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