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YD/T 2375-2019: Technical requirements for high accuracy time synchronization
YD/T 2375-2019
COMMUNICATION INDUSTRY STANDARD
OF THE PEOPLE’S REPUBLIC OF CHINA
ICS 33.040.20
M33
Replacing YD/T 2375-2011
Technical requirements for high accuracy time
synchronization
ISSUED ON: NOVEMBER 11, 2019
IMPLEMENTED ON: JANUARY 01, 2020
Issued by: Ministry of Industry and Information Technology of PRC
Table of Contents
Foreword ... 4 
1 Scope ... 6 
2 Normative references ... 6 
3 Abbreviations ... 7 
4 Time synchronization requirements and precision grade division ... 8 
4.1 Classification of time synchronization precision ... 8 
4.2 Requirements for high-precision time synchronization ... 10 
5 Requirements for high-precision time synchronization networking ... 10 
5.1 Hierarchical structure of high-precision time synchronization network ... 10 
5.2 Composition and basic functions of time synchronization device ... 11 
5.3 Principles of time synchronization networking ... 11 
6 Requirements for high-precision time synchronization performance indicators ... 15 
6.1 Overview ... 15 
6.2 Allocation of performance indicators of time synchronization network when satellite
timing is available ... 16 
6.3 Allocation of performance indicators of time synchronization network when satellite
timing service is unavailable ... 17 
7 High-precision time synchronization transmission technology ... 18 
7.1 High-precision time synchronization technology ... 18 
7.2 Inter-office transmission technology ... 19 
7.3 Intra-office distribution technology ... 19 
8 Requirements for high-precision time synchronization interface ... 19 
8.1 Overview ... 20 
8.2 PTP time interface requirements ... 20 
8.3 1PPS+ToD time interface ... 22 
9 Reliability requirements of high-precision time synchronization network ... 27 
9.1 Reliability requirements for time sources ... 27 
9.2 Requirements for time synchronization device and time link settings ... 27 
9.3 Redundant configuration requirements of time synchronization device ... 28 
9.4 Selection requirements for time reference source ... 28 
10 Basic requirements for high-precision time synchronization related device ... 31 
10.1 High-precision time synchronization device ... 31 
10.2 Basic requirements for time synchronization of bearer device ... 33 
10.3 Basic Requirements for time synchronization of synchronized devices ... 35 
Appendix A (Informative) IRIG/DCLS time coding ... 37 
Appendix B (Informative) Setting location and quantity of time synchronization device
... 41 
Appendix C (Informative) Engineering feasibility requirements ... 42 
Appendix D (Informative) Estimation of time distribution of time source part in case of
satellite timing failure ... 44 
Appendix E (Informative) Key factors affecting inter-office transmission accuracy . 45 
Appendix F (Informative) 1588V2 protocol and BMC algorithm ... 48 
Technical requirements for high accuracy time
synchronization
1 Scope
This standard specifies the networking requirements for high-precision time
synchronization, the performance index requirements for high-precision time
synchronization, the reliability requirements for high-precision time synchronization
networks, the basic requirements for equipment related to high-precision time
synchronization.
This standard applies to high-precision time synchronization networks, based on ground
transmission using PTP technology.
2 Normative references
The following documents are essential to the application of this document. For the dated
documents, only the versions with the dates indicated are applicable to this document;
for the undated documents, only the latest version (including all the amendments) is
applicable to this standard.
YD/T 900-1997 Technical requirement for SDH equipment - Clock
YD/T 1012-1999 Node clock set of digital synchronization network and its timing
feature
YD/T 1479-2006 Technical requirements and testing methods of primary reference
clock equipment
YD/T 2879-2015 (OAM) technical requirements based on the synchronous network
operation management and maintenance of a packet network
ITU-T G.8262 Timing characteristics of synchronous Ethernet equipment slave
clock
ITU-T G.8275.1 Precision time protocol telecom profile for phase/time
synchronization with full timing support from the network
IEEE 1588-2008 Standard for a precision clock synchronization protocol for
networked measurement and control systems
3GPP TR 25.836 Node B synchronization of time division duplex (TDD)
Figure 1 -- Hierarchical structure of time synchronization network
5.2 Composition and basic functions of time synchronization device
The level-1 time synchronization device shall be composed of two cesium clocks and
two satellite timing receivers, etc., which can be traced to a higher-level domestic time-
keeping reference (for example, the National Time Service Center), through a dedicated
comparison method.
The level-2 time synchronization device shall be equipped with at least rubidium clocks.
The device consists of two rubidium clocks and two satellite timing receivers. It shall
support the traceability of time to the level-1 time synchronization device, through
ground means; support the punctuality function of ground frequency signals. It shall be
able to be reliably traced to China's frequency synchronization network.
The level-3 time synchronization device shall be equipped with at least a high-stable
crystal oscillator. The device consists of two high-stable crystal oscillators and at least
one satellite timing receiver. It shall support time traceability to the level-2 time
synchronization device or the level-1 time synchronization device, through ground
means; support the punctuality function of ground frequency signals. It shall be able to
be reliably traced to China's frequency synchronization network.
See Appendix B, for the location and quantity of time synchronization devices, at all
levels.
5.3 Principles of time synchronization networking
5.3.1 General principles of time synchronization networking
Under normal circumstances, the time synchronization device shall prefer the signal of
the satellite timing receiver. When the satellite signal is unavailable, the low-level time
synchronization device shall trace to the high-level time synchronization device,
through the ground time link. In the case where both the satellite signal and the ground
time link are unavailable, the low-level time synchronization device shall be able to use
the signal from the frequency synchronization network, to keep time. If conditions
permit, the time synchronization network shall be traced to the national time-frequency
standard system.
