A Guide to Network Topologies

An interconnected collection of autonomous computers is called "NETWORK", and two computers are said to be connected if they are able to exchange the information among themselves. By autonomous we refer only that system that excludes the "master/slave" relationship i.e. if a computer forcibly starts, control, or stop another system, the computer are not autonomous.

Topology refers to the way how the network is laid out physically. Topology of a network is the geometric representation of all the link and linked device to one another. A link is the communication path that transfers data from one device to another. For communication, the devices must be connected in some way at same time to the same link. There are mainly two type of connection:

Ø Point-to-point

Ø Multipoint

Point -to-point:

It provides a dedicated link between the devices. A wire/cable of actual length is used to connect the two ends, but we can also use microwave or satellite links. When you are using remote control to change the channel of your tv set than you are establishing a point-to-point connection between tv set and remote control.

Multipoint:

Multipoint is the connection that includes more than two systems for participating in networking. If link is used by several devices simultaneously, it is "spatially shared" connection and if the user must take turn, it is "timeshare" connection.

There are four types of topologies:

Mash:

It is a dedicated point-to-point link. Dedicated refers that the link carries data only between two devices it connects. For n devices a fully mashed network has n(n-1)/2 physical channel, and every device must have (n-1) input/output ports.

Advantage:

· Eliminate the traffic problem as each connection can carry its own data load.

· Mesh topology is robust because failure of one link will not affect the entire system.

· It also supports privacy and security.

· Mesh topology makes the fault tolerance and fault isolation very easy.

Disadvantages:

· High cost of cable and input/output ports.

· Installation is difficult.

Star:

It is also a dedicated point-to-point link. But, the devices are not connected directly to one another. If one device wants to send data to another device, it first sends the data to the controller known as "hub".

Advantages:

· As each device requires only one link and one input/output port. So it is less expensive than a mesh topology.

· It is also robust.

· Fault tolerance and fault isolation is very easy.

Limitation:

In star topology more cabling is required because, each node must be linked to a central hub, than in other topologies like bus and ring.

Bus:

Bus topology is multipoint. One cable is used to link all the devices. Nodes are connected to the cable by taps and drop lines. Drop line is the connection between device and main cable, and tap is the connection between metallic core and main cable.

Advantages:

· Easy to install.

· Less cabling is required than mesh and star.

Disadvantages:

· Fault isolation and reconnection is very difficult.

· A fault in the bus cable will stop all transmission.

· Signal reflection at the taps can cause degradation in quality.

Ring:

It is point-to-point connection. Each device has a dedicated link with two devices on either side of it. Each device will acts as repeater because each device regenerates the bits and passes them. A signal is passed along the ring in one direction from one device to another.

Advantages:

· Easy to install and reconfigure.

· Fault tolerance and fault isolation is simplified.

Limitations:

A single break will disable the entire network. To solve this concept of double ring is there.