Fibre Channel Data Frames - HP A7533A - Brocade 4Gb SAN Switch Base Administrator's Manual

The following table describes Fibre Channel data frames.
Table 81

Fibre Channel data frames

Fibre Channel Frame fields
Start of frame
Standard frame header
Data (payload)
CRC
End of frame
Total (Number bits/frame)
NOTE: The term byte used in
You can allocate buffer credit using the portCfgLongDistance command, which allows you to allocate
sufficient numbers of full-size frame buffers on a particular port or to support a long- distance link. Only
E_Ports can be configured for extended distances. Changes made by this command are persistent across
switch reboots and power cycles.
Enter the portCfgLongDistance command to select one of the following four options for buffer credit
allocation:
NOTE: Long distance modes L0.5, L1, and L2 are not supported on Fabric OS 6.x.
• Level 0 static mode (L0)–L0 is the normal (default) mode for a port. Each user port reserves eight buffer
credits and competes with other ports for additional buffer credits. No buffer credits are reserved for
extended distance ISLs.
• Level E static mode (LE)–LE reserves a static number of buffer credits, which supports distances up to 10
km. The number reserved depends on the port speed. The baseline for the calculation is one credit per
km at 2 Gb/s. This yields the following values for 10 km:
• 5 credits per port at 1 Gb/s
• 10 credits per port at 2 Gb/s
• 20 credits per port at 4 Gb/s
• 40 credits per port at 8 Gb/s
• Dynamic Mode (LD)–LD calculates buffer credits based on the distance measured during port
initialization. An upper limit is placed on the calculation by providing a desired distance value. If the
measured distance is more than desired distance, the desired distance is used in the calculation;
otherwise, the measured distance is used. This is a mechanism for controlling the number of reserved
buffer credits ensure buffer availability for other ports in the same group.
• Static long-distance mode (LS)–LS calculates a fixed number of buffer credits based on a desired
distance value.
NOTE: For the LD and LS distance levels, see
distance" on page 425 to get an approximation of the calculated number of buffer credits.
424 Administering extended fabrics
4 bytes
24 bytes
0–21 12 bytes
4 bytes
4 bytes
36–2148 bytes
Table 81 equals 8 bits. The maximum Fibre Channel frame is 2148 bytes.
"Determining how many ports can be used for long
Field size
32 bits
192 bits
0–16,896 bits
32 bits
32 bits
288–17,184 bits