IEEE 802.3 100Base-X
The Ethernet interface 100Base-X was developed by the standardization committee IEEE 802.3u, almost at the same time as 100Base- VG. It is an interface specification of Fast Ethernet with a transmission rate of 100 Mbit/s.
100Base-X aims at a combination of CSMA/ CD and FDDI. Here, the X stands for a box with which all the physical connection options of FDDI can be used for CSMA/CD. 100Base-X works with 4B5B coding and can be operated in the 100Base-FX version via optical fiber and in the 100Base- TX version via STP cable.