Internet Engineering Task Force (IETF) Y. Jiang, Ed.

Internet Engineering Task Force (IETF) Y. Jiang, Ed.
Request for Comments: 8575 Huawei
Category: Standards Track X. Liu
ISSN: 2070-1721 Independent
J. Xu
Huawei
R. Cummings, Ed.
National Instruments
May 2019

YANG Data Model for the Precision Time Protocol (PTP)

Abstract

This document defines a YANG data model for the configuration of
devices and clocks using the Precision Time Protocol (PTP) as
specified in IEEE Std 1588-2008. It also defines the retrieval of
the configuration information, the data sets and the running states
of PTP clocks. The YANG module in this document conforms to the
Network Management Datastore Architecture (NMDA).

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/rfc8575.

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Copyright Notice

Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved.

This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(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
1.1. Conventions Used in This Document . . . . . . . . . . . . 4
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
2. IEEE Std 1588-2008 YANG Data Model Hierarchy . . . . . . . . 5
2.1. Interpretations from IEEE 1588 Working Group . . . . . . 7
2.2. Configuration and State . . . . . . . . . . . . . . . . . 8
3. IEEE Std 1588-2008 YANG Module . . . . . . . . . . . . . . . 9
4. Security Considerations . . . . . . . . . . . . . . . . . . . 21
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 22
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 22
6.1. Normative References . . . . . . . . . . . . . . . . . . 22
6.2. Informative References . . . . . . . . . . . . . . . . . 23
Appendix A. Transferring YANG Work to the IEEE 1588 WG . . . . . 25
A.1. Assumptions for the Transfer . . . . . . . . . . . . . . 26
A.2. Intellectual Property Considerations . . . . . . . . . . 26
A.3. Namespace and Module Name . . . . . . . . . . . . . . . . 27
A.4. IEEE 1588 YANG Modules in ASCII Format . . . . . . . . . 28
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 29
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 30

1. Introduction

As a synchronization protocol, IEEE Std 1588-2008 [IEEE1588] is
widely supported in the carrier networks, industrial networks,
automotive networks, and many other applications. It can provide
high precision time synchronization as fine as nanoseconds. The
protocol depends on a Precision Time Protocol (PTP) engine to decide
its own state automatically, and a PTP transportation layer to carry
the PTP timing and various quality messages. The configuration
parameters and state data sets of IEEE Std 1588-2008 are numerous.

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According to the concepts described in [RFC3444], IEEE Std 1588-2008
itself provides an information model in its normative specifications
for the data sets (in IEEE Std 1588-2008 clause 8). Some
standardization organizations, including the IETF, have specified
data models in MIBs (Management Information Bases) for IEEE Std
1588-2008 data sets (e.g., [RFC8173] and [IEEE8021AS]). These MIBs
are typically focused on retrieval of state data using the Simple
Network Management Protocol (SNMP); furthermore, configuration of PTP
data sets is not considered in [RFC8173].

Some service providers and applications require that the management
of the IEEE Std 1588-2008 synchronization network be flexible and
more Internet based (typically overlaid on their transport networks).
Software-Defined Networking (SDN) is another driving factor, which
demands an improved configuration capability of synchronization
networks.

YANG [RFC7950] is a data modeling language used to model
configuration and state data manipulated by network management
protocols like the Network Configuration Protocol (NETCONF)
[RFC6241]. A small set of built-in data types is defined in
[RFC7950]; a collection of common data types is also defined in
[RFC6991]. Advantages of YANG include Internet-based configuration
capabilities, validation, rollback, and so on. All of these
characteristics make it attractive to become another candidate
modeling language for IEEE Std 1588-2008.

This document defines a YANG data model for the configuration of IEEE
Std 1588-2008 devices and clocks as well as retrieval of the state
data of IEEE Std 1588-2008 clocks. The data model is based on the
PTP data sets as specified in [IEEE1588]. The technology-specific
PTP information (e.g., those specifically implemented by a bridge, a
router, or a telecom profile) is out of scope of this document.

The YANG module in this document conforms to the Network Management
Datastore Architecture (NMDA) [RFC8342].

When used in practice, network products in support of synchronization
typically conform to one or more IEEE Std 1588-2008 profiles. Each
profile specifies how IEEE Std 1588-2008 is used in a given industry
(e.g., telecom or automotive) and application. A profile can require
features that are optional in IEEE Std 1588-2008, and it can specify
new features that use IEEE Std 1588-2008 as a foundation.

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The readers are assumed to be familiar with IEEE Std 1588-2008. It
is expected that the IEEE Std 1588-2008 YANG module will be used as
follows:

- The IEEE Std 1588-2008 YANG module can be used as is for products
that conform to one of the default profiles specified in IEEE Std
1588-2008.

- When the IEEE Std 1588 standard is revised (e.g., the IEEE Std
1588 revision in progress at the time of writing this document),
it will add some new optional features to its data sets. The YANG
module of this document can be revised and extended to support
these new features. Moreover, the YANG "revision" MUST be used to
indicate changes to the YANG module under such a circumstance.

