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INTERNATIONAL TELECOMMUNICATION UNION

TELECOMMUNICATION
STANDARDIZATION SECTOR

STUDY PERIOD 2017-2020

SG15-TD148r1/WP3

STUDY GROUP 15

Original: English

Question(s):

14/15

Geneva, 29 January - 9 February, 2017

TD

Source:

G.sync-mgmt Editors

Title:

Editors’ Draft of G.sync-mgmt v0.05

Purpose:

 

Contact:

Rongduo(Rod) LU
ZTE Corporation
China

Tel: +86-13121951971
Email: lu.rongduo@zte.com.cn

Contact:

Lei WANG
CMCC
China

Tel: +86-13910628561
Email: wangleiyj@chinamobile.com

Please do not change the structure of this table, just insert the necessary information.

 

The document contains the latest draft of G. sync-mgmt Management Requirement and Information Model for Synchronization ”. The document will be used for preparing the future Amendment or Revision of the Recommendation.

 

Document history:

Version

Date

Description

0.01

w d2 5(06/2017)

Geneva

=TD113/3(06/2017)

Initial version based on wd091014-41R1 ( 4 /201 7 ).

0.02

wd1214-08r1(09/2017)

Ottwa, Canada

Output draft of Q12&Q14 Ottawa interim meeting. Updated items:

1 ) Specify the clause of Scope by the text from A.1 justification;

2 ) Add the clause of Management requirement of sync per the contribution wd11.

3 ) Update the UML model per the contribution wd31. Rename the NeTechSpec to ClockSpec as discussed in the meeting.

4 ) Make the file directory of UML model project aligned with G.874.1 (UMLprofiles, Diagrams etc.).

0.03

wd14-28(12/2017)

London, UK

  • S ome typos fixed.
  • Unify the ssm with capital case.

0.04

wd14-28 r2 (12/2017)

London, UK

Output draft of Q14 London interim meeting. Updated items:

1 ) Add the UML model description to clause 7 as section 7.5 as per wd14-27 ;

2 ) Reconstruction: merged the clause 7 model sketch and clause 8 model attributes into a single clause Synchronization management model .

0 . 05

Wd14-xx(02/2018)

Geneva

Output draft of Q14 London interim meeting. Updated items:

1)   Update the text as per c ontribution s : C507, C611, wd13-11 ( revised C612)

2) UML update to v0.05 :

Upgrade model profiles to   OpenModel Profile v0.2.13, OpenInterfaceModel Profile v0.0.8   and   ProfileLifecycle Profile v0.0.4

Update the model with Eclipse Oxygen.2 Release (4.7.2), Papyrus version 3.2.0.20171206084

Update the model as per C611, wd13-11( revised C612)

3 ) U pdate   data dictionary   with   Gendoc 0.6.0 , update f igure s in section 7.1.5

4 ) F ill up the sections of summary, keyword, introduction, term s , reference, convention , bibliography , clause 8 , fix the format of footnote

5) Unify formats of text.

 

 

 

 

Draft Recommendation ITU-T G.sync-mgmt

Management Requirement and Information Model for Synchronization

Summary

Recommendation ITU-T G. sync -mgmt provides the management requirements and a protocol-neutral management information model for managing network elements and network of synchronization .   <Mandatory>

Keywords

Information model, protocol-neutral, synchronization , management , unified modelling language (UML) < Mandatory >

Introduction

<Optional This clause should appear only if it contains information different from that in Scope and Summary>

1          Scope

This Recommendation will specify the management requirements and information model for managing synchronization network and equipment based on the synchronization architecture and equipment specification defined in the ITU-T Recommendations. The management information model will be described using extension to the model artefacts defined in G. [ITU-T G. 7711 ] . The extensions enable synchronization networks to be managed using the same patterns found in G. [ITU-T G. 7711 ] .

2          References

The following ITU-T Recommendations and other references contain provisions which, through reference in this text, constitute provisions of this Recommendation. At the time of publication, the editions indicated were valid. All Recommendations and other references are subject to revision; users of this Recommendation are therefore encouraged to investigate the possibility of applying the most recent edition of the Recommendations and other references listed below. A list of the currently valid ITU-T Recommendations is regularly published. The reference to a document within this Recommendation does not give it, as a stand-alone document, the status of a Recommendation.

[ITU-T G.7710] Recommendation ITU-T G.7710 (02/2012), Common equipment management function requirements .

[ITU-T G.7711] Recommendation ITU-T G.7711 (12/2016), Generic protocol-neutral information model for transport resources .

[ITU-T G.781] Recommendation ITU-T G.781 (08/2017), Synchronization layer functions .

[ITU-T G.798] Recommendation ITU-T G.798 (12/2017), Characteristics of optical transport network hierarchy equipment functional blocks .

[ITU-T G.8021] Recommendation ITU-T G.8021 (11/2016), Characteristics of Ethernet transport network equipment functional blocks .

[ITU-T G.8052] Recommendation ITU-T G.8052 (11/2016), Protocol-neutral management information model for the Ethernet transport capable network element .

[ITU-T G.8152] Recommendation ITU-T G.8152 (12/2016), Protocol-neutral management information model for the MPLS-TP network element .

[ITU-T G.8264] Recommendation ITU-T G.8264 (08/2017), Distribution of timing information through packet networks .

[ITU-T G.8265.1] Recommendation ITU-T G.8265.1 (07/2014), Precision time protocol telecom profile for frequency synchronization .

[ITU-T G.8271] Recommendation ITU-T G.8271 (08/2017), Time and phase synchronization aspects of telecommunication networks .

[ITU-T G.8275.1] Recommendation ITU-T G.8275.1 (06/2016), Precision time protocol telecom profile for phase/time synchronizatio n with full timing support from.

[ITU-T G.8275.2] Recommendation ITU-T G.8275.2 (06/2016), Precision time protocol telecom profile for time/phase synchronization with partial timing support from the network .

[ITU-T G.874.1] Recommendation ITU-T G.874.1 (11/2016), Optical transport network: Protocol-neutral management information model for the network element view .   [ ITU-T X.yyy ]               R ecommendation ITU-T X.yyy ( date ) ,   Title .

[ITU-T G.810] Recommendation ITU-T G.810 (1996), Definitions and terminology for synchronization networks .

[ITU-T G.8260] Recommendation ITU-T G.8260 (2015), Definitions and terminology for synchronization in packet networks .

