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Module 3
Lesson 3
Logical vs. physical topology

Differentiate between the logical and physical topology of the network.

Although the term "network topology" is most often used to refer to the physical shape or layout of the network, each network also has a logical topology that may or may not be the same as its physical topology. For example, on a linear bus network, physical and logical topologies are the same: the cable is laid in a line and the data travels up and down that line. With some network architectures, however, it's not that simple.

A physical star that operates as a logical ring

The Token Ring is the most common example of a network with different logical and physical topologies. Here, the physical topology is a star bus; that is, there is a length of cable from each computer that connects it to a central hub (called a Multi-Station Access Unit, or MSAU).

Inside the hub, however, the ports are wired together sequentially in a ring, and they send data around the ring instead of sending it out to all ports simultaneously as it would if the network were a logical star.

The MouseOver below illustrates how the physical star/logical ring configuration works.



Importance of logical topology

The media access method, the way network access is controlled and collisions prevented, is based on the logical topology rather than the physical topology. To effectively troubleshoot communications problems, it is important to know not only the physical topology of a network but also the logical topology, so that you know what path the data packets take as they travel from one computer to another.
Next lesson

In the next lesson, you will learn about the characteristics of the linear bus topology.
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