High-precision time synchronization technical requirements
1Key Takeaways
Standard Name: Technical Requirements for High Accuracy Time Synchronization Standard Code: YD/T 2375-2019 Scope: This standard specifies the networking requirements, performance indicators, network reliability, and basic requirements for related equipment in high-accuracy time synchronization. It is appli…
2Expert Interpretation
An in-depth interpretation of the YD/T 2375-2019 high-precision time synchronization standard, covering core contents such as PTP technology implementation, three-level networking architecture, ±1.5μs accuracy requirements, satellite/ground dual-source switching mechanism, etc., and providing a guide for the selection of carrier equipment and engineering implementation recommendations.
Standard Evolution and Technical Background
As an upgrade of the 2011 version of the standard, YD/T 2375-2019 integrates international standards such as IEEE 1588v2 and ITU-T G.8275.1, focusing on solving the requirements of ±1.5μs-level synchronization accuracy for services such as TD-LTE and MBSFN in the 5G era. The standard adds key technologies such as dual-mode satellite receiver support and BMC replacement algorithm, forming a three-level time synchronization architecture:
| Level | Core Components | Timekeeping Accuracy | Application Scenario |
|---|---|---|---|
| Level 1 | Cesium Clock + Dual Satellite Receiver | ±150ns | National Backbone Network |
| Level 2 | Rubidium Clock + Dual Satellite Receiver | ±250ns | Provincial Backbone Network |
| Level 3 | High-stable crystal oscillator + satellite receiver | ±1μs | Local access network |
Key technology implementation
PTP protocol enhancement features
The standard stipulates the use of IEEE 1588v2 protocol, and the key parameters are configured as follows:
- Message encapsulation: mandatory support for Ethernet II (0x88F7), optional UDP/IPv4/IPv6
- Clock mode: BC/OC/TC three-mode hybrid networking
- Delay mechanism: E2E mandatory support, P2P optional
- Time stamp mode: One-step is mandatory, Two-step is optional
1PPS+ToD interface specification
RS422 electrical interface is adopted for intra-office distribution, key technical indicators are:
| Parameter | Requirement | Tolerance |
|---|---|---|
| Pulse rising edge | ≤50ns | 20-200ms pulse width |
| ToD information transmission | 9600bps without check | Start within 1ms |
| Frame check | CRC-8 polynomial | Initial value 0xFF |
Key points of project implementation
Reliability design
A provincial operator adopts dual rubidium clock + GPS/Beidou dual-mode receiver configuration, and carries the PTP protocol through the PTN network. Key measures:
- The primary and backup time source devices are located in different offices
- The ground link adopts underground optical cable dual routing
- The number of network elements of the carrying equipment is ≤20/segment
- Asymmetric compensation step length is ≤10ns
Fault switching logic
The standard defines a two-level switching scheme:
| Conditions | Scheme 1 | Scheme 2 |
|---|---|---|
| Satellite failure | Prioritize tracking of upper-level equipment | Select the optimal frequency source |
| Status code | 0x01(PRC punctuality) | 0x05(SSU-A) |
| Hierarchical constraints | Strict superior-subordinate relationship | Quality priority principle |