Method and system for detecting congestion and over subscription in a fibre channel network

• US 7,522,529 B2
• Filed: 07/20/2004
• Issued: 04/21/2009
• Est. Priority Date: 07/21/2003
• 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., Ross, Edward C.
• Primary Examiner(s): Yao; Kwang B
• Assistant Examiner(s): Lai; Andrew
• Application Number:
  US10/895,175
• Publication Number:
  US 20050030893A1
• Time in Patent Office: 1,736 Days
• Field of Search: 370/237, 370/230.1, 370/235, 370/235.1, 370/236, 370242-244, 370/395.4, 370/474
• US Class Current: 370/237
• CPC Class Codes: H04L 47/10 Flow control; Congestion control
• CPC Class Codes: H04L 47/266 Stopping or restarting the source, e.g. X-on or X-off
• CPC Class Codes: H04L 47/29 using a combination of thresholds
• CPC Class Codes: H04L 47/39 Credit based
• CPC Class Codes: H04L 49/357 Fibre channel switches

Abstract

A method and system for detecting congestion and over-subscription in a fiber channel switch element is provided. A counter is updated if a frame cannot be transmitted due to lack of credit; then the counter value is compared to a threshold value; and an event is triggered if the counter value varies from the threshold value. Also, provided is a first register that maintains information regarding a rate at which a source port can transfer data; a counter that counts entries corresponding to a number of frames to be transmitted at a given time; and a second register that determines an over-subscription rate.

Claims

1. A system for detecting congestion at a receive segment of a port of a fibre channel switch element, comprising:

a counter at the receive segment that is incremented when an indicator is set indicating that a receive buffer at the receive segment is full;

wherein the receive buffer is used for temporarily storing fibre channel frames at the receive segment;

a threshold register for storing a threshold value for detecting congestion at the receive segment;

wherein an output value from the counter is compared with the threshold value and if the output value is greater than the threshold value, then congestion is detected at the receive segment; and

a receive buffer log that stores a destination identifier value and a source identifier value for frames received at the receive segment; and

the rate at which the receive buffer log changes, indicates how quickly frames are moving through the receive segment to a transmit segment of the port.

2. The system of claim 1, wherein a threshold event is triggered if the output from the counter is greater than the threshold value;

and the threshold event generates an interrupt for a processor of the fibre channel switch element, notifying the processor of congestion at the receive segment of the port.

3. The system of claim 1, further comprising:

a register that maintains count for frames that are routed to another switch element and by comparing the register count with an overall received frame count, a percentage of frames that are routed within the fibre channel switch element is determined.

4. A system for determining over-subscription in a transmit segment of a port of a fibre channel switch element, comprising:

an over-subscription module that receives information regarding a rate at which a plurality of source ports transmit frames and a number of frames that are waiting to be transmitted by the plurality of source ports, at any given time;

wherein the over-subscription rate is determined by the following;

((R0*F0)+(R1*F1)+ . . . (R(n−

1)*F(n−

1)))/T;

 

where “

n”

is a number of the plurality of source ports, “

R”

is a rate at which the plurality of source ports operate, “

T”

is a number of frames that are waiting to be transmitted at any given time, and “

T”

is a transmit rate for the transmit segment;

wherein the transmit segment is over-subscribed if frames arrive faster than a rate at which the transmit segment transmit the frames.

5. The system of claim 4, further comprising:

a register that stores information regarding a rate at which the plurality of source ports transfer data; and

a counter that counts entries indicating a number of frames waiting to be transmitted at each of the plurality of source ports, at any given time;

wherein values from the register and the counter are input into the over-subscription module for determining the over-subscription rate.

6. The system of claim 4, wherein the determined over-subscription value is compared to a stored threshold value and if the determined over-subscription value is greater than the threshold value, then an over-subscription status is set for the port.

7. A method for determining over-subscription in a transmit segment of a port for a fibre channel switch element, comprising:

determining an over-subscription value based on following;

((R0*F0)+(R1*F1)+ . . . (R(n−

1)*F(n−

1)))/T;

 

where “

n”

is a number of a plurality of source ports sending frames to the port, “

R”

is a rate at which the plurality of source ports operate, “

F”

is a number of frames that are waiting to be transmitted at any given time, and “

T”

is a transmit rate for the transmit segment;

wherein the transmit segment is over-subscribed if frames arrive faster than a rate at which the transmit segment transmits the frames; and

notifying a processor for the fibre channel switch element of the over-subscription, if the determined over-subscription value is different from a stored threshold value.

8. The method of claim 7, wherein the threshold value is programmable.

9. The method of claim 7, wherein a register stores information regarding a rate at which the plurality of source ports transfer data;

and a counter counts entries indicating a number of frames waiting to be transmitted at each of the plurality of source ports, at any given time;

wherein values from the register and the counter are input into an over-subscription module for determining the over-subscription value.

10. The method of claim 7, wherein if the determined over-subscription value is greater than the threshold value, then an over-subscription status is set for the port.