IBM ATM OC-3c - Manual (Page 93)

ATM Cable Specification C-3
To check that the bandwidth of your fiber is within an
acceptable range:
1 Divide the amount of bandwidth available according
to the fiber specification by the total length of fiber
(km).
2 If the result is lower than 250MHz, the link may be
prone to bit errors. You should shorten the length of
the fiber or use a different fiber until the result of the
calculation reaches 250MHz.
Example:
A cable with modal bandwidth of 500 MHz.km will
have 250 MHz of bandwidth at 2km (1.25 miles).
The same cable would have a 500MHz of bandwidth
at 1km (0.625 miles).
A fiber cable with a bandwidth specification of
200 MHz.km would have only 100MHz of bandwidth
at 2km (1.25 miles), which would not support ATM.
In this case, another type of fiber which has a
bandwidth of 155MHz would be required.