 Per this document, IANA has allocated the following values in the
 "STAMP Timestamping Methods" subregistry:
                 +=======+===============+===========+
                 | Value |  Description  | Reference |
                 +=======+===============+===========+
                 | 0     |    Reserved   | RFC 8972  |
                 +-------+---------------+-----------+
                 | 1     |   HW Assist   | RFC 8972  |
                 +-------+---------------+-----------+
                 | 2     |    SW Local   | RFC 8972  |
                 +-------+---------------+-----------+
                 | 3     | Control Plane | RFC 8972  |
                 +-------+---------------+-----------+
                 | 255   |    Reserved   | RFC 8972  |
                 +-------+---------------+-----------+
                  Table 9: STAMP Timestamping Methods

5.6. STAMP Return Codes Subregistry

 IANA has created the "STAMP Return Codes" subregistry.  The code
 points in this registry are allocated according to the registration
 procedures [RFC8126] described in Table 10.
                +===========+=========================+
                | Range     | Registration Procedures |
                +===========+=========================+
                | 1 - 127   |       IETF Review       |
                +-----------+-------------------------+
                | 128 - 239 | First Come First Served |
                +-----------+-------------------------+
                | 240 - 249 |     Experimental Use    |
                +-----------+-------------------------+
                | 250 - 254 |       Private Use       |
                +-----------+-------------------------+
                   Table 10: Registration Procedures
                       for the STAMP Return Codes
                              Subregistry
 Per this document, IANA has allocated the following values in the
 "STAMP Return Codes" subregistry:
              +=======+=====================+===========+
              | Value |     Description     | Reference |
              +=======+=====================+===========+
              | 0     |       Reserved      | RFC 8972  |
              +-------+---------------------+-----------+
              | 1     |  Network available  | RFC 8972  |
              +-------+---------------------+-----------+
              | 2     | Network unavailable | RFC 8972  |
              +-------+---------------------+-----------+
              | 255   |       Reserved      | RFC 8972  |
              +-------+---------------------+-----------+
                      Table 11: STAMP Return Codes

6. Security Considerations

 This document defines extensions to STAMP [RFC8762] and inherits all
 the security considerations applicable to the base protocol.
 Additionally, the HMAC TLV is defined in this document.  Though the
 HMAC TLV protects the integrity of STAMP extensions, it does not
 protect against a replay attack.  The use of the HMAC TLV is
 discussed in detail in Section 4.8.
 To protect against a malformed TLV, an implementation of a Session-
 Sender and Session-Reflector MUST:
  • check the setting of the M flag and
  • validate the Length field value.
 As this specification defines the mechanism to test DSCP mapping,
 this document inherits all the security considerations discussed in
 [RFC2474].  Monitoring and optional control of DSCP using the CoS TLV
 may be used across the Internet so that the Session-Sender and the
 Session-Reflector are located in domains that use different CoS
 profiles.  Thus, it is essential that an operator verify the set of
 CoS values that is used in the Session-Reflector's domain.  Also, an
 implementation of a Session-Reflector SHOULD support a local policy
 to confirm whether the value sent by the Session-Sender can be used
 as the value of the DSCP field.  Section 4.4 defines the use of that
 local policy.

7. References

7.1. Normative References

 [RFC2104]  Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
            Hashing for Message Authentication", RFC 2104,
            DOI 10.17487/RFC2104, February 1997,
            <https://www.rfc-editor.org/info/rfc2104>.
 [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>.
 [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
            Writing an IANA Considerations Section in RFCs", BCP 26,
            RFC 8126, DOI 10.17487/RFC8126, June 2017,
            <https://www.rfc-editor.org/info/rfc8126>.
 [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>.
 [RFC8762]  Mirsky, G., Jun, G., Nydell, H., and R. Foote, "Simple
            Two-Way Active Measurement Protocol", RFC 8762,
            DOI 10.17487/RFC8762, March 2020,
            <https://www.rfc-editor.org/info/rfc8762>.

7.2. Informative References

 [GPS]      "Global Positioning System (GPS) Standard Positioning
            Service (SPS) Performance Standard", GPS SPS 5th Edition,
            April 2020.
 [IEEE.1588.2008]
            "IEEE Standard for a Precision Clock Synchronization
            Protocol for Networked Measurement and Control Systems",
            IEEE Std. 1588-2008, DOI 10.1109/IEEESTD.2008.4579760,
            July 2008, <https://doi.org/10.1109/IEEESTD.2008.4579760>.
 [NUM-IDS-GEN]
            Gont, F. and I. Arce, "On the Generation of Transient
            Numeric Identifiers", Work in Progress, Internet-Draft,
            draft-irtf-pearg-numeric-ids-generation-06, 13 January
            2021, <https://tools.ietf.org/html/draft-irtf-pearg-
            numeric-ids-generation-06>.
 [RFC2474]  Nichols, K., Blake, S., Baker, F., and D. Black,
            "Definition of the Differentiated Services Field (DS
            Field) in the IPv4 and IPv6 Headers", RFC 2474,
            DOI 10.17487/RFC2474, December 1998,
            <https://www.rfc-editor.org/info/rfc2474>.
 [RFC4868]  Kelly, S. and S. Frankel, "Using HMAC-SHA-256, HMAC-SHA-
            384, and HMAC-SHA-512 with IPsec", RFC 4868,
            DOI 10.17487/RFC4868, May 2007,
            <https://www.rfc-editor.org/info/rfc4868>.
 [RFC5357]  Hedayat, K., Krzanowski, R., Morton, A., Yum, K., and J.
            Babiarz, "A Two-Way Active Measurement Protocol (TWAMP)",
            RFC 5357, DOI 10.17487/RFC5357, October 2008,
            <https://www.rfc-editor.org/info/rfc5357>.
 [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>.
 [TS23501]  3GPP, "Technical Specification Group Services and System
            Aspects; System Architecture for the 5G System (5GS);
            Stage 2 (Release 16)", 3GPP TS 23.501, 2019.

Acknowledgments

 The authors very much appreciate the thorough review and thoughtful
 comments received from Tianran Zhou, Rakesh Gandhi, Yuezhong Song,
 and Yali Wang.  The authors express their gratitude to Al Morton for
 his comments and valuable suggestions.  The authors greatly
 appreciate the comments and thoughtful suggestions received from
 Martin Duke.

Contributors

 The following individual contributed text to this document:
 Guo Jun
 ZTE Corporation
 68# Zijinghua Road
 Nanjing
 Jiangsu, 210012
 China
 Phone: +86 18105183663
 Email: guo.jun2@zte.com.cn

Authors' Addresses

 Greg Mirsky
 ZTE Corp.
 Email: gregimirsky@gmail.com
 Xiao Min
 ZTE Corp.
 Email: xiao.min2@zte.com.cn
 Henrik Nydell
 Accedian Networks
 Email: hnydell@accedian.com
 Richard Foote
 Nokia
 Email: footer.foote@nokia.com
 Adi Masputra
 Apple Inc.
 One Apple Park Way
 Cupertino, CA 95014
 United States of America
 Email: adi@apple.com
 Ernesto Ruffini
 OutSys
 via Caracciolo, 65
 20155 Milan
 Italy
 Email: eruffini@outsys.org
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