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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Mirsky & Meilik Standards Track [Page 1]RFC 8186 1588 Timestamp Format in TWAMP June 2017
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
Mirsky & Meilik Standards Track [Page 2]RFC 8186 1588 Timestamp Format in TWAMP June 2017
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
Mirsky & Meilik Standards Track [Page 3]
RFC 8186 1588 Timestamp Format in TWAMP June 2017
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.
Mirsky & Meilik Standards Track [Page 4]RFC 8186 1588 Timestamp Format in TWAMP June 2017
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
Mirsky & Meilik Standards Track [Page 5]RFC 8186 1588 Timestamp Format in TWAMP June 2017
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].
Mirsky & Meilik Standards Track [Page 6]RFC 8186 1588 Timestamp Format in TWAMP June 2017
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.
Mirsky & Meilik Standards Track [Page 7]RFC 8186 1588 Timestamp Format in TWAMP June 2017
Authors' Addresses
Greg Mirsky
ZTE Corp.
Email: gregimirsky@gmail.com
Israel Meilik
Broadcom
Email: israel@broadcom.com
Mirsky & Meilik Standards Track [Page 8]
