100base

100BASE refers to a family of Ethernet standards that provide a nominal data rate of 100 Mbit/s for local area networks. Introduced as Fast Ethernet, the 100BASE standards were formalized in IEEE 802.3u in 1995 as an evolution of the 10 Mbit/s Ethernet specifications. They enabled higher throughput over existing LAN cabling and helped organizations upgrade networks without a complete infrastructure overhaul.

The main variants are 100BASE-TX, 100BASE-FX, and 100BASE-T4. 100BASE-TX uses two copper twisted pairs (transmit and receive) and commonly runs over Category 5 or better cabling up to 100 meters, with RJ-45 connectors. 100BASE-FX uses fiber optic cables (typically multimode) and supports distances up to about 2 kilometers, depending on fiber type and optics. 100BASE-T4 is an older copper option that used all four paired conductors to achieve 100 Mbit/s and is much less common today.

Technically, 100BASE networks often operate using CSMA/CD access, though in modern installations with switches many links run in full-duplex mode, effectively eliminating collisions. 100BASE-TX employs 4B/5B encoding with MLT-3 line signaling at a 125 megabaud symbol rate. 100BASE-FX employs optical signaling appropriate to the fiber medium. The copper variants require suitable category cabling (typically Cat 5 or better) and support up to 100 meters for 100BASE-TX, with fiber links extending much farther.

Impact and legacy: 100BASE established Fast Ethernet as a widely deployed standard in the 1990s, serving as a transitional technology between 10BASE-T and gigabit Ethernet. It has largely been supplanted by 1000BASE-T and newer standards but remains in use in legacy networks and some industrial environments.