RAD Data comm AMC-101 - Manual (Page 15)

AMC-101 Installation & Operation Manual Chapter 1 - Introduction
General Applications 1-5
The FDDI applies scrambling to data when operating over UTP, but not
doing so when operating over fiber. Because of this, AMC-101 can only
work in pairs for extending FDDI connections over fiber (see Figure 1-5).
FDDI FDDI
UTP Cat 5 UTP Cat 5 Fiber
AMC-101 AMC-101
Figure 1-5 FDDI and Fast Ethernet Operations