What are topologies ? Why are they important ? Discuss different topologies and advantages/disadvantages they offer.

The patterns of interconnection of nodes in a network are called Topologies. Topology is important as it affects the choice of media and the access method used.

The types of topologies are as follows:

1. Star Topology — This topology consists of a central node to which all other nodes are connected by a single path.
   Advantages are :

   1. It provide easy access for service.
   2. Access protocols are very simple in star topology.
   3. There is a centralized control/problem diagnosis.
   4. Failure of single connection involves disconnecting only that node without affecting network.

   Disadvantages are :

   1. It requires long cable length.
   2. It is difficult to expand.
   3. There is a central node dependency.

2. Bus or Linear topology — This topology consists of a single length of the transmission medium onto which the various nodes are attached. Transmission from any station travels the length of the bus in both directions and can be received by all other stations. The destination device, on identifying the address on data packet copies the data onto its disk. When the data packet reaches at either end the terminator on that end absorbs the signal, removing it from the bus.
   Advantages :

   1. It requires short cable length and simple wiring layout.
   2. It provides resilient architecture.
   3. This topology can be expanded easily.

   Disadvantages :

   1. Fault diagnosis is difficult in this topology.
   2. Fault isolation is difficult in bus topology.
   3. Repeater configuration is necessary.
   4. Nodes must be intelligent in bus topology.

3. Tree Topology — This topology is combination of bus and star topologies. The shape of the network is that of an inverted tree with the central root branching and sub-branching to the extremities of the network. Transmission in this topology takes place in the same way as in bus topology.
   Advantages :

   1. It uses point-to-point wiring for individual segments.
   2. It is supported by several hardware and software vendors.
   3. It is flexible and scalable.

   Disadvantages :

   1. Overall length of each segment is limited by the type of cabling used.
   2. If the backbone line breaks, the entire segment goes down.
   3. It is more difficult to configure and wire than other topologies.

4. Ring or Circular Topology — In this topology, each node is connected to two and only two neighbouring nodes. Thus data travels in one direction only, from node to node around the ring. After passing through each node, it returns to the sending node, which removes it.
   Advantages :

   1. The chances of data collisions are low due to unidirectional flow of data.
   2. They are simple to design and implement.

   Disadvantages :

   1. Node failure breaks the ring and communication stops.
   2. Difficulty in troubleshooting.

5. Mesh topology — In this topology, each node is connected to more than one node to provide an alternative route in the case the host is either down or too busy.
   Advantages :

   1. It provides extensive back-up and rerouting capabilities.
   2. Each node is connected to more than one node to provide an alternative route in the case the host is either down or too busy.

   Disadvantages :

   1. Mesh networks can be complex to design, implement, and manage, especially as the number of nodes increases.
   2. Maintenance and troubleshooting in mesh networks can be challenging due to their decentralized nature.

6. Fully Connected topology — When in a network, there is a direct link between each host, then the network is said to be fully connected. This characteristic is termed as full connectivity.
   Advantages :

   1. Data travels quickly because devices are directly connected to each other.
   2. If one connection fails, there are other paths for communication to continue, making the network robust.

   Disadvantages :

   1. Managing all the connections can be complicated.
   2. Setting up and maintaining a fully connected network can be expensive.