Network Topology Tutorial

Topologies are either physical or logical. Physical topologies deal with how the devices on a network are wired together. Logical topology deals with how information is passed from one device on a network to another. The common types of network topology are:

• bus
• ring
• star
• tree
• mesh

Hybrids are a combination of 2 of the above.

Bus Topology

In a bus topology, all devices on the network are connected to a main cable using an interface connector. This main cable is called the bus or another name for it is the backbone. The main cable must have a terminator at each end. A terminator absorbs the signal, thus removing it from the bus. Coax Cable, 10Base5, is typically used in this topology.

A Bus topology is the simplist network configuration; however, you can only connect a limited number of computers to the bus; more than 12 and performance degrades. There can be problems when two clients want to transmit at the same time on the same bus. This necessitates the use of some type of collision handling or collision avoidance system. Bus topology is used mainly in small network situations.

As the signal travels down the bus, it loses strength. If you want to add more computers to the network, you must use a repeater at fixed locations to strengthen the signal.

A bus topology is considered to be a passive topology. The computers on the bus sit and listen. When they hear data that belongs to them, they accept it but are not responsible for moving the signal along.

When one device on the network wants to send a broadcast message to another device on the network, it first makes sure no one else on the bus is transmitting, then it sends information out on the backbone. All other devices on the network see it, but only the intended recipient accepts and processes the it. This is accomplished by using data frames which contain source and destination addresses.

Advantages

1. Relatively inexpensive compared to other topologies
2. Easy to connect computers and peripherals to a linear bus
3. Requires less cable length than a star topology.

Disadvantages

1. If there's a break anywhere in the cable, the entire network goes down.
2. Terminators are required at both ends of the backbone.
3. A bad network card can produce enough noise on the bus to cause the entire network to malfunction.
4. If the entire network goes down, it can be difficult troubleshooting the problem.
5. Hard to reconfigure once it's set up.

References

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Revised: Friday, November 28, 2008 10:47:10 AM