User guide

Compaq StorageWorks RAID Array 4000 User Guide
Data is sent over Fibre Channel cable in a structured format. The smallest
structure of data sent is called a frame. Addressing is done within the frame
header. Frames are not visible to the upper-level protocols and consist of the
following fields:
■ Start of Frame (SOF) - 4 bytes
■ Frame Header - 24 bytes
■ Data Payload - (0-2048) bytes
■ Cyclic Redundancy Check (CRC) - 4 bytes
■ End of Frame (EOF) - 4 bytes
Figure D-3 shows a Fibre Channel data frame structure.
4 bytes
Start of
Frame
24 bytes
Frame
Header
4 bytes
CRC
Error
Check
4 bytes
End
of
Frame
64 bytes
Optional
Header
2048-byte Payload
2112-byte Payload
Figure D-3. Fibre Channel data frame structure
The second level in the hierarchy is the sequence. The sequence is composed
of one or more frames that contain data payload and are specific to a given
protocol. SCSI protocol is sent on the Fibre Channel cable of the Compaq
StorageWorks RAID Array 4000.
The third level in the hierarchy is the exchange. The exchange relates to a
complete I/O transfer operation, such as a SCSI read operation. An exchange
is composed of at least one sequence. SCSI protocol uses individual sequences
for the command phase, status phase, and data phase.