[ ITU-T P.562] Recommendation ITU-T P.562(05/2004), Analysis and interpretation of INMD voice-service measurements.

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

3          Definitions

<Check in the ITU-T terms and definitions database at www.itu.int/go/terminology-database whether the term has already been defined in another Recommendation. It would be more consistent to refer to such a definition rather than to redefine the term>

3.1 Terms defined elsewhere

<Normally , terms defined elsewhere will simply refer to the defining document. In certain cases, it may be desirable to quote the definition to allow for a stand-alone document>

This Recommendation uses the following terms defined elsewhere:

<   STM-N Term 1 > [ ITU-T G.8021(10/2010) Reference ] : <optional quoted definition> .

<   E1 Term 2 > [ ITU-T P.562(05/2004) Reference ] : <optional quoted definition> .

The terms and definitions used in this Recommendation are contained in [ITU-T G.810] and [ITU T G.8260].

3.2 Terms defined in t his Recommenda tion

This Recommendation defines the following terms:

<Term 3> : <definition> .

4          Abbreviations and acronyms

< Editors’ Note: Need to fill up and check the terms with question mark. >

This Recommendation uses the following abbreviations and acronyms:

1PPS One Pulse Per Second

BC Boundary Clock

BMCA Best Master Clock Algorithm

C&SC Configuration and Switch Controller

CES Circuit Emulation Services

CLK Clock

DNU Do Not Use

FC Forwarding Construct

FD Forwarding Domain

GE Gigabit Ethernet

ID Identification

LTP Logical Termination Point

MAC Media Access Control

NE Network Element

OC Ordinary Clock

OSS Operations Support System

P2P Point To Point

PRC Primary Reference Clock

PTP Precision Time Protocol

SDN Software Defined Network

SSM Synchronization Status Message

SSU Synchronization Supply Unit

SyncE Synchronous Ethernet

SyncO ?

TC Transparent Clock

T o D Time of Day

UDP User Datagram Protocol

UML Unified Modelling Language

UNK UNKnown

VLAN Virtual Local Area Network <abbr> < expansion >

<Include all abbreviations and acronyms used in this Recommendation>

5          Conventions

Information modeling conventions

UML modeling conventions

See [ ITU-T G.771 1] clause 5.1.

Model Artefact Lifecycle Stereotypes conventions

See [ ITU-T G.771 1] clause 5.2.

Forwarding entity terminology conventions

See [ ITU-T G.771 1] clause 5.3.

Conditional package conventions

See [ ITU-T G.771 1] clause 5.4.

Pictorial diagram conventions

See [ ITU-T G.771 1] clause 5.5.

< Mandatory clause. Describe any particular notation, style, presentation, etc. used within the Recommendation , if any . If none, write "None." >

6          Management requirements for synchronization

The management requirements for synchronization in this recommendation are common to multiple transport technologies. The management of the synchronization network is based upon the traditional OSS or SDN controller.

The management of the equipment synchronization function includes the FCAPS functions (fault, configuration, accounting, performance and security) for synchronization. Each function includes the management of frequency and time respectively.

The common equipment management requirements are defined in [ITU-T G.7710].

6.1 Configuration management

Configuration management provides functions to collect data from and provide data to NEs. Configuration management for synchronization supports (1) planning and setup of the sync path based on the sync network topology and avoiding clock loop in the sync path; (2) to setup at least two paths for each device to avoid the breakdown of clock synchronization due to the failure of some link or device; (3) reconfiguration of the sync path if the sync network topology changes; (4) configuration of the frequency sync and time/phase sync parameters for the transport equipments.

6.1.1                 Configuration management of frequency synchronization

The functions of frequency synchronization of NEs should be configurable and manageable.

1)       Configure the priority list of frequency system clock. The clocks below could be selected.

-External clock (e.g. 2MHz or 2Mbit/s)

-Clock extracted from line-side input signals (e.g. STM-N, GE, SyncO )

-Clock extracted from CES services (e.g. E1, STM-N )

-Clock recovered from PTP messages

-Internal clock (free run or hold-over)

2)       Configure the type of input/output external clock: e.g. 2MHz or 2Mbit/s.

3)       Enable/disable synchronization status messages ( SSM ) for the NE.

4)       Configure timing recovery methods for CES: differential, adaptive, and network timing.

5)       Query the status of frequency system clock (locked, free-run, and holdover, etc.).

6)       Configure the SSM value of internal clock of the NE.

7)       Extended SSM parameters for GE and SyncO

8)       Configure wait to restore time (WTR).

9)       Switch commands for each Sync port; lockout, manual switch, and forced switch.

10) Configure whether the clock to switches back to previously selected source or not after recovery.

11) Configure whether to take UNK as one of the SSM quality levels or not. If UNK is enabled, its level lies between PRC and SSU_T; otherwise it is taken as DNU.

 

The following configuration and management functions of in-band clock ports could be required.

1)       Enable/disable synchronization status messages (SSM) for the port.

2)       Query current input/output SSM values of the port.

3)       Configure to use manual or automatic input/output SSM values.

4)       Configure input/output SSM values for the port.

 

The following configuration and management functions of external clock ports could be required.

1)       Enable/disable the port.

2)       Configure the type of input/output external clock: 2MHz or 2Mbit/s.

3)       Configure the source used for the external clock output port. The clocks below could be selected.

-System clock

-Clock extracted from line-side input signals (e.g. STM-N, GE)

4)       Configure sa-bit bits to carry input and output SSM message.

5)       Configure the SSM out-threshold, used to decide whether to send SSM messages or not when the SSM value is lower than the threshold.

6)       Query current input/output SSM values of the port.

7)       Configure to use manual or automatic input/output SSM values.

8)       Configure input/output SSM values for the port.

6.1.2                 Configuration management of time synchronization

The function of time synchronization protocols, such as PTP protocol, should be configurable and manageable for NEs.

1)       Enable/disable the PTP function of the NE. (Causes the system clock to enter free run)

2)       Query the running mode of the PTP system clock, including tracing and non-tracing.

3)       Configure the PTP domain number of the NE.

4)       Configure the PTP device type, including boundary clock (BC), transparent clock (TC), TC+BC and ordinary clock (OC).

5)       Configure the PTP delay mechanism of the NE, including E2E and P2P.

6)       Configure the NE to PTP slave only.

