FAULT TOLERANT NETWORK UTILIZING BI-DIRECTIONAL POINT-TO-POINT COMMUNICATIONS LINKS BETWEEN NODES

• US 20100188972A1
• Filed: 01/27/2009
• Published: 07/29/2010
• Est. Priority Date: 01/27/2009
• Status: Active Grant

• Current Assignee: Lutron Technology Company LLC
• Original Assignee: Smsc Holdings Sarl
• Inventors: Knapp, David J.
• Granted Patent: US 8,179,787 B2
• Time in Patent Office: Days
• US Class Current: 370/226
• CPC Class Codes: H04L 12/43 with synchronous transmission, e.g. time division multiplex [TDM], slotted rings
• CPC Class Codes: H04L 12/437 Ring fault isolation or reconfiguration for SDH/SONET ring networks H04J3/085
• CPC Class Codes: H04L 2012/40273 the transportation system being a vehicle
• CPC Class Codes: H04L 45/28 using route fault recovery

Abstract

A data communication system and an associated network node implementation is disclosed that, in certain embodiments, uses single-channel bi-directional communication links between nodes to send frames of data. The network nodes can be connected together in a ring or daisy chain topology with data frames sent in alternating directions through the bi-directional links. Such networks initially configured in a physical ring topology can tolerate single point failures by automatically switching to a logical daisy chain topology.

Claims

1. A method for use in a network node within an interconnected network of nodes, said method comprising:

forwarding data frames received on a first bi-directional port of the network node to a second bi-directional port of the network node for outbound transmission on the second bi-directional port;

forwarding data frames received on the second bi-directional port to the first bi-directional port for outbound transmission on the first bi-directional port; and

if a data frame received on a given bi-directional port includes a message addressed to the network node, then inserting a message status symbol into the next data frame transmitted outbound on the given bi-directional port.

2. The method as recited in claim 1 wherein the first and second ports comprise single-channel bi-directional ports.

3. The method as recited in claim 2 wherein the first and second ports each comprise an optical fiber port.

4. The method as recited in claim 1 further comprising synchronizing bit timing of data frames transmitted on one port to bit timing of data frames received on the other port.

5. The method as recited in claim 1 further comprising re-timing transmission of outbound data frames to an internal timing reference of the network node.

6. The method as recited in claim 1 wherein the next data frame transmitted outbound on the given bi-directional port is a forwarded data frame previously received on the other port of the network node.

7. The method as recited in claim 1 wherein the message status symbol comprises an acknowledge symbol (ACK) if the message was received without errors by the network node, and comprises an error symbol (ERC) if the message was received by the network node but contained one or more errors.

8. The method as recited in claim 6 further comprising:

inserting, into a data frame received on one port, a new message for outbound transmission of the data frame including the new message on the other port.

9. The method as recited in claim 8 further comprising:

if the new message comprises a broadcast message, inserting the broadcast message into a second data frame received on the other port, for outbound transmission of the second data frame including the broadcast message on the one port.

10. The method as recited in claim 8 further comprising:

arbitrating the relative priority of the new message and any existing message carried by the data frame received on the one port; and

if the new message wins arbitration, inserting the new message into the data frame and preempting the existing message, for outbound transmission of the data frame including the new message on the other port.

11. The method as recited in claim 10 wherein:

the arbitrating is performed bit-serially, and a new priority indicator inserted as soon as the network node wins the arbitration.

12. The method as recited in claim 10 wherein:

if the new message is shorter than the preempted message, padding the new message to the length of the preempted message.

13. The method as recited in claim 10 wherein:

if the preempted message is a broadcast message, inserting a negative acknowledge (NOT ACK) message status symbol in next frame transmitted outbound on the port which received the data frame containing the preempted broadcast message.

14. The method as recited in claim 10 wherein:

if the new message loses arbitration and is not inserted into the data frame, queueing the new message for retransmission in a subsequent data frame and increasing the priority of the new message to increase likelihood of winning a subsequent arbitration.

15. The method as recited in claim 8 further comprising:

if the next data frame received on the other port includes an ACK symbol, removing the ACK symbol from said next data frame before forwarding to the one port; and

if the next data frame received on the other port does not include an ACK symbol, queueing the new message for retransmission in the next available data frame.

16. The method as recited in claim 8 further comprising:

maintaining a table of network node addresses reachable by a data frame transmitted on each respective port; and

sending a message to a destination node only in a data frame transmitted on the corresponding port.

