Patent ID: 8259758
Filing Date: 2012-09-04
Classification: H04J

Abstract:
1. A precision time synchronization method for a network having a local master node and at least one slave node, the method comprising steps of: outputting a synchronization packet from the local master node to the slave node, and recording, by the local master node, a first time of outputting the synchronization packet; recording, by the slave node, a second time of receiving the synchronization packet when the slave node receives the synchronization packet; adding, by the slave node, the second time to a sync response packet after receiving the synchronization packet, and returning, by the slave node, the sync response packet to the local master node; extracting, by the local master node, the second time from the sync response packet after the local master node receives the sync response packet, so that the local master node establishes a first time difference equation expressing that a difference between the second time and the first time is equal to a time offset plus a packet transmission delay time; sending, by the slave node, a slave sync packet to the local master node, and recording, by the slave node, a third time of outputting the slave sync packet; recording, by the local master node, a fourth time of receiving the slave sync packet after the local master node receives the slave sync packet; adding, by the slave node, the third time to a slave node notification packet; and sending, by the slave node, the slave node notification packet to the local master node; establishing, by the local master node, a second time difference equation expressing that a difference between the fourth time and the third time is equal to the packet transmission delay time minus the time offset, wherein the local master node calculates the time offset between the local master node and the slave node and the packet transmission delay time according to the first and second time difference equations; and outputting, by the local master node, a clock update packet to the slave node, wherein the clock update packet carries the time offset between the local master node and the slave node and the packet transmission delay time, so that the slave node is time synchronized with the local master node after the slave node performs time calibration according to the time offset.