Latency Floor Estimation in Packet Networks
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Solution Overview
Problem
Packet-switched networks face challenges in maintaining accurate time and frequency alignment due to transit delay variation, which is exacerbated by network congestion, leading to reduced accuracy and reliability of conventional alignment systems.
Innovation Solution
A method and system that collect transit times of multiple packets, compute average and fastest transit times, perform a curve fit, and estimate the latency floor to improve clock frequency correction in packet-switched networks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional time alignment protocols (NTP, PTP) are used in packet-switched networks, then time and frequency alignment can be achieved, but alignment accuracy deteriorates due to transit delay variation from network congestion
Solution Approach 1:
The system performs preliminary characterization of network latency by collecting transit times of multiple packets and computing the latency floor before using this pre-computed value to correct clock frequency. This preliminary action separates the latency measurement from the time alignment process, making the alignment less sensitive to transient congestion effects.
Solution Approach 2:
The patent introduces an intermediary latency floor value that mediates between the variable network transit delay and the clock frequency correction. Instead of directly using variable transit times for alignment, the system uses the computed latency floor as a stable reference point, filtering out the harmful variations caused by congestion.
2Ease of manufacture
If packet-switched networks are used for cost-effective time alignment, then GPS satellite signal requirements are eliminated, but transit delay variation from statistical switching reduces alignment precision
Solution Approach 1:
The patent extracts the essential timing information from packets by computing the latency floor from multiple transit time measurements. This extraction process separates the useful timing data from the noisy variable delays, allowing packet-switched networks to provide accurate time alignment without requiring GPS infrastructure.
Solution Approach 2:
The network system performs self-characterization by automatically measuring its own latency properties through packet transit time collection and analysis. This self-service approach allows the system to adapt to its specific network conditions and compensate for its statistical switching behavior without external intervention.
3Measurement precision
If multiple packets are used to compute latency floor, then measurement accuracy improves, but time collection duration increases
Solution Approach 1:
The patent uses a sufficient number of packets (at least 100) to achieve accurate latency floor measurement, accepting the time required to collect this data. This partial action approach balances measurement accuracy with practical time constraints, using enough samples to filter out statistical variations without requiring excessive collection time.
Data Source
AI summary
A latency floor between two nodes of a packet-switched network is estimated using transit times of a group of packets traversing the two nodes. In particular, a periodically generated histogram of packet transit times is used to estimate the latency floor. In some packet-switched networks, the behavior of some network elements changes drastically when the network is congested. Because latency floor cannot be accurately estimated under such conditions, packet transit times collected during a congested state of the network are discarded.