Network Topologies
Networks are made by connecting computers together in different ways. These different types of connecting computers are called topology. The topology is chosen keeping in mind the cost of setting up the network, time complexity and future expansion etc. Some important topologies are as follows-
- Linear or Bus Topology
- Circular or Ring Topology
- Star Topology
- Tree Topology
- Graph Topology or Mesh Topology
- Completely Connected Network
Linear Topology
It is also called bus topology. It consists of a co-axial cable called a backbone. In this cable, another small twisted or co-axial cable is connected to the computer (node). This short cable is called a drop cable. Each node (computer) has a network interface card (NIC) that transmits information to each other computer. Each NIC has a unique address.
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| Linear Topology |
Advantages
- In this, the cost of laying cables is less.
- Its expansion is easy i.e. new nodes can be added anywhere on the bus.
- When one computer fails, the rest of the network continues to function smoothly.
- It is more convenient than other networks.
- In this topology there is no centralization of network control, so error finding is easy.
Limitations
- Repeaters have to be used when the bus length is more.
- Only one packet can be transmitted at a time. Collision can occur when two nodes transmit packets simultaneously.
- Each node is directly connected to the bus. Hence it is necessary for the nodes to be intelligent.
- If the cable fails, the entire network may stop working.
Circular or Ring Topology
To connect computers in Ring Topology, twisted pair, co-axial cable or optical fiber cable are used. Each node is connected to the node adjacent to it. There is no host or main controlling computer in this network. All computers are connected in the form of a circular shape. So in this topology the data travels in only one direction and it passes through each node until it reaches its destination. Each intermediate node sees what is the destination address of the data. If it is the destination itself then after receiving the data does not forward it otherwise it sends the data to the next node. Each node can amplify the data signals before transmitting them further. That is, each node can also perform the function of a repeater.
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| Ring Topology |
Advantages
- It is more reliable than star topology because communication does not depend on a computer.
- Separate repeaters are not required.
- There is no data collision in this because the ring is divided into many parts. There is a segment between two nodes. Only one node in a segment can transmit data.
Limitations
- If even one node is not able to transfer data properly then the whole network may fail.
- Its speed depends on the computers in the network, if the computer is less then the speed is high and if the number of computers is more then the speed decreases in the same proportion.
- The communication software used in ring topology is more complex than in star topology.
- When a node is removed or a new node is added, the entire network is disrupted.
Star Topology
In Star Topology all nodes are connected to a central computer which is also called hub or host. No two nodes can connect directly to each other. Communication between nodes is done through the central computer. The central computer controls the communication between all the nodes.
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| Star topology |
Advantages
- In this topology, the cost of laying a line connecting a host computer to a computer is reduced.
- Failure of one node does not affect the rest of the network.
- Network management is comparatively easy.
- Transmission delay is not affected by adding new nodes.
- Any two nodes communicate only through the central computer. Hence there is no problem of collision.
Limitations
- The entire network depends on the central computer or node. If the central node fails, the entire network stops working.
- More cables are required than other topologies, if the distance between the central computer and the nodes is large, then a lot of cables are required because each node is connected to the central computer itself.
Tree Topology
In this network, from one cable to another cable and from other cable to third cable comes out like branches of a tree and is connected to each other. Therefore, this topology is used to connect one or more nodes in a hierarchical manner. The node at the top of the chain is called the root node. Root node can have zero or more child nodes which are connected to the root node. Each child node can have zero or more child nodes. In Tree Topology, there is only one path for data transmission between any two nodes. It can be considered a slightly modified form of bus topology.
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| Tree Topology |
In this topology, the data transmission is like a bus topology. There is no need to remove the packets after transmission as the terminator ends them when they reach the end of the medium. Tree topology is more suitable for applications in which data and control flows are chained.
Graph or Mesh Topology
In this topology, no special structure is used to connect the nodes to each other. A node can be connected to any other node. A node can also be connected to more than one node. In this topology it is also not necessary that all the nodes are connected to each other.
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| Graph or Mesh Topology |
Completely Connected Network
In this topology, there is a separate physical link to connect any node to any other node, that is, all the nodes are directly connected through some channel or communication medium. There is no central computer in it. Each node handles its own communication.
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| Completely Connected Network |
Advantages
- Very high speed transmission is possible.
- The reliability of this topology is very high, if a link fails, only communication between two computers connected to it will be affected.
Limitation
The cost of transmission medium is the highest. Adding a single node increases the cost significantly. Each new node requires N-1 number of lines. (Here N is the total number of nodes in the network.)