7)       Query the PTP status dataset of current tracing source, including grandmasterIdentity, parent ID, priority 1, priority 2, clockClass, accuracy, offsetScaledLogVariance, timesource, stepsRemoved, currentUtcOffset, ptpTimescale, timeTraceable, frequencyTraceable, 1588 protocol version, and current absolute time.

8)       Configure the PTP status dataset of internal clock of the NE, including CLK ID, priority 1, priority 2, clockClass, accuracy, offsetScaledLogVariance, timesource, stepsRemoved, and 1588 protocol version.

 

The following configuration and management functions of PTP ports could be required.

1)       Enable/disable the PTP function of the port.

2)       Query the state of the PTP port, including master, slave, passive, initializing, listening, premaster, uncalibrated, and faulty.

3)       Configure the transmission interval of PTP announce messages.

4)       Configure the receipt timeout of PTP announce messages.

5)       Configure the transmission interval of PTP sync messages.

6)       Configure the transmission interval of PTP delay_req/ Pdelay_req messages.

7)       Configure the PTP delay mechanism of the port, including E2E and P2P.

8)       Configure the one-step or two-step mechanism of the port.

9)       Configure the asymmetry correction value of the PTP port.

10) Configure the configuration of UDP encapsulation, including source IP address, destination IP address and IPv4/IPv6 protocol.

11) Configure the configuration of MAC encapsulation, including source MAC address, destination MAC address and VLAN configuration.

 

The following configuration and management functions of 1PPS+TOD time ports could be required.

1)       Configure the status of the external time port: input or output port.

2)       Configure the status dataset of the external time port, including grandmasterIdentity, priority 1, priority 2, clockClass, accuracy, offsetScaledLogVariance, timesource, stepsRemoved, and currentUtcOffset.

3)       Configure the delay compensation value of the external time port.

6.2 Fault management

Fault management for synchronization supports the detection, isolation and correction of abnormal operation of the synchronization network and elements.

Fault management of the physical layer frequency supports the reporting and handling for the following alarms:

- Loss of timing inputs (dLTI)

- Clock unlock

- Frequency offset source performance degradation

- SSM level degradation

- Loss of SSM

Fault management of the packet-based time/frequency synchronization supports the reporting and handling for the following alarms:

- Time unlock

- TOD (or PTP) input degradation

- Time offset/accumulated time offset over the limit

- Loss of PTP message

- Loss of PPS+TOD

6.3 Performance management

Performance management for synchronization supports evaluating and reporting the synchronization performance of the network or NE.

Performance management of the physical layer frequency supports the handling for the following performance monitoring function:

- Frequency offset monitoring

Performance management of the packet-based time/frequency synchronization supports the handling for the following performance monitoring function:

- PTP time offset/accumulated time offset monitoring

- Time error measurement at a passive port

7          Synchronization management model

7.1 Synchronization model overview

Editor Note: Import from C33

The clause provides an initial sketch of the information model for synchronization management.

7.1.1                 Management view of the synchronization network

A NE that supports a slave clock function (i.e. a local frequency or time reference) will terminate several interfaces that support trails and links in one or more layer networks. These links may support user traffic, synchronization information or both.

The synchronization distribution trails will be present within some of these interfaces. The selection of the synchronization input and the distribution of the output of the slave clock are independent. For example, at the edge of a network a NE may have two links that support an incoming synchronization signal but the output of the slave clock would not be distributed to other NEs. It is more convenient to describe the functional model for synchronization using uni-directional constructs.

7.1.1.1     Simplified equipment model

Figure 7 1 and Figure 7 2 below show a simplified equipment model for a network element that has an internal clock. The connection to an external clock (e.g. a boundary clock for PTP or Stand Alone Synchronization Equipment (SASE) for frequency synchronization) is for further study. The management abstractions required to represent an external clock are provided later in this document.

The simplified equipment model for time synchronization using PTP is shown in Figure 7 1 below.

The figures include numbers that show the flow of a synchronization signal from the input of the NE to the output of the NE.

Figure 7 1 Simplified sync equipment model of a transport NE using PTP.

The processes associated with the functions in Figure 7 1 are outlined below. Note that steps 4-8 also apply to the case of physical layer sync using SSM described below.

1)     Terminate the server layer

a)        Specification provided in Recommendations under the responsibility of ITU-T Study Group 15 Q10 (e.g. [ITU-T G.8021]) or Q11 (e.g. [ITU-T G.798 ])

2)     Synchronization sink function extracts the Synchronization information [1] from the sync links (identified by the management plane) as “potential” sync inputs and forwards it to (3)

a)        Report the content of the status of the synchronization trail including the contents of the PTP announce messages to management

3)     Selects a sub-set of the “potential” inputs as candidates to provide the synchronization information to the protection process (4) (i.e. enabling or disabling the associated port). This process is optional and may be null.

a)        Management plane configures this process

4)     Selector

a)        Based on the quality of the synchronization inputs (PTP announce messages) and priorities provided by the management plane the selection process selects one of the candidates and forwards it to the clock function (5). Note: in case of PTP the input selection process may use BMCA.

5)     Clock function processes the input sync information (frequency and SSM or time stamp and PTP announce messages) and provides the modified sync information to the sync distribution function (6)

a)        If none of the inputs meet the quality defined by the management plane the clock may enter a hold-over or free run mode. The status of the clock will be reported to the management system.

6)     Distribute the synchronization information from the clock to the output ports via (7)

a)        The management system must define which outputs are intended to carry the synchronization information.

b)       The PTP announce messages sent by the sync source that is bound to the server layer adaptation/termination that is currently used as the sync input to the clock may be different from the PTP announce messages sent by the other sync source.

7)     Encodes the synchronization information provided by the clock function to allow it to be carried by the server layer

8)     Terminate the server layer

a)        Specification provided in Recommendations under the responsibility of Q10 (e.g. G. [ITU-T G. 8021 ] ) or Q11 (e.g. G. [ITU-T G. 798 ] )

Figure 7 2 below shows the model for frequency synchronization using SSM as described in [ITU-T G.781].

Figure 7 2 Simplified equipment model of a transport NE that uses physical layer based frequency sync with SSM

Note : The candidate selection shown above can select an input from any suitable server layer adaptation/termination function. This is normally preconfigured by management.

The processes associated with the functions in Figure 7 2 are outlined below.

Note : The Selection of candidate inputs function (3) is between the server layer (1) and sync layer functions (2) and operates only in the input (sink) direction.

