andardized protocols are not exactly equal to the original Ethernet but they can operate in the same LAN. An Ethernet LAN is logically a bus although its physical structure is often a star where all stations are connected to wiring center called a hub. We discuss Ethernet in more detail later in this section. Another common LAN is the token ring, developed by IBM, and it is standardized as ISO 8802-5 or IEEE 802-5. The typical data rate of this LAN is 16 Mbps. In a token ring network, only a computer holding a special short frame called a token is able to transmit to the ring. The transmitted frame propagates via all computers in the ring and the station with the desti- nation address reads it. The sending computer takes the frame from the ring and passes the token to the next station in the ring, which is then able to transmit. Physically the token ring is always built as a star although logically it still makes up a ring as shown in Figure 6.25. All computers are connected to a wire center that bypasses the workstations in the power off condition. When the power is switched on, the frames propagate from a workstation via a wire center to the next workstation in a logical ring. The token ring has some technical advantages over the Ethernet (no collisions, better bandwidth utilization, and deterministic operation) but it is much more complicated because of the token management and thus more expensive. One important high-speed LAN is the fiber distributed digital interface (FDDI). Its operating principle is quite similar to that of a token ring but the data rate is higher, 100 Mbps. FDDI also allows longer distances and the maximum length of the ring is 100 km. The original transmission media of FDDI was optical fiber, but currently copper cables are also used for the con- nections between computers and a station attachment unit that connects workstations to the ring. The FDDI has been around since the 1980s and for many years it was the only technology that provided bandwidth higher than 10 or 16 Mbps. It was use