Network Topology:-

      In communication networks, a topology is a usually schematic description of the arrangement of a network, including its nodes and connecting lines.
         There are two ways of defining network geometry:-
                            The physical topology and
                            The logical (or signal) topology.

  Basic topologies are:-
·           Bus

·          Star

·          Ring or circular

·          Mesh

·          Tree

·          Hybrid

BUS:-
    In local area networks where bus topology is used, each node is connected to a single cable. Each computer or server is connected to the single bus cable. A signal from the source travels in both directions to all machines connected on the bus cable until it finds the intended recipient. 

·      Advantages of Bus Topology:-

·      Works well for small networks

·      Relatively inexpensive to implement

·      Easy to add to it.

Disadvantages of Bus Topology:-   

•        Management costs can be high

•       Potential for congestion with network traffic.

Star:-

In local area networks with a star topology, each network host is connected to a central hub with a point-to-point connection. In Star topology every node (computer workstation or any other peripheral) is connected to central node called hub or switch.

Advantage:-

•        Good option for modern networks

•        Low startup costs

•        Easy to manage

•        Offers opportunities for expansion

•        Most popular topology in use; wide variety of equipment available.

Disadvantages:-

•        Hub is a single point of failure

•                    •   Requires more cable than the bus.

Ring:-
  A network topology that is set up in a circular fashion in which data travels around the ring in one direction and each device on the ring acts as a repeater to keep the signal strong as it travels. Each device incorporates a receiver for the incoming signal and a transmitter to send the data on to the next device in the ring. The network is dependent on the ability of the signal to travel around the ring. When a device sends data, it must travel through each device on the ring until it reaches its destination.

Advantages of Ring Topology:-

•Easier to manage; easier to locate a defective node or cable problem

•Well-suited for transmitting signals over long distances on a LAN

•Handles high-volume network traffic

•Enables reliable communication.

Disadvantages of Ring Topology:-

•Expensive

•Requires more cable and network equipment at the start

•Not used as widely as bus topology

–Fewer equipment options

–Fewer options for expansion to high-speed communication

Mesh:-

A fully connected network is a communication network in which each of the nodes is connected to each other. In graph theory it known as a complete graph. A fully connected network doesn't need to use switching nor broadcasting. However, its major disadvantage is that the number of connections grows quadratically with the number of nodes, per the formula

and so it is extremely impractical for large networks. A two-node network is technically a fully connected network.

Tree:-

This particular type of network topology is based on a hierarchy of nodes. The highest level of any tree network consists of a single, 'root' node, this node connected either a single (or, more commonly, multiple) node(s) in the level below by (a) point-to-point link(s). These lower level nodes are also connected to a single or multiple nodes in the next level down.

Advantages:-

• It is scalable Secondary nodes allow more devices to be connected to a central node.

• Point to point connection of devices.
• Having different levels of the network makes it more manageable hence easier fault identification and isolation.

• Disadvantages:-
  

  • Maintenance of the network may be an issue when the network spans a great area.
  • Since it is a variation of bus topology, if the backbone fails, the entire network is crippled.
    
    
    NOTE:-
    
    definition: Tree topology is a combination of Bus and Star topology.
    An example of this network could be cable TV technology. Other examples are in dynamic tree based wireless networks for military, mining and otherwise mobile applications. The Naval Postgraduate School, Monterey CA, demonstrated such tree based wireless networks for border security. In a pilot system, aerial cameras kept aloft by balloons relayed real time high resolution video to ground personnel via a dynamic self healing tree based network.

  

Hybrid:-

Hybrid networks use a combination of any two or more topologies in such a way that the resulting network does not exhibit one of the standard topologies (e.g., bus, star, ring, etc.). For example a tree network connected to a tree network is still a tree network topology. A hybrid topology is always produced when two different basic network topologies are connected. Two common examples for Hybrid network are: star ring network and star bus network

• A Star ring network consists of two or more star topologies connected using a multistation access unit (MAU) as a centralized hub.
• A Star Bus network consists of two or more star topologies connected using a bus trunk (the bus trunk serves as the network's backbone).