Patent ID: 7688862

Claim:
A method of synchronizing at least one node in a real-time scheduled packet network, comprising: transmitting first heartbeat packets at a predetermined frequency to the at least one node; receiving the first heartbeat packets at the at least one node; synchronizing an internal frequency reference in each of the at least one node according to at least two of the received first heartbeat packets; and calculating a link phase of a link over which the heartbeat packets are received by the at least one node by subtracting a time at which the node transmitted a second heartbeat packet from a time at which the node received a first heartbeat packet, wherein the link phase from a first node to a second node is different than a link phase from said second node to said first node, wherein said link phase from said first node to said second node is determined in accordance with at least one of the group consisting of the formula: LinkPhase AB =(Delay AB −Φ B )mod T wherein Delay AB is the propagation delay of the link from the first node (A) to the second node (B), Φ B is the phase offset of the second node, and mod T is the time interval between heartbeats, and LinkPhase BA =(Delay BA +Φ B )mod T wherein Delay BA is the propagation delay of the link from the second node (B) to the first node (A), Φ B is the phase offset of the second node, and mod T is the time interval between heartbeats.