Ultra-high precision time synchronization interface requirements
1Key Takeaways
This document is applicable to the research and development, testing and application of time synchronization equipment, transmission bearer equipment and synchronization networks with ultra-high-precision time synchronization interfaces.
2Expert Interpretation
An in-depth interpretation of the communications industry standard "Ultra-High Precision Time Synchronization Interface Requirements", covering the technical specifications of the in-band PTP synchronization interface, dedicated PTP interface and 1PPS output interface, and analyzing protocol encapsulation, optimal master clock algorithm and hybrid networking compatibility requirements.
Interpretation of the core content of the standard
This specification defines the interface requirements for ultra-high precision time synchronization systems with synchronization accuracy better than ±30ns, mainly including three types of interfaces: in-band PTP synchronization interface, dedicated PTP synchronization interface and 1PPS output interface.
Key Technical Requirements
| Interface Type | Physical Layer Requirements | Protocol Requirements | Typical Applications |
|---|---|---|---|
| In-band PTP | GE/10GE/25GE and other Ethernet interfaces MTN/FlexE interfaces | Support Two-step mode Message rate adjustable from 1 to 64Hz | Transmission bearer equipment |
| Dedicated PTP | ≥GE optical port | Support BMC algorithm Delay compensation ±100μs | Time synchronization equipment |
| 1PPS | SMA connector/50Ω impedance | Rising edge trigger Rise time<5ns | Synchronization performance test |
Protocol enhancement features
Ultra-high precision PTP protocol improvement
The specification adds Protocol type 2 protocol type (PTP profile Specific 2=TRUE), which carries the Link accuracy indication TLV in the Announce message, including:
- Accuracy Level 1: 5ns accuracy device hop count
- stepsRemoved field: total path hop count statistics
The improved BMC algorithm adds the Link accuracy dimension when comparing data sets to ensure that ultra-high precision clock sources are selected first.
Hybrid networking compatibility solution
The standard requires the device to support three working modes:
- Adaptive mode: automatically switch according to the protocol of the other end
- Forced high-precision mode (compatible with YD/T 2375-2019)
- Forced ultra-high-precision mode (TLV extension enabled)
In MTN/FlexE networking, synchronization information is transmitted through the first valid PHY link, and is switched in order of numbering in case of a fault. The WTR mechanism complies with ITU-T G.781 requirements.
Implementation recommendations
Device selection considerations
- The time server must support OC mode, and the edge device must support BC mode
- Check whether the PTP timestamp plane is located in the PHY layer (AM/PMA sublayer)
- Verify the 1PPS interface rise time indicator (10%-90% range <5ns)
Network deployment recommendations
- It is recommended to enable the protocol conversion function on the edge devices between the ultra-high precision domain and the high precision domain
- It is recommended to configure multiple physical PHY link redundancy in MTN/FlexE networking
- The length of the 1PPS test cable should be controlled within 3 meters