MAC Layer Timestamp Accuracy with FEC Feedback
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Solution Overview
Problem
In IEEE 10G-BASE KR networks, the latency of the physical coding sub-layer (PCS) is not fixed or known, which complicates the accurate determination of timestamp values for Precision Time Protocol (PTP) messages, especially with forward error correction (FEC) introducing delays that need to be accounted for.
Innovation Solution
The proposed solution involves a feedback link between the FEC layer and the MAC layer, using a feedback signal generated by a signal checking block within the FEC layer to determine the timestamp value, which compensates for delays caused by FEC changes and other latency shifts, ensuring accurate timestamp determination for PTP messages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a feedback link is implemented between FEC layer and MAC layer to accurately determine timestamp values, then synchronization accuracy is improved, but device complexity increases
Solution Approach 1:
The patent implements a feedback link between the FEC layer and MAC layer that transmits information about FEC processing delays. The MAC layer receives feedback regarding the actual delay introduced by FEC encoding/decoding operations, allowing it to compensate for variable latency when calculating PTP timestamps. This feedback mechanism enables accurate timestamp determination despite the added system complexity.
2Reliability
If FEC encoding is applied to ensure reliable data transmission, then reliability is improved, but transmission latency increases
Solution Approach 1:
The patent performs preliminary measurement and characterization of FEC processing delays. The system pre-determines the latency introduced by FEC operations and uses this information to adjust timestamp calculations in advance, rather than attempting to reduce the actual FEC processing time. This allows the system to maintain both reliability through FEC and accuracy in timing measurements.
3Adaptability or versatility
If variable buffering delays are introduced in network nodes, then adaptability is improved, but measurement precision deteriorates
Solution Approach 1:
The patent uses feedback links at multiple layers (FEC layer feedback to MAC layer, and MAC layer timestamp generation) to track and compensate for variable buffering delays. By continuously monitoring actual delay values and feeding this information back to the timestamp calculation logic, the system maintains precision even when buffering conditions vary dynamically across network nodes.
Data Source
AI summary
Systems and methods and systems are disclosed for allowing the medium access control (MAC) layer in a communication system within an integrated circuit or device to accurately determine a timestamp point and a timestamp value when, for example, the Precision Time Protocol (PTP) protocol is in use by the communication system. Such determination of accurate timestamp point and timestamp value may be used by the communication system to account for and to compensate for the time shift(s) from forward error correction (FEC) sublayer changes in a data frame that is transmitted by the MAC layer. Feedback is provided to the MAC from the FEC to allow the MAC to accurately determine the timestamp point and timestamp value align preamble of the data frame to the beginning of the FEC bit block that is output by the FEC sublayer.