Basic Concept of LAN Topologies

2

Standard Topologies

Are classified into:

  • Bus
  • Star
  • Ring

Bus Topology

  • Bus topology is also known as linear bus topology
  • Has several computers attached to a common cable called the trunk line
  • Sends data to all the computers on the network
  • Enable the computer with specified address in the signal to accept the data
  • Allows only one computer at a time to send messages
  •  Is a passive topology
  • Does not bring down the network if one computer fails

bus1

          Figure : A Bus Topology.

Advantages of Star Topology

  • Is reliable for small networks
  • Is easy to use
  • Require least amount of cable to connect computers
  • Can be easily extended

Disadvantages of Bus Topology

  • Performance is adversely affected by heavy network traffic
  • Electric signals weaken when several extensions are attached
  • Troubleshooting is difficult

Star Topology

  • Connects computers by cables to a centralized device called a hub
  • Sends signals weaken from the sending computer to the receiving computer through the hub
  • Requires more cable since each computer is connected to the central point
  • May have a disable network if its central controller fails
  • Can be expanded by attaching another star hub
  • A hub is the central point in a star topology

star

Figure: A Star Topology

Advantages of Star Topology

  •  Is easy to modify
  • New computers can be added easily
  • Network problems are easy to diagnose
  • Failure of a signal computer does not bring down the entire network
  • Several cable types can be used with the hub

Disadvantages of Star Topology

  • If the central hub fails, the entire network fails
  • Cabling costs are more

 

Ring Topology:

In Ring Topology, all the nodes are connected to each-other in such a way that they make a closed loop. Each workstation is connected to two other components on either side, and it communicates with these two adjacent neighbors. Data travels around the network, in one direction. Sending and receiving of data takes place by the help of TOKEN.

Ring

 

Figure : A Ring Topology.

Advantages of Ring Topology

  • This type of network topology is very organized. Each node gets to send the data when it receives an   empty token. This helps to reduces chances of collision. Also in ring topology all the traffic flows in only one direction at very high speed.
  • Even when the load on the network increases, its performance is better than that of bus topology.
  • There is no need for network server to control the connectivity between workstations.
  • Additional components do not affect the performance of network.
  • Each computer has equal access to resources.

Disadvantages of Ring Topology

  • Each packet of data must pass through all the computers between source and destination. This makes it slower than star topology.
  •  If one workstation or port goes down, the entire network gets affected.
  • Network is highly dependent on the wire which connects different components.
  • MAU’s and network cards are expensive as compared to Ethernet cards and hubs.

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