- A profile standard based on IEEE Std 1588-2008 may create a
dedicated YANG module for its profile. The profile's YANG module
SHOULD use YANG "import" to import the IEEE Std 1588-2008 YANG
module as its foundation. Then the profile's YANG module SHOULD
use YANG "augment" to add any profile-specific enhancements.

- A product that conforms to a profile standard may also create its
own YANG module. The product's YANG module SHOULD "import" the
profile's module, and then use YANG "augment" to add any product-
specific enhancements.

1.1. Conventions Used in This Document

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.

1.2. Terminology

Most terminology used in this document is extracted from [IEEE1588].

BC Boundary Clock, see Section 3.1.3 of [IEEE1588]

DS Data Set, see Section 8.1.1 of [IEEE1588]

E2E End-to-End, see Section 3.2 of [IEEE1588]

IANA Internet Assigned Numbers Authority

OC Ordinary Clock, see Section 3.1.22 of [IEEE1588]

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P2P Peer-to-Peer, see Section 3.2 of [IEEE1588]

PTP Precision Time Protocol, see Section 3.1.28 of [IEEE1588]

TAI International Atomic Time, see Section 3.2 of [IEEE1588]

TC Transparent Clock, see Section 3.1.46 of [IEEE1588]

UTC Coordinated Universal Time, see Section 3.2 of [IEEE1588]

PTP data set
Structured attributes of clocks (an OC, BC, or TC) used for PTP
decisions and for providing values for PTP message fields; see
Section 8 of [IEEE1588].

PTP instance
A PTP implementation in the device (i.e., an OC or BC)
represented by a specific PTP data set.

2. IEEE Std 1588-2008 YANG Data Model Hierarchy

This section describes the hierarchy of a YANG module for IEEE Std
1588-2008; specifically, query and configuration of device-wide or
port-specific configuration information and clock data sets are
described.

Query and configuration of clock information include:

(Note: The attribute names are consistent with IEEE Std 1588-2008,
but changed to the YANG style, i.e., using all lowercase, with dashes
between words.)

- Clock data set attributes in a clock node, including the
following: current-ds, parent-ds, default-ds, time-properties-ds,
and transparent-clock-default-ds.

- Port-specific data set attributes, including the following:
port-ds and transparent-clock-port-ds.

As all PTP terminology and PTP data set attributes are described in
detail in IEEE Std 1588-2008, this document only outlines each of
them in the YANG module.

A simplified YANG tree diagram [RFC8340] representing the data model
is typically used by YANG modules. This document uses the same tree
diagram syntax as described in [RFC8340].

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module: ietf-ptp
+--rw ptp
+--rw instance-list* [instance-number]
| +--rw instance-number uint32
| +--rw default-ds
| | +--rw two-step-flag? boolean
| | +--ro clock-identity? clock-identity-type
| | +--rw number-ports? uint16
| | +--rw clock-quality
| | | +--rw clock-class? uint8
| | | +--rw clock-accuracy? uint8
| | | +--rw offset-scaled-log-variance? uint16
| | +--rw priority1? uint8
| | +--rw priority2? uint8
| | +--rw domain-number? uint8
| | +--rw slave-only? boolean
| +--rw current-ds
| | +--rw steps-removed? uint16
| | +--rw offset-from-master? time-interval-type
| | +--rw mean-path-delay? time-interval-type
| +--rw parent-ds
| | +--rw parent-port-identity
| | | +--rw clock-identity? clock-identity-type
| | | +--rw port-number? uint16
| | +--rw parent-stats? boolean
| | +--rw observed-parent-offset-scaled-log-variance? uint16
| | +--rw observed-parent-clock-phase-change-rate? int32
| | +--rw grandmaster-identity? clock-identity-type
| | +--rw grandmaster-clock-quality
| | | +--rw clock-class? uint8
| | | +--rw clock-accuracy? uint8
| | | +--rw offset-scaled-log-variance? uint16
| | +--rw grandmaster-priority1? uint8
| | +--rw grandmaster-priority2? uint8
| +--rw time-properties-ds
| | +--rw current-utc-offset-valid? boolean
| | +--rw current-utc-offset? int16
| | +--rw leap59? boolean
| | +--rw leap61? boolean
| | +--rw time-traceable? boolean
| | +--rw frequency-traceable? boolean
| | +--rw ptp-timescale? boolean
| | +--rw time-source? uint8
| +--rw port-ds-list* [port-number]
| +--rw port-number uint16
| +--rw port-state? port-state-enumeration
| +--rw underlying-interface? if:interface-ref
| +--rw log-min-delay-req-interval? int8

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| +--rw peer-mean-path-delay? time-interval-type
| +--rw log-announce-interval? int8
| +--rw announce-receipt-timeout? uint8
| +--rw log-sync-interval? int8
| +--rw delay-mechanism? delay-mechanism-enumeration
| +--rw log-min-pdelay-req-interval? int8
| +--rw version-number? uint8
+--rw transparent-clock-default-ds
| +--ro clock-identity? clock-identity-type
| +--rw number-ports? uint16
| +--rw delay-mechanism? delay-mechanism-enumeration
| +--rw primary-domain? uint8
+--rw transparent-clock-port-ds-list* [port-number]
+--rw port-number uint16
+--rw log-min-pdelay-req-interval? int8
+--rw faulty-flag? boolean
+--rw peer-mean-path-delay? time-interval-type

2.1. Interpretations from IEEE 1588 Working Group

The preceding model and the associated YANG module have some subtle
differences from the data set specifications of IEEE Std 1588-2008.
These differences are based on interpretation from the IEEE 1588
Working Group, and they are intended to provide compatibility with
future revisions of the IEEE Std 1588 standard.

