Physical and Logical Topologies

Physical and Logical Topologies

A topology defines the arrangement of nodes, cables, and connectivity devices that make up the network. Two basic categories form the basis for all discussions of topologies:

Physical topology. Describes the actual layout of the network transmission media
Logical topology. Describes the logical pathway a signal follows as it passes among the network nodes

Another way to think about this distinction is that a physical topology defines the way the network looks, and a logical topology defines the way the data passes among the nodes. At a glance this distinction may seem nit-picky, but as you learn in this chapter, the physical and logical topologies for a network can be very different. A network with a star physical topology, for example, may actually have a bus or a ring logical topology.

In common usage, the word “topology” applies to a complete network definition, which includes the physical and logical topologies and also specifications for elements such as the transmission medium. The term topology as used in Microsoft’s test objectives for the Networking Essentials exam applies not to the physical and logical topology archetypes described in this section but to the complete network specifications (such as 10BASE-T or 10BASE5) described in the “Ethernet” and “Token Ring” sections of this chapter.

Physical and logical topologies can take several forms. The most common—and the most important for understanding the Ethernet and Token Ring topologies described later in this chapter—are the following:

Bus topologies
Ring topologies
Star topologies

The following sections discuss each of these important topology types.

Further Information