R-PHY Holdover Synchronization via Boundary Clock and Offset Feedback
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Solution Overview
Problem
In R-PHY network architectures, synchronization between the core and Remote PHY Devices (RPDs) becomes problematic when either loses connection to the timing clock, leading to frequency and phase drift, which is costly to address with better oscillators or frequency assistance, and often inefficient in networks without supported protocols.
Innovation Solution
Implementing a system where RPDs communicate with the core to discover relevant parameters for resynchronization, such as timing state, cable modem status, and MAP advance time, to select between phase step or frequency adjustments, and temporarily adjusting MAP advance time to regain synchronization, along with using a boundary clock for multicast timing information during holdover.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If better oscillators are used to reduce frequency drift during holdover, then synchronization performance is improved, but device cost and power consumption increase
Solution Approach 1:
The system measures and records the oscillator offset during the holdover period before reconnection. This preliminary measurement allows the RPD to compensate for the drift that occurred during holdover by adjusting its timing based on the measured offset, rather than relying solely on expensive high-precision oscillators to prevent drift in the first place.
Solution Approach 2:
The system implements a feedback mechanism where the RPD measures its oscillator offset from the master clock after reconnection, communicates this offset to the core, and receives timing adjustment instructions. This closed-loop feedback allows the system to correct synchronization errors after they occur, enabling the use of lower-cost oscillators while maintaining synchronization performance.
2Reliability
If frequency assistance is used to prevent frequency drift during holdover, then synchronization performance is improved, but network complexity and protocol requirements increase
Solution Approach 1:
The system uses the existing DOCSIS communication channel as an intermediary to transmit oscillator offset information between the RPD and the core. Rather than implementing a new dedicated synchronization protocol, the invention leverages the already-established data communication infrastructure to carry timing information, thereby avoiding additional network protocol complexity.
Solution Approach 2:
The RPD autonomously measures its own oscillator offset from the master clock and initiates the correction process by communicating with the core. The system enables itself to detect and correct its own synchronization errors without requiring complex external control mechanisms, reducing overall network protocol requirements.
3Productivity
If MAP advance time is temporarily adjusted to regain synchronization, then resynchronization speed is improved, but timing precision may be temporarily reduced
Solution Approach 1:
The system dynamically adjusts the MAP advance time parameter during the resynchronization process. By making this parameter adjustable and time-dependent, the system can temporarily increase MAP advance time to accelerate resynchronization when needed, then restore it to normal values to maintain timing precision during steady-state operation.
Solution Approach 2:
The system pre-adjusts the MAP advance time before actual data transmission resumes after holdover. By cushioning or buffering the timing adjustment in advance, the system can regain synchronization without causing timing errors in actual data packets, separating the resynchronization function from the data transmission function.
Data Source
AI summary
Systems and methods for retaining synchronization between a CMTS core and an RPD when the RPD loses synchronization to a timing grandmaster, where both the core and the RPD are configured for individual synchronization in a slave configuration to the timing grandmaster, by operating the core as a boundary clock that sends timing information to the RPD.