Method and system for keeping a fibre channel arbitrated loop open during frame gaps

• US 7,822,057 B2
• Filed: 08/14/2008
• Issued: 10/26/2010
• Est. Priority Date: 07/20/2004
• Status: Active Grant

• Current Assignee: Marvell Asia Pte Limited (Marvell Technology Group Limited)
• Original Assignee: QLogic Corporation (Marvell Technology Group Limited)
• Inventors: Dropps, Frank R., Papenfuss, Gary M., Kohlwey, Ernest G.
• Primary Examiner(s): Yao; Kwang B
• Assistant Examiner(s): Lai; Andrew
• Application Number:
  US12/191,890
• Publication Number:
  US 20090046736A1
• Time in Patent Office: 803 Days
• Field of Search: 370/227, 370/389, 370401-405, 370/410, 370/412, 370/424, 370/440, 370/445, 370/461, 370/528, 709/240, 710/241, 702/54
• US Class Current: 370/424
• CPC Class Codes: H04L 12/42 Loop networks
• CPC Class Codes: H04L 47/245 using preemption

Abstract

A method and system for keeping an arbitrated loop open during a frame gap using a fiber channel switch element is provided. The switch element includes a port control module having a receive and transmit segment, wherein the transmit segment activates a timer whose value determines a duration during which the arbitrated loop remains open; determines if a last frame from a sequence of frames from a source port has been transmitted; modifies the timer value if a higher priority frame for transmission is unavailable; and keeps the arbitrated loop open until the timer reaches a certain value. If a higher priority frame is available for transmission before the timer value is modified then the higher priority frame is transmitted and the timer value is re-initialized.

Claims

1. A method for keeping an arbitrated loop open during a frame gap using a fibre channel switch element, comprising:

activating a timer whose value determines a duration during which the arbitrated loop remains open;

transferring a frame;

determining if a last frame from a sequence of frames from a source port has been transmitted;

during the frame gap, modifying the timer value; and

keeping the arbitrated loop open during the frame gap until the timer reaches a certain value, wherein if a frame is received from the source port after the timer value is modified then the frame is transmitted and the timer value is reinitialized.

2. The method of claim 1, further comprising determining if a higher priority frame is available for transmission.

3. The method of claim 2, wherein during the frame gap if a higher priority frame is available for transmission the higher priority frame is transmitted without regard to the timer.

4. The method of claim 2, wherein if a higher priority frame is available for transmission before the timer value is modified then the higher priority frame is transmitted and the timer value is re-initialized.

5. The method of claim 2, wherein any frames received from other ports when the arbitrated loop is being held open, other than higher priority frames, are ignored.

6. The method of claim 1, wherein a frame from the source port, if available, is transmitted before the timer value is modified.

7. The method of claim 1, wherein the timer value is pre-programmed by using a processor.

8. A fibre channel switch element coupled to an arbitrated loop of a fibre channel network, comprising:

a port control module having a receive and transmit segment;

wherein the transmit segment is configured to activate a timer whose value determines a duration during which the arbitrated loop remains open, transfer a frame, determine if a last frame from a sequence of frames from a source port has been transmitted, during a frame gap, modify the timer value, and keep the arbitrated loop open during the frame gap until the timer reaches a certain value, wherein if a frame is received from the source port after the timer value is modified then the frame is transmitted and the timer value is reinitialized.

9. The fibre channel switch element of claim 8, wherein the transmit segment is further configured to determine if a higher priority frame is available for transmission.

10. The fibre channel switch element of claim 9, wherein the transmit segment is configured to modify the timer value only if no higher priority frame is available for transmission.

11. The fibre channel switch element of claim 9, wherein if a higher priority frame is received, when the arbitrated loop is being held open, the higher priority frame is transmitted without regard to the timer value.

12. The fibre channel switch element of claim 9, wherein if a higher priority frame is available for transmission before the timer value is modified then the higher priority frame is transmitted and the timer value is re-initialized.

13. The fibre channel switch element of claim 9, wherein any frames received from other ports when the arbitrated loop is being held open, other than higher priority frames, are ignored.

14. The fibre channel switch element of claim 8, wherein a frame from the source port, if available, is transmitted before the timer value is modified.

15. The fibre channel switch element of claim 8, wherein the timer value is pre-programmed by using a processor.

16. An arbitration module in a fibre channel switch element with a port control module having a receive segment and a transmit segment coupled to an arbitrated loop of a fibre channel network, comprising:

a loop hold timer whose value determines a duration during which the arbitrated loop remains open;

wherein the arbitration module is configured to determine if a last frame from a sequence of frames from a source port has been transmitted, during a frame gap, modify the timer value and keep the arbitrated loop open during the frame gap until the timer reaches a certain value, wherein if a frame is received from the source port after the timer value is modified then the frame is transmitted and the timer value is reinitialized.

17. The arbitration module of claim 16, wherein the arbitration module is further configured to determine if a higher priority frame is available for transmission.

18. The arbitration module of claim 17, wherein the arbitration module is configured to modify the timer value only if no higher priority frame is available for transmission.

19. The arbitration module of claim 17, wherein if a higher priority frame is received after the timer value is modified then the higher priority frame is transmitted and the timer value is re-initialized.

20. The arbitration module of claim 17, wherein if a higher priority frame is available for transmission before the timer value is modified then the higher priority frame is transmitted and the timer value is re-initialized.

21. The arbitration module of claim 16, wherein a frame from the source port, if available, is transmitted before the timer value is modified.

22. The arbitration module of claim 16. wherein the timer value is pre-programmed by a processor.

23. The arbitration module of claim 16, wherein any frames received from other ports when the arbitrated loop is being held open, other than higher priority frames, are ignored.