Fast Ethernet
Fast Ethernet operates at 100 Mbps and is based on the IEEE 802.3u standard. The Ethernet cabling schemes, CSMA/CD operation, and all upper-layer protocol operations have been maintained with Fast Ethernet. Fast Ethernet is also backward compatible with 10 Mbps Ethernet. Compatibility is possible because the two devices at each end of a network connection can automatically negotiate link capabilities so that they both can operate at a common level. This negotiation involves the detection and selection of the highest available bandwidth and half-duplex or full-duplex operation. For this reason, Fast Ethernet is also referred to as 10/100 Mbps Ethernet. Cabling for Fast Ethernet can be either UTP or fiber optic. Specifications for these cables are shown in Table 1.5.
| Technology | Wiring Type | Pairs | Cable Length |
| 100BaseTX | EIA/TIA Category 5 UTP | 2 | 100 m |
| 100BaseT2 | EIA/TIA Category 3,4,5 UTP | 2 | 100 m |
| 100BaseT4 | EIA/TIA Category 3,4,5 UTP | 4 | 100 m |
| 100BaseFX | Multimode fiber (MMF) with 62.5 micron core; 1300 nm laser Single-mode fiber (SMF) with 62.5 micron core; 1300 nm laser | 1 | 400 m (half-duplex) 2,000 m (full-duplex) |
TABLE 1.5: Fast Ethernet Cabling and Distance Limitations