1)       Terminate the server layer

a)       Specification provided in Recommendations under the responsibility of Q10 (e.g. G. [ITU-T G. 8021 ] ) or Q11 (e.g. G. [ITU-T G. 798 ] )

2)       Selects a sub-set of the “potential” inputs as candidates to provide the synchronization information to the synchronization sink function (2) (this in effect enables or disables a port).

a)       Management plane configures this process

Editor/Modeller NOTE - Some clarification on the Selection of candidates inputs is required: should the enabling/disabling of a port for SyncE been made above the sync sink, like the case of PTP as shown in Figure 7 1 ? Some text justifying the answer should be added to the document. Some participants believe that when trying to model the SASE it would be better to have a diagram like the PTP one where the selection of candidate inputs is in a position like the case of PTP. From a Q14/15 information model perspective the model must accommodate either arrangement the “generic” technology independent definition of the management artefacts will be independent of the answer. This issue should be addressed by Q13/15. From an information model perspective, it only impacts the creation of an interface to manage synchronous Ethernet.

3)       Synchronization sink function extracts the Synchronization information [2] from the sync links (identified by the management plane) as “potential” sync inputs and forwards it to (4)

a)       Report the content of the status of the synchronization trail including the contents of the SSM messages to management

The other functions (4-8) are as described above for the PTP case.

7.1.1.1.1                   Optional redundant NE clock

Support of a redundant NE clock, is illustrated in Figure 7 3 below.

Figure 7 3 Simplified sync equipment model using PTP with redundant NE clocks

Note that in normal operation one clock is selected as the “master” and this participates in the BCMA algorithm, the other (slave) clock tracks the same input and is phase aligned to the “master” clock. The protection selector at the output of the clock functions is driven by the (internally monitored) status of the NE clocks. This selection process determines the roles of the clocks (master/slave). The assignment of the master/slave roles may be changed as a result of the detection of an equipment failure or by external (management) commands.

Editor NOTE : additional redundancy schemes are possible. These are for further study.

7.1.1.2     Management abstractions

For the purposes of management, the functions (and/or processes) described above will be represented as described below. Note that these are described in terms of instances of the LogicalTerminationPoint (LTP) or ForwardingConstruct (FC) classes from this Recommendation (and [b-ONF TR-512]) or the Clock class defined in this Recommendation, which represent the specific synchronization function. These are described in terms of uni-directional instances since this simplifies the description. Normally bidirectional instances will be used.

1)     Termination of the server layer

a)        Sink part of a bi-directional server layer LTP instance as defined in [ITU-T G.874.1] (OTN), [ITU-T G.8052] (Ethernet), [ITU-T G.8152] (MPLS-TP).

2)     Synchronization sink function

a)        Sink part of a client layer LTP object instance that supports uni-directional Synchronization Sink function [3]

b)       Server layer specific optional packages may be required to allow management of the adaptation/termination processes.

3)     Selection of candidate inputs for the Selector process (4)

a)        For frequency synchronization
Creation/removal of the relationship between an instance of the server layer LTP and an instance of the client layer Sync LTP

b)       For PTP:
Creation/removal of the relationship between an instance of the client layer Sync LTP and an instance of the Selector FC (4)

4)     Selector process:

a)        New object instance uni-directional Sync selection ForwardingConstruct

5)     Clock function:

a)        New object instance Clock.

6)     Clock distribution

a)        This is modelled indirectly by the creation or removal of the relationship between the Clock and a Sync So LTP.

7)     Synchronization source function

a)        Source part of a client layer LTP object instance that supports uni-directional Sync Source function

b)       Server layer specific optional packages may be required to allow management of the adaptation/termination processes.

8)     Terminate server layer

a)        Source part of a bi-directional server layer LTP instance as defined in G. [ITU-T G. 874.1 ] (OTN), G. [ITU-T G. 8052 ] (Ethernet), G. [ITU-T G. 8152 ] (MPLS-TP).

7.1.1.3     Object construction

Object instances of LTP, FC, ForwardingDomain (FD) are used to represent the synchronization functions and are constructed from the base classes using composition. This aligns with the approach taken in this Recommendation (and [bONF TR-512]) and avoids the creation of specialized object classes. A sketch of the relationships for the synchronization LTP instances is provided below in Figure 7 4 .

Figure 7 4 Synchronization LTP construction

Additional (technology specific) optional packages may be required to describe any server specific properties.

The clock function is represented by an instance of Clock object class constructed as shown in Figure 7 5 .

Figure 7 5 Clock object class construction

Additional (technology specific) optional packages will be required to describe clocks with different quality levels or functions (e.g. transparent clock, boundary clock, stratum 2 clock etc.).

The uni-directional synchronization selection FC instance will be based on one of the G. [ITU-T G. 7711 ] [2] protected point-to-multi-point FCs together with the Configuration&SwitchControl (C&SC) from this Recommendation.

7.1.2                 Mapping of synchronization equipment functions to management artefacts

The following figures illustrate the mapping of the synchronization equipment functions to the management information model artefacts.

Figure 7 6 Mapping Figure 7 1 – Simplified sync equipment model using PTP to object instances

Different types of clocks or server layers would be modelled using different instances (constructed from using the appropriate optional pacs) of the same object classes.

Figure 7 7 above do not show the control information that is passed between the Sync LTPs, the selector and the clock, this has been added in the figure below, for clarity the Configuration and Switch Control (C&SC) has been separated from the Selector FC.

Editor/Modeler NOTE : The control information should be confirmed with Q13 and the equipment functional model should be updated.

 

Figure 7 7 Mapping Figure 7 1 – with relationships for control information added

The Sync Si LTP separates the incoming PTP message into “control information” (e.g. source quality, identifier) and “time” information (e.g. time stamp).

The C&SC uses the source input information to select the best available input (or instructs the local clock to go into holdover or free run mode). The C&SC also informs the Sync So LTP which input (if any) has been selected so that the appropriate control messages can be transmitted.

 

 

Figure 7 8 Mapping Figure 7 3 – Simplified sync equipment model using PTP with redundant NE clocks to object instances

7.1.2.1     Refactoring management artefacts

The management artefacts could be refactored to reduce the number of object instances in the case where some details are not of interest. An (extreme) example is provided in Figure 7 9 below. In this example the input selection FD/FC, the pair of redundant clocks and the output protection FD/FC are encompassed by a single instance of the clock. This would provide a simplified model but with limited visibility of the details of the implementation.

