Receive PHY Pipeline Timestamping for Network Clock Synchronization
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Solution Overview
Problem
Achieving precise synchronization of real-time clocks in network nodes is challenging due to latency and jitter in clock synchronization messages, and existing hardware timestamping methods may not provide sufficient accuracy, especially in devices with variable delay PHY pipelines.
Innovation Solution
A network device with receive PHY pipeline circuitry that uses a counter to compute timestamps close to the beginning of the pipeline, accounting for symbol timing and pipeline delay, and inserts these timestamps into data packets, allowing for accurate time synchronization even in devices with variable latency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If hardware timestamping is used in NIC to avoid CPU load inaccuracy, then timestamp accuracy is improved, but pipeline latency and jitter still affect the timestamping precision
Solution Approach 1:
The patent applies preliminary action by capturing the timestamp at the very beginning of the PHY pipeline when the packet first arrives, before it undergoes any processing that would introduce variable delays. The timestamp is generated at the packet capture stage, prior to any pipeline operations, ensuring that the measured time reflects the actual arrival time without being contaminated by subsequent processing latencies.
Solution Approach 2:
The patent uses feedback by measuring the actual pipeline delay through round-trip time calculations with delay request messages, then using this measured delay information to compensate for pipeline effects in the timestamp. The system feeds back the observed latency characteristics to adjust and correct the timestamp values, eliminating the harmful effects of pipeline delay.
2Measurement precision
If PTP protocol is used to synchronize clocks among network nodes, then clock synchronization accuracy is improved, but latency and jitter in message distribution worsen the synchronization precision
Solution Approach 1:
The patent applies preliminary action by performing timestamping at the earliest possible point in the receive pipeline, immediately when packets are captured from the network interface. This preliminary timestamping occurs before any protocol processing, queuing, or pipeline operations that would introduce latency and jitter, thereby capturing the true arrival time for accurate PTP synchronization calculations.
Solution Approach 2:
The patent extracts the timestamping function from the main packet processing pipeline and performs it separately at the packet capture stage. By separating the timestamping operation from the subsequent PTP protocol processing and pipeline operations, the system eliminates the confounding effects of pipeline latency and jitter on the timestamp measurement, achieving more accurate clock synchronization.
3Adaptability or versatility
If timestamping is performed in software to handle PTP packets, then flexibility is improved, but CPU load causes timestamp inaccuracy
Solution Approach 1:
The patent introduces an intermediary hardware timestamping mechanism in the PHY layer that operates independently of the software processing path. This intermediary hardware component captures timestamps at packet arrival, mediating between the network interface and the software PTP processing, thereby providing accurate timestamps without burdening the CPU and maintaining both flexibility and precision.
Data Source
AI summary
In one embodiment, a network device, includes a network interface port configured to receive data symbols from a network node over a packet data network, at least some of the symbols being included in data packets, and controller circuitry including physical layer (PHY) circuitry, which includes receive PHY pipeline circuitry configured to process the received data symbols, and a counter configured to maintain a counter value indicative of a number of the data symbols in the receive PHY pipeline circuitry.