100BASE-X Ethernet, FDDI, and CDDI
The title 100BASE-X encompasses 100BASE-TX and 100BASE-FX. The 100BASE-X title was coined because even though 100BASE-TX transmits onto twisted-pair cable and 100BASE-FX transmits onto optical fiber, these technologies have a lot in common. The physical layers for 100BASE-FX and 100BASE-TX were derived from the FDDI and CDDI physical layers.
Figure A.3 shows a division of the physical layer into a part that is independent of the medium and a part that is dependent on the medium. The medium-independent parts of 100BASE-TX and 100BASE-FX are the same.
Figure A.3. A view of the physical layer.