 1Gbps 1 Gbps 100Mbps 10Mbps 100Mbps Ethernet Ethernet Ethernet Switch Switch Switch 100Mbps 10Mbps 100Mbps Office Data-Intensive Desktop Desktop Servers Figure 6.3 An example of Gigabit Ethernet Chapter 6 Local Area Networking LAN Access Methods The third main LAN characteristic is the access methods, which are involved in determining who gets to use the network and when they get to use it. There are two main approaches to LAN access: token passing and Carrier Sense Multiple Access/Collision Detection (CSMA/CD). Token Passing Token passing, shown in Figure 6.4, is used with the token-ring and FDDI archi- tectures. Here is how token ring works: 1. The active master, chosen through a process called beaconing, inserts a token (i.e., a specially formatted packet) into the ring. 2. The token circulates around the ring and is regenerated by each workstation it passes. (In token-ring networks, a workstation obtains data from only its upstream neighbor, regenerates it, and sends it to its downstream neighbor.) 3. When a workstation has data to send, it waits for the token to pass by and grabs it off the wire, holding it until it has finished its transmission. The sta- tion then injects its data packets onto the wire. 4. The packets circulate around the ring and are examined and regenerated by each workstation. When the receiving workstation receives the packets, it marks them as received when it regenerates and reinjects them. This marking notifies the sender that the data was in fact received when it finally returns to the sender. The sender then generates a new token and injects it into the ring. Token Figure 6.4 Token passing LAN Characteristics To prevent any particular workstation from hogging the ring, a transmitting station can hold the token (and thus transmit data packets) for a specific interval, called the token hold time. If the time expires before the station has transmitted all its information, it must stop transmitting and put a new token back on the ring SO that other stations have a chance to communicat