What does "802.3u" specify in Ethernet networking?

The designation "802.3u" refers specifically to the Fast Ethernet standard, which defines Ethernet networking speeds of 100 Mbps. This standard was developed to enhance the existing Ethernet capabilities outlined in the original IEEE 802.3 specification, which primarily focused on 10 Mbps Ethernet.

Fast Ethernet operates over twisted pair (Category 5 or better) cabling and maintains compatibility with the original Ethernet standards, facilitating smoother transitions in network infrastructure. It can support various physical medium specifications, including 100Base-TX, which employs two pairs of twisted copper wiring, and 100Base-FX, which uses fiber optics.

This advancement allowed businesses and organizations to achieve faster data transmissions over typical Ethernet infrastructure without the need for a complete overhaul. By establishing a standard for higher-speed networking, 802.3u addressed the increasing demands for bandwidth that arose as networks evolved and applications became more data-intensive.