Network Topology

What is Network Topology?

Network Topology

A network topology refers to the physical layout of the network in which all devices i.e.all the hardware that makes up the network,are connected.The points of connection to the network by the station are call nodes or link station.
Example is a local area network (LAN): Any given node in the LAN has one or more physical links to other devices in the network; graphically mapping these links results in a geometric shape that can be used to describe the physical topology of the network. Conversely, mapping the data flow between the components determines the logical topology of the network.
Basic categories of network topologies:

• Physical topologies
• Logical topologies

Physical Topology:

The shape of the cabling layout used to link devices is called the physical topology of the network. This refers to the layout of cabling, the locations of nodes, and the interconnections between the nodes and the cabling. The physical topology of a network is determined by the capabilities of the network access devices and media, the level of control or fault tolerance desired, and the cost associated with cabling or telecommunications circuits.

Logical topologies:

The logical topology in contrast, is the way that the signals act on the network media, or the way that the data passes through the network from one device to the next without regard to the physical interconnection of the devices. A network's logical topology is not necessarily the same as its physical topology. For example, the original twisted pair Ethernet using repeater hubs was a logical bus topology with a physical star topology layout. Token Ring is a logical ring topology, but is wired a physical star from the Media Access Unit.

There are several types of topographical design and strategies are used to implement different networks.The types are-

• Star Topology
• Ring Topology.
• Bus Topology
• Tree Topology
• Mesh Topology
•  Hybrid Topology
• Point-to-point Topology
•  Daisy chain Topology

Star topology:

Star Topology

When all computers attach to the central point is called star topology.It is a star shaped network resembles the spokes of a wheel.The centre of the star network is often call a hub or central controller.A typical hub consists of an electronic device that accepts data from the sending computer and delivers it to the appropriate destination. 
Advantages of the Star Topology:

• Here,in star topology, failure of a single connection disconnects one node only from the healthy network.
• Since here the central node is connected directly to every other node,the faults when occur can be easily detected and isolated.

Disadvantages of the Star Topology:

• Although the cost of the cables is small,but congestion in cables ducts,maintenance and installation problems increase the costs considerably.
• It is central node dependent and if the central node fails,the entire networks becomes stall.  

Ring Topology:

The network that arranges computers to be connected in a closed loop is called Ring Topology.Here a cable connects the first computer to a second computer,another cable connects the second computer to a third and

Ring Topology

so on,untill a cable connects the final computer back to the first.
Advantages of Ring Topology:

• Since one cable connecting each node,the space required in the building for wiring is minimum.

• In a ring topology although the length of cables is that of a bus,but here less connections are needed and hence reliability is increased.

Disadvantages of Ring Topology:

• Since the failure of one node affects all the other,fault diagnosis is therefore very difficult.

• It is not possible to shut down only a small segments of the ring keeping the majority of it in normal working condition.

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