SWITCH 300-115 1.2 Configure and verify Layer 2 protocols

1.2.b UDLD

it is not the case that udld is used on fiber ports, and loopguard is used on copper exclusively. they provide some functional differences in the network regardless of the media used. see below:

from: http://www.cisco.com/c/en/us/support/docs/lan-switching/spanning-tree-protocol/10596-84.html

loopguard_v_udld