Brocade Fabric OS Administrators Guide (Supporting Fabric OS v7.3.0) - Manual (Page 119)

Fibre Channel gigabit values reference definition
The following table shows the Fibre Channel gigabit values that you can use to calculate buffer
requirements.
Fibre Channel gigabit values TABLE 15
Gigabit value Buffer requirements
1 Gbps 1.0625
2 Gbps 2.125
4 Gbps 4.25
8 Gbps 8.5
10 Gbps 10.625
16 Gbps 17
Buffer credit allocation based on full-size frames
Assuming that the frame is a full-size frame, one buffer credit allows a device to send one payload up to
2,112 bytes (2,148 with headers). Assuming that each payload is 2,112, you need one credit per 1 km
of link length at 2 Gbps (smaller payloads require additional buffer credits to maintain link utilization).
Refer to
Allocating buffer credits based on average-size frames on page 121 for additional information.
Fibre Channel data frames
The final frame size must be a multiple of 4 bytes. If the data (payload) needs to be segmented, it will
be padded with 1 to 3 "fill-bytes" to achieve an overall 4-byte frame alignment. The standard frame
header size is 24 bytes. If applications require extensive control information, up to 64 additional bytes
(for a total of an 88-byte header) can be included. Because the total frame size cannot exceed the
maximum of 2,148 bytes, the additional header bytes will subtract from the data segment by as much as
64 bytes (per frame). This is why the maximum data (payload) size is 2,112 (because [2,112 - 64] =
2,048, which is 2 kb of data). The final frame, after it is constructed, is passed through the 8-byte-to-10-
byte conversion process.
Table 16 describes Fibre Channel data frames.
Fibre Channel data frames TABLE 16
Fibre Channel frame fields Field size Final frame size
Start of frame 4 bytes 32 bits
Standard frame header 24 bytes 192 bits
Data (payload) 0-2,112 bytes 0-16,896 bits
CRC 4 bytes 32 bits
Fibre Channel gigabit values reference definition
Fabric OS Administrators Guide 119
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