Method and apparatus for calculating the longitudinal redundancy check in a mixed stream channel

A method for checking data integrity in a fibre channel communications system in which plural data streams can be intermixed, each data stream having a sequence of data blocks and wherein communications of a complete data block is a logical termination of the data stream, said method comprising the steps of:

• (a) receiving a first incoming data stream,
• (b) determining a running longitudinal redundancy check for said received data stream as it is being received,
• (c) storing an intermediate value of said longitudinal redundancy check, if said stream is interrupted at a frame boundary which is not a said logical termination of said stream, in a context storage associated only with said stream,
• (d) storing with said intermediate value in said context storage, the number of frame words remaining in said frame, the number of words per block, and the number of words remaining to fill the current block,
• (e) recognizing a continuation of said interrupted data stream,
• (f) recalling said intermediate value from said context storage associated with said interrupted data stream,
• (g) continuing to determine said running longitudinal redundancy check for said received data stream using said recalled intermediate redundancy value, and
• (h) repeating steps (c), (d), (e), (f), and (g), if said received data stream is interrupted prior to a said logical termination of said stream.

Apparatus for checking data integrity in a data communication system in which plural data streams can be intermixed comprising

• a data receiver for receiving a first incoming data stream,
• a data processor for determining a running longitudinal redundancy check for said received data stream as it is being received,
• a context storage associated with each said data stream for storing an intermediate value of said longitudinal redundancy check each time said stream is interrupted at other than a logical termination of said stream,
• said data processor recognizing each continuation of said interrupted data stream, and recalling said intermediate value from said context storage associated with said interrupted data stream, and
• said data processor determining said running longitudinal redundancy check for said continued received data stream using the last recalled intermediate value.

Apparatus for checking data integrity in a fibre channel data communications system in which plural data streams can be intermixed, said channel operating according to a fibre channel protocol having a sequence of frames, and each frame consisting of a group of blocks, comprising

• a data receiver for receiving a first incoming data stream,
• a data processor for determining a running longitudinal redundancy check for said received data stream as it is being received, said processor having an EXCLUSIVE-OR circuit for EXCLUSIVE-OR'ing successive groups of data from said data stream to generate said longitudinal redundancy check,
• a context storage associated only with said stream for storing an intermediate value of said longitudinal redundancy check each time said stream is interrupted prior to a logical termination of said stream, said storage storing with said intermediate value, the number of frame words remaining in said frame, the number of words per block, and the number of words remaining to fill a current block,
• said data processor recognizing each continuation of said interrupted data stream, and recalling said intermediate value from said context storage associated with said interrupted data stream, and
• said data processor determining said running longitudinal redundancy check for said continued received data stream using the last recalled intermediate value.