17. The method as recited in claim 1 further comprising:

if no data frames are received on the one port, then

noting the one port as an inactive port;

extinguishing each data frame received on the other port; and

launching a subsequent data frame on the other port.

18. The method as recited in claim 17 further comprising:

if a data frame is received on said inactive port, triggering a network topology reconfiguration.

19. The method as recited in claim 18 further comprising:

periodically transmitting a data frame on the inactive port to solicit a response thereto.

20. The method as recited in claim 1 further comprising:

assigning an address for the network node in response to a received data frame which includes an address discovery command.

21. The method as recited in claim 20 wherein the assigning step comprises:

incrementing an address conveyed in the address discovery command data frame;

storing the incremented address as the network node address; and

forwarding the address discovery command with the incremented address in the next transmitted data frame.

22. The method as recited in claim 1 further comprising:

triggering a network topology reconfiguration after a certain period of inbound inactivity on a previously active port.

23. The method as recited in claim 8 wherein each data frame comprises an arbitration field, an address field, a data field, a message status field, and a CRC checksum field.

24. The method as recited in claim 23 wherein each data frame further comprises:

a start sequence including a plurality of bit transitions for synchronizing an internal reference clock of the network node receiving the data frame.

25. The method as recited in claim 23 wherein the arbitration field conveys a priority value for indicating the priority of the message included within the data frame, and when such priority value is a predetermined value in its range, for indicating that the data frame is empty and thus does not include a message.

26. The method as recited in claim 1 wherein the network node is conditionally operable as a timing master node, and wherein the method further comprises:

arbitrating with other devices which are likewise conditionally operable as a timing master node, to determine whether the network node will operate as the timing master node for the network.

27. The method as recited in claim 1 further comprising:

forwarding data frames received on a third bi-directional port of the network node to a fourth bi-directional port of the network node for outbound transmission on the fourth bi-directional port;

forwarding data frames received on the fourth bi-directional port to the third bi-directional port for outbound transmission on the third bi-directional port; and

if a data frame received on one of the first and second bi-directional ports addresses a network node reachable from the third or fourth ports, forwarding the data frame to said third or fourth port.

28. A system comprising

a plurality of network nodes, each having at least two bi-directional ports capable of transmitting and receiving data frames;

a plurality of bi-directional communication links connecting said plurality of network nodes in a physical topology which includes a serially-connected string of said network nodes;

wherein said plurality of network nodes are configured to communicate successive data frames alternately in opposite directions from node to node along the string.

29. The system as recited in claim 28 wherein said plurality of bi-directional communication links comprise single-channel bi-directional communication links.

30. The system as recited in claim 29 wherein said plurality of bi-directional communication links comprise optical fiber by which said data frames are communicated between nodes.

31. The system as recited in claim 28 wherein the serially-connected string of said network nodes is closed to form a physical and logical ring topology.

32. The system as recited in claim 31 configured to detect a faulty node or faulty link between nodes in the physical ring topology, isolate the fault, and reconfigure the logical network topology of the system into a logical daisy chain topology having first and second end nodes.

33. The system as recited in claim 32 wherein one of the network nodes functions as a timing master node for providing bit and frame timing to which all other network nodes are synchronized.

34. The system as recited in claim 33 wherein, when configured in a logical ring topology:

the timing master node is configured to launch successive data frames alternately in one direction from one of its ports and in the other direction from the other of its ports; and

a data frame sent from one timing master port is received some time later on the other port.

35. The system as recited in claim 32 wherein an end node of a daisy chain sends a next data frame from the same port that received the previous data frame.

36. The system as recited in claim 35 wherein the timing master node, if not also an end node, forwards a data frame received on one port to the other port for transmission and re-times the transmission.

37. The system as recited in claim 33 wherein each data frame comprises an arbitration field, an address field, a data field, a message status field, and a CRC checksum field.

38. The system as recited in claim 37 wherein each data frame further comprises a start sequence including a plurality of bit transitions for synchronizing an internal reference clock of the network node receiving the data frame.

39. The system as recited in claim 37 wherein a message is sent from a source node to a destination node by the source node filling the address field of a data frame with the address of the destination node, and filling the data field of the same data frame with the message.

40. The system as recited in claim 39 wherein the source node sends the same message on successive data frames, each traveling in opposite directions along the string of network nodes.

41. The system as recited in claim 39 wherein the destination node, after receiving a message, inserts an acknowledge symbol in the message status field of the next data frame traveling in the other direction.

