Method and apparatus for tracking buffer availability

• US 5,610,745 A
• Filed: 10/26/1995
• Issued: 03/11/1997
• Est. Priority Date: 10/26/1995
• Status: Expired due to Term

• Current Assignee: Brocade Communications Systems, Inc. (Broadcom, Inc.)
• Original Assignee: Hewlett-Packard Company (HP Inc.)
• Inventors: Bennett, Dwayne
• Primary Examiner(s): Chin, Wellington
• Assistant Examiner(s): NEGASH, KINFE MICHAEL
• Application Number:
  US08/548,505
• Time in Patent Office: 502 Days
• Field of Search: 359/117, 359/118, 359/128, 359/139, 370/17, 370/60, 370/60.1
• US Class Current: 398/52
• CPC Class Codes: H04L 2012/5681 Buffer or queue management
• CPC Class Codes: H04L 49/107 using shared medium
• CPC Class Codes: H04L 49/3081 ATM peripheral units, e.g. policing, insertion or extraction
• CPC Class Codes: H04L 49/351 for local area network [LAN], e.g. Ethernet switches
• CPC Class Codes: H04L 49/357 Fibre channel switches
• CPC Class Codes: H04Q 11/0478 Provisions for broadband connections

Abstract

The invention is a method and apparatus for transmitting frames from a plurality of node ports (N_-- ports) to their associated fabric ports (F_-- ports) for forwarding to other interconnected F_-- ports on a Fibre Channel switch in which the transmitted frames are stored in a plurality of receive buffers at the associated F_-- port prior to forwarding to an interconnected F_-- port, and a receive credit counter, a smart credit counter and a transmit credit counter are employed for tracking the availability of the receive buffers.

Claims

1. A fibre channel switch apparatus for interconnecting a plurality of devices having node ports (N_-- ports), comprising:

a plurality of interconnected fabric ports (F_-- ports), each further comprising;

a plurality of receive buffers for storing frames received from an N_-- port,

a receive credit counter for counting the number of frames that the N_-- port is currently allowed to transmit at one time, and

a smart credit counter for counting the number of receive buffers available to receive frames from the N_-- port,

status/control logic on the F_-- port for transmitting a receiver ready signal to the N_-- port when the F_-- port is ready to receive another frame, the status/control logic further comprising;

a transmit credit counter located on each N_-- port for counting the number of frames that the N_-- port is currently allowed to transmit to the F_-- port at one time, wherein the transmit credit counter is decremented by one after a frame is transmitted to an F_-- port and incremented by one upon the receipt of the receiver ready signal.

2. The fibre channel switch apparatus as claimed in claim 1, wherein the transmit credit counter is initialized at login at a number corresponding to the maximum number of frames that the N_-- port can transmit to the F_-- port without receiving the receiver ready signal from the F_-- port.

3. The fibre channel switch apparatus as claimed in claim 2, wherein the N_-- port is only allowed to transmit a frame to the F_-- port if the transmit credit counter has a value greater than 0.

4. The fibre channel switch apparatus as claimed in claim 3, wherein each receive credit counter is initialized at login with an initial value defined as the login receive buffer-to-buffer credit (login rx_-- bb_-- credit) corresponding to the maximum number of frames that the N_-- port can transmit to the F_-- port at one time.

5. The fibre channel switch apparatus as claimed in claim 4, wherein the difference between the current value of the smart credit counter and the login receive buffer-to-buffer credit is the number of spare buffers on the F_-- port.

6. The fibre channel switch apparatus as claimed in claim 5, wherein, upon receipt of a frame, the current value of the smart credit counter is compared to the login receive buffer-to-buffer credit, and if the smart credit counter value is greater than the login receive buffer-to-buffer credit, the status control logic sends the receiver ready signal to the N_-- port, and wherein, both the receive credit counter and the smart credit counter are decremented by one upon receipt of the frame.

7. The fibre channel switch apparatus as claimed in claim 6, wherein upon receipt of the receiver ready signal, the transmit credit counter is incremented.

8. The fibre channel switch apparatus as claimed in claim 6, wherein upon receipt of a frame:

if the value of the smart credit counter is less than or equal to the login receive buffer-to-buffer credit, then the number of available buffers is limited to the current count of the receive credit counter, and wherein, both the receive credit counter and the smart credit counter are decremented by one upon receipt of the frame, and wherein, the receiver ready signal is generated and sent to the N_-- port upon forwarding the frame to another F_-- port.

9. The fibre channel switch apparatus as claimed in claim 8, wherein upon forwarding the frame to another F_-- port, the smart credit counter and the receive credit counter are incremented as long as the current count of the receive credit counter is less than the initial value of the receive credit counter.

10. A method for transmitting frames from a plurality of node ports (N_-- ports) to their associated fabric ports (F_-- ports) for forwarding to other interconnected F_-- ports, comprising the steps of:

transmitting a frame from an N_-- port to its associated F_-- port,

storing the transmitted frame in a plurality of receive buffers at the associated F_-- port prior to forwarding to an interconnected F_-- port,

counting a receive credit count at each F_-- port that corresponds to the number of frames that an N_-- port is currently allowed to transmit to its associated F_-- port at one time,

counting a smart credit count at each F_-- port that corresponds to the number of receive buffers available on an F_-- port to receive frames,

transmitting a receiver ready signal from an F_-- port to its associated N_-- port when the F_-- port has forwarded a frame to another F_-- port,

counting a transmit credit count at each N_-- port corresponding to the number of frames that an N_-- port is currently allowed to transmit to its associated F_-- port at one time,

decrementing an N_-- port transmit credit count by one upon transmitting a frame from the N_-- port, and

incrementing the transmit credit count by one when the N_-- port receives a receiver ready signal.

11. The method for transmitting frames as claimed in claim 10, further comprising the step of:

initializing each transmit credit count at login to a number corresponding to the maximum number of frames that the associated N_-- port can transmit to the F_-- port without receiving a receiver ready signal from an F_-- port.

12. The method for transmitting frames as claimed in claim 11, wherein an N_-- port is only allowed to transmit a frame to an F_-- port if the N_-- ports transmit credit count has a value greater than 0.

13. The method for transmitting frames as claimed in claim 12, further comprising the step of:

initializing each receive credit count at login with an initial value defined as the login receive buffer-to-buffer credit (login rx_-- bb_-- credit) corresponding to the maximum number of frames that the N_-- port can transmit to the F_-- port at one time.

14. The method for transmitting frames as claimed in claim 13, further comprising the step of:

comparing an F_-- ports login receive buffer-to-buffer credit count to the current value of the smart credit count upon receipt of a frame,

sending a receiver ready signal immediately to the associated N_-- port, if the smart credit count value is greater than the login receive buffer-to-buffer credit, and

decrementing the F_-- ports receive credit count and the F_-- ports smart credit count by one upon receipt of the frame.

15. The method for transmitting frames as claimed in claim 14, further comprising the step of:

incrementing an F_-- ports transmit credit count upon receipt of a receiver ready signal, wherein the associated N_-- port may now send an extra frame to the F_-- port.

16. The method for transmitting frames as claimed in claim 15, further comprising the step of:

comparing the count of the F_-- ports smart credit count to the login receive buffer-to-buffer credit count upon receipt of a frame, wherein if the smart credit count is less than or equal to the buffer-to-buffer credit count, then the number of available buffers on the F_-- port is limited to the F_-- ports current receive credit count, and

generating a receiver ready signal and sending it to the N_-- port upon forwarding the frame to another F_-- port,

decrementing both the receive credit count and the smart credit count by one.