Method and apparatus for rendering a cell-based switch useful for frame based protocols

1. A method for adapting to different data rates between a source for a data frame and a cell-based switch fabric, the switch fabric requiring cells having a data payload and a cell header, the method comprising:

a) constructing a first data cell from the data frame, the first data cell containing a full data payload and a packet length value in the cell header, the packet length value being indicative of the number of data cells in the data frame; and

b) constructing a second data cell from the data frame, the second data cell containing a partially filled data payload and a valid data value in the cell header, the valid data value being indicative of the amount of valid data, in the data payload.

2. The method of claim 1 , wherein the data frame is a variable-length data frame.

3. The method of claim 2 , wherein the data frame is a Fibre Channel frame.

4. The method of claim 1 , wherein the valid data value is equal to the number of valid data bytes in the partially filled data payload.

5. The method of claim 1 , further comprising:

c) transmitting the first and second data cell through the cell-based switch fabric; and

d) reconstructing the data frame from the transmitted first and second data cells, the reconstructed data frame containing data from the entire full data payload of the first data cell and that portion of the partially filled data payload of the second data cell that contains valid data as indicated by the valid data value.

6. The method of claim 5 , wherein the step of transmitting the first and second data cells through the cell-based switch fabric includes the following steps:

i) establishing a path through the cell-based switch fabric; and

ii) establishing a duration for maintaining the path, the duration being determined by the packet length value in the first data cell.

7. The method of claim 1 , wherein the valid data value and the packet length value are both located in the same field of the cell header.

8. The method of claim 1 , wherein the packet length field is located in the data payload.

9. The method of claim 1 , wherein the packet length field indicates the length of the packet in number of cells.

10. The method of claim 1 , further comprising:

c) establishing a path through the cell-based switch fabric; and

d) establishing a duration for maintaining the path, the duration being determined by the packet length value in the first data cell.

11. The method of claim 10 , further comprising:

e) constructing a third data cell from the data frame, the third data cell containing an end of packet indicator.

12. The method of claim 11 , wherein the end of packet indicator is in the cell header.

13. The method of claim 11 , further comprising:

f) receiving the third data cell on a destination port side of the cell-based switch fabric;

g) detecting the end of packet indicator; and

h) terminating the path through the cell-based switch fabric after detecting the end of packet indicator, even though the duration has not completed.

14. The method of claim 13 , wherein the packet length field indicates the length of the packet in cells and the duration is set to allow a number of cells through the path equal to the packet length value in the first data cell.

15. The method of claim 14 , wherein the data frames have a variable length, and the packet length value is equal to a number sufficient to allow a maximum sized data frame to pass through the path.

16. A method for adapting to different data rates between an input data frame and a cell-based switch fabric within a data switch, the switch fabric having fixed-sized cells each having a data payload, the method comprising:

a) receiving a first portion of the data frame at an input port;

b) establishing a path through the cell-based switch fabric to a destination port selected by examining a destination address found in the first portion of the data frame;

c) sending a first data cell containing at least part of the first portion of the data frame across the path;

d) after sending the first data cell, receiving a second portion of the data frame;

e) partially filling the data payload of a second data cell with the second portion of the data frame;

f) sending the second data cell across the path even though the data payload of the second data cell is not filled;

g) detecting an end of the data frame;

h) after detecting the end of the data frame, sending an End of Packet indicator across the data path to the destination port; and

i) closing the path through the cell-based switch fabric when the End of Packet indicator has been detected at the destination port.

17. The method of claim 16 , wherein the first cell has a completely filled data payload, and further wherein the first cell has a packet length value indicating a maximum number of cells that would be necessary to transmit a maximum-sized data frame.

18. The method of claim 17 , wherein the second cell has a valid data value indicating the number of valid data bytes in the data payload of the second cell, and wherein the packet length value of the first data cell and the valid data value of the second data cell are both found in an identical field in a cell header that does not form part of the data payload.

19. The method of claim 16 , wherein the End of Packet indicator is found in the data payload of a third data cell.

20. A data switch comprising:

a) a cell based switch fabric using fixed size data cells;

b) an input port having logic to:

i) receive a data frame,

ii) establish a path across the cell-based switch fabric,

iii) partition the data frame into data cells to be sent across the path, with at least two data cells having a partially filled and partially empty cell payload and with a third data cell having an end-of-packet indicator to inform the output port that the entire data frame has been sent across the path; and

c) an output port having logic to: i) receive the data cells across the path, and ii) terminate the path upon receipt of the end-of-packet indicator.