Topology is the pattern of interconnection of nodes in a local area network(LAN).The topology used helps to select the communication medium and the other network devices.While choosing a topology,care has to be taken that the installation cost is minimum,the network so designed should be reliable and flexible.
Network topologies are categorized into the following basic types:
- bus
- star
- tree
Bus Topology
Bus topology is also known as Linear Topology. In this type of topology, each node attaches directly to a
common cable which acts as the backbone and therefore functions as a shared communication medium
onto which various nodes are attached. A device wanting to communicate with another device on the
network sends a broadcast message in both directions onto the wire that all other devices see, but only the intended recipient actually accepts and processes the message. Data is transmitted in small blocks called packets. Each packet has a header containing the destination address. When data is transmitted on the cable, the destination node identifies the address on the packet and thereby processes the data.
Advantages of Bus Topology
- Since there is a single common data path connecting all the nodes, the bus topology uses a very short cable length which considerably reduces the installation cost.
- The linear architecture is very simple and reliable.
- Additional nodes can be easily connected to the existing bus network at any point along the length of the transmission medium.
Disadvantages of Bus topology
- Fault detection and isolation is difficult. This is because control of the network is not centralized in any particular node. If a node is faulty on the bus, detection of fault may have to be performed at many points on the network. The faulty node has then to be rectified at that connection point.
- If the central bus length becomes too long, then repeaters might have to be used to amplify the signal. The use of repeaters makes reconfiguration necessary.
- Since each node is directly connected to the central bus, so there has to be some way of deciding who can use the network at any given time.
Star Topology
A star network features a central connection point called a “hub node” to which all other nodes are
connected by a single path. Each node has a dedicated set of wires connecting it to a central network hub. Since all traffic passes through the hub, the hub becomes a central point for isolating network problems and gathering network statistics. This type of topology is used in most existing information networks involving data communications or voice communications
Advantages of Star Topology
- Failure of a single connection does not affect the entire network. It just involves disconnecting one
node from an otherwise fully functional network. This also helps in easy reconfiguration of the
network. - Fault detection is easier.
- Access protocols being used in a Star network are very simple since the central node has the control of the transmission medium for data transmission.
Disadvantages of Star Topology
- Since every node is directly connected to the centre, so large amount of cable is needed which increases the installation cost of the network.
- The entire network is dependent on the central node. If the central node fails the entire network goes down.
Tree Topology
Tree topology is a combination of bus and star topology. The network looks like an inverted tree with the
central root branching and sub-branching down to the nodes. It integrates multiple star topologies together onto a bus. Tree topology is best suited for applications which have a hierarchical flow of data and control.
