Introduction to Data Communications
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40. Hubs

Hubs are also called Multiport Repeaters or Concentrators. They are physical hardware devices.

Some Hubs are basic hubs with minimum intelligence - no microprocessors. Intelligent Hubs can perform basic diagnostics and test the nodes to see if they are operating correctly. If they are not, the Smart Hubs or Intelligent Hubs will remove the node from the network. Some Smart Hubs can be polled and managed remotely.

40a. Purpose of Hubs

Hubs are used to provide a Physical Star Topology. The Logical Topology is dependant on the Medium Access Control Protocol. At the center of the star is the Hub with the network nodes on the tips of the star.

Star Topology

The Hub is installed in a central wiring closet with all the cables extending to the network nodes. The advantage of having a central wiring location is that it is easier to maintain and troubleshoot large networks. All of the network cables come to the central hub, it is especially easy to detect and fix cable problems. You can easily move a workstation in a star topology by changing the connection to the hub at the central wiring closet.

The disadvantages to a star topology are:

failure of the Hub can disable a major section of the network
The Star Topology requires more cabling than does the ring or the bus topology because all stations must be connected to the hub, not to the next station.

Introduction to Data Communications
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