Figure 7 9 Example of a refactored/simplified view

7.1.3                 Example use of the model

An example of the instantiation of the model for a NE with an internal clock is provided below in Figure 7 10 .

Figure 7 10 Example of the use of the synchronization management model

Notes for Figure 7 10 and Figure 7 11

  • Each green LTP is an instance of the LTP class that represents the termination of the server layer.
  • Each blue LTP is an instance of the client layer LTP class that represent the sync function.
  • The yellow FC is an instance of the FC class that represents the sync selection functions.
  • The Peach Clock is an instance of the Clock class that represents the NE clock function.
  • For the purposes of illustrating the signal flow the Sync Si LTP and Sync So LTP are shown  separate instances. However, particularly for PTP, a bidirectional instance of the Sync LTP can be used.
  • When detailed management of sync protection is not required the status of the Sync protection FC may be provided by the Clock by including the information on the sync protection (from the Sync protection FC) in the clock. In this case instances representing the sync protection FC and sync FD will not be created.

This set of managed object will be used to manage the (frequency or time) synchronization functions of the network element with an internal clock. Typically the server layer LTPs would also terminate user traffic. Also the NE will normally support additional LTPs and FDs/FCs in multiple layer networks to support the management (termination and/or connectivity) of user traffic.

The rules for the instantiation of the Sync LTP instances depend on the capabilities of the hardware and the policy of the network operator. At least the following options for the behaviours should be supported by the model:

1)     Created by management action: The management system explicitly creates (and deletes) the sync LTP instances

a)        The management system also creates/breaks the associations between the Sync LTP instances and the Sync FC (for time) instance or server layer LTP instances (for frequency).

2)     Auto created: The NE instantiates the Sync LTP instances when sync status messages or PTP announce messages are detected.

a)        The relationship between the Sync LTP instances and the Sync FC (for time) instance or server layer LTP instances (for frequency) is initially “null” and must be configured by the manager

b)       The relationship between the Sync LTP instances and the Sync FC (for time) instance or server layer LTP instances (for frequency) is automatically created when the Sync LTP instances are created.

2.b.1.           The Sync protection priority should be set to “low” and may be reconfigured by management or PTP protocol actions.

Note that the same set of managed object classes (with different pacs to reflect the different clock quality and capability) could be used to represent for example a boundary clock NE or a stratum 2 clock

An example of the instantiation of the model of a transport NE connected to a standalone external clock is provided in Figure 7 11 .

Figure 7 11 External clock and Transport NE

To avoid adding clutter in the figure the server layer LTP instances and the FD instances are not shown in Figure 7 12 . The standalone external clock could be a boundary clock (for time) or a stratum 2 clock (for frequency). Other configurations are possible, for example the output from the transport NE could be provided by the NE clock.

An example of the instantiation of the model for a NE with redundant internal clocks is provided below in Figure 7 13 .

Figure 7 12 Example of a NE with redundant internal clocks

An example where the sync protection status is reported by the Clock is provided below in Figure 7 13 .

 

Figure 7 13 Example of the clock reporting the sync protection status

7.1.4                 Synchronization network topology

The information in clause 6.1 through 6 . 3 is focussed on the management of a single node. Information on the synchronization network topology is provided below.

Figure 7 14 below shows a (simple) example of a synchronization network.

Figure 7 14 Example synchronization distribution network

From a management perspective, the Master Clock can be represented by an instance of the clock and the node containing a network equipment clock can be represented by instances of forwarding domains with links to interconnect the nodes. This is illustrated in the Figure 7 15 below.

Figure 7 15 Full timing distribution topology

This view shows all the links that could be used to carry timing information. The configuration of the FCs in the FDs that reduces this topology is shown in Figure 7 16 below.

Figure 7 16 Reduced/selected timing distribution topology

The topology selected topology could be defined manually or: By allowing the nodes to be autonomously configured by PTP (using BCMA) or sync status messages or: Some combination of manual and autonomous configuration. If some degree of autonomous control is permitted, then the selected topology will be updated when a failure occurs. Typically, a network operator would define the set of inputs that are used in the autonomous selection process and the priority assigned to each of these enabled inputs.

7.1.5                 Description of UML model

<Editors’ Note> The object class NetworkElement of G.7711 will be replaced by ConstraintDomain in the future. Once the G.7711 updated, the  description in this section and the sync model should be updated.

For better understanding and review of the synchronization UML model attached in Clause 9 , this clause describes model skeleton and approaches of the UML model.

7.1.5.1     Skeleton of synchronization model

The Figure 7 17 which describes the skeleton of Sync model is extracted from the UML model file.

The object classes ForwardingDomain, NetworkElement, ForwardingDomain and LogicalTerminationPoint and the associations between them are imported from G. [ITU-T G. 7711 ] , except the association FcChooseLtp is a new association to present the “Clock distribution” function in section 7.1.2 .

F o r decoupling from the G. [ITU-T G. 7711 ] , the Spec model approach of G. [ITU-T G. 7711 ] is applied for the relationship between NetworkElement and Clock. A new object class ClockSpec which is contained in the NetworkElement is specified by C l ock by the association ClockSpecifyNe.

The meaning of associations between the Clock and other object classes is assumed to be easily understood by the semantic of their names. If not, the explanation of the associations can be found in the Applied comments of the association in UML model file or data dictionary.

 

Figure 7 17 UML model diagram - SyncSkeleton

7.1.5.2     Specific v iew of Sync LTP

T h e Figure 7 18 describes the specific structure of Sync LTP. A new object class SyncTermination_Pac is used to contain the attributes packages defined in the section 8.3 and specify the TerminationSpec of LTP in G. [ITU-T G. 7711 ] .

Figure 7 18 UML model diagram - LtpSpecificView

7.1.5.3     Specific view of NE

T h e Figure 7 19 describes how the NeSyncSpec specify the NetworkElement. A new object class ClockSpecProfiles contained in the NetworkElement is specified by NeSyncSpec which is the attribute package defined in the section 8.1 .

Figure 7 19 UML model diagram - NeSpecificView

7.1.5.4     Specific v iew of Clock

T h Figure 7 20 describes the specific structure of Clock. The Clock object class contains two attribute packages defined in the section 8.2 .

