TCP/IP Clock Synchronization Using Timestamped Packets
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Solution Overview
Problem
Synchronizing clocks between two communication terminals over a network is challenging due to independent clock operations, clock drift, and varying propagation delays, especially in packet data networks where the path changes with network traffic and router responsiveness.
Innovation Solution
Implementing a method using TCP/IP to continuously synchronize clocks by adding time stamps to packets and adjusting a bias value based on latency measurements, allowing for accurate timing measurements without additional packet overhead, even when clocks have separate and independent operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If clocks of two communication terminals are synchronized using a special signal or separate communications channel, then clock synchronization accuracy is improved, but system cost and complexity increase
Solution Approach 1:
The patent uses existing TCP/IP data packets to carry timestamp information for clock synchronization, making the data communication channel serve dual purposes: both data transmission and timing synchronization. This eliminates the need for separate synchronization hardware or dedicated signaling channels, thereby reducing system complexity while maintaining synchronization accuracy.
Solution Approach 2:
The synchronization mechanism leverages the natural bidirectional communication already present between terminals. Each terminal independently timestamps outgoing packets and processes incoming packets with timestamps, allowing the system to self-synchronize without external master clock intervention or additional specialized components.
2Device complexity
If clock synchronization is performed using packet data networks, then system cost is reduced, but synchronization accuracy deteriorates due to varying propagation delays
Solution Approach 1:
The patent implements a feedback mechanism where terminals exchange timestamped packets bidirectionally. Each terminal measures the round-trip time and calculates propagation delay based on the time difference between sending a timestamped packet and receiving the corresponding response. This feedback loop allows continuous measurement and compensation of varying network delays, maintaining synchronization accuracy despite changing network conditions.
Solution Approach 2:
The system performs preliminary timestamping of packets at the source terminal before transmission. By embedding the departure timestamp in advance, the system prepares the necessary timing data before the variable network propagation occurs, enabling accurate delay calculation when the packet arrives at the destination.
3Length of moving object
If terminals are at different distances from the master clock, then propagation delay varies, but synchronization cannot be achieved unless propagation delay differences are determined
Solution Approach 1:
The patent recognizes and exploits the asymmetry in propagation delays for different terminals. Instead of assuming symmetric delays, the system independently measures the propagation delay for each terminal-to-master and master-to-terminal path using timestamped packet exchanges. This asymmetric measurement approach allows accurate compensation for varying distances without requiring uniform network topology.
Data Source
AI summary
Clocks of communication terminals can be synchronized using packets over TCP/IP. In one example, an Internet Protocol packet is received at the first terminal from the second terminal, the packet having a time stamp indicating the time at which it was sent from the second terminal. The time is determined at which the packet arrived at the first terminal and compared to the time stamp to determine a minimal feasible bias. The determined minimal feasible bias is compared to a stored bias and the stored bias is set to the determined minimal feasible bias if the stored bias is less than the minimal feasible bias. A clock time difference is then determined at the second terminal using the stored bias.