rol (MAC) addresses on each frame, ignoring the ones that were addressed to others. Transmission depended on an arbitration protocol called Carrier Sense Multiple Access with Collision Detection (CSMA/CD). This was very clever; it allowed any station on the LAN to transmit when it had data, but every station had to simultane- ously listen to see if another station transmitted at the same time. If such a colli- sion occurred, each station would back off a random length of time before retransmitting. It worked brilliantly well and was amenable to mass production. But it had firm limits. The distance between stations on a given coaxial Ethernet was strictly limited by the speed of light: No two stations could be farther apart than the distance that a bit could travel during the duration of a minimum-size frame (64 octets). Otherwise, collisions would be missed. Bridges, packet switches working at line speed at the MAC address level, were needed to relay frames in order to form an extended network. Ethernet was a technology star of the 1980s. It beat off a challenge from IBM, which promoted the Token Ring LAN as an alternative. It evolved to sup- port unshielded twisted-pair desktop wiring, typically collapsing the CSMA/CD backbone into a small box (hub), which could be bridged to other hubs. It evolved into a fully switched form, wherein the hub became a multiport bridge, no longer sharing a single 10-Mbps pool of bandwidth among its ports. And it fended off almost all competition. In the late 1980s, a 100-Mbps fiber-optic LAN called fiber distributed data interface (FDDI) was designed as an upgrade, but it was slow to market and did not catch on. In the early 1990s, ATM net- works, originally proposed by the CCITT for broadband ISDN public net- works, had a flurry of interest as a LAN backbone. They too failed: The killer LAN technology of the mid-1990s was Fast Ethernet. This usually was not even based on Ethernet's key CSMA/CD technology, although CSMA/CD Fast Eth- ernet hubs were possible. More often, it was dep