Support of the IEEE 1588 Timestamp Format in a Two-Way Active Measurement Protocol (TWAMP)
RFC 8186

Internet Engineering Task Force (IETF)                         G. Mirsky
Request for Comments: 8186                                     ZTE Corp.
Category: Standards Track                                      I. Meilik
ISSN: 2070-1721                                                 Broadcom
                                                               June 2017

             Support of the IEEE 1588 Timestamp Format in a
              Two-Way Active Measurement Protocol (TWAMP)

Abstract

   This document describes an OPTIONAL feature for active performance
   measurement protocols that allows use of the Precision Time Protocol
   timestamp format defined in IEEE 1588v2, as an alternative to the
   Network Time Protocol that is currently used.

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
   http://www.rfc-editor.org/info/rfc8186.

Copyright Notice

   Copyright (c) 2017 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   described in the Simplified BSD License.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Conventions Used in This Document . . . . . . . . . . . .   3
       1.1.1.  Terminology . . . . . . . . . . . . . . . . . . . . .   3
       1.1.2.  Requirements Language . . . . . . . . . . . . . . . .   3
   2.  OWAMP and TWAMP Extensions  . . . . . . . . . . . . . . . . .   3
     2.1.  Timestamp Format Negotiation in OWAMP Connection Setup  .   4
     2.2.  Timestamp Format Negotiation in TWAMP Connection Setup  .   5
     2.3.  OWAMP-Test and TWAMP-Test Updates . . . . . . . . . . . .   5
       2.3.1.  Consideration for TWAMP Light Mode  . . . . . . . . .   6
   3.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   5.  Normative References  . . . . . . . . . . . . . . . . . . . .   7
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .   7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Introduction

   The One-Way Active Measurement Protocol (OWAMP) [RFC4656] defines
   that only the NTP format [RFC5905] of a timestamp can be used in the
   OWAMP-Test protocol.  The Two-Way Active Measurement Protocol (TWAMP)
   [RFC5357] adopted the OWAMP-Test packet format and extended it by
   adding a format for a reflected test packet.  Both the sender's and
   reflector's packets timestamps are expected to follow the 64-bit-long
   NTP format [RFC5905].  NTP, when used over the Internet, typically
   achieves clock accuracy within 5 ms to 100 ms.  Surveys conducted
   recently suggest that 90% of devices achieve accuracy better than 100
   ms and 99% of devices achieve accuracy better than 1 sec.  It should
   be noted that NTP synchronizes clocks on the control plane, not on
   data plane.  Distribution of clock within a node may be supported by
   an independent NTP domain or via interprocess communication in a
   multiprocessor distributed system.  Any of the mentioned solutions
   will be subject to additional queuing delays that negatively affect
   data-plane clock accuracy.

   The Precision Time Protocol (PTP) [IEEE.1588] has gained wide support
   since the development of OWAMP and TWAMP.  PTP, using on-path support
   and other mechanisms, allows sub-microsecond clock accuracy.  PTP is
   now supported in multiple implementations of fast-forwarding engines;
   thus, accuracy achieved by PTP is the accuracy of the clock in the
   data plane.  Having an option to use a more accurate clock as a
   source of timestamps for IP performance measurements is one of the
   advantages of this specification.  Another advantage is realized by
   simplification of hardware in the data plane.  To support OWAMP or
   TWAMP, test protocol timestamps must be converted from PTP to NTP.
   That requires resources, use of microcode or additional processing
   elements, that are always limited.  To address this, this document

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   proposes optional extensions to Control and Test protocols to support
   use of the IEEE 1588v2 timestamp format as an optional alternative to
   the NTP timestamp format.

   One of the goals of this specification is not only to allow endpoints
   of a test session to use a timestamp format other than NTP, but to
   support backwards compatibility with nodes that do not yet support
   this extension.

1.1.  Conventions Used in This Document

1.1.1.  Terminology

   NTP: Network Time Protocol

   PTP: Precision Time Protocol

   TWAMP: Two-Way Active Measurement Protocol

   OWAMP: One-Way Active Measurement Protocol

1.1.2.  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.

