Physical Versus Logical Topology

A distinction needs to be made between physical and logical topologies. A physical topology describes how devices are physically cabled together. For instance, 10BaseT has a physical star topology and FDDI has a physical dual ring topology. A logical topology describes how devices communicate across the physical topology.

The physical and logical topologies are independent of each other. For example, any variety of Ethernet uses a logical bus topology when
devices communicate. This means that in Ethernet, you might be using 10BaseT with a physical star topology to connect devices together; however, these devices are using a logical bus topology to communicate.

Token Ring is actually a good example of a media type that has a different physical topology from
its logical one. Physically, Token Ring uses a star topology, similar to 10BaseT Ethernet. Logically, however, Token Ring devices use a ring topology to communicate. This can create confusion when you are trying to determine how devices are connected together and how they communicate. FDDI, on the other hand, is straightforward. FDDI’s physical and logical topologies are the same: a ring. Table 1-2 shows common media types and their physical and logical topologies.