Time Synchronization In Networks Research Articles

Long-term propagation delay characteristics of telecommunication lines

The variations in outgoing path delay and incoming delay of a paired transmission path have been measured simultaneously and independently for over one year. The characteristics will allow the performance of delay compensation schemes for precise time synchronization of digital telecommunication networks to be evaluated. The annual delay variation is caused by temperature changes, and its magnitude is about 3 mu s for the 2400-km line investigated. It is shown that the variation of annual delay can be estimated by measuring air temperature above the cable. The delay variations, which vary slowly with a period of over 10/sup 3/ s, such as annual and daily variations, are clearly correlated for the outgoing and incoming paths. Asymmetry of slow delay variation is below 1 ns (indicated noise deviation). The cause of the delay variation that has a period of 10/sup 0/< tau <102 s is the noise generated by the multiplexing and demultiplexing equipment.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Transmission delay variation compensation in precision time-synchronous networks

This paper analyzes the performance of transmission delay variation compensation between two nodes in precision time-synchronous networks. The compensation methods predict transmission delay using round-trip path and compensate delay variations by employing a phase-locked loop. Two methods for compensating delay variations in the master node (scheme A) and in the slave node (scheme B) are compared. Results show that scheme B is more accurate and more stable than scheme A. Then the total compensation error, which equals the sum of the delay variation, delay measurement error, and PLL internal noise, is calculated using the measured delay of actual telecommunication lines. Minimum compensation deviation of 2 ns is obtained by optimizing the PLL parameter. This deviation is determined by the flicker phase noise of the difference delay between the outgoing and incoming paths.

Some practical applications of the isotropic time in rotating coordinates

This paper uses the isotropic time in a noninertial frame to discuss the principle of the ring-laser gyro and related phase-coherent systems. The gravitational effects of a slowly rotating massive body, such as the Earth, are also allowed for. The use of time-synchronization networks and very long baseline radio interferometry as probes of both the stationary and low-frequency gravitational fields near the Earth is suggested.