Figure 7 20 UML model diagram - ClockSpecificView

7.1.5.5     Specific v iew of C&SC

T h Figure 7 21 describes how the SyncProtection_Pac is contained in the C&SC (ConfigurationAndSwitchController) of G. [ITU-T G. 7711 ] .

<Editor s’ Note> The SyncProtection_Pac which is the attribute package defined in a missing section of clause 8 .

Figure 7 21 UML model diagram - CascSpecificView

7.2 Synchronization model attributes

Editor Note: This clause is imported from C32 and TD549R1. Attributes haven t been checked yet.

7.2.1                 Existing NE object

Add NE sync status:

Attribute Name

Description

Type

R elated Recommendations

Sync_Support _Physical _freq

Indicate whether the NE has the capability to support physical layer frequency synchronization.

Boolean – Read only :

Enumeration – Read only:
G.813; G.812; etc.

Physical layer frequency: G. [ITU-T G. 781 ]

 

Sync_Support_ Packet_ freq

Indicate whether the NE has the capability to support packet frequency synchronization . and which frequency profile to support .

Boolean – Read only:

Enumeration – Read only :

G.8265.1 , ;

G.8275.2 , ;

Packet frequency: G. [ITU-T G. 8265.1 ] , G. [ITU-T G. 8275.2 ]

Packet Freq Sync support enabled and Profile selector

Freq Sync support enabled

Allows which packet frequency sync functions to be enabled

Allows the frequency sync functions to be deactivated

Enumeration - Read/Write:

Enable G.8265.1 , ;  

Enable G.8275.2 , ;

Disable ,

Boolean – Read/Write:

Default : enabled

Packet frequency: G. [ITU-T G. 8265.1 ] , G. [ITU-T G. 8275.2 ]

Sync_Support_time

Indicate whether the NE has the capability to support time synchronization   and which time profile to support .

Enumeration – Read only:

G.8275.1 , ;

  G.8275.2

etc.
Boundary clock (BC); Transparent clock (TC) etc.

G. [ITU-T G. 8275.1 ] , G. [ITU-T G. 8275.2 ]

Time Sync support enabled   and Profile selector

Allows which time sync profiles to be enabled

Allows the time sync functions to be deactivated

Enumeration       Read/Write:

Enable G.8275.1 , ;

Enable G.8275.2 ;

Disable ,

Boolean – Read/Write:
Default: enabled

G. [ITU-T G. 8275.1 ] , G. [ITU-T G. 8275.2 ]

 

7.2.2                 Clock

7.2.2.1     Physical Layer Frequency sync (SSM) pac

Attribute Name

Description

Type

Related Recommendations

system clock ID

The ID of the SyncClock_Frequency object.

Object ID   read only :  
frequ and PTP could use a common attribute definition

Object ID   read only

G. [ITU-T G. 8264 ]   (extended SSM)

associated node ID

The SyncClock_Frequency object is associated with the NE of this node ID.

Object ID   read only :
frequ and PTP could use a common attribute definition

Object ID   read only

 

run-mode

The run-mode of the frequency system clock, such as freerun, locked, and holdover.

Enumeration - Read only;
Freerun;

  locked;

  holdover .
frequ and PTP could use a common attribute definition

Enumeration – r ead only

G. [ITU-T G. 781 ]

 

internal clock SSM

The SSM quality level of internal clock of the NE.

Enumeration - Read only
QL- PRC, QL- SSU-A, QL- SSU-B, QL- E EC 1 , QL- DNU , QL- PRTC, QL- ePRTC, QL- eEEC , etc.

Should use quality levels, not use SSM code s and enhanced SSM codes Use the clock quality levels listed in section 5.4.1 of [ITU-T G. 781 ] . The corresponding SSM codes and enhanced SSM codes for SyncE refer to table 11-7 and table 11-8 of [ITU-T G. 8264 ] .

G.813; G.812; ???
frequ and PTP could use a common attribute definition

Enumeration – r ead   only

G. [ITU-T G. 781 ] ,

G. [ITU-T G. 8264 ]

 

7.2.2.2     PTP Sync pac Time Sync (PTP) pac

Attribute Name

Description

Type

Related Recommendations

PTP system clock ID

The ID of the SyncClock_Time object.

Object ID   read only :
frequ and PTP could use a common attribute definition

Object ID   read only

G. [ITU-T G. 8275.1 ] , G. [ITU-T G. 8275.2 ] ,

G. [ITU-T G. 8265.1 ]

associated node ID

The SyncClock_Time object is associated with the NE of this node ID.

Object ID   read only :
frequ and PTP could use a common attribute definition

Object ID   read only

 

PTP enable status

Indicate whether the NE enables PTP function or not.

Boolean – read/write?

Boolean – read/write

 

run-mode

The run-mode of the PTP system clock, such as tracing and non-tracing.

Enumeration - Read only:
Freerun;

  locked;

  holdover .
frequ and PTP could use a common attribute definition

Enumeration – r ead only

G. [ITU-T G. 8275.1 ] , G. [ITU-T G. 8275.2 ] ,

G. [ITU-T G. 8265.1 ]

PTP domain

The PTP domain number of the NE.

Integer or string – Read/write ?

Integer – r ead/write

G. [ITU-T G. 8275.1 ] , G. [ITU-T G. 8275.2 ] ,

G. [ITU-T G. 8265.1 ]

PTP device-type

Three PTP device types are included: boundary clock (BC), transparent clock (TC), and ordinary clock (OC).

Enumeration - Read only
boundary clock (BC), transparent clock (TC), and ordinary clock (OC).
frequ and PTP could use a common attribute definition with different enumerations

Enumeration – r ead /write

G. [ITU-T G. 8275.1 ] , G. [ITU-T G. 8275.2 ] ,

G. [ITU-T G. 8265.1 ]

PTP slaveonly

Indicate whether the NE can only be used as PTP slave or not.

Boolean - Read only ?

Boolean – read/write

G. [ITU-T G. 8275.1 ] , G. [ITU-T G. 8275.2 ] ,

G. [ITU-T G. 8265.1 ]

PTP source dataset

The PTP status dataset of current tracing source.

Ordered list - Read only:

grandmasterIdentity – Object ID – Read only ,

parent ID – Object ID – Read only ,

priority 1 – Integer – Read only,

priority 2 – Integer – Read only,

clockClass – Integer – Read only,

accuracy – Integer – Read only,

offsetScaledLogVariance – Integer – Read only,

timesource – Enumeration – Read only,

stepsRemoved – Integer – Read only,

currentUtcOffset – Integer – Read only,

ptpTimescale – Enumeration – Read only,

timeTraceable – Boolean – Read only,

frequencyTraceable – Boolean – Read only,

1588 protocol version – Integer – Read only,,

current absolute time – Integer – Read only.

