Ruxandra Scheiterer

Synchronization Performance of the Precision Time Protocol in Industrial Automation Networks

This paper analyzes the factors that affect the synchronization performance in peer-to-peer precision time protocol (PTP). We first study the influence of frequency drift in the absence of jitter and compare the gravity of the master drift with that of the slave drift. Then, we study the influence of jitter under the assumption of constant frequencies and the effect of averaging. The analytic formulas provide a theoretical ground for understanding the simulation results, some of which are presented, as well as the guidelines for choosing both system and control parameters.

Synchronization Performance of the Precision Time Protocol

This paper analyzes the factors that affect the synchronization performance in using the precision time protocol (FTP). We first study the influence of jitter under the assumption of no frequency drifts. Then we study the influence of frequency drift in the absence of jitter. The analytic formulas provide a theoretical ground for the understanding of simulation results as well as guidelines for choosing both system and control parameters when applying FTP.

Optimal estimation and control of clock synchronization following the Precision Time Protocol

Using the Precision Time Protocol (PTP) specified by the IEEE 1588 standard, synchronization of distributed clocks is achieved by propagating the timing information of a preselected master clock throughout the entire network. Based on this directly or indirectly obtained noisy timing information, each slave clock tries to follow as closely as possible the master time. This paper formulates the PTP based clock synchronization as an estimation-control problem. An LQG controller is designed which produces an optimal reconstruction of the master time at each slave in the sense of minimizing the mean square error of the estimator and minimizing an LQR cost function for the controller. The performance of the proposed optimal controller is verified by simulation results.

A Kalman Filter Approach to Clock Synchronization of Cascaded Network Elements

Abstract The Precision Time Protocol specified by IEEE 1588 standard has been proved to be an appropriate network synchronization protocol. The PTP protocol is based on exchanging appropriate timing information, generated by time stamping according to the local clocks, between adjacent clocks. Using the time-stamps, a slave element learns the relation between its own clock and the master clock so that it can synchronize its time to the reference time provided by the master. Uncertainties, e.g., random stamping and quantization errors, greatly affect the synchronization precision. This paper presents a probabilistic state-space model which quantifies the uncertainties and represents the relation between the system variables. Then clock synchronization is posed as a state estimation problem and solved by using Kalman filter. The performance of this approach is verified by numerical results.

An optimal control approach to clock synchronization

Algorithms following the peer-to-peer Precision Time Protocol (PTP) specified by the IEEE 1588 standard achieve synchronization of distributed clocks by propagating the timing information of a preselected master clock throughout the entire network. Based on this noisy timing information, each slave clock tries to follow as closely as possible the master time. In this work we formulate clock synchronization as a stochastic estimation-control problem. A two dimensional LQG controller is derived which produces an optimal reconstruction of the master time at each slave in the sense of minimizing the mean square error of the estimated master counter and frequency. Owing to its specific structure, the LQG controller does not violate the transparent clock concept. The performance of the proposed controller is verified by simulations.

Probabilistic model for clock synchronization of cascaded network elements

Precision Time Protocol (PTP) synchronizes clocks of networked elements by exchanging messages containing precise time-stamps. A master clock is carefully chosen to provide the reference clock to the rest elements in the network, called slaves. Using the time-stamps, slave element learns the relation between its own clock and the master clock so that it can synchronize its time to the reference time. Uncertainties, e.g., random stamping and quantization errors, affect the synchronization precision. This paper presents a probabilistic state-space model which quantifies the uncertainties and represents the relation between system variables. Estimation of hidden variables, i.e. the system states, is carried out by using Kalman filter. The performance of this approach is verified by numerical results.

Knowledge Acquisition and Automated Generation of Bayesian Networks for a Medical Dialogue and Advisory System

Probabilistic models such as Bayesian networks [6] are well suited for medical decision support and are the basis of many successful applications [1],[3],[4],[8],[9],[10]. Bayesian networks provide a rigorous and efficient framework for inference, i.e. for calculating the probability of each stochastic variable given a set of observations. However, knowledge acquisition and generation of the network are still demanding tasks when large medical domains have to be modelled.

1μs-conform line length of the Transparent Clock Mechanism defined by the Precision Time Protocol (PTP Version 2)

This paper quantifies the ldquo1 mus-conformrdquo line-length of the Transparent Clock Mechanism of peer-to-peer Precision Time Protocol (PTP Version 2), i.e. the number of elements that stay within the plusmn1 mus sync error tolerance, for crystal oscillator output frequencies of 100 MHz, 250 MHz, 500 MHz and 1 GHz, i.e. for time quantization errors of 10 ns, 4 ns, 2 ns and 1 ns.

Synchronization performance of the Precision Time Protocol in the face of slave clock frequency drift

This paper studies the performance of the precision time protocol (PTP) of the IEEE 1588 standard for drifting slave frequencies. The error expression for the master time estimate at the nth slave is analytically derived and demonstrated in simulation runs. We show that single-slave frequency drift is very benign compared to master frequency drift, which is only matched by all slaves drifting.

Troubleshooting in GSM mobile telecommunication networks based on domain model and sensory information

Mobile cellular telecommunication networks are complex dynamic systems whose troubleshooting presents formidable challenges. Typically, the network performance analysis is carried out on a network cell basis and it is based on the traffic information obtained from various sensors such as the number of requested calls, number of dropped calls, number of handovers, etc. This paper presents a novel troubleshooting system, which provides likelihood of different user-specified root causes of performance degradation based on the observed sensory information and the underlying domain model. This domain model has a form of a Causal Network whose structure is appropriately chosen. The novelty of the herein presented approach is that the domain model is initially based on expert knowledge and later on refined via supervised learning with the data gathered during system operation.