100BASE-TX

This is the Fast Ethernet twisted-pair standard. When we say Fast Ethernet, we mean 100 Mbps operation. While the data rate increased ten-fold, the maximum cabling length remained at 100 m and the number of pairs remained at two. The RJ-45 connector and pin-out remained the same as 10BASE-T — allowing for the potential for a migration path from 10 Mbps to 100 Mbps while retaining the existing infrastructure. This would be true if the cabling had adequate bandwidth for 100 Mbps operation.

Instead of CAT 3 cable, at least CAT 5 cable is required. To increase the data rate ten-fold while retaining the maximum cabling length, encoding became much more sophisticated. A multi-level signaling scheme using three logic levels (MLT-3) replaced the two-level scheme of 10BASE-T. Not only are the signal levels different, but the 4B/5B encoding scheme is completely unlike that of Manchester encoding. The Fast Ethernet standard introduced the Auto-Negotiation protocol which defined a means for low-speed devices to communicate with high-speed devices upon initial connection — thus allowing support for legacy devices. A Fast Link Pulse (FLP) replaced the NLP.

10BASE-FL

Although not the first fiber optic standard for Ethernet, this standard became the most popular for 10 Mbps Ethernet. A single pair of 62.5/125 µm multimode fiber optic cabling was specified using ST connectors — thus allowing full-duplex operation when using switching hubs. Like 10BASE-T, Manchester encoding was employed, but cabling length over fiber can extend to 2 km (demonstrating one of the advantages of using fiber). At each end of the link are separate transmitter (TX) and receiver (RX) ports. To implement the crossover function, cable connections are reversed at either end of the link. Unlike 10BASE-T, there is no NLP. Instead, a 1 MHz carrier is transmitted during idle conditions.

100BASE-FX

This standard was created to match the newer 100 Mbps operation of 100BASE-TX but over fiber optics. Although the same single pair of 62.5/125 µm multimode fiber optic cabling was used, a new connector was introduced called the SC connector. To maintain the same maximum cabling distance of 2 km, a critical decision was made. Instead of maintaining the lower cost 850 nm (short wave) transceivers, the 100BASE-FX standard specified 1300 nm (long wave) transceivers because of the lower signal attenuation at this frequency. Transceivers operating at different frequencies cannot communicate with one another. This decision eliminated the possibility of a 100BASE-FX device communicating with a legacy 10BASE-FL device. Instead of Manchester encoding, non-return to zero inverted (NRZI) encoding was used in combination with the same 4B/5B encoding scheme used on 100BASE-TX.

100BASE-SX

The "fiber to the desktop" movement embraced the latest 100 Mbps fiber optic standard that is based upon short wave fiber optic technology. This standard is basically the same as 100BASE-FX except that 850 nm transceivers and ST connectors were specified — providing a possibility of connecting new 100 Mbps fiber optic equipment to legacy 10 Mbps fiber optic links. Instead of achieving a 2 km distance, 100BASE-SX is limited to 300 m. For desktop applications, this should be adequate. Like 100BASE-TX, the new 100BASE-SX standard supports auto-negotiation. The intent was to achieve the same degree of communication with fiber legacy devices as with copper legacy ones.

Media converters usually fit between an end station and a port on a hub. However, they can also fit between two hub ports.