G. [ITU-T G. 8275.1 ] , G. [ITU-T G. 8275.2 ] ,

G. [ITU-T G. 8265.1 ]

PTP default dataset

The PTP status dataset of internal clock of the NE

Ordered list – Read/Write:

CLK ID – Object ID – Read/Write,

priority 1 – Integer – Read/Write,

priority 2 – Integer – Read/Write,

clockClass – Integer – Read/Write,

accuracy – Integer – Read/Write,

offsetScaledLogVariance – Integer – Read/Write,

timesource – Integer – Read/Write,

stepsRemoved – Integer – Read/Write,

1588 protocol version – Integer – Read/Write.

maxStepsRemoved- – Integer – Read/Write. (only for G. [ITU-T G. 8275.1 ] )

G. [ITU-T G. 8275.1, ] G. [ITU-T G. 8275.2 ] ,

G. [ITU-T G. 8265.1 ]

 

7.2.3                 Sync LTP

Note: The model uses the terminationDirection attribute of LTP to indicate the Sync LTP is a source or sink LTP, e.g. Sync source LTP with terminationDirection as SOURCE, Sync sink LTP with terminationDirection as SINK.

7.2.3.1     SSM in band pac

All of the attributes that report/manage SSM quality level can use a common enumeration.

Attribute Name

Description

Type

Related Recommendations

clock port ID

The ID of the SyncLTP_In_Band_Clock object.

Object ID – read only

 

associated port ID

The SyncLTP_In_Band_Clock object is associated with the physical port LTP of this port ID.

Object ID – read only

 

SSM output enable status

Indicate whether to send SSM messages or not.

Boolean – read/write

G. [ITU-T G. 781 ]

SSM information

Current input and output SSM quality levels used by the port. The SSM quality level can be set manually or automatically.

The port should have SSM quality levels for input and output respectively .

 

Enumeration – Read only : /Write

QL-PRC, QL-SSU-A, QL-SSU-B, QL-EEC1, QL-DNU, QL-PRTC, QL-ePRTC, QL-eEEC, etc.

Should use quality levels, not use SSM codes and enhanced SSM codes . Use the clock quality levels listed in section 5.4.1 of [ITU-T G. 781 ] . The corresponding SSM codes and enhanced SSM codes for SyncE refer to table 11-7 and table 11-8 of [ITU-T G. 8264 ] .

e.g: PRC, SSU-A, SSU-B, QL-SEC, DNU, etc.

G. [ITU-T G. 781 ]

G. [ITU-T G. 8264 ]

SSM mode

Indicate whether to use manual or automatic input and output SSM quality levels.

SSM mode should be set for input and output respectively.

Enumeration   – Read/Write:

Manual or ;

Automatic

 

G. [ITU-T G. 781 ]

SSM configuration value

The input and output SSM quality levels set manually.

The   SSM quality level s should be manually c onfigurable for input and output   respectively .

Enumeration – read/write

 

G. [ITU-T G. 781 ]

G. [ITU-T G. 8264 ]

 

7.2.3.2     SSM external clock   pac

Attribute Name

Description

Type

Related Recommendations

external port ID

The ID of the SyncLTP_External_Clock object.

Object ID – read only

 

external port enable status

Indicate whether to enable this external port or not.

Boolean – read/write

 

bits-type

The type of this port, such as 2048kb/s or 2048kHz.

Enumeration     -   read only

G. [ITU-T G. 781 ]

SSM sa-bit

Indicate which sa-bit bits are used for carrying input and output SSM quality levels.

The port should have sa-bit bits for input and output respectively.

Enumeration – read/write

 

G. [ITU-T G. 781 ]

SSM out-threshold

The external port stops transmitting when the SSM quality level is lower than the threshold.

Enumeration – read/write

G. [ITU-T G. 781 ]

SSM information

Current input and output SSM quality levels used by the port. The SSM quality level can be set manually or automatically.

The port should have SSM quality levels for input and output respectively.

Enumeration – read only

 

G. [ITU-T G. 781 ] ,

G. [ITU-T G. 8264 ]

SSM mode

Indicate whether to use manual or automatic input and output SSM quality levels.

SSM mode should be set for input and output respectively.

Enumeration   – Read/Write:

Manual or Automatic

 

G. [ITU-T G. 781 ]

SSM configuration value

The input and output SSM quality levels set manually.

The SSM quality levels should be manually configurable for input and output respectively.

Enumeration – read/write

 

G. [ITU-T G. 781 ] ,

G. [ITU-T G. 8264 ]

 

7.2.3.3     PTP pac

Attribute Name

Description

Type

Related Recommendations

PTP port ID

The ID of the SyncLTP_PTP object.

Object ID – read only

G. [ITU-T G. 8275.1 ] , G. [ITU-T G. 8275.2 ] ,

G. [ITU-T G. 8265.1 ]

associated port ID

The SyncLTP_PTP object is associated with the physical port LTP of this port ID.

Object ID – read only

 

PTP port enable status

Indicate whether to enable this PTP port or not.

Boolean – read/write

G. [ITU-T G. 8275.1 ] , G. [ITU-T G. 8275.2 ] ,

G. [ITU-T G. 8265.1 ]

PTP port state

The current PTP state of the PTP port, such as master, slave, passive, initializing, listening, premaster, uncalibrated, and faulty.

Enumeration – read only

G. [ITU-T G. 8275.1 ] , G. [ITU-T G. 8275.2 ] ,

G. [ITU-T G. 8265.1 ]

PTP asymmetry-correction

The asymmetry correction value of this PTP port.

Integer – read/write , nano seconds   – read/write
same as external time port delay compensation ?

Integer – read/write

G. [ITU-T G. 8275.1 ] , G. [ITU-T G. 8275.2 ]

PTP clock-step

Indicate whether one-step or two-step mechanism is adopted.

Enumeration – read only

G. [ITU-T G. 8275.1 ] , G. [ITU-T G. 8275.2 ] ,

G. [ITU-T G. 8265.1 ]

PTP udp-egress  configuration

The configuration of PTP UDP encapsulation, including   source IP address, destination IP address and IPv4/IPv6 protocol .

