Clock Controller Queue Delay Asymmetry Compensation
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Solution Overview
Problem
Conventional clock synchronization protocols in packet-data networks face challenges in compensating for dynamic asymmetry caused by queue-induced delays, which can lead to inaccuracies in time synchronization between master and slave clocks, especially under heavy network loads and in end-to-end secured communication paths.
Innovation Solution
A clock management method and a clock controller that periodically collect data on queue sizes and link rates from transit nodes to estimate and compensate for queue-induced delay asymmetry, providing correction parameters to slave clocks to improve synchronization accuracy without relying on 'lucky' packets.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional clock synchronization protocols are used in packet-data networks, then basic time synchronization is achieved, but synchronization accuracy deteriorates under heavy network loads due to queue-induced delays
Solution Approach 1:
The system performs preliminary measurement of queue sizes and link rates at transit nodes before timing packets traverse the network path. This advance collection of network state data enables the calculation of expected queue-induced delays, which are then used to pre-compensate the measured delay values, thereby maintaining synchronization accuracy even under heavy network loads
Solution Approach 2:
The system implements a feedback mechanism where synchronization performance is continuously monitored and compared against expected values derived from queue size and link rate measurements. When deviations are detected, the system adjusts its delay compensation calculations accordingly, creating a closed-loop control system that maintains synchronization accuracy despite varying network conditions
2Measurement precision
If static asymmetry compensation is used, then compensation for fixed delay differences is achieved, but dynamic queue-induced delay asymmetry cannot be compensated
Solution Approach 1:
The system transitions from static asymmetry compensation to dynamic compensation by continuously measuring queue sizes and link rates at transit nodes. These time-varying measurements enable the system to calculate and apply dynamic delay compensation values that adapt to changing network conditions, thereby compensating for both static and dynamic components of delay asymmetry
Solution Approach 2:
The system changes the compensation parameters from fixed static values to dynamic values derived from real-time queue size and link rate measurements. By adjusting the delay compensation parameter based on measured network state, the system achieves accurate compensation for dynamic queue-induced delays while maintaining compatibility with existing synchronization protocols
3Measurement precision
If 'lucky' packets are relied upon for asymmetry measurement, then delay asymmetry can be estimated, but accuracy is lost when network nodes are heavily loaded and lucky packets are unavailable
Solution Approach 1:
The system extracts delay asymmetry information from the measured queue sizes and link rates at transit nodes, rather than relying on the arrival of specially timed 'lucky' packets. This extraction approach separates the measurement process from packet timing luck, enabling continuous and reliable asymmetry measurement regardless of network load conditions
Solution Approach 2:
The system enables transit nodes to self-report their queue sizes and link rates, providing the necessary data for delay asymmetry calculation without requiring special measurement packets. This self-service approach ensures that measurement data is continuously available from all transit nodes, eliminating the unreliability associated with lucky packet availability under heavy load
4Reliability
If end-to-end secured communication paths are used, then security is improved, but queue-induced delay asymmetry compensation becomes more difficult
Solution Approach 1:
The system introduces an intermediary component that collects queue size and link rate measurements from transit nodes and provides delay compensation data to the synchronization protocol. This intermediary layer handles the complexity of measuring and compensating for queue-induced delays, allowing the secured communication path to maintain both security and synchronization accuracy without requiring complex modifications to the encryption/decryption process
Data Source
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AI summary
There is provided a method of clock management in a packet data network (PDN) implementing a time-transfer protocol and a clock controller configured to operate therein. The clock controller is configured to: obtain topology data informative of a master clock node and a slave clock node constituting end points of a PTP path in the PDN and further informative of at least part of transit nodes of said PTP path; periodically obtain data informative of queue size and link rate characterizing, during a collection period, the at least part of transit nodes in master-slave (MS) and slave-master (SM) directions; for each collection period, use the obtained queue-related data to estimate queue-induced delay asymmetry of the PTP path; and send the estimated value of queue-induced delay asymmetry to the slave node, the estimated value to be used by a clock residing on the slave node as delay asymmetry correction parameter.