In IEEE Std 1588-2008, a physical product can implement multiple PTP
clocks (i.e., an ordinary, boundary, or transparent clock). As
specified in IEEE Std 1588-2008 subclause 7.1, each of the multiple
clocks operates in an independent domain. However, the organization
of multiple PTP domains was not clear in the data sets of IEEE Std
1588-2008. This document introduces the concept of a PTP instance,
which is a PTP implementation in a device (i.e., an OC or BC)
represented by a specific PTP data set. Each instance operates in
exactly one domain. The instance concept is used exclusively to
allow for optional support of multiple domains. The instance number
has no usage within PTP messages.

Based on statements in IEEE Std 1588-2008 subclauses 8.3.1 and 10.1,
most transparent clock products have interpreted the transparent
clock data sets to reside as a singleton at the root level of the
managed product, and this YANG data model reflects that location.

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2.2. Configuration and State

The information model of IEEE Std 1588-2008 classifies each member in
PTP data sets as one of the following:

Configurable: Writable by management.

Dynamic: Read-only to management, and the value is changed by
PTP protocol operation.

Static: Read-only to management, and the value typically does
not change.

For details on the classification of each PTP data set member, refer
to the specification of that member in IEEE Std 1588-2008.

Under certain circumstances, the classification of an IEEE Std 1588
data set member may change for a YANG implementation, for example, a
configurable member needs to be changed to read-only. In such a
case, an implementation SHOULD choose to return a warning upon
writing to a read-only member or use the deviation mechanism to
develop a new deviation model as described in Section 7.20.3 of
[RFC7950].

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3. IEEE Std 1588-2008 YANG Module

This module imports typedef "interface-ref" from [RFC8343]. Most
attributes are based on the information model defined in [IEEE1588],
but their names are adapted to the YANG style of naming.

<CODE BEGINS> file "[email protected]"
module ietf-ptp {
yang-version 1.1;
namespace "urn:ietf:params:xml:ns:yang:ietf-ptp";
prefix ptp;

import ietf-interfaces {
prefix if;
reference
"RFC 8343: A YANG Data Model for Interface Management";
}

organization
"IETF TICTOC Working Group";
contact
"WG Web: https://datatracker.ietf.org/wg/tictoc/
WG List: <mailto:[email protected]>
Editor: Yuanlong Jiang
<mailto:[email protected]>
Editor: Rodney Cummings
<mailto:[email protected]>";
description
"This YANG module defines a data model for the configuration
of IEEE Std 1588-2008 clocks, and also for retrieval of the state
data of IEEE Std 1588-2008 clocks.";

revision 2019-05-07 {
description
"Initial version";
reference
"RFC 8575: YANG Data Model for the Precision Time Protocol";
}

typedef delay-mechanism-enumeration {
type enumeration {
enum e2e {
value 1;
description
"The port uses the delay request-response mechanism.";
}
enum p2p {
value 2;

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description
"The port uses the peer delay mechanism.";
}
enum disabled {
value 254;
description
"The port does not implement any delay mechanism.";
}
}
description
"The propagation-delay measuring option used by the
port. Values for this enumeration are specified
by the IEEE Std 1588 standard exclusively.";
reference
"IEEE Std 1588-2008: 8.2.5.4.4";
}

typedef port-state-enumeration {
type enumeration {
enum initializing {
value 1;
description
"The port is initializing its data sets, hardware, and
communication facilities.";
}
enum faulty {
value 2;
description
"The port is in the fault state.";
}
enum disabled {
value 3;
description
"The port is disabled and is not communicating PTP
messages (other than possibly PTP management
messages).";
}
enum listening {
value 4;
description
"The port is listening for an Announce message.";
}
enum pre-master {
value 5;
description
"The port is in the pre-master state.";
}
enum master {

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value 6;
description
"The port is behaving as a master port.";
}
enum passive {
value 7;
description
"The port is in the passive state.";
}
enum uncalibrated {
value 8;
description
"A master port has been selected, but the port is still
in the uncalibrated state.";
}
enum slave {
value 9;
description
"The port is synchronizing to the selected master port.";
}
}
description
"The current state of the protocol engine associated
with the port. Values for this enumeration are specified
by the IEEE Std 1588 standard exclusively.";
reference
"IEEE Std 1588-2008: 8.2.5.3.1, 9.2.5";
}

typedef time-interval-type {
type int64;
description
"Derived data type for time interval, represented in units of
nanoseconds and multiplied by 2^16";
reference
"IEEE Std 1588-2008: 5.3.2";
}

typedef clock-identity-type {
type binary {
length "8";
}
description
"Derived data type to identify a clock";
reference
"IEEE Std 1588-2008: 5.3.4";
}

