Two-Way Time Transfer Protocol for Reciprocal Path Synchronization
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Solution Overview
Problem
Current network synchronization methods, such as the 'send and pray' distribution approach, are limited by path quality, lack of traceability, and inability to assure path diversity, leading to performance degradation and accuracy issues in timing distribution, especially with the presence of faulty oscillators and timing loops.
Innovation Solution
A two-way time transfer protocol that sends signals between nodes with time interval counters to ensure reciprocal path latency and constant delays, allowing for precise time and frequency transfer over existing T1/E1 physical layers, eliminating the need for external GPS antennas and enabling indoor GPS-based timing antennas.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single-ended timing distribution approach is used, then the system complexity is reduced, but the measurement precision and reliability of time transfer deteriorate due to unverified path quality and potential timing loops
Solution Approach 1:
The patent implements a two-way time transfer protocol where timing messages are exchanged bidirectionally between master and client clocks. The client sends its timestamp back to the master, enabling the master to calculate round-trip delay and verify path quality. This feedback mechanism allows precision measurement while maintaining manageable system complexity through standardized protocol implementation.
Solution Approach 2:
Instead of the traditional single-ended approach where only the master sends timing references, the patent inverts the model by having both master and client actively participate in the timing exchange. The client becomes an active participant by sending timestamp feedback, transforming it from a passive receiver to an active contributor in the synchronization process.
2Measurement precision
If external GPS antennas are required for PRS systems, then time transfer accuracy is improved, but the ease of operation and installation deteriorate due to complex antenna mounting requirements
Solution Approach 1:
The patent replaces expensive, complex external GPS antenna systems with standard indoor building infrastructure (T1/E1 physical layers). By using existing copper wiring and standard telecommunication equipment, the system achieves adequate timing accuracy without requiring specialized outdoor antenna installations, rooftop mounting, or line-of-sight GPS reception.
Solution Approach 2:
The patent enables existing T1/E1 communication infrastructure to serve dual purposes: both data/voice transmission and precise timing distribution. The same copper pairs and network equipment used for telephony and data communications can simultaneously carry timing references, eliminating the need for separate GPS antenna systems and simplifying installation.
3Adaptability or versatility
If legacy synchronization messaging schemes are used, then compatibility with existing systems is maintained, but the reliability deteriorates due to inability to detect and resolve timing loops and marginal performance issues
Solution Approach 1:
The two-way protocol provides feedback about path quality and clock performance that enables detection of timing loops and faulty oscillators. By measuring round-trip delay and comparing timestamps bidirectionally, the system can identify abnormal conditions such as timing loops, degraded paths, or malfunctioning clocks, and take corrective action.
Solution Approach 2:
The patent introduces dynamic performance monitoring and verification capabilities to the previously static timing distribution system. The system continuously measures path quality, detects anomalies, and can dynamically switch references or alert operators to problems, transforming rigid legacy infrastructure into an adaptive, self-monitoring system.
Data Source
AI summary
A two-way time transfer protocol includes: sending a signal from a first node including a first clock and a first time interval counter coupled to the first clock over a transport physical layer coupled to the first node to a second node coupled to the transport physical layer, the second node including a second clock and a second time interval counter coupled to the second clock; then sending a last second node time interval counter value from the second time interval counter of the second node over the transport physical layer to the first node; and then comparing at the first node a last first node time interval counter value to the last second node time interval counter value. A first-way path latency from the first node to the second node is substantially equal to a second-way path latency from the second node to the first node, and all of a first node transmit delay, a first node receive delay, a second node transmit delay and a second node receive delay are substantially constant.