Auto-Negotiation for Twisted-Pair Interfaces
Some of the vendors that built the first 10/100 twisted-pair Ethernet adapters and hubs created proprietary protocols that enabled link partners to negotiate and check whether both ends could operate at 100Mbps and whether both could operate in full-duplex mode.
Users wanted a standard negotiation protocol. The IEEE 802.3 committee acted quickly and published 802.3u, which was based on National Semiconductor's NWay negotiation method. IEEE Auto-Negotiation was defined as an optional feature of 10BASE-T, 100BASE-T4, and 100BASE-TX interfaces. It became a mandatory part of the 1000BASE-T and 1000BASE-X interfaces that were introduced later.
Twisted-pair Ethernet interfaces that support Auto-Negotiation ...