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Module 3
Lesson 5
Star bus topology

Objective
Illustrate the characteristics of the star bus topology.

Another important topology is the star bus topology. The star topology is so called because each computer (or other network device) connects to a central hub, with the cable forming the shape of a star.

The star bus has become the most popular topology for local area networks, and it is often combined with the linear bus in large networks. In such cases the linear bus provides a backbone that connects multiple stars, as shown in the graphic below.
 

backbone



The combination of linear bus and star bus topologies that make up a backbone network is sometimes referred to as a tree topology.

A star network usually uses twisted pair cabling, although fiber optic can also be wired in a star configuration.
 

Advantages and disadvantages of the star bus

The star bus is one of the most popular LAN technologies, and with good reason. The table below lists some of the advantages and disadvantages of the star bus.


 

  Advantages of star bus   Disadvantages of star bus

  • Fault tolerant

  • Inexpensive, flexible, and easy-to-use cable or media type

  • Easy to troubleshoot by removing computers from the hub or adding "smart" hubs to diagnose problem for you

  • Simple to add more computers to network

  • Fast processing capability--up to 1000Mbps (1Gbps)

  • Active topology set-up (with hub as a multi-station repeater) that amplifies signal

  • Expensive because of additional cable and the purchase of a hub


 

 
How computers communicate on a star bus

When a computer on a typical star bus sends a message, it travels to the hub. If the hub is an active hub, it regenerates the signal and then sends it out via all ports to the rest of the computers on the network. If the hub is a switching hub, it sends the message out via only the port to which the destination computer is attached.
 

TIP:You will learn more about the available types of hubs later in the course.




 
Equipment requirements

The star bus requires:
  • At least one hub, as the hub is the basis of the star.

  • Multiple hubs can be cascaded
     

The graphic below shows multiple hubs can be cascaded from hub to hub in a multiple hub star bus layout.

hub

In addition to the hub(s), a star network requires that each computer have an NIC with an RJ-45 connector (similar to a phone jack, only larger). No terminators are required on a star network, because each cable segment has only two nodes: the computer on one end and the hub on the other.
 


TIP:Hubs are sometimes called concentrators.




 
Next lesson

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