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

Table 76 describes Fibre Channel data frames
Table 76

Fibre Channel data frames

Start of frame
Standard frame
header
Data (payload)
CRC
End of frame
Total (Nbr
bits/frame)
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 up to 500
km. The port can only be used as an E_Port. Changes made by this command are persistent across switch
reboots and power cycles.
Use the portCfgLongDistance --distance_level command to select one of the following four
options for buffer credit allocation.
• Level 0 static mode (L0) - L0 is the normal mode for a port. An extended ISL port competes with other
ports for buffers. No buffer credits are reserved for extended ISLs.
Level E static mode (LE) - LE reserves a static number of buffer credits that 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 Gbps. This yields the following values for 10 km:
• 5 credits per port at 1 Gbps.
• 10 credits per port at 2 Gbps.
• 20 credits per port at 4 Gbps.
• 40 credits per port at 8 Gbps.
• 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. When
the measured distance is more than desired distance, the desired distance is used in the calculation.
This is a mechanism for controlling the number of reserved buffer credits ensuring buffer availability for
other ports in the same group.
• Static long distance mode (LS) - LS calculates a static number of buffer credits based on a desired
distance value.
For both LD and LS distance levels, you can use the following formula to get an approximation of the
calculated number of buffer credits.
348 Administering Extended Fabrics
4 bytes
24 bytes
{0 - 2,1 12 bytes
4 bytes
4 bytes
{36 0 2,148} bytes
Table 76 means 8 bits. The maximum fibre channel frame is 2,148 bytes.
32 bits
192 bits
{0 - 16,896} bits
32 bits
32 bits
288 - 17, 184 bits