Connecting Networks

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Ring

Star

The star pattern connects everything to a host computer, a network switch, or a network hub, which handles the network tasks. All communications between computers go through the host/switch/hub. This configuration is good for home networks, often using a wireless hub instead of a host computer. Using a very large host computer, it is good for businesses that have large amounts of rapidly changing data, like banks and airline reservation offices.

Advantages:

Gives close control of data.
Each PC sees all the data.
User sees up-to-date data always.
If a computer other than the host fails, no other computer is affected.
Printers and scanners can be connected to the network hub instead of a specific computer to be shared by the whole network.

Disadvantages:

If host computer or its software goes down, the whole network is down. (A backup computer system would be necessary to keep going while repairs are made.)

Bus

The bus pattern connects the computer to the same communications line. Communications goes both directions along the line. All the computers can communicate with each other without having to go through the server.

Advantages:	Any one computer or device being down does not affect the others.
Disadvantages:	Can't connect a large number of computers this way. It's physically difficult to run the one communications line over a whole building, for example.

The ring pattern connects the computers and other devices one to the other in a circle. There is no central host computer that holds all the data. Communication flows in one direction around the ring. This configuration is good when the processing of data can be done on the local PC.

Advantages:	Requires less cabling and so is less expensive.
Disadvantages:	If one node goes down, it takes down the whole network.

In the token ring form of a ring network, a token is constantly passed along the network. A device must wait until the token is at that device. Then it can attach the message it wants to send to the token. When the token reaches the intended recipient device on the network, it will release the message. The token circulates very fast, but this obviously means that most of the time a device will have to do some waiting before it can send out a message.

Networks can be connected to each other, too. There are difficulties in doing so, however. A combination of software and hardware must be used to do the job.

A gateway connects networks of different kinds, like connecting a network of PCs to a main frame network. This can be complex!
A bridge connects networks of the same type. This job is simple.
A router connects several networks. A router is smart enough to pick the right path for communications traffic. If there is a partial failure of the network, a router looks for an alternate route. Home wireless networks often use a network router along with a modem to allow several computers or devices to connect to the Internet.

Suppose the accounting, advertising, and shipping departments of a company each have networks of PCs. These departments need to communicate with each other, but only sometimes. It would be easier and cheaper to connect them to each other than to put them all on the same larger network. The best arrangement would be for the departmental networks to be of the same kind so that a bridge could be used.

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