Patent ID: 8189624
Filing Date: 2012-05-29
Classification: H04J,H04L

Abstract:
1. A communication system, in which a master node apparatus having a reference clock and a plurality of slave node apparatuses each having an internal clock are connected to form a ring, for circulating a packet among a plurality of node apparatuses by transferring the packet according to a packet transferring order prescribed for each node apparatus, wherein the master node apparatus sends a measurement packet to a slave node apparatus being a receiver according to the packet transferring order, and receives the measurement packet which has been circulated among the plurality of slave node apparatuses; according to time-keeping of the reference clock, stores a sending time of the measurement packet and a received time of the measurement packet; generates a measurement result notifying packet showing the sending time of the measurement packet and the received time of the measurement packet; and sends the measurement result notifying packet generated to a slave node apparatus being a receiver according to the packet transferring order, and wherein each of the plurality of slave node apparatuses receives the measurement packet from a node apparatus being a sender according to the packet transferring order, and sends the measurement packet received to a node apparatus being a receiver according to the packet transferring order; according to time-keeping of the internal clock, stores at least either of a received time of the measurement packet and a sending time of the measurement packet; and receives the measurement result notifying packet from a node apparatus being a sender according to the packet transferring order; calculates a time correction value using the sending time of the measurement packet and the received time of the measurement packet shown in the measurement result notifying packet received, at least either of the received time of the measurement packet stored and the sending time of the measurement packet stored, a total number of node apparatuses, and a difference between an order of the slave node apparatus and an order of the master node apparatus according to the packet transferring order; and corrects a time of the internal clock using the time correction value calculated.