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grouping clock-quality-grouping {
description
"Derived data type for quality of a clock, which contains
clockClass, clockAccuracy, and offsetScaledLogVariance.";
reference
"IEEE Std 1588-2008: 5.3.7";
leaf clock-class {
type uint8;
default "248";
description
"The clockClass denotes the traceability of the time
or frequency distributed by the clock.";
}
leaf clock-accuracy {
type uint8;
description
"The clockAccuracy indicates the expected accuracy
of the clock.";
}
leaf offset-scaled-log-variance {
type uint16;
description
"The offsetScaledLogVariance provides an estimate of
the variations of the clock from a linear timescale
when it is not synchronized to another clock
using the protocol.";
}
}

container ptp {
description
"The PTP struct containing all attributes of PTP data set,
other optional PTP attributes can be augmented as well.";
list instance-list {
key "instance-number";
description
"List of one or more PTP data sets in the device (see IEEE
Std 1588-2008 subclause 6.3).
Each PTP data set represents a distinct instance of
PTP implementation in the device (i.e., distinct
Ordinary Clock or Boundary Clock).";
leaf instance-number {
type uint32;
description
"The instance number of the current PTP instance.
This instance number is used for management purposes
only. This instance number does not represent the PTP
domain number and is not used in PTP messages.";

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}
container default-ds {
description
"The default data set of the clock (see IEEE Std
1588-2008 subclause 8.2.1). This data set represents
the configuration/state required for operation
of Precision Time Protocol (PTP) state machines.";
reference
"IEEE Std 1588-2008: 8.2.1";
leaf two-step-flag {
type boolean;
description
"When set to true, the clock is a two-step clock;
otherwise,the clock is a one-step clock.";
}
leaf clock-identity {
type clock-identity-type;
config false;
description
"The clockIdentity of the local clock.";
}
leaf number-ports {
type uint16;
description
"The number of PTP ports on the instance.";
}
container clock-quality {
description
"The clockQuality of the local clock.";
uses clock-quality-grouping;
}
leaf priority1 {
type uint8;
description
"The priority1 attribute of the local clock.";
}
leaf priority2 {
type uint8;
description
"The priority2 attribute of the local clock.";
}
leaf domain-number {
type uint8;
description
"The domain number of the current syntonization
domain.";
}
leaf slave-only {

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type boolean;
description
"When set to true, the clock is a slave-only clock.";
}
}
container current-ds {
description
"The current data set of the clock (see IEEE Std
1588-2008 subclause 8.2.2). This data set represents
local states learned from the exchange of
Precision Time Protocol (PTP) messages.";
reference
"IEEE Std 1588-2008: 8.2.2";
leaf steps-removed {
type uint16;
default "0";
description
"The number of communication paths traversed
between the local clock and the grandmaster clock.";
}
leaf offset-from-master {
type time-interval-type;
description
"The current value of the time difference between
a master and a slave clock as computed by the slave.";
}
leaf mean-path-delay {
type time-interval-type;
description
"The current value of the mean propagation time between
a master and a slave clock as computed by the slave.";
}
}
container parent-ds {
description
"The parent data set of the clock (see IEEE Std 1588-2008
subclause 8.2.3).";
reference
"IEEE Std 1588-2008: 8.2.3";
container parent-port-identity {
description
"The portIdentity of the port on the master, it
contains two members: clockIdentity and portNumber.";
reference
"IEEE Std 1588-2008: 5.3.5";
leaf clock-identity {
type clock-identity-type;

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description
"Identity of the clock.";
}
leaf port-number {
type uint16;
description
"Port number.";
}
}
leaf parent-stats {
type boolean;
default "false";
description
"When set to true, the values of
observedParentOffsetScaledLogVariance and
observedParentClockPhaseChangeRate of parentDS
have been measured and are valid.";
}
leaf observed-parent-offset-scaled-log-variance {
type uint16;
default "65535";
description
"An estimate of the parent clock's PTP variance
as observed by the slave clock.";
}
leaf observed-parent-clock-phase-change-rate {
type int32;
description
"An estimate of the parent clock's phase change rate
as observed by the slave clock.";
}
leaf grandmaster-identity {
type clock-identity-type;
description
"The clockIdentity attribute of the grandmaster clock.";
}
container grandmaster-clock-quality {
description
"The clockQuality of the grandmaster clock.";
uses clock-quality-grouping;
}
leaf grandmaster-priority1 {
type uint8;
description
"The priority1 attribute of the grandmaster clock.";
}
leaf grandmaster-priority2 {
type uint8;

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description
"The priority2 attribute of the grandmaster clock.";
}
}
container time-properties-ds {
description
"The timeProperties data set of the clock (see
IEEE Std 1588-2008 subclause 8.2.4).";
reference
"IEEE Std 1588-2008: 8.2.4";
leaf current-utc-offset-valid {
type boolean;
description
"When set to true, the current UTC offset is valid.";
}
leaf current-utc-offset {
when "../current-utc-offset-valid='true'";
type int16;
description
"The offset between TAI and UTC when the epoch of the
PTP system is the PTP epoch in units of seconds, i.e.,
when ptp-timescale is TRUE; otherwise, the value has
no meaning.";
}
leaf leap59 {
type boolean;
description
"When set to true, the last minute of the current UTC
day contains 59 seconds.";
}
leaf leap61 {
type boolean;
description
"When set to true, the last minute of the current UTC
day contains 61 seconds.";
}
leaf time-traceable {
type boolean;
description
"When set to true, the timescale and the
currentUtcOffset are traceable to a primary
reference.";
}
leaf frequency-traceable {
type boolean;
description
"When set to true, the frequency determining the
timescale is traceable to a primary reference.";

