Industrial controller providing deterministic communication on Ethernet

• US 20040141517A1
• Filed: 01/22/2003
• Published: 07/22/2004
• Est. Priority Date: 01/22/2003
• Status: Active Grant

• Current Assignee: Rockwell Automation Technologies Incorporated (Rockwell Automation, Inc.)
• Original Assignee: Rockwell Automation Technologies Incorporated (Rockwell Automation, Inc.)
• Inventors: Harris, Kendal R., Balasubramanian, Sivaram, Moldovansky, Anatoly
• Granted Patent: US 7,339,948 B2
• Time in Patent Office: Days
• US Class Current: 370/462
• CPC Class Codes: H04L 12/56 Packet switching systems

Abstract

A transmission schedule is overlaid on the Ethernet protocol to allow use of this readily available high speed protocol for transmission of I/O data communicated in an industrial control environment and requiring a high degree of determinism. Scheduling improves load leveling and bandwidth utilization and by producing a more consistent delay may be teamed with time synchronization to produce more accurate clock synchronization.

Claims

1. A method of providing deterministic transmission of I/O data between nodes of an industrial controller communicating on an Ethernet network having a network bandwidth, the method comprising the steps of:

(a) communicating information between the nodes to establish a common schedule defining for each node an owned transmission time exclusive to each node so that total transmissions by the nodes during the owned transmission times consumes less than the network bandwidth; and

(b) operating each node to transmit during the nodes owned transmission times.

2. The method recited in claim 1 wherein the common schedule also defines an unowned transmission time that may be used by any node.

3. The method recited in claim 1 wherein step (a) employs the unowned transmission times.

4. The method recited in claim 2 wherein the unowned transmission time is of predetermined duration.

5. The method recited in claim 2 wherein the unowned transmission time concludes with a transmission abort time at which any pending transmission must be aborted.

6. The method recited in claim 2 wherein the unowned transmission time concludes with a no new transmission time at which any pending transmission may be completed but no new transmissions may be initiated.

7. The method recited in claim 1 wherein the information communicated between the nodes is provided to a single schedule coordinator node which collects the information for dissemination to the other nodes.

8. The method recited in claim 1 wherein the information communicated between the nodes includes transmission requirements of each node selected from the group consisting of packet transmission start time, packet length, packet frequency and allowable packet jitter.

9. The method recited in claim 8 wherein each node recreates the schedule from information communicated between the nodes.

10. The method recited in claim 9 wherein the node recreates the schedule by:

(i) dividing transmission time into I/O cycles holding multiple Ethernet data packets;

(ii) determining the node with the lowest packet frequency to define a schedule length of I/O cycles;

(iii) scheduling a yet unscheduled node with the highest packet frequency in each of the I/O cycles of the schedule length required to meet its schedule frequency preferring least filled I/O cycles; and

(iv) repeating step (iii) until all nodes are scheduled.

11. The method recited in claim 10 wherein step (iii) reviews jitter requirements of node communications and selects scheduling only that meets the nodes'"'"' jitter requirements.

12. The method recited in claim 7 including the further step of periodically transmitting from the schedule coordinator to the other nodes a keep alive signal, and deleting a node from the schedule if it does not reply to the keep alive signal.

13. The method recited in claim 7 including the further step of transmitting from the schedule coordinator to the other nodes a recreate schedule message causing a recreation of the schedule at each node from new information provided by the schedule coordinator.

14. The method recited in claim 1 wherein the schedule is organized into I/O cycles during which multiple nodes have owned transmission time and wherein the schedule further provides for periodic transmission of time synchronization signals between a time master node and other nodes.

15. The method recited in claim 14 wherein each I/O cycle also includes unowned time during which any node may transmit and wherein the periodic transmission of time synchronization signals occurs in the place of unowned time in the I/O cycle.

16. The method recited in claim 10 wherein the information communicated between the nodes is provided to a single schedule coordinator node which collects the information for dissemination to the other nodes and wherein the time master node is the schedule coordinator.

17. The method recited in claim 14 wherein a period of time prior to the transmission of time synchronization signals is scheduled for no unowned transmissions by the nodes.

18. The method recited in claim 1 including the step of communicating between nodes over the Ethernet network using Internet protocols.

25. The communication system recited in claim 16 wherein the nodes intercommunicate through a designated schedule coordinator to establish the common schedule and wherein the schedule coordinator executes the stored program to further transmit to the other nodes a remake schedule message causing each node to recreate the schedule from information communicated between the nodes and the schedule coordinator.

19. A communications system providing deterministic message transmission for industrial control comprising:

(a) an Ethernet network;

(b) a set of nodes communicating on the network, the nodes executing a stored program to;

(i) intercommunicate to establish a common schedule defining an owned transmission time exclusive to each node so that transmissions by the nodes during the scheduled transmission times consumes less than the network bandwidth; and

(ii) operate to transmit during their scheduled transmission times.

20. The communication system recited in claim 19 wherein the common schedule also defines an unowned transmission time that may be used by any node.

21. The communication system recited in claim 20 wherein the unowned transmission time is of predetermined duration.

22. The communication system recited in claim 20 wherein the unowned transmission time concludes with a transmission abort time at which any pending transmission must be aborted.

23. The communication system recited in claim 20 wherein the unowned transmission time concludes with a no new transmission time at which any pending transmission may be completed but no new transmissions may be initiated.

24. The communication system recited in claim 19 wherein the information communicated between the nodes includes transmission requirements of each node selected from the group consisting of packet transmission start time, packet length, packet frequency and allowable packet jitter.

26. The communication system recited in claim 19 wherein the nodes execute the stored program to establish the schedule by:

(1) dividing transmission time into I/O cycles holding multiple Ethernet data packets;

(2) determining the node with the lowest packet frequency to define a schedule length of I/O cycles;

(3) scheduling a yet scheduled node with the highest packet frequency in each of the I/O cycles required to meet its schedule frequency preferring least filled I/O cycles; and

(4) repeating step (4) until all nodes are scheduled.

27. The communication system recited in claim 26 wherein step (3) of scheduling reviews jitter requirements of node communications and selects scheduling only that meets the nodes'"'"' jitter requirements.

28. The communication system recited in claim 19 wherein the nodes intercommunicate through a designated schedule coordinator to establish the common schedule and wherein the schedule coordinator executes the stored program to further periodically transmit from the schedule coordinator to the other nodes a keep alive signal and to delete a node from the schedule if it does not reply to the keep alive signal.

29. The communication system recited in claim 19 wherein the schedule is organized into I/O cycles during which multiple nodes have owned transmission time and wherein the schedule further provides for periodic transmission of time synchronization signals between a time master node and other nodes.

30. The communication system recited in claim 29 wherein the periodic transmission of time synchronization signals occurs in the place of unowned time in the I/O cycle.

31. The communication system recited in claim 19 wherein a period of time prior to the transmission of time synchronization signals is scheduled for no unowned transmissions by the nodes.