Ordered list – Read/Write:

source IP address – String – Read/Write ,

destination IP address – String – Read/Write ,

IPv4/IPv6 protocol – Enumeration – Read/Write .

G. [ITU-T G. 8275.2 ] ,

G. [ITU-T G. 8265.1 ]

PTP mac-egress  configuration

The configuration of PTP MAC encapsulation, including source MAC address, destination MAC address and VLAN configuration.

Ordered list – Read/Write:

source MAC address – String – Read only ,

destination MAC address – String – Read only ,

VLAN configuration – String – Read/Write

G. [ITU-T G. 8275.1 ]

PTP announce-interval

The sending interval of PTP announce message.

Integer: milli seconds – read/write

G. [ITU-T G. 8275.1 ] , G. [ITU-T G. 8275.2 ] ,

G. [ITU-T G. 8265.1 ]

PTP announce receipt-timeout

It is used for fault detection of PTP announce messages.

Integer: milli seconds – read/write

G. [ITU-T G. 8275.1 ] , G. [ITU-T G. 8275.2 ] ,

G. [ITU-T G. 8265.1 ]

PTP sync-interval

The sending interval of PTP Sync message.

Integer: milli seconds – read/write

G. [ITU-T G. 8275.1 ] , G. [ITU-T G. 8275.2 ] ,

G. [ITU-T G. 8265.1 ]

PTP min-delayreq-interval

The sending interval of PTP Delay_req message.

Integer: milli seconds – read/write

G. [ITU-T G. 8275.1 ] , G. [ITU-T G. 8275.2 ] ,

G. [ITU-T G. 8265.1 ]

PTP masterOnly

T he per-port attribute masterOnly

Boolean – read/write

G. [ITU-T G. 8275.1 ] ,

G. [ITU-T G. 8275.2 ]

PTP localPriority

The per-port attribute localPriority

Integer – Read/Write .

G. [ITU-T G. 8275.1 ] , G. [ITU-T G. 8275.2 ] ,

G. [ITU-T G. 8265.1 ]

 

7.2.3.4     PTP   1PPS + ToD pac

Attribute Name

Description

Type

Related Recommendations

external port ID

The ID of the SyncLTP_External_Time object.

Object ID – read only

 

external time port status

Indicate whether this external time port is used as an input or output port.

Boolean - read only

 

external time port dataset

The status dataset of this port

Ordered list – Read / W rite :

grandmasterIdentity – Object ID – Read / W rite ,

priority 1 – Integer – Read / W rite ,

priority 2 – Integer – Read / W rite ,

clockClass – Integer – Read / W rite ,

accuracy – Integer – Read / W rite ,

offsetScaledLogVariance – Integer – Read / W rite ,

timesource – Integer – Read / W rite ,

stepsRemoved – Integer – Read / W rite ,

currentUtcOffset – Integer – Read / W rite .

G. [ITU-T G. 8271 ]

external time port delay compensation

The delay compensation value of this external port.

Integer – read/write , :

  nano seconds ; – read/write
Same as PTP asymmetry-correction ?

Integer – read/write

G. [ITU-T G. 8271 ]

 

Sync protection FC pac

 

Attribute Name

Description

Type

current source port  ID  

The ID of the clock port traced by the f requency s ystem c lock currently.

Object ID – read only

system clock source priority list

The list is used to select clock port. It is composed of clock port IDs in the order of priorities.

List of object ID – read/write

switch type

Three switch types are included: lockout, m anual switch , and forced switch.

Enumeration – read/write ;
Need more discussion on meaning of lockout/manual/forced

switch mode

Indicate whether to switch to the previous-failed synchronization source after its recovery.

Enumeration – r ead /write

Wtr

Wait to restore time. A previous - failed synchronization source is only again considered as available by the selection process if it is fault-free for wtr time .

Integer r ead /write ;

Unit of minutes:
Default value: 15 minutes

SSM enable status

In automatic reference selection process , if SSM is enabled, the selection of clock source is performed based on SSM and priority; otherwise the selection depends on priority only.

Boolean – read/write

UNK status

Indicate whether to take UNK as one of the SSM quality levels or not. If UNK is enabled, its level lies between PRC and SSU_T; otherwise it is taken as DNU.

Boolean – read/write

external clock source priority list

The list is used to select output clock source for this external clock port. It is composed of IDs of system clock and in-band clock ports in the order of priorities.

Object id – read only

Enumeration – r ead /write

Editors’ NOTE: Need to add a column ‘Related Recommendation’ for Sync protection FC pac.

8          UML Model file

This section contains the information model files with data dictionary and the companion profile fil s e specified using the “Papyrus” modelling tool.

G. syncmgmt Model File:

NOTE – The ITU-T G. sync -mgmt UML information models and the Open Model Profile are s pecified using the Papyrus open- source model l ing tool. In order to view and further extend or modify the information model, one will need to install the open source Eclipse software and the Papyrus tool, which are available at [b-Eclipse-Papyrus]. The installation guide for Eclipse and Papyrus can be found in [b-IISOMI-515].

Editor NOTE: Need to add the profile file.

Annex A

< xxx >

(This annex forms an integral part of this Recommendation.)

<Body of annex A>

 

Annex B

< xxx >

(This annex forms an integral part of this Recommendation.)

<Body of annex A>

 

Appendix I

< zzz >

(This appendix does not form an integral part of this Recommendation.)
 

<Body of appendix I>

Bibliography

[b-ONF TR-512] ONF TR-512 (2015),   Core Information Model (CoreModel) .

[b- Eclipse-Papyrus ] Papyrus Eclipse UML Modelling Tool   < https://www.eclipse.org/papyrus/ >

[b-IISOMI-515] IISOMI-515_Papyrus-Guidelines.docx   < https://community.opensourcesdn.org/wg/EAGLE/document/171 >

[b- ITU-T X.yyy] Recommendation ITU-T X.yyy (date) ,   Title .


[1] Synchronization information includes: For frequency synchronization, the frequency and synchronization status messages, and for precision time, the time stamp and other contents of the PTP announce messages.

[2] Synchronization information includes: For frequency synchronization the frequency and synchronization status messages, and for precision time the time stamp and PTP messages.

[3] For all of the object instance s representing “Sync” separate conditional packages will be defined for frequency and precision time. The objects will be constructed from the base class using composition (as defined in G.7711).