42. The system as recited in claim 41 wherein the acknowledge symbol is sent from the same port on which the message was received in the previous frame.

43. The system as recited in claim 41 wherein the acknowledge symbol comprises an error symbol (ERC) if the message was received by the destination node but contained one or more errors.

44. The system as recited in claim 39 further comprising:

inserting, into a data frame received on one port of a source node, a new message for outbound transmission to the destination node of the data frame including the new message on the other port of the source node.

45. The system as recited in claim 39 wherein, if the new message comprises a broadcast message, the source node inserts the broadcast message into a second data frame traveling the other direction than the first data frame.

46. The system as recited in claim 28 wherein:

each network node is configured such that, if no data frames are received on one of its ports, that port is noted as an inactive port, and each data frame received on the remaining active port is extinguished; and

subsequent data frames are launched in the other direction on its remaining active port.

47. The system as recited in claim 46 further comprising:

if a data frame is received on a previously noted inactive port, the corresponding network node triggers a network topology reconfiguration.

48. The system as recited in claim 47 wherein one or more network nodes are configured to periodically transmit a data frame on an inactive port to solicit a response thereto.

49. The system as recited in claim 28 wherein one or more network nodes are configured to trigger a network topology reconfiguration after a certain period of inbound inactivity on a previously active port.

50. The system as recited in claim 28 having at least two network nodes that are conditionally operable as a timing master node, each of which is configured to arbitrate with other devices which are likewise conditionally operable as a timing master node, to determine which such network node will operate as the timing master node for the network.

51. The system as recited in claim 28 further comprising:

a second network respectively comprising

a second plurality of network nodes, each having at least two bi-directional ports capable of transmitting and receiving data frames;

a second plurality of bi-directional communication links connecting said second plurality of network nodes in a physical topology which includes a second serially-connected string of said network nodes;

wherein said second plurality of network nodes are configured to communicate successive data frames alternately in opposite directions from node to node along the second string;

a bridge network node common to both the first-mentioned string of nodes and the second string of nodes.

52. A method of communicating information in a system comprising a network topology including a string of serially-connected network nodes, each node including respective first and second ports, said method comprising:

launching successive data frames alternately from a first port of a first network node to travel in one direction along the string of network nodes until the first data frame either reaches a second port of the first network node, or reaches an end node of the string of network nodes, and then from either the second port of the first network node or from the end node to travel in the other direction along the string of network nodes to reach the first port of the first network node; and

inserting a first message into a first data frame received on the first port of a source node and forwarding the first data frame on the second port of the source node toward downstream nodes.

53. The method as recited in claim 52 further comprising:

in a destination node, receiving the first message from the first data frame traveling in one direction along the string of network nodes, and inserting a first message status symbol into a second data frame traveling in the other direction along the string.

54. The method as recited in claim 53 further comprising:

in the source node, if the first message status symbol is not received from the destination node in the second data frame, inserting the first message into the second data frame traveling in said other direction along the string of network nodes.

55. A network node device for use in a system of interconnected network nodes, said network node device comprising:

a first port configured to interface with a bi-directional communication link for transmitting and receiving data frames to a first external device connected thereto;

a second port configured to interface with a bi-directional communication link for transmitting and receiving data frames to a second external device connected thereto;

first circuitry for synchronizing an associated internal clock to data frames received on the first port, and for forwarding such first-port received data frames to the second port for transmission;

second circuitry for synchronizing an associated internal clock to data frames received on the second port, and for forwarding such second-port received data frames to the first port for transmission; and

third circuitry for inserting a message into a data frame passing from one port to the other port through the device in either direction.

56. The network node as recited in claim 55 wherein:

data frames are only received on one of said first and second ports at a given time.

57. The network node as recited in claim 55 wherein the first and second ports comprise single-channel bi-directional ports.

58. The network node as recited in claim 55 wherein:

the first-port received data frames are forwarded bit-by-bit to the second port for transmission;

the second-port received data frames are forwarded bit-by-bit to the first port for transmission; and

messages are inserted bit-by-bit into a passing data frame.

59. A network node device for use in a system of interconnected network nodes, said network node device configured to:

forward data frames received on one of first and second bi-directional ports for outbound transmission on the other of said first and second bi-directional ports; and

insert, if a data frame received on the first bi-directional port includes a message addressed to the network node device, a message status symbol into the next data frame transmitted outbound on the first bi-directional port.

60. The method as recited in claim 59 wherein the first and second ports comprise single-channel bi-directional optical fiber ports.