Method and system in a local area network switch for dynamically changing operating modes

• US 5,491,687 A
• Filed: 09/28/1994
• Issued: 02/13/1996
• Est. Priority Date: 09/28/1994
• Status: Expired due to Term

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Siegel, Michael S., Strole, Norman C., Christensen, Kenneth J., Zeisz, Raymond L. Jr.
• Primary Examiner(s): Chin, Wellington
• Application Number:
  US08/314,111
• Time in Patent Office: 503 Days
• Field of Search: 370/17, 370/60, 370/60.1, 370/94.1, 370/94.2, 370/85.13, 370/85.14, 395/182.02, 395/182.01, 340/825.5, 340/825.51, 340/825.06, 340/825.07, 340/825.05, 340/825.16
• US Class Current: 370/253
• CPC Class Codes: H04L 49/251 Cut-through or wormhole routing
• CPC Class Codes: H04L 49/351 for local area network [LAN], e.g. Ethernet switches
• CPC Class Codes: H04L 49/55 Prevention, detection or correction of errors

Abstract

In a local area network switch, a first mode of operation is selected wherein frames are examined for errors as the frames are passed from a source port to a destination port. The LAN switch calculates an error rate as a function of a percentage of the frames passing through the local area network switch which have errors. In response to the error rate exceeding a high error rate threshold, the operating mode is switched to a second mode wherein the entire frame is buffered and examined for errors before the frame is passed from the source port to the destination port. Thereafter, the operating mode may be returned to the first mode if the error rate falls below a low error rate threshold. The local area network switch may also change operating modes as a function of a trend, which indicates a rate of increase or decrease of the error rate.

Claims

1. A method for changing operating modes of a local area network switch, wherein said local area network switch includes a plurality of ports connected to a plurality of local area network segments, and wherein said local area network switch selectively transfers frames from a source port to a destination port, said method comprising the steps of:

operating said local area network switch in a first mode of operation wherein said frames are examined for errors as said frames are transferred from said source port to said destination port within said local area network switch;

calculating an error rate as a function of a percentage of said frames having errors; and

switching said local area network switch to a second mode of operation if said error rate exceeds a high error rate threshold, wherein said second mode of operation includes the steps of examining each frame for errors within said local area network switch, and transferring said frame from said source port to said destination port only after completely examining said frame and determining that a number of errors within said frame is equal to or below a preselected number.

2. The method in a local area network switch according to claim 1 further including the step of returning said local area network switch to said first mode of operation if said error rate falls below a low error rate threshold, wherein said local area network switch operates in a selected mode in response to said error rate and said low and high error rate thresholds.

3. The method in a local area network switch according to claim 1 wherein said step of operating in a first mode of operation wherein said frames are examined for errors as said frames are transferred from a source port to a destination port within said local area network switch includes operating in a first mode of operation wherein said frames are examined for frame check sequence errors as said frames are transferred from a source port to a destination port within said local area network switch.

4. The method in a local area network switch according to claim 1 wherein said second mode of operation includes the steps of:

storing said frame in a buffer until said frame is examined for said errors;

transferring said frame from said buffer to said destination port within said local area network switch in response to determining that said number of errors within said frame is equal to or below said preselected number; and

discarding said frame in response to determining that said number of errors within said frame is above said preselected number.

5. The method in a local area network switch according to claim 1 further including the steps of:

calculating a trend, wherein said trend indicates a rate of increase or decrease of said error rate;

switching to said second mode of operation if said error rate is above said low error rate threshold, and said trend exceeds a rising trend threshold; and

returning to said first mode if said error rate is below a high error rate threshold, and said trend exceeds a falling trend threshold.

6. A local area network switch including a plurality of ports for connecting to a plurality of local area network segments, wherein said local area network switch includes means for selectively transferring frames from a source port to a destination port, said local area network switch comprising:

means for operating said local area network switch in a first mode of operation including means for examining said frames for errors as said frames are transferred from said source port to said destination port within said local area network switch;

means for calculating an error rate as a function of a percentage of said frames having errors; and

means for switching said local area network switch to a second mode of operation if said error rate exceeds a high error rate threshold;

means for operating said local area network switch in a second mode of operation including means for examining each frame for errors within said local area network switch, means for transferring said frame from said source port to said destination port, and means for determining that a number of errors within said frame is equal to or below a preselected number, wherein said frames are transferred from said source port to said destination port only after said frame has been completely examined and a number of errors within said frame is equal to or below a preselected number.

7. The local area network switch according to claim 6 further including means for returning said local area network switch to said first mode of operation if said error rate falls below a low error rate threshold, wherein said local area network switch operates in a selected mode in response to said error rate and said low and high error rate thresholds.

8. The local area network switch according to claim 6 wherein said means for means for examining said frames for errors includes means for examining said frames for frame check sequence errors.

9. The local area network switch according to claim 6 wherein said means for operating said local area network switch in a second mode of operation includes:

means for storing said frame in a buffer until said frame is examined for said errors;

means for transferring said frame from said buffer to said destination port within said local area network switch in response to a determination that said number of errors within said frame is equal to or below said preselected number; and

means for discarding said frame in response to a determination that said number of errors within said frame is above said preselected number.

10. The local area network switch according to claim 6 further including:

means for calculating a trend, wherein said trend indicates a rate of increase or decrease of said error rate;

means for switching to said second mode of operation if said error rate is above said low error rate threshold, and said trend exceeds a rising trend threshold; and

means for returning to said first mode if said error rate is below a high error rate threshold, and said trend exceeds a falling trend threshold.