IBM ATM OC-3c - Manual (Page 79)

ATM Physical Layer Statistics 9-13
7 If you suspect that the fiber optic cable is not
working, replace the cable with a cable known to be
working, and check the Link Status LED.
8 Check that the cable has not been accidently plugged
into an FDDI connector at one end of the connection.
9 Check that the ATM Module and ATM Switch are
using compatible transmit clocking options.
10 Check that the Line Rate settings on the two devices
are compatible.
11 If there is still a problem, contact your repair center
for advice. For more details, refer to Appendix E.