SELF-CHECKING PAIR-BASED MASTER/FOLLOWER CLOCK SYNCHRONIZATION

• US 20080144668A1
• Filed: 12/13/2006
• Published: 06/19/2008
• Est. Priority Date: 12/13/2006
• Status: Active Grant

• Current Assignee: Honeywell International Inc.
• Original Assignee: Honeywell International Inc.
• Inventors: Hall, Brondan, Driscoll, Kevin R., Paulitsch, Michael
• Granted Patent: US 7,912,094 B2
• Time in Patent Office: Days
• US Class Current: 370/503
• 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, the method comprising:

providing a network communication schedule for 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 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 from the second node, 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 common sending point for transmitting a first synchronization message, wherein the common sending point is calculated based on the time difference; and

selectively sending the first synchronization message to the braided ring network when the common sending point is reached based on the time difference.

2. The method of claim 1 further comprising:

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

sending 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 one or both of the first synchronizing message on a first channel of the network and a second synchronizing message on a second channel of the network; and

setting a local reference time based on one or both of the first synchronizing message and the second synchronizing 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 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 synchronizing message is received with integrity and the second synchronizing message is received with integrity, the method further comprises:

determining a first message send time of the first synchronization message;

determining a second message send time of the second synchronization message;

calculating a third message send time based on a function of the first message send time and the second message send time; and

setting the local reference time based on the third message send time.

8. The method of claim 6, wherein when the first synchronizing message is received with integrity and the second synchronizing message is received without integrity, the method further comprises:

determining a first message send time of the first synchronization message; and

setting the local reference time based on the first message send time.

9. The method of claim 6, wherein when the first synchronizing message is received without integrity and the second synchronizing message is received without integrity, the method further comprises:

determining if the first synchronizing message agrees with the second synchronizing message;

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

determining a first message send time of the first synchronization message;

determining a second message send time of the second synchronization message;

calculating a third message send time based on a function of the first message send time and the second message send time; and

setting the local reference time based on the third message send time.

10. A method for clock synchronization in a network having a plurality of nodes, the method comprising:

receiving a first synchronizing message from a self-checking pair on a first channel of the network and a second synchronizing message from the self-checking pair on a second channel of the network;

determining whether one or both of a first synchronizing message and the second synchronizing message are received with integrity; and

setting a local reference time based on one or both of the first synchronizing message and the second synchronizing message.

11. The method of claim 10, wherein setting the local reference time further comprises:

performing an instantaneous correction to the local reference time based on a known propagation delay and one or both of a message send time of the first synchronizing message and a message send time of the second synchronizing message.

12. The method of claim 10, wherein when the first synchronizing message is received with integrity and the second synchronizing message is received with integrity, the method further comprises:

determining a first message send time of the first synchronization message;

determining a second message send time of the second synchronization message;

calculating a third message send time based on a function of the first message send time and the second message send time; and

setting the local reference time based on the third message send time.

13. The method of claim 10, wherein when the first synchronizing message is received with integrity and the second synchronizing message is received without integrity, the method further comprises:

determining a first message send time of the first synchronization message; and

setting the local reference time based on the first message send time.

14. The method of claim 10, wherein when the first synchronizing message is received without integrity and the second synchronizing message is received without integrity, the method further comprises:

determining if the first synchronizing message agrees with the second synchronizing message;

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

determining a first message send time of the first synchronization message;

determining a second message send time of the second synchronization message;

calculating a third message send time based on a function of the first message send time and the second message send time; and

setting the local reference time based on the third message send time.

15. The method of claim 10, further comprising determining whether one or both of the first synchronizing message and the second synchronizing message were sent by a designated master self-checking pair.

16. The method of claim 15, further comprising determining whether one or both of the first synchronizing message and the second synchronizing message were sent by a designated master self-checking pair based on one or both of an predetermined selection scheme and a dynamic selection scheme.

17. 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 configured to communicatively couple the first node to the second node, wherein the first node and the second node are configured to transmit rendezvous messages to each other over the at least one link;

wherein the first node is further configured to determine when a rendezvous message is received from the second node, and determine 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 is further configured to calculate a first common sending point for transmitting a first synchronization message on the first channel based on the first time difference;

wherein the second node is further configured to determine when a rendezvous message is received from the first node, and determine 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 is further configured to calculate a second common sending point for transmitting a second synchronization message on the second channel based on the second time difference.

18. The system of claim 17, wherein when the first time difference is less than a reference bound, the first node is further configured to transmit 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 is further configured to transmit the second synchronization message when the second common sending point is reached.

19. The system of claim 17, wherein when the first time difference is not less than the reference bound, the first node is further configured to refrain from transmitting the first synchronization message;

and

wherein when the second time difference is not less than the reference bound, the second node is further configured to refrain from transmitting the second synchronization message.

20. The system of claim 17, wherein the first node is further configured to determine 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 is further configured to determine 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.