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}
leaf ptp-timescale {
type boolean;
description
"When set to true, the clock timescale of the
grandmaster clock is PTP; otherwise, the timescale is
ARB (arbitrary).";
}
leaf time-source {
type uint8;
description
"The source of time used by the grandmaster clock.";
}
}
list port-ds-list {
key "port-number";
description
"List of port data sets of the clock (see IEEE Std
1588-2008 subclause 8.2.5).";
reference
"IEEE Std 1588-2008: 8.2.5";
leaf port-number {
type uint16;
description
"Port number.
The data sets (i.e., information model) of IEEE Std
1588-2008 specify a member portDS.portIdentity, which
uses a typed struct with members clockIdentity and
portNumber.

In this YANG data model, portIdentity is not modeled
in the port-ds-list. However, its members are provided
as follows:
portIdentity.portNumber is provided as this
port-number leaf in port-ds-list, and
portIdentity.clockIdentity is provided as the
clock-identity leaf in default-ds of the instance
(i.e., ../../default-ds/clock-identity).";
}
leaf port-state {
type port-state-enumeration;
default "initializing";
description
"Current state associated with the port.";
}
leaf underlying-interface {
type if:interface-ref;

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description
"Reference to the configured underlying interface that
is used by this PTP port (see RFC 8343).";
reference
"RFC 8343: A YANG Data Model for Interface Management";
}
leaf log-min-delay-req-interval {
type int8;
description
"The base-2 logarithm of the minDelayReqInterval
(the minimum permitted mean time interval between
successive Delay_Req messages).";
}
leaf peer-mean-path-delay {
type time-interval-type;
default "0";
description
"An estimate of the current one-way propagation delay
on the link when the delayMechanism is P2P; otherwise,
it is zero.";
}
leaf log-announce-interval {
type int8;
description
"The base-2 logarithm of the mean
announceInterval (mean time interval between
successive Announce messages).";
}
leaf announce-receipt-timeout {
type uint8;
description
"The number of announceIntervals that have to pass
without receipt of an Announce message before the
occurrence of the event ANNOUNCE_RECEIPT_TIMEOUT_
EXPIRES.";
}
leaf log-sync-interval {
type int8;
description
"The base-2 logarithm of the mean SyncInterval
for multicast messages. The rates for unicast
transmissions are negotiated separately on a per-port
basis and are not constrained by this attribute.";
}
leaf delay-mechanism {
type delay-mechanism-enumeration;

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description
"The propagation delay measuring option used by the
port in computing meanPathDelay.";
}
leaf log-min-pdelay-req-interval {
type int8;
description
"The base-2 logarithm of the
minPdelayReqInterval (minimum permitted mean time
interval between successive Pdelay_Req messages).";
}
leaf version-number {
type uint8;
description
"The PTP version in use on the port.";
}
}
}
container transparent-clock-default-ds {
description
"The members of the transparentClockDefault data set (see
IEEE Std 1588-2008 subclause 8.3.2).";
reference
"IEEE Std 1588-2008: 8.3.2";
leaf clock-identity {
type clock-identity-type;
config false;
description
"The clockIdentity of the transparent clock.";
}
leaf number-ports {
type uint16;
description
"The number of PTP ports on the transparent clock.";
}
leaf delay-mechanism {
type delay-mechanism-enumeration;
description
"The propagation delay measuring option
used by the transparent clock.";
}
leaf primary-domain {
type uint8;
default "0";
description
"The domainNumber of the primary syntonization domain (see
IEEE Std 1588-2008 subclause 10.1).";

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reference
"IEEE Std 1588-2008: 10.1";
}
}
list transparent-clock-port-ds-list {
key "port-number";
description
"List of transparentClockPort data sets of the transparent
clock (see IEEE Std 1588-2008 subclause 8.3.3).";
reference
"IEEE Std 1588-2008: 8.3.3";
leaf port-number {
type uint16;
description
"Port number.
The data sets (i.e., information model) of IEEE Std
1588-2008 specify a member
transparentClockPortDS.portIdentity, which uses a typed
struct with members clockIdentity and portNumber.

