Packet Network Clock Synchronization with Delay Variation Filtering
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Solution Overview
Problem
Existing network synchronization methods, such as those using the Network Time Protocol (NTP) and IEEE 1588, face challenges in asymmetrical networks where propagation delays and phase offsets are affected by queuing delays caused by bridges and routers, leading to variations in jitter and wander that do not meet requirements for applications like wireless base stations and digital video/audio transmission.
Innovation Solution
A synchronizing apparatus and method that measures time differences using multiple two-way message packets, estimates frequency and propagation delays using a baseline algorithm, and verifies these estimates to remove errors caused by network delay variations, thereby generating a synchronized slave clock signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If standard two-way message scheme is used for synchronization, then basic clock synchronization is achieved, but synchronization accuracy deteriorates due to network delay variation caused by queuing delays
Solution Approach 1:
The patent applies preliminary action by pre-classifying delay samples into delayed and non-delayed groups before performing synchronization calculations. The system proactively identifies and separates non-delayed samples (which accurately reflect propagation delay) from delayed samples (affected by queuing delays), ensuring that only reliable data is used for baseline formation and synchronization parameter calculation. This preliminary classification prevents delay variation from degrading synchronization accuracy.
2Adaptability or versatility
If messages are transmitted through bridges and routers with non-preemptive scheduling, then network infrastructure requirements are met, but delay variation increases due to packet queuing
Solution Approach 1:
The patent applies the taking out principle by extracting and isolating the non-delayed delay samples from the mixed delay samples. The system identifies samples that were not subjected to queuing delays and separates them from samples affected by bridge and router processing. This extraction creates a clean subset of data that accurately represents propagation delay without the contaminating effect of network scheduling variations, thereby maintaining measurement precision while working within standard network infrastructure constraints.
3Device complexity
If baseline algorithm is applied to all time difference samples, then frequency offset estimation is simplified, but estimation accuracy deteriorates due to inclusion of delayed samples
Solution Approach 1:
The patent applies segmentation by dividing the set of all delay samples into two distinct segments: delayed samples and non-delayed samples. This segmentation allows the baseline algorithm to be applied specifically to the non-delayed segment, where it can accurately estimate frequency offset without being corrupted by queuing delay variations. The segmentation maintains algorithmic simplicity while dramatically improving estimation accuracy by ensuring the baseline is formed from reliable data only.
Data Source
AI summary
Provided are a synchronizing apparatus and method for performing synchronization in a packet network. The synchronizing apparatus includes a sampling unit to measure a time difference using a plurality of time stamps included in a plurality of two-way message packets, an estimating unit to estimate a frequency offset by applying a baseline algorithm to the time difference, a verifying unit to verify the frequency offset to remove an error caused by network delay variation, and a synchronizing unit to remove the frequency offset from a local slave clock signal and generate a slave clock signal synchronized to a clock signal of a master device.