Self-checking pair-based master/follower clock synchronization

• US 7,912,094 B2
• Filed: 12/13/2006
• Issued: 03/22/2011
• Est. Priority Date: 12/13/2006
• Status: Active Grant

• Current Assignee: Honeywell International Inc.
• Original Assignee: Honeywell International Inc.
• Inventors: Paulitsch, Michael, Driscoll, Kevin R., Hall, Brendan
• Primary Examiner(s): Rao; Seema S
• Assistant Examiner(s): HUYNH, KHOA B
• Application Number:
  US11/610,454
• Publication Number:
  US 20080144668A1
• Time in Patent Office: 1,560 Days
• Field of Search: 370/464, 370/498, 370/503, 370/351, 370/389, 370/395.1, 370/395.2, 370/395.21, 340/825, 340/825.2, 375/354, 375/355, 375/356, 375/357, 375/358, 375/359, 455/7, 455/11.1, 455/12.1, 455/13.2, 709/248
• US Class Current: 370/508
• CPC Class Codes: H04J 3/0652 Synchronisation among time division multiple access [TDMA] nodes, e.g. time triggered protocol [TTP] bus network with centralized control in which slots are of a TDMA packet structure H04L12/4035
• CPC Class Codes: H04J 3/0676 Mutual
• CPC Class Codes: H04L 12/4637 Interconnected ring systems

Abstract

Systems and methods for network clock synchronization are provided. In one embodiment, a method for clock synchronization in a braided ring network comprises: providing a schedule for a braided ring network comprising a plurality of nodes, wherein at least two nodes comprise a self-checking pair of a first node and a second node, the first node performing a method comprising: determining when a first rendezvous message is received from the second node; when the second rendezvous message is received, calculating a time difference between the send instance of the first rendezvous message and a local time; when the time difference is not greater than a reference bound, calculating a sending point for transmitting a synchronization message, wherein the sending point is calculated based on the time difference; and selectively sending the synchronization message to the braided ring network when the sending point is reached based on the time difference.

Claims

1. A method for clock synchronization in a braided ring network comprising a plurality of nodes, wherein at least two nodes of the plurality of nodes comprise a self-checking pair of a first node and a second node, the method comprising:

determining at the first node when a first rendezvous message is received from the second node;

when the first rendezvous message is received from the second node, calculating at the first node a time difference between a send instance of the first rendezvous message and a local time;

when the time difference is not greater than a reference bound, calculating at the first node a common sending point for transmitting a first synchronization message, wherein the common sending point is calculated based on the time difference so that the first synchronization message is transmitted at approximately the same point in time as a second synchronization message transmitted from the second node; and

selectively sending the first synchronization message from the first node to at least one node in the braided ring network other than the second node when the common sending point is reached based on the time difference.

2. The method of claim 1 further comprising:

determining at the first node when it is time to resynchronize with the second node based on the network communication schedule; and

sending from the first node a second rendezvous message to the second node.

3. The method of claim 1, wherein when the time difference is greater than the reference bound, selectively sending the first synchronization message further comprises:

refraining from sending the first synchronization message when the common sending point is reached.

4. The method of claim 1, further comprising:

receiving at the at least one node one or both of the first synchronization message on a first channel of the network and the second synchronization message from the second node on a second channel of the network; and

setting a local reference time at the at least one node based on one or both of the first synchronization message and the second synchronization message.

5. The method of claim 4, wherein setting the local reference time further comprises one of:

performing an instantaneous correction to the local reference time; and

incrementally correcting the local reference time over a period of time.

6. The method of claim 1 further comprising:

propagating the first synchronization message around the braided ring network based on high-integrity data propagation.

7. The method of claim 6, wherein when the first synchronization message is received at the at least one node with integrity and the second synchronization message from the second node is received with integrity at the at least one node, the method further comprises:

determining at the at least one node a first message send time of the first synchronization message;

determining at the at least one node a second message send time of the second synchronization message;

calculating at the at least one node a third message send time based on a function of the first message send time and the second message send time; and

setting at the at least one node a local reference time based on the third message send time.

8. The method of claim 6, wherein when the first synchronization message is received with integrity at the at least one node and the second synchronization message from the second node is received at the at least one node without integrity, the method further comprises:

determining at the at least one node a first message send time of the first synchronization message; and

setting a local reference time at the at least one node based on the first message send time.

9. The method of claim 6, wherein when the first synchronization message is received at the at least one node without integrity and the second synchronizing synchronization message from the second node is received at the at least one node without integrity, the method further comprises:

determining at the at least one if the first synchronization synchronizing message agrees with the second synchronization synchronizing message;

verifying at the at least one node that the first synchronization synchronizing message and the second synchronization synchronizing message do not originate from a single node;

determining at the at least one node a first message send time of the first synchronization message;

determining at the at least one node a second message send time of the second synchronization message;

calculating at the at least one node a third message send time based on a function of the first message send time and the second message send time; and

setting a local reference time at the at least one node based on the third message send time.

10. A synchronizing system for a network, the system comprising:

a first node having a first local clock, the first node communicatively coupled to a first channel of the network;

a second node having a second local clock, the second node communicatively coupled to a second channel of the network;

at least one link communicatively coupling the first node to the second node, wherein the first node and the second node transmit rendezvous messages to each other over the at least one link;

wherein the first node determines when a rendezvous message is received from the second node, and determines a first time difference between the first local clock and the second local clock based on a send time instance of the rendezvous message from the second node;

wherein the first node calculates a first common sending point for transmitting a first synchronization message to at least one node other than the second node on the first channel based on the first time difference;

wherein the second node determines when a rendezvous message is received from the first node, and determines a second time difference between the first local clock and the second local clock based on a send time instance of the rendezvous message from the first node; and

wherein the second node calculates a second common sending point for transmitting a second synchronization message to at least one node other than the first node on the second channel based on the second time difference;

wherein the first common sending point and the second common sending point are calculated so that the first synchronization message is transmitted at approximately the same point in time as the second synchronization message.

11. The system of claim 10, wherein when the first time difference is less than a reference bound, the first node transmits the first synchronization message when the first common sending point is reached;

and

wherein when the second time difference is less than the reference bound, the second node transmits the second synchronization message when the second common sending point is reached.

12. The system of claim 10, wherein when the first time difference is not less than the reference bound, the first node refrains from transmitting the first synchronization message;

and

wherein when the second time difference is not less than the reference bound, the second node refrains from transmitting the second synchronization message.

13. The system of claim 10, wherein the first node further determines the first time difference between the first local clock and the second local clock based on a difference in the send time instance of the rendezvous message from the second node and a rendezvous message sent by the first node;

and

wherein the second node further determines the second time difference between the first local clock and the second local clock based on a difference in the send time instance of the rendezvous message from the first node and a rendezvous message sent by the second node.