In this YANG data model, portIdentity is not modeled in
the transparent-clock-port-ds-list. However, its
members are provided as follows:
portIdentity.portNumber is provided as this leaf member
in transparent-clock-port-ds-list and
portIdentity.clockIdentity is provided as the
clock-identity leaf in transparent-clock-default-ds
(i.e., ../../transparent-clock-default-ds/clock-
identity).";
}
leaf log-min-pdelay-req-interval {
type int8;
description
"The logarithm to the base 2 of the
minPdelayReqInterval (minimum permitted mean time
interval between successive Pdelay_Req messages).";
}
leaf faulty-flag {
type boolean;
default "false";
description
"When set to true, the port is faulty.";
}
leaf peer-mean-path-delay {
type time-interval-type;
default "0";

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description
"An estimate of the current one-way propagation delay
on the link when the delayMechanism is P2P; otherwise,
it is zero.";
}
}
}
}

<CODE ENDS>

4. Security Considerations

The YANG module specified in this document defines a schema for data
that is designed to be accessed via network management protocols such
as NETCONF [RFC6241] or RESTCONF [RFC8040]. The lowest NETCONF layer
is the secure transport layer, and the mandatory-to-implement secure
transport is Secure Shell (SSH) [RFC6242]. The lowest RESTCONF layer
is HTTPS, and the mandatory-to-implement secure transport is TLS
[RFC8446]. Furthermore, general security considerations of time
protocols are discussed in [RFC7384].

The Network Configuration Access Control Model (NACM) [RFC8341]
provides the means to restrict access for particular NETCONF or
RESTCONF users to a preconfigured subset of all available NETCONF or
RESTCONF protocol operations and content.

There are a number of data nodes defined in this YANG module that are
writable, and the involved subtrees that are sensitive include:

/ptp/instance-list specifies an instance (i.e., PTP data sets) for an
OC or BC.

/ptp/transparent-clock-default-ds specifies a default data set for a
TC.

/ptp/transparent-clock-port-ds-list specifies a list of port data
sets for a TC.

Write operations (e.g., edit-config) to these data nodes without
proper protection can have a negative effect on network operations.
Specifically, an inappropriate configuration of them may adversely
impact a PTP synchronization network. For example, loss of
synchronization on a clock, accuracy degradation on a set of clocks,
or even break down of a whole synchronization network.

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5. IANA Considerations

This document registers the following URI in the "IETF XML Registry"
[RFC3688]:

URI: urn:ietf:params:xml:ns:yang:ietf-ptp
Registrant Contact: The IESG
XML: N/A; the requested URI is an XML namespace

This document registers the following YANG module in the "YANG Module
Names" registry [RFC6020]:

Name: ietf-ptp
Namespace: urn:ietf:params:xml:ns:yang:ietf-ptp
Prefix: ptp
Reference: RFC 8575

6. References

6.1. Normative References

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

[RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
DOI 10.17487/RFC3688, January 2004,
<https://www.rfc-editor.org/info/rfc3688>.

[RFC6020] Bjorklund, M., Ed., "YANG - A Data Modeling Language for
the Network Configuration Protocol (NETCONF)", RFC 6020,
DOI 10.17487/RFC6020, October 2010,
<https://www.rfc-editor.org/info/rfc6020>.

[RFC6241] Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
and A. Bierman, Ed., "Network Configuration Protocol
(NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
<https://www.rfc-editor.org/info/rfc6241>.

[RFC6242] Wasserman, M., "Using the NETCONF Protocol over Secure
Shell (SSH)", RFC 6242, DOI 10.17487/RFC6242, June 2011,
<https://www.rfc-editor.org/info/rfc6242>.

[RFC6991] Schoenwaelder, J., Ed., "Common YANG Data Types",
RFC 6991, DOI 10.17487/RFC6991, July 2013,
<https://www.rfc-editor.org/info/rfc6991>.

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[RFC7950] Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
RFC 7950, DOI 10.17487/RFC7950, August 2016,
<https://www.rfc-editor.org/info/rfc7950>.

[RFC8040] Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017,
<https://www.rfc-editor.org/info/rfc8040>.

[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>.

[RFC8341] Bierman, A. and M. Bjorklund, "Network Configuration
Access Control Model", STD 91, RFC 8341,
DOI 10.17487/RFC8341, March 2018,
<https://www.rfc-editor.org/info/rfc8341>.

[RFC8342] Bjorklund, M., Schoenwaelder, J., Shafer, P., Watsen, K.,
and R. Wilton, "Network Management Datastore Architecture
(NMDA)", RFC 8342, DOI 10.17487/RFC8342, March 2018,
<https://www.rfc-editor.org/info/rfc8342>.

[RFC8343] Bjorklund, M., "A YANG Data Model for Interface
Management", RFC 8343, DOI 10.17487/RFC8343, March 2018,
<https://www.rfc-editor.org/info/rfc8343>.

[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/info/rfc8446>.

[IEEE1588] 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, July
2008.

6.2. Informative References

[IEEE8021AS]
IEEE, "IEEE Standard for Local and Metropolitan Area
Networks - Timing and Synchronizations for Time-Sensitive
Applications in Bridged Local Area Networks", IEEE
802.1AS-2001.

[RFC3444] Pras, A. and J. Schoenwaelder, "On the Difference between
Information Models and Data Models", RFC 3444,
DOI 10.17487/RFC3444, January 2003,
<https://www.rfc-editor.org/info/rfc3444>.

Jiang, et al. Standards Track [Page 23]

RFC 8575 YANG Data Model for PTP May 2019

[RFC4663] Harrington, D., "Transferring MIB Work from IETF Bridge
MIB WG to IEEE 802.1 WG", RFC 4663, DOI 10.17487/RFC4663,
September 2006, <https://www.rfc-editor.org/info/rfc4663>.

