Improving the PTP synchronization accuracy under asymmetric delay conditions

Tight synchronization timing is expected to play a crucial role for the realization of emerging Internet of Things (IoT) high value real-time applications such as smart transportation and smart grid. Most packet-based synchronization protocols require two-way communications delay symmetry for precise accuracy. The Precision Time Protocol (PTP) provides mechanisms to measure and take into account the delay asymmetry problem, such as the residence time measurements, but recommend PTP support at all nodes. In this paper, we consider partial on-path PTP support, where a subset of the nodes are PTP unaware. We propose probing-based mechanisms in order to estimate asymmetry and improve the synchronization performance. The extensive simulation results show that the proposed lightweight per-packet asymmetry mitigation (PPAM) mechanism, aiming at estimating the per-packet delay components, outperforms the other considered protocols mainly at low to mid network loads, while under certain conditions the regular PTP with QoS support provides more stable synchronization accuracy.