Network Interface Device Clock Synchronization via Transmission Monitoring
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Solution Overview
Problem
In optical networks, particularly passive optical networks (PONs), there is a challenge in synchronizing the time of day (TOD) clock between network interface devices (ONUs) and optical line terminals (OLTs) due to high asymmetry in propagation delays, which affects the accurate distribution of phase information for mobile backhaul applications like wireless voice and data transmissions.
Innovation Solution
The implementation of techniques that allow network interface devices to synchronize their TOD clocks with OLT clocks by monitoring transmission instances, determining the correct time to receive frames, and loading TOD information based on precise frame identifiers, using external circuitry to ensure synchronization within ±1 microsecond, as per standards like G.984.3 Am. 2, even for devices not originally compliant with these standards.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional clock synchronization methods are used in optical networks, then basic timekeeping is maintained, but synchronization precision deteriorates due to high asymmetry in propagation delays
Solution Approach 1:
The patent applies preliminary action by having the ONU determine in advance when it should receive the start of frame pulse from the OLT based on its transmission instances. The ONU calculates the expected reception time of frames before they arrive, allowing it to prepare for precise synchronization. This proactive timing calculation enables the system to compensate for propagation delay asymmetry before it affects synchronization accuracy.
2Reliability
If the network interface device waits for incoming frames to synchronize clocks, then clock synchronization is achieved, but time loss increases due to uncertain frame arrival times
Solution Approach 1:
The patent eliminates time loss by having the ONU perform preliminary calculations to determine exactly when it should receive frames from the OLT. Instead of waiting passively for frame arrival, the ONU proactively calculates reception times based on its transmission instances and the round-trip delay. This allows the ONU to be ready to synchronize its TOD clock precisely when frames arrive, eliminating unnecessary waiting time.
Solution Approach 2:
The patent uses feedback by having the ONU monitor its own transmission instances and use this information to calculate when it should receive frames. The synchronization process continuously adapts based on actual transmission and reception timing, allowing the system to maintain accurate synchronization while minimizing time loss through dynamic adjustment of expected frame arrival times.
3Adaptability or versatility
If the network interface device uses standard synchronization protocols, then basic compliance is achieved, but adaptability deteriorates for devices not originally compliant with synchronization standards
Solution Approach 1:
The patent introduces an intermediary synchronization mechanism that works between the OLT and ONU without requiring changes to the core device architectures. The ONU acts as an active participant in the synchronization process by calculating expected frame reception times and adjusting its TOD clock accordingly. This intermediary approach allows non-compliant devices to achieve synchronization through the standardized OLT-ONU interaction framework, bridging the gap without requiring full protocol compliance from legacy devices.
Data Source
AI summary
Techniques are disclosed that relate to synchronizing a clock on a network interface device with a clock on an optical line terminal (OLT). In one example, the technique to synchronizing the clocks may include monitoring one or more instances when the network interface device transmits information to the OLT and determining when a frame should be received by the network interface device based on the monitored one or more instances when the network interface device transmits information the OLT.