[RFC7384] Mizrahi, T., "Security Requirements of Time Protocols in
Packet Switched Networks", RFC 7384, DOI 10.17487/RFC7384,
October 2014, <https://www.rfc-editor.org/info/rfc7384>.

[RFC8340] Bjorklund, M. and L. Berger, Ed., "YANG Tree Diagrams",
BCP 215, RFC 8340, DOI 10.17487/RFC8340, March 2018,
<https://www.rfc-editor.org/info/rfc8340>.

[RFC8173] Shankarkumar, V., Montini, L., Frost, T., and G. Dowd,
"Precision Time Protocol Version 2 (PTPv2) Management
Information Base", RFC 8173, DOI 10.17487/RFC8173, June
2017, <https://www.rfc-editor.org/info/rfc8173>.

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Appendix A. Transferring YANG Work to the IEEE 1588 WG

This Appendix is informational.

This appendix describes a future plan to transition responsibility
for IEEE Std 1588 YANG modules from the IETF TICTOC Working Group
(WG) to the IEEE 1588 WG, which develops the time synchronization
technology that the YANG modules are designed to manage.

This appendix is forward-looking with regard to future
standardization roadmaps in the IETF and IEEE. Since those roadmaps
cannot be predicted with significant accuracy, this appendix is
informational, and it does not specify imperatives or normative
specifications of any kind.

The IEEE Std 1588-2008 YANG module of this standard represents a
cooperation between the IETF (for YANG) and IEEE (for 1588). For the
initial standardization of IEEE-1588 YANG modules, the information
model is relatively clear (i.e., IEEE Std 1588 data sets), but
expertise in YANG is required, making IETF an appropriate location
for the standards. The TICTOC WG has expertise with IEEE Std 1588,
making it the appropriate location within the IETF.

The IEEE 1588 WG anticipates future changes to its standard on an
ongoing basis. As IEEE 1588 WG members gain practical expertise with
YANG, the IEEE 1588 WG will become more appropriate for
standardization of its YANG modules. As the IEEE 1588 standard is
revised and/or amended, IEEE 1588 members can more effectively
synchronize the revision of this YANG module with future versions of
the IEEE 1588 standard.

This appendix is meant to establish some clear expectations between
IETF and IEEE about the future transfer of IEEE 1588 YANG modules to
the IEEE 1588 WG. The goal is to assist in making the future
transfer as smooth as possible. As the transfer takes place, some
case-by-case situations are likely to arise, which can be handled by
discussion on the IETF TICTOC WG mailing lists and/or appropriate
liaisons.

This appendix obtained insight from [RFC4663], an informational memo
that described a similar transfer of MIB work from the IETF Bridge
MIB WG to the IEEE 802.1 WG.

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A.1. Assumptions for the Transfer

For the purposes of discussion in this appendix, assume that the IESG
has approved the publication of an RFC containing a YANG module for a
published IEEE 1588 standard. As of this writing, this is IEEE Std
1588-2008, but it is possible that YANG modules for subsequent 1588
revisions could be published from the IETF TICTOC WG. For discussion
in this appendix, we use the phrase "last IETF 1588 YANG" to refer to
the most recently published 1588 YANG module from the IETF TICTOC WG.

The IEEE-SA Standards Board New Standards Committee (NesCom) handles
new Project Authorization Requests (PARs) (see
<http://standards.ieee.org/board/nes/>). PARs are roughly the
equivalent of IETF Working Group Charters and include information
concerning the scope, purpose, and justification for standardization
projects.

Assume that IEEE 1588 has an approved PAR that explicitly specifies
development of a YANG module. The transfer of YANG work will occur
in the context of this IEEE 1588 PAR. For discussion in this
appendix, we use the phrase "first IEEE 1588 YANG" to refer to the
first IEEE 1588 standard for YANG.

Assume that as part of the transfer of YANG work, the IETF TICTOC WG
agrees to cease all work on standard YANG modules for IEEE 1588.

Assume that the IEEE 1588 WG has participated in the development of
the last IETF 1588 YANG module, such that the first IEEE 1588 YANG
module will effectively be a revision of it. In other words, the
transfer of YANG work will be relatively clean.

The actual conditions for the future transfer can be such that the
preceding assumptions do not hold. Exceptions to the assumptions
will need to be addressed on a case-by-case basis at the time of the
transfer. This appendix describes topics that can be addressed based
on the preceding assumptions.

A.2. Intellectual Property Considerations

During review of the legal issues associated with transferring Bridge
MIB WG documents to the IEEE 802.1 WG (Sections 3.1 and 9 of
[RFC4663]), it was concluded that the IETF does not have sufficient
legal authority to make the transfer to the IEEE without the consent
of the document authors.

If the last IETF 1588 YANG is published as an RFC, the work is
required to be transferred from the IETF to the IEEE, so that IEEE
1588 WG can begin working on the first IEEE 1588 YANG.

