Precision Time Protocol

A synchronization protocol that aligns multiple devices' clocks over Ethernet to sub-microsecond precision.

The Precision Time Protocol (PTP) is defined by the IEEE 1588 standard, used to synchronize clocks across devices on a local network. The network elects one device as the master clock; the others exchange timestamped messages with it to measure link delay and clock offset, then correct themselves accordingly. When network cards support hardware timestamping, accuracy can reach the sub-microsecond range, far tighter than common NTP synchronization. gPTP, defined by IEEE 802.1AS, is a trimmed-down profile of PTP used mainly in automotive and other time-sensitive networks. On a robot, the camera, lidar, IMU, and main computer each have their own clock, and without synchronization, multi-sensor fusion and data logging end up misaligned in time — which is why PTP is often used to give everything a common time base. On Linux, linuxptp (ptp4l, phc2sys) is the common implementation.

ExampleOn a data-collection rig, the main computer acts as the PTP master clock, with the lidar and industrial cameras as slaves, so every point-cloud frame and image frame carries a directly comparable timestamp.

Also called

PTP, IEEE 1588, gPTP

Related

Multi-sensor Time Synchronization / Timestamp Alignment · Multi-Sensor Fusion · LiDAR · EtherCAT (Ethernet for Control Automation Technology) · PREEMPT_RT

Sources

Precision Time Protocol (Wikipedia)
The Linux PTP Project