2.  OWAMP and TWAMP Extensions

   OWAMP connection establishment follows the procedure defined in
   Section 3.1 of [RFC4656] and additional steps in TWAMP described in
   Section 3.1 of [RFC5357].  In these procedures, the Modes field has
   been used to identify and select specific communication capabilities.
   At the same time, the Modes field has been recognized and used as an
   extension mechanism [RFC6038].  The new feature requires one bit
   position for the Server and Control-Client to negotiate which
   timestamp format can be used in some or all test sessions invoked
   with this control connection.  The endpoint of the test session,
   Session-Sender and Session-Receiver (for OWAMP) or Session-Reflector
   (for TWAMP), that supports this extension MUST be capable of
   interpreting the NTP and PTPv2 timestamp formats.  If the endpoint
   does not support this extension, then the value of the PTPv2
   Timestamp flag MUST be 0 because it is in Must Be Zero field.  If the
   value of the PTPv2 Timestamp flag is 0, then the advertising node can
   use and interpret only the NTP timestamp format.  Implementations of
   OWAMP and/or TWAMP MAY provide a configuration knob to bypass the

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   timestamp format negotiation process and use the locally configured
   values instead.

   Use of PTPv2 Timestamp flags is discussed in the following
   subsections.  For details on the assigned values and bit positions,
   see the Section 3.

2.1.  Timestamp Format Negotiation in OWAMP Connection Setup

   In OWAMP-Test [RFC4656], the Session-Receiver and/or Fetch-Client
   interpret collected timestamps.  Thus, the Server uses the Modes
   field timestamp format to indicate which formats the Session-Receiver
   is capable of interpreting.  The Control-Client inspects values set
   by the Server for timestamp formats and sets values in the Modes
   field of the Set-Up-Response message according to the timestamp
   formats the Session-Sender can use.  The rules for setting timestamp
   flags in the Modes field in Server Greeting and Set-Up-Response
   messages and interpreting them are as follows:

   o  If the Session-Receiver supports this extension, then the Server
      that establishes test sessions on its behalf MUST set the PTPv2
      Timestamp flag to 1 in the Server Greeting message per the
      requirement listed in Section 2.  Otherwise, the PTPv2 Timestamp
      flag will be set to 0 to indicate that the Session-Receiver
      interprets only the NTP format.

   o  If the Control-Client receives a greeting message with the PTPv2
      Timestamp flag set to 0, then the Session-Sender MUST use the NTP
      format for the timestamp in the test session, and the Control-
      Client SHOULD set the PTPv2 Timestamp flag to 0 in accordance with
      [RFC4656].  If the Session-Sender cannot use NTP timestamps, then
      the Control-Client SHOULD close the TCP connection associated with
      the OWAMP-Control session.

   o  If the Control-Client receives a greeting message with the PTPv2
      Timestamp flag set to 1 and the Session-Sender can set the
      timestamp in PTPv2 format, then the Control-Client MUST set the
      PTPv2 Timestamp flag to 1 in the Modes field in the Set-Up-
      Response message and the Session-Sender MUST use PTPv2 timestamp
      format.

   o  If the Session-Sender doesn't support this extension and can set
      the timestamp in NTP format only, then the PTPv2 Timestamp flag in
      the Modes field in the Set-Up-Response message will be set to 0 as
      part of the Must Be Zero field and the Session-Sender will use the
      NTP format.

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   If OWAMP-Control uses Fetch-Session commands, then selection and use
   of one timestamp format or another is a local decision for both
   Session-Sender and Session-Receiver.

2.2.  Timestamp Format Negotiation in TWAMP Connection Setup

   In TWAMP-Test [RFC5357], the Session-Sender interprets collected
   timestamps.  Hence, in the Modes field, a Server advertises timestamp
   formats that the Session-Reflector can use in the TWAMP-Test message.
   The choice of the timestamp format to be used by the Session-Sender
   is a local decision.  The Control-Client inspects the Modes field and
   sets timestamp flag values to indicate the format that will be used
   by the Session-Reflector.  The rules of setting and interpreting flag
   values are as follows:

   o  The Server MUST set the PTPv2 Timestamp flag value to 1 in its
      greeting message if the Session-Reflector can set the timestamp in
      the PTPv2 format.  Otherwise, the PTPv2 Timestamp flag MUST be set
      to 0.

   o  If the value of the PTPv2 Timestamp flag in the received Server
      Greeting message is 0, then the Session-Reflector does not support
      this extension and will use the NTP timestamp format.  The
      Control-Client SHOULD set the PTPv2 Timestamp flag to 0 in the
      Set-Up-Response message in accordance with [RFC4656].

   o  The Control-Client MUST set the PTPv2 Timestamp flag value to 1 in
      the Modes field in the Set-Up-Response message if the Server
      advertised that the Session-Reflector has the ability to use the
      PTPv2 format for timestamps.  Otherwise, the flag MUST be set to
      0.

   o  If the value of the PTPv2 Timestamp flag in the Set-Up-Response
      message is 0, then that means that the Session-Sender can only
      interpret the NTP timestamp format.  Therefore, the Session-
      Reflector MUST use the NTP timestamp format.  If the Session-
      Reflector does not support the NTP format, then the Server MUST
      close the TCP connection associated with the TWAMP-Control
      session.