When building a time synchronization network, according to the actual network
conditions, flexible networking structures (for example, level-2 or level-3 networking)
and setting methods (for example, a level-3 time synchronization device with a
rubidium clock) can be used.
5.3.2 Relationship between time synchronization network and frequency
the best network element of frequency time keeping as the reference. See 8.3.4, for the
specific mapping mechanism of scheme 1 and scheme 2. See 9.4.2, for the source
selection processing mechanism.
5.3.3 Principles of reference source setting
5.3.3.1 The principle of setting the timing reference of the level-1 time
synchronization
The principle of setting the timing reference of level-1 time synchronization is as
follows:
a) Under normal circumstances, the level-1 time synchronization device shall track
the signal of the satellite timing receiver;
b) When the satellite timing receiver fails, the level-1 time synchronization device
shall be able to keep time, based on the cesium clock;
c) If the relevant technical conditions are available, the level-1 time synchronization
device can be traced to the national time-frequency system, as the fundamental
guarantee for the entire time synchronization network.
5.3.3.2 The principle of setting the timing reference of the level-2 time
synchronization
The principle of setting the level-2 time synchronization timing reference is as follows:
a) Under normal circumstances, the level-2 time synchronization device shall track
the signal of the satellite timing receiver;
b) The level-2 time synchronization device shall be equipped with at least two
ground time input reference signals, which are respectively connected to the
level-1 time synchronization device, from different physical routes. When the
satellite signal is unavailable, the level-2 time synchronization device shall be
able to track the ground time input reference signal;
c) The level-2 time synchronization device shall be equipped with at least one ground
frequency input reference signal, which shall be traceable to the frequency
synchronization network. In the event that satellite signals are not available, the
level-2 time synchronization device shall be able to track the ground frequency
input reference signal. In the event that both satellite signals and ground time
input reference signals are unavailable, the level-2 time synchronization device
shall be able to use the signal, which is from the frequency synchronous network,
to keep time.
5.3.3.3 The principle of setting the timing reference of the level-3 time
synchronization
The principle of setting the timing reference of the level-3 time synchronization are as
follows:
a) Under normal circumstances, the level-3 time synchronization device shall track
the signal of satellite timing receiver;
b) The level-3 time synchronization device shall be equipped with two ground time
input reference signals, which are respectively connected to the level-1 or level-
2 time synchronization device, from different physical routes. When the satellite
signal is unavailable, the level-3 time synchronization device shall be able to track
the ground time input reference signal;
c) The level-3 time synchronization device shall be equipped with a ground
frequency input reference signal, which shall be traceable to the frequency
synchronization network. When the satellite signal is unavailable, the level-3 time
synchronization device shall be able to track the ground frequency input reference
signal. When both the satellite signal and the ground time input reference signal
are unavailable, the level-3 time synchronization device shall be able to use the
signal, which is from the frequency synchronous network, to keep time.
5.3.4 Principles for organizing time synchronization path
In order to ensure the reliability of the time synchronization network and the precision
of time allocation, the organization of time synchronization paths shall follow the
following principles:
a) Ground time transmission shall follow the principle of one-way layer-by-layer
downward (applicable to scheme 1 only);
b) Ground time signal transmission is only allowed from high-level time
synchronization device to low-level time synchronization device; it is not allowed
for the low-level time synchronization device to transmit timing to high-level or
same-level time synchronization device (only applicable to scheme 1);
c) The time transfer between the ground offices, between the time synchronization
device and the synchronized device (such as base station), shall use PTP
technology; the time transfer, between the ground offices between time
synchronization devices, can use PTP technology or other technologies;
d) Level 2 and Level 3 time synchronization device shall be able to obtain time
synchronization, from at least two different physical routing ground timing links;
the ground timing physical links are preferably buried optical cables;
e) The number of time synchronization devices, which are connected in series to the
time synchronization path, shall not exceed 3, of which there are at most one
level-1 time synchronization device, one level-2 time synchronization device, one
level-3 time synchronization device;
f) The number of bearer device network elements, which are connected in series in
the time synchronization path, from the time synchronization device to the
synchronized device, should not exceed 30. The number of bearer device network
elements, which are connected in series between any two adjacent levels of time
synchronization devices (including the OA station, which supports the PTP
function) should not exceed 20. Refer to clause 10.2 for the time synchronization
function and performance requirements of the bearer device;
g) For bearer device, the frequency reference shall be taken from the frequency
synchronization network;
h) For the level-2/level-3 time synchronization device, when the satellite timing
receiver is unavailable, the frequency reference shall preferably come from the
intra-office frequency synchronization device, OR trace to the frequency
synchronization network, through the shortest path.
6 Requirements for high-precision time synchronization
performance indicators
6.1 Overview
The working state of the satellite timing receiver will cause changes in the time
transmission link of the time synchronization network. When the satellite signal is
available, the time synchronization network forms a single-level structure, that is, there
is only one time synchronization device, in the time path, as the time source, as shown
in Figure 3. When the satellite timing is unavailable, it may connect, in series, multiple
time synchronization devices, into the time synchronization network, to form a multi-
level structure, that is, a maximum of three time synchronization devices may be
connected in series in the time path, as the time source, as shown in Figure 4.
For the above two cases, the end-to-end time performance indicator consists of three
parts: The time source part, the bearer network part, the end distribution part.
Considering that the time deviation, which is introduced by the line asymmetry and
compensation error, that may exist in the engineering construction, will adversely affect
the end-to-end indicator allocation, the de...