 of Ethernet and the extremely low cost of the hard- ware required, most manufacturers today build the functionality of an Ethernet NIC directly into PC motherboards. Even though Ethernet has gone through quite a few generational changes, from thick coax supporting 10Mbps in traditional LAN environments to the emerging use of Gigabit Ethernet in the local loop and 10Gbps LAN Characteristics point-to-point links in MANs and WANs, from the programmer's perspective, the variations are pretty much the same Ethernet and are easily interconnected using inexpensive and readily available hardware. Many Ethernet cards and switch ports support multiple speeds, using autonegotiation to set the speed and duplexing to match the best parameters supported by both devices. In the event that autonegoti- ation fails, a device designed to support multiple speeds senses the speed used by the other device but assumes half-duplex mode. For example, a 10/100 Ethernet port supports 10BASE-T and 100BASE-TX, while a 10/100/1000 Ethernet port sup- ports 10BASE-T, 100BASE-TX, and 1000BASE-T. Token Ring originated in the IBM environment in the early 1980s. Although it was very successful initially, after the Ethernet twisted-pair standard emerged in the early 1990s, the use of Token Ring declined. IBM no longer uses or promotes the Token Ring technology, but Madge Networks (www.madge.com) continues to provide it. The IEEE 802.5 working group has standardized token-ring LAN speeds of 4Mbps, 16Mbps, 100Mbps, and 1Gbps. Despite the fact that FDDI was the first LAN standard to provide 100Mbps for use in a backbone application, it did not capture a major market share. The transition to a higher grade of Ethernet is much simpler for companies than is a transition to an entirely new protocol. The prevailing standard in the world is Ethernet, which generally appears as Fast Ethernet or Gigabit Ethernet in the backbone, connecting individual Fast Ethernet or 10Mbps Ethernet LAN segments (see Figure 6.3). Gigabit Switch Gigabit Switch Interswitch Link