The following rules determine the number of buffers that you might need:
For 1 Gbps, calculate buffer credits as:
(length-in-km) x (0.6)
Round the result up to the next whole number. For example, a 10 km connection requires 6 buffer credits, and a 7 km connection requires 5 buffer credits.
For 2 Gbps, calculate buffer credits as:
(length-in-km) x (1.2)
Round the result up to the next whole number. For example, a 10 km connection requires 12 buffer credits, while a 7 km connection requires 9 buffer credits.
For greater speeds or for more details, refer to your switch documentation for information about computing buffer credits.