Recent years have witnessed an increased interest in Precision Time Protocol (PTP) in telecommunication networks, either as an alternative to Global Positioning System (GPS) or as synchronization back-up. To achieve n...
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ISBN:
(纸本)9781479918607
Recent years have witnessed an increased interest in Precision Time Protocol (PTP) in telecommunication networks, either as an alternative to Global Positioning System (GPS) or as synchronization back-up. To achieve node synchronization at the mu s-level, very accurate measurements of time offsets are needed. However, unless PTP is fully supported throughout the network, timing packets may be subjected to propagation delays whose variability can significantly impair measurement. In the PTP telecommunication profile Sync packets can be broadcast at high rate, providing a slave node with statistical information that can be employed to detect and estimate such network effects. The accuracy of these estimates is analyzed in the paper, which considers the assumed underlying probability models and discusses statistical aspects for PTP packets affected by variable queuing delays. Characteristics of packet selection algorithms in ITU-T Recommendations are analyzed, providing indications on performance.
Clock synchronization is one of the popular research topics in Distributed Measurement and Control Systems (DMCSs). In most industrial fields, such as Smart Grid and Flight Test, the highest requirement for synchroniz...
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Clock synchronization is one of the popular research topics in Distributed Measurement and Control Systems (DMCSs). In most industrial fields, such as Smart Grid and Flight Test, the highest requirement for synchronization accuracy is 1 mu s. IEEE 1588 Precision Time Protocol-2008 (PTPv2) can theoretically achieve sub-microsecond accuracy, but it relies on the assumption that the forward and backward delays of PTP packets are symmetrical. In practice, PTP packets will experience random queue delays in switches, making the above assumption challenging to satisfy and causing poor synchronization accuracy. Although using switches supporting the Transparent Clock (TC) can improve synchronization accuracy, these dedicated switches are generally expensive. This paper designs a PTP clock servo for compensating Queue-Induced Delay Asymmetry (QIDA), which can be implemented based on ordinary switches. Its main algorithm comprises a minimum window filter with drift compensation and a fuzzy proportional-integral (PI) controller. We construct a low-cost hardware platform (the cost of each node is within USD 10) to test the performance of the clock servo. In a 100 Mbps network with background (BG) traffic of less than 70 Mbps, the maximum absolute time error (max |TE|) does not exceed 0.35 mu s, and the convergence time is about half a minute. The accuracy is improved hundreds of times compared with other existing clock servos.
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