Primary Network Topologies
The way in which devices are interconnected to form a network is called network topology. Some of the factors that affect choice of topology for a network are −
- Cost− Installation cost is a very important factor in overall cost of setting up an infrastructure. So cable lengths, distance between nodes, location of servers, etc. have to be considered when designing a network.
- Flexibility− Topology of a network should be flexible enough to allow reconfiguration of office set up, addition of new nodes and relocation of existing nodes.
- Reliability− Network should be designed in such a way that it has minimum down time. Failure of one node or a segment of cabling should not render the whole network useless.
- Scalability− Network topology should be scalable, i.e. it can accommodate load of new devices and nodes without perceptible drop in performance.
- Ease of installation− Network should be easy to install in terms of hardware, software and technical personnel requirements.
- Ease of maintenance− Troubleshooting and maintenance of network should be easy.
Data network with bus topology has a linear transmission cable, usually coaxial, to which many network devices and workstations are attached along the length. Server is at one end of the bus. When a workstation has to send data, it transmits packets with destination address in its header along the bus.
The data travels in both the directions along the bus. When the destination terminal sees the data, it copies it to the local disk.
Advantages of Bus Topology
- Easy to install and maintain
- Can be extended easily
- Very reliable because of single transmission line
Disadvantages of Bus Topology
- Troubleshooting is difficult as there is no single point of control
- One faulty node can bring the whole network down
- Dumb terminals cannot be connected to the bus
In ring topology each terminal is connected to exactly two nodes, giving the network a circular shape. Data travels in only one pre-determined direction.
When a terminal has to send data, it transmits it to the neighboring node which transmits it to the next one. Before further transmission data may be amplified. In this way, data raverses the network and reaches the destination node, which removes it from the network. If the data reaches the sender, it removes the data and resends it later.
Advantages of Ring Topology
- Small cable segments are needed to connect two nodes
- Ideal for optical fibres as data travels in only one direction
- Very high transmission speeds possible
Disadvantages of Ring Topology
- Failure of single node brings down the whole network
- Troubleshooting is difficult as many nodes may have to be inspected before faulty one is identified
- Difficult to remove one or more nodes while keeping the rest of the network intact
In star topology, server is connected to each node individually. Server is also called the central node. Any exchange of data between two nodes must take place through the server. It is the most popular topology for information and voice networks as central node can process data received from source node before sending it to the destination node.
Advantages of Star Topology
- Failure of one node does not affect the network
- Troubleshooting is easy as faulty node can be detected from central node immediately
- Simple access protocols required as one of the communicating nodes is always the central node
Disadvantages of Star Topology
- Long cables may be required to connect each node to the server
- Failure of central node brings down the whole network
Tree topology has a group of star networks connected to a linear bus backbone cable. It incorporates features of both star and bus topologies. Tree topology is also called hierarchical topology.
Advantages of Tree Topology
- Existing network can be easily expanded
- Point-to-point wiring for individual segments means easier installation and maintenance
- Well suited for temporary networks
Disadvantages of Tree Topology
- Technical expertise required to configure and wire tree topology
- Failure of backbone cable brings down entire network
- Insecure network
- Maintenance difficult for large networks