On the accuracy of packet-based measurements in the PTP telecom profile

Abstract

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 μs-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.