What is Fast Ethernet?

Kurt Inman

Fast Ethernet is a set of Ethernet standards for 100 Megabit per second (Mbps) computer networking. Using Fast Ethernet, data can be transmitted over copper-twisted pair or longer-distance fiber-optic cables. Its low cost and relatively high speed often make it a good choice for everyday network connectivity. It is frequently used by desktop and portable computers to communicate with network hubs, routers and switches.

Cat 5 cable with RJ45 plug.
Cat 5 cable with RJ45 plug.

During the early 1990s, the 10 Mbps speed limitation of existing Ethernet networks was creating frequent bottlenecks. High-speed optical technologies such as Fiber Distributed Data Interface (FDDI) were often too expensive to implement. The Institute of Electrical and Electronics Engineers (IEEE) introduced Fast Ethernet as a low-cost solution in 1995. Supporters originally claimed that this 100 Mbps technology could be used without replacing existing network cables. In reality, many installations had to be rewired with a newer cable standard to fully support the higher device bandwidths.

Ethernet cables plugged into an Internet switch.
Ethernet cables plugged into an Internet switch.

American National Standards Institute (ANSI) Category (CAT) 3 cables were widely used in 10 Mbps Ethernet networks. The IEEE 100BASE-T2 and 100BASE-T4 standards introduced Fast Ethernet over twisted pair cables. These standards used the same CAT 3 cables as the older 10 Mbps networks. IEEE 100BASE-TX became the most widely-used standard, utilizing CAT 5 or better copper cables. Like CAT 3, CAT 5 cables are limited to a maximum length of 328 feet (100 meters) and use the same type of connector.

Four additional standards in the IEEE 100BASE family define fiber optic-based 100 Mbps connections. These have maximum cable lengths from 1,310 feet (400 meters) to over 24 miles (40 kilometers). The type of optics and fibers used determine the allowable cable length and design.

To help ease the transition from 10 Mbps to Fast Ethernet, many devices were sold which support both speeds. So-called "10/100" network interface cards, laptop interfaces and hubs can automatically negotiate the highest-supported line speed. Routers, switches and other network equipment may also include this ability, as well as boot-time speed configuration.

The term fast Ethernet is relative to the network technology available at the time. In 1995, regular Ethernet operated at just 10 Mbps, and Fast Ethernet was 10 times faster. Since the late 1990s, however, Ethernet speeds have increased considerably. 1 Gigabit per second (Gbps) Etherne—also known as Gigabit Ethernet—was introduced in 1999. This was soon followed by 10, 40 and 100 Gigabit Ethernet in the 2000s.

An Ethernet network adapter has a jack that accepts an Ethernet cable which is used to transfer data at high speeds from a router or modem.
An Ethernet network adapter has a jack that accepts an Ethernet cable which is used to transfer data at high speeds from a router or modem.

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