Frame-level fibre channel CRC on switching platform

• US 7,391,723 B2
• Filed: 04/22/2003
• Issued: 06/24/2008
• Est. Priority Date: 04/22/2002
• Status: Expired due to Fees

• Current Assignee: McData Services Corp. (Broadcom, Inc.)
• Original Assignee: Computer Network Technology Corp. (Broadcom, Inc.)
• Inventors: Vogel, Mark J., Ketchum, Bret, Flattum, Steve, Collette, William C.
• Primary Examiner(s): HSU, ALPUS
• Application Number:
  US10/420,953
• Publication Number:
  US 20040015691A1
• Time in Patent Office: 1,890 Days
• Field of Search: 370/230, 370/244, 370/392, 370/412, 370/429, 370/463, 370/471, 398/17, 713/160, 714/758, 714/776, 714/819
• US Class Current: 370/230
• CPC Class Codes: H04L 12/56 Packet switching systems

Abstract

A method and apparatus is presented for performing a sequence-level CRC calculation on fiber channel communications within a switching platform domain. A CRC generator searches the data communication for frames that contain the type of data for which a sequence-level CRC is desired, such as for a sequence containing SCSI data. If found, and the type of data allows multiple frames per sequence, the present invention creates a CRC value for the sequence. An intermediate CRC value is stored in a queue to allow the simultaneous calculation of sequence level CRC values for multiple frames. With inbound data, the sequence-level CRC is appended to the end of the sequence data. With outbound data, the calculated value is compared with the appended, expected value, With single-frame fiber channel protocols, the frame-level CRC value is obtained directly from the frames entering the switching platform domain. This value is placed in a local queue, from which it is appended to the data payload by a processor for transmission within the switching platform. When the single frame is leaving the switching platform domain, the flow of data leaving the switching platform domain is monitored and the frame-level CRC value calculated by the fiber channel controller is replaced with the original frame-level CRC value.

Claims

1. A fibre channel interface to a fibre channel communications line comprising:

a) an external interface connected to the communications line so as to receive and transmit fibre channel frames having headers and data payloads over the communications line;

b) a fibre channel controller converting frames received from the external interface into data and for converting data into frames to be transmitted by the external interface; and

c) a CRC module connected between the external interface and the fibre channel controller, the CRC module connected so as to monitor data flowing from the external interface to the fibre channel controller and connected so as to have data flowing from the fibre channel controller to the external interface pass through the CRC module;

the CRC module having

i) a first CRC generator that generates a CRC value based on a starting value and data to be analyzed,

ii) a first frame header processor with circuitry to analyze headers and transmit data payloads to the CRC generator as data to be analyzed,

iii) a first memory in communication with the first CRC generator, and

iv) a frame-level CRC component having a buffer, the data flowing from the fibre channel controller being stored temporarily in the buffer before being passed to the external interface;

d) wherein the fibre channel interface operates in a first mode by generating a sequence-level CRC across multiple frames by storing intermediate CRC values for a sequence in the first memory for later use by the first CRC generator as the starting value when analyzing a next frame in the sequence; and

e) wherein the fibre channel interface operates in a second mode wherein a newly generated frame level CRC value generated by the fibre channel controller is replaced in the buffer of the frame-level CRC component by an previous frame level CRC value.

2. The fibre channel interface of claim 1, further comprising a queue in the first memory for storage of and retrieval of intermediate CRC values according to a queue index.

3. The fibre channel interface of claim 2, wherein the queue index is the same as an exchange ID that is determined by the fibre channel interface.

4. The fibre channel interface of claim 3, further comprising a queue in the first memory for storage and retrieval of the data payload data used to calculate the CRC value.

5. The fibre channel interface of claim 1, wherein the first frame header processor passes less than all of the data payloads monitored by the CRC module based upon the analysis of the headers.

6. The fibre channel interface of claim 1, wherein the fibre channel controller has a memory interface in communication with the first memory of the CRC module, and further wherein the fibre channel controller has a bus interface for allowing accessing to the first memory of the CRC module over the bus interface.

7. In a switching platform having

a) a communications bus;

b) a system buffer connected to the communications bus;

c) a first interface connected the communications bus;

d) a fibre channel interface connected to a fibre channel communications line and the communications bus; and

e) a processor connected to the communications bus, the processor translating data between the first interface and the fibre channel interface using the system buffer as temporary storage;

an improved fibre channel interface wherein the fibre channel interface comprises;

i) a fibre channel controller for generating fibre channel frames including a frame-level CRC value from data received from the communications bus and for extracting the data payload from frames received from the fibre channel communications line;

ii) a CRC generator that generates a CRC value based on a staffing value and data to be analyzed;

iii) a frame header processor that monitors communications between the fibre channel controller and the fibre channel communications line at the level of a fibre channel frame, the frame header processor having circuitry to analyze a header within the frame to determine the type of data within the frame and a sequence to which the frame belongs, the frame header processor being in communication with the CRC generator so as to transmit a data payload of the frame to the CRC generator as data to be analyzed;

iv) memory in communication with the CRC generator that stores intermediate CRC values for later use by CRC generator as the starting value when analyzing a next frame in the sequence;

v) a frame-level CRC component having a buffer, the data flowing from the fibre channel controller being stored temporarily in the buffer before being passed to the external interface;

wherein the fibre channel interface operates in a first mode by generating a sequence-level CRC across multiple frames by storing intermediate CRC values for a sequence in the memory for later use by the first CRC generator as the starting value when analyzing a next frame in the sequence; and

wherein the fibre channel interface operates in a second mode wherein a newly generated frame level CRC value generated by the fibre channel controller is replaced in the buffer of the frame-level CRC component by a previous frame level CRC value forwarded to the fibre channel interface over the communications bus.

8. The switching platform of claim 7, wherein, in the first mode, the frame header processor selectively transmits the data payload of the frame to the CRC generator based on the header of the frame.

9. The switching platform of claim 7, wherein, in the first mode, data being transmitted from fibre channel interface to the first interface is altered by the processor by appending the final sequence-level CRC calculation stored in memory to the data of the sequence.

10. The switching platform of claim 9, wherein, in the second mode, data being transmitted from fibre channel interface to the first interface is altered by the processor by appending a frame-level CRC value found in the frame received over the fibre channel communications line to the data payload of the frame.

11. The switching platform of claim 7, wherein, in the second mode, data being transmitted from fibre channel interface to the first interface is altered by the processor by appending a frame-level CRC value found in the frame received over the fibre channel communications line to the data payload of the frame.

12. The switching platform of claim 7, wherein, in the first mode, the data being transmitted from the first interface to the fibre channel interface contains an expected, sequence-level CRC value appended to the data, wherein the CPU strips the expected CRC value before submitting the data to the fibre channel interface.

13. The switching platform of claim 11, wherein the CPU compares the stripped-off expected CRC value with the CRC value calculated for the data by the CRC generator.

14. The switching platform of claim 11, wherein the fibre channel interface further comprises CRC compare circuitry that compares the final sequence-level CRC calculation to the stripped-off expected CRC value.

15. The switching platform of claim 7, wherein, in the second mode, the data being transmitted from the first interface to the fibre channel interface contains an frame-level CRC value appended to the data, wherein the CPU strips the expected CRC value before submitting the data to the fibre channel interface, and wherein the newly generated frame level CRC value generated by the fibre channel controller is replaced in the buffer of the expected CRC value.

16. The switching platform of claim 7, wherein the first interface is a wide area network interface.

17. The switching platform of claim 7, wherein the first interface is a channel interface.