DOCSIS Timing Protocol Phase Error Compensation
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Solution Overview
Problem
The synchronization of DOCSIS networks with cellular networks is challenging due to conflicting timing requirements, particularly when phase corrections are needed after losing and re-establishing connection to a master clock, which can result in significant drift and lengthy correction times, especially in hybrid fiber coaxial networks used for x-haul in cellular communications.
Innovation Solution
The implementation of the DOCSIS Timing Protocol (DTP) with dynamic compensation mechanisms, such as modifying the DTP time adjustment parameter to accommodate phase errors, allows for rapid phase and frequency synchronization within DOCSIS limitations, avoiding outages by using virtual phase steps and frequency slewing to align the DOCSIS symbol rate with mobile network requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional DOCSIS phase correction methods are used after losing and re-establishing connection to a master clock, then the system can recover synchronization, but the correction time becomes excessively long (potentially minutes) and may cause network outages
Solution Approach 1:
The system performs preliminary actions by pre-configuring alternative master clock sources and maintaining holdover capability in case of master clock failure. When a phase error is detected, the system can immediately switch to a backup master clock or use holdover mode, avoiding the need to wait for lengthy phase correction processes after connection restoration.
Solution Approach 2:
The invention changes the synchronization parameters by allowing dynamic adjustment of the master clock source and modifying the phase correction methodology. Instead of using traditional slow frequency-tracking methods, the system employs parameter changes such as virtual phase steps and frequency slewing to rapidly align the DOCSIS symbol rate with mobile network requirements, reducing correction time from minutes to seconds.
2Reliability
If large phase adjustments are made to re-lock to a new master clock source with a large time offset (e.g., 20 microseconds), then the system can resynchronize, but the adjustment conflicts with DOCSIS timing requirements and may disrupt mobile network synchronization
Solution Approach 1:
The system introduces an intermediary mechanism that mediates between the DOCSIS timing protocol requirements and the mobile network synchronization needs. This intermediary allows the system to perform necessary phase adjustments while maintaining compliance with both DOCSIS specifications and mobile network timing requirements, preventing conflicts that would otherwise disrupt service.
Solution Approach 2:
The invention implements dynamic timing adjustment capabilities that allow the system to adapt its behavior based on real-time conditions. The phase correction process becomes dynamic rather than static, enabling the system to make large adjustments when needed while maintaining compliance with DOCSIS requirements through controlled, gradual transitions and virtual phase step mechanisms.
3Manufacturing precision
If frequency adjustments are made to correct phase errors, then synchronization can be achieved, but the adjustment rate is limited by DOCSIS specifications (10 ppb/s), resulting in lengthy correction times
Solution Approach 1:
The system employs a skipping mechanism that allows the synchronization process to rush through large portions of the correction path by using virtual phase steps. Instead of making continuous small adjustments limited by the 10 ppb/s DOCSIS frequency change rate, the system can effectively skip ahead by applying larger virtual corrections, then use the limited frequency adjustment capability to finish the synchronization process, dramatically reducing the overall correction time from minutes to seconds.
Solution Approach 2:
The invention implements periodic action through the use of virtual phase steps that can be applied at different rates and intervals. The system can periodically apply larger virtual corrections when conditions permit, then transition to more conservative frequency adjustments, creating a multi-stage synchronization process that achieves high precision while improving overall speed compared to continuous slow adjustment.
Data Source
AI summary
A method for adjusting a phase error includes a first device detecting a phase error at a timing interface of the first device. The first device modifying a DOCSIS timing protocol parameter based upon the detected phase error. The first device causing a modification of a second device's timestamp output in a manner based upon the detected phase error by the modification of the DOCSIS timing protocol parameter.