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RFC 8575 YANG Data Model for PTP May 2019

When work on the first IEEE YANG module begins in the IEEE 1588 WG,
that work derives from the last IETF YANG module of this RFC,
requiring a transfer of that work from the IETF to the IEEE. In
order to avoid having the transfer of that work be dependent on the
availability of this RFC's authors at the time of its publication,
the IEEE Standards Association department of Risk Management and
Licensing provided the appropriate forms and mechanisms for this
document's authors to assign a non-exclusive license for IEEE to
create derivative works from this document. Those IEEE forms and
mechanisms will be updated as needed for any future IETF YANG modules
for IEEE 1588 (the signed forms are held by the IEEE Standards
Association department of Risk Management and Licensing.). This will
help to make the future transfer of work from the IETF to the IEEE
occur as smoothly as possible.

As stated in the initial "Status of this Memo", the YANG module in
this document conforms to the provisions of BCP 78. The IETF will
retain all the rights granted at the time of publication in the
published RFCs.

A.3. Namespace and Module Name

As specified in Section 5 "IANA Considerations", the YANG module in
this document uses IETF as the root of its URN namespace and YANG
module name.

Use of IETF as the root of these names implies that the YANG module
is standardized in a Working Group of IETF, using the IETF processes.
If the IEEE 1588 Working Group were to continue using these names
rooted in IETF, the IEEE 1588 YANG standardization would need to
continue in the IETF. The goal of transferring the YANG work is to
avoid this sort of dependency between standards organizations.

IEEE 802 has an active PAR (IEEE P802d) for creating a URN namespace
for IEEE use (see <http://standards.ieee.org/develop/
project/802d.html>). It is likely that this IEEE 802 PAR will be
approved and published prior to the transfer of YANG work to the IEEE
1588 WG. If so, the IEEE 1588 WG can use the IEEE URN namespace for
the first IEEE 1588 YANG module, such as:

urn:ieee:Std:1588:yang:ieee1588-ptp

where "ieee1588-ptp" is the registered YANG module name in the IEEE.

Under the assumptions of Appendix A.1, the first IEEE 1588 YANG
module's prefix will be the same as the last IETF 1588 YANG module's
prefix (i.e., "ptp"). Consequently, other YANG modules can preserve

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the same import prefix "ptp" to access PTP nodes during the migration
from the last IETF 1588 YANG module to the first IEEE 1588 YANG
module.

The result of these name changes are that for complete compatibility,
a server (i.e., IEEE 1588 node) can choose to implement a YANG module
for the last IETF 1588 YANG module (with IETF root) as well as the
first IEEE 1588 YANG module (with IEEE root). Since the content of
the YANG module transferred are the same, the server implementation
is effectively common for both.

From a client's perspective, a client of the last IETF 1588 YANG
module (or earlier) looks for the IETF-rooted module name; and a
client of the first IEEE 1588 YANG module (or later) looks for the
IEEE-rooted module name.

A.4. IEEE 1588 YANG Modules in ASCII Format

Although IEEE 1588 can certainly decide to publish YANG modules only
in the PDF format that they use for their standard documents, without
publishing an ASCII version, most network management systems cannot
import the YANG module directly from the PDF. Thus, not publishing
an ASCII version of the YANG module would negatively impact
implementers and deployers of YANG modules and would make potential
IETF reviews of YANG modules more difficult.

This appendix recommends that the IEEE 1588 WG consider future plans
for:

- Public availability of the ASCII YANG modules during project
development. These ASCII files allow IETF participants to access
these documents for pre-standard review purposes.

- Public availability of the YANG portion of published IEEE 1588
standards, provided as an ASCII file for each YANG module. These
ASCII files are intended for use of the published IEEE 1588
standard.

As an example of public availability during project development, IEEE
802 uses the same repository that IETF uses for YANG module
development (see <https://github.com/YangModels/yang>). IEEE
branches are provided for experimental work (i.e., pre-PAR) as well
as standard work (post-PAR drafts). IEEE-SA has approved use of this
repository for project development, but not for published standards.

Jiang, et al. Standards Track [Page 28]

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As an example of public availability of YANG modules for published
standards, IEEE 802.1 provides a public list of ASCII files for MIB
(see <http://www.ieee802.org/1/files/public/MIBs/> and
<http://www.ieee802.org/1/pages/MIBS.html>), and analogous lists are
planned for IEEE 802.1 YANG files.

Acknowledgments

The authors would like to thank Tom Petch, Radek Krejci, Mahesh
Jethanandani, Tal Mizrahi, Opher Ronen, Liang Geng, Alex Campbell,
Joe Gwinn, John Fletcher, William Zhao, and Dave Thaler for their
valuable reviews and suggestions. They would like to thank Benoit
Claise and Radek Krejci for their validation of the YANG module, and
thank Jingfei Lv and Zitao Wang for their discussions on IEEE 1588
and YANG, respectively.

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Authors' Addresses

Yuanlong Jiang (editor)
Huawei
Bantian, Longgang district
Shenzhen 518129
China

Email: [email protected]

Xian Liu
Independent
Shenzhen 518129
China

Email: [email protected]

Jinchun Xu
Huawei
Bantian, Longgang district
Shenzhen 518129
China

Email: [email protected]

Rodney Cummings (editor)
National Instruments
11500 N. Mopac Expwy Bldg. C
Austin, TX 78759-3504
United States of America

Email: [email protected]

Jiang, et al. Standards Track [Page 30]