Coherent DSP Frame Timing Reference for PTP Jitter Reduction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Precision Time Protocol (PTP) over optical networks faces challenges due to non-deterministic timing delays caused by elastic First-In-First-Out (FIFO) and enhanced high coding gain soft-decision Forward Error Correction (SD-FEC) schemes, leading to uncertainty in time transfer between network nodes.
Innovation Solution
The use of a coherent Digital Signal Processor (DSP) frame with periodic training and pilot symbols as timing reference points to minimize delay uncertainty and jitter in PTP timestamping, allowing for precise timing transfer over coherent optical interfaces like 400ZR and G.709.3, by detecting timing reference points in padding or reserved areas of the DSP frame.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If elastic FIFO and SD-FEC schemes are used in optical networks, then error correction capability and data transmission reliability are improved, but timing delay uncertainty and jitter increase
Solution Approach 1:
The patent applies preliminary action by pre-defining specific bit patterns (such as 0x5E or 0xAA) in predetermined positions within the DSP frame structure before transmission. These training symbols serve as known reference points that enable deterministic timing measurement. By establishing these reference patterns in advance, the system can accurately identify frame boundaries and calculate timing delays without being affected by the variable processing delays introduced by elastic FIFO and SD-FEC schemes, thus resolving the contradiction between error correction capability and timing precision.
2Productivity
If coherent optical interfaces with DSP frames are used, then data transmission performance is improved, but delay uncertainty at start-up and after fault recovery increases
Solution Approach 1:
The patent implements feedback by using the detected training symbols to continuously monitor and measure actual timing delays in the transmitted and received frames. The system compares the expected position of training symbols with their actual detected positions, calculates the timing offset, and uses this feedback information to compensate for delay uncertainties. This feedback mechanism enables the system to adapt to changing conditions during operation and maintain accurate timing synchronization even after start-up or fault recovery events.
Solution Approach 2:
The patent applies preliminary action by incorporating known training symbol patterns into the DSP frame structure before transmission begins. These pre-defined patterns (such as repeated 0x5E or 0xAA sequences) provide immediate reference points that can be detected as soon as the frame is received, enabling rapid timing measurement without waiting for complex synchronization procedures. This preliminary structuring of reference data eliminates delay uncertainty during start-up and fault recovery scenarios.
3Measurement precision
If PTP timestamping is performed over optical networks, then time synchronization is achieved, but timing accuracy deteriorates due to non-deterministic delays
Solution Approach 1:
The patent introduces an intermediary element - the training symbol pattern - that serves as a mediator between the transmitted data and the timing measurement process. Instead of attempting to measure timing directly from arbitrary data bits, the system uses these known intermediate patterns as reference markers. The training symbols act as a bridge that allows the PTP timestamping mechanism to anchor its measurements to deterministic, known positions within the frame structure, thereby isolating the timing measurement from the non-deterministic processing delays introduced by optical network components.
Data Source
AI summary
A coherent optical modem includes an optical interface; and circuitry connected to the optical interface and configured to detect a first timing reference point in a transmit Digital Signal Processor (DSP) frame in a transmit direction from a first node to a second node, and detect a second timing reference point in a receive DSP frame in a receive direction from the second node to the first node, wherein the first timing reference point and the second timing reference point are determined based on a pattern in any DSP frame field including i) padding area, ii) a reserved area, and iii) a DSP Multi-Frame Alignment Signal (MFAS) area. The pattern can be input in select DSP frames for a time period that is greater than a time period for each DSP frame.