A point-to-point topology has a single connection between two devices. In this topology, two devices can directly communicate without interference from other devices. These types of connections are
not common when many devices need to be connected together. An example of a point-to-point topology is when you connect two routers across a dedicated WAN circuit.
In a star topology, a central device has many point-to-point connections to other devices. Star topologies are used in environments where many devices need to be connected. An example of a media type that uses a star topology is 10BaseT Ethernet. When connecting devices together, you connect your computers to a hub or switch (the center of the star). An extended star topology is basically multiple star topologies interconnected.
A bus topology uses a single connection or wire to connect all devices. Certain media types, like 10Base5 and 10Base2 Ethernet, use a bus topology. Typically, special types of connectors or transceivers are used to connect the cables in order to provide the bus topology. In 10Base2, for example, each device connects to a single strand of coaxial cable via a vampire tap. This device taps into the single strand of coaxial cable and provides the physical connection from a networking device to the single strand of cable.
In a ring topology, device one connects to device two, device two connects to device three, and so on to the last device, which connects back to device one. Ring topologies can be implemented with a single ring or a dual ring. Dual rings are typically used when you need redundancy. For example, if one of the devices fails
in the ring, the ring can wrap itself, as shown in Figure 1-2, to provide a single, functional, ring. Fiber Distributed Data Interface (FDDI) is an example of a media technology that uses dual rings to connect computer devices.
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