2.3.  OWAMP-Test and TWAMP-Test Updates

   Participants of a test session need to indicate which timestamp
   format is being used.  Currently, the Z field in the Error Estimate
   defined in Section 4.1.2 of [RFC4656] is used for this purpose.
   However, this document extends the Error Estimate to indicate the
   format of a collected timestamp, in addition to the estimate of error
   and synchronization.  This specification also changes the semantics

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   of the Z bit field (the field between S and Scale fields) to be
   referred to as the Timestamp format; the value MUST be set as
   follows:

   o  0 - NTP 64-bit format of a timestamp.

   o  1 - PTPv2-truncated format of a timestamp.

   As a result of this value of the Z field from the Error Estimate, the
   Sender Error Estimate (in TWAMP) or Send Error Estimate (in OWAMP)
   and Receive Error Estimate SHOULD NOT be ignored and MUST be used
   when calculating delay and delay-variation metrics based on collected
   timestamps.

2.3.1.  Consideration for TWAMP Light Mode

   This document does not specify how the Session-Sender and Session-
   Reflector in TWAMP Light mode are informed of the timestamp format to
   be used.  It is assumed that, for example, configuration could be
   used to direct the Session-Sender and Session-Reflector to use the
   timestamp format per their capabilities and rules listed in
   Section 2.2.

3.  IANA Considerations

   IANA has registered a new PTPv2 Timestamp in the "TWAMP-Modes"
   registry [RFC5618] as follows:

   +------+-----------------------------+-----------+------------------+
   | Bit  | Description                 | Semantics | Reference        |
   | Pos  |                             |           |                  |
   +------+-----------------------------+-----------+------------------+
   | 9    | PTPv2 Timestamp Capability  | Section 2 | RFC 8186 (this   |
   |      |                             |           | document)        |
   +------+-----------------------------+-----------+------------------+

                     Table 1: New Timestamp Capability

4.  Security Considerations

   Use of a particular timestamp format in a test session does not
   appear to introduce any additional security threat to hosts that
   communicate with OWAMP and/or TWAMP as defined in [RFC4656] and
   [RFC5357], respectively.  The security considerations that apply to
   any active measurement of live networks are relevant here as well.
   See the Security Considerations sections in [RFC4656] and [RFC5357].

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5.  Normative References

   [IEEE.1588]
              IEEE, "IEEE Standard for a Precision Clock Synchronization
              Protocol for Networked Measurement and Control Systems",
              IEEE Std 1588-2008, DOI 10.1109/IEEESTD.2008.4579760.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC4656]  Shalunov, S., Teitelbaum, B., Karp, A., Boote, J., and M.
              Zekauskas, "A One-way Active Measurement Protocol
              (OWAMP)", RFC 4656, DOI 10.17487/RFC4656, September 2006,
              <http://www.rfc-editor.org/info/rfc4656>.

   [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,
              <http://www.rfc-editor.org/info/rfc5357>.

   [RFC5618]  Morton, A. and K. Hedayat, "Mixed Security Mode for the
              Two-Way Active Measurement Protocol (TWAMP)", RFC 5618,
              DOI 10.17487/RFC5618, August 2009,
              <http://www.rfc-editor.org/info/rfc5618>.

   [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,
              <http://www.rfc-editor.org/info/rfc5905>.

   [RFC6038]  Morton, A. and L. Ciavattone, "Two-Way Active Measurement
              Protocol (TWAMP) Reflect Octets and Symmetrical Size
              Features", RFC 6038, DOI 10.17487/RFC6038, October 2010,
              <http://www.rfc-editor.org/info/rfc6038>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <http://www.rfc-editor.org/info/rfc8174>.

Acknowledgements

   The authors would like to thank Ramanathan Lakshmikanthan and Suchit
   Bansal for their insightful suggestions.  The authors would also like
   to thank David Allan for his thorough review and thoughtful comments.

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Authors' Addresses

   Greg Mirsky
   ZTE Corp.

   Email: gregimirsky@gmail.com

   Israel Meilik
   Broadcom

   Email: israel@broadcom.com

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