"Fast Ethernet" gets plug-and-play

The IEEE 802.3 "Fast Ethemet" standard implements an "Auto-Negotiation" mechanism which allows any existing or future Ethernet LAN using an RJ-45 connector and unshielded twisted pair cable to simply "plug and play." The mechanism is designed to ensure interoperability between the variety of standards based Ethemet networks, including exiting 10 Mbls devices, and new 100 Mbls half duplex and full duplex capable devices. Automatic configuration occurs without user intervention, and will negotiate the optimal mode at which the devices at both ends of a link can commonly operate. In the event the devices share no common mode, the Auto-Negotiation scheme ensures that operation of the rest of the network is not disrupted, and allows the absence of a shared operational mode to be reported via network management. This paper will examine the key aspects of the technology surrounding the Auto-Negotiation scheme, as well as specific examples of the use of the Auto-Negotiation approach and how it solves potential interoperability problems.