Dynamic preamble configuration on a shared bus

• US 6,735,635 B1
• Filed: 05/18/2000
• Issued: 05/11/2004
• Est. Priority Date: 05/18/2000
• Status: Expired due to Fees

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Suffern, Edward Stanley, Feeney, James William, Bartoldus, Robert William, Rodriquez, Jorge R.
• Primary Examiner(s): Dinh, Dung C.
• Assistant Examiner(s): BARQADLE, YASIN M
• Application Number:
  US09/574,753
• Time in Patent Office: 1,454 Days
• Field of Search: 709/227, 709/228, 709/213, 709/214, 709/248, 709/249, 709/250, 709/251-253, 370/444, 370/447, 370/445, 370/446, 370/509, 370/510
• US Class Current: 709/248
• CPC Class Codes: H04L 12/40 Bus networks
• CPC Class Codes: H04L 12/413 with random access, e.g. carrier-sense multiple-access with collision detection [CSMA-CD]
• CPC Class Codes: H04L 12/417 with deterministic access, e.g. token passing
• CPC Class Codes: H04L 7/10 Arrangements for initial synchronisation

Abstract

A method and system for adjusting a message preamble on a shared bus, wherein the message preamble includes N synchronization characters, and each of the synchronization characters is separated in time by a random delay interval. First, an activity status is determined for the shared bus in terms of the number of stations that are currently active on the bus. The number of synchronization characters is then adjusted according to the bus activity status. The activity status is also utilized as a dynamic adjustment parameter for the random delay interval that includes a fixed delay term, D, added to a randomly determined delay increment, d. In this manner the message preamble specification is optimized according to real-time network demands, such that latency and data collisions are minimized.

Claims

1. A method for adjusting the length of a message preamble during data transmissions among a plurality of stations connected to a shared bus, said method comprising:

determining an activity status on said shared bus by ascertaining a number of currently active stations, M, from among said plurality of stations connected to said shared bus; and

dynamically adjusting a number of synchronization characters, N, within a message preamble according to said determined activity status on said shared bus such that latency and data collisions on said shared bus are minimized.

2. The method of claim 1, wherein said determining further includes:

retrieving active station control signals from said determined active stations during a fixed time interval;

storing said retrieved active station control signals as M within a bus activity table; and

reading M from said bus activity table.

3. The method of claim 1, wherein said dynamically adjusting further includes:

increasing N in response to a determination that M has increased; and

decreasing N in response to a determination that M has decreased.

4. The method of claim 1, wherein each of said N synchronization characters is separated in time by a random delay interval, and wherein said random delay interval includes a fixed delay term, D, added to a random delay increment which is randomly selected from a time range, t, wherein said method further includes adjusting D according to said determined activity status on said shared bus.

5. The method of claim 4, wherein said plurality of stations further includes a first correlation table that includes a correlation factor, Y, that provides a one-to-one mapping from each value of M to each value of D, and wherein said adjusting D further includes determining D in accordance with M and Y.

6. The method of claim 4, wherein said method further includes adjusting t according to said determined activity status on said shared bus.

7. The method of claim 6, wherein said plurality of stations further includes a second correlation table that includes a correlation factor, Z, that provides a one-to-one mapping from each value of M to each value of t, and wherein said adjusting t further includes determining t in accordance with M and Z.

8. The method of claim 1, wherein each of said plurality of stations includes a third correlation table in which a correlation factor, X, is stored and updated, and wherein X provides a one-to-one mapping from each value of M to each value of N, and wherein said dynamically adjusting further includes determining N in accordance with M and X.

9. The method of claim 8, wherein said method further includes updating M at a fixed time interval.

10. The method of claim 9, wherein said plurality of stations includes a primary station and at least one secondary station, and wherein said updating M at a fixed time interval further includes:

delivering an active status message from said at least one secondary station to said primary station at the beginning of each fixed time interval;

determining M within said primary station in accordance with the number of active status messages received by said primary station during said delivering; and

in response to said determined M within said primary station, delivering M to said at least one secondary station within said fixed time interval.

11. An apparatus for adjusting the length of a message preamble during data transmissions among a plurality of stations connected to a shared bus, said apparatus comprising:

processing means for determining an activity status on said shared bus by ascertaining a number of currently active stations, M, from among said plurality of stations connected to said shared bus; and

processing means for dynamically adjusting a number of synchronization characters, N, within a message preamble according to said determined activity status on said shared bus such that latency and data collisions on said shared bus are minimized.

12. The apparatus of claim 11, wherein said processing means for determining further includes:

processing means for retrieving active station control signals from said determined active stations during a fixed time interval;

processing means for storing said retrieved active station control signals as M within a bus activity table; and

processing means for reading M from said bus activity table.

13. The apparatus of claim 11, wherein said processing means for dynamically adjusting further includes:

processing means for increasing N in response to a determination that M has increased; and

processing means for decreasing N in response to a determination that M has decreased.

14. The apparatus of claim 11, wherein each of said N synchronization characters is separated in time by a random delay interval, and wherein said random delay interval includes a fixed delay term, D, added to a random delay increment which is randomly selected from a time range, t, wherein said apparatus further includes processing means for adjusting D according to said determined activity status on said shared bus.

15. The apparatus of claim 14, wherein said plurality of stations further includes a first correlation table that includes a correlation factor, Y, that provides a one-to-one mapping from each value of M to each value of D, and wherein said processing means for adjusting D according to said activity status further includes processing means for determining D in accordance with M and Y.

16. The apparatus of claim 14, wherein said apparatus further includes processing means for adjusting t according to said determined activity status on said shared bus.

17. The apparatus of claim 16, wherein said plurality of stations further includes a second correlation table that includes a correlation factor, Z, which provides a one-to-one mapping from each value of M to each value of t, and wherein said processing means for adjusting t further includes processing means for determining t in accordance with M and Z.

18. The apparatus of claim 11, wherein each of said plurality of stations includes a third correlation table in which a correlation factor, X, is stored and updated, and wherein X provides one-to-one mapping from each value of M to each value of N, and wherein said processing means for dynamically adjusting N according to said activity status on said shared bus further includes processing means for determining N in accordance with M and X.

19. The apparatus of claim 18, wherein said apparatus further includes processing means for updating M at a fixed time interval.

20. The apparatus of claim 19, wherein said plurality of stations includes a primary station and at least one secondary station, and wherein said processing means for updating M at a fixed time interval further includes:

processing means for delivering an active status message from said at least one secondary station to said primary station at the beginning of each fixed time interval;

processing means for determining M within said primary station in accordance with the number of active status messages received by said primary station during said delivering step; and

processing means, responsive to said determined M within said primary station, for delivering M to said at least one secondary station within said fixed time interval.