Network Topologies:
Topology refers to the physical or logical layout of a network. The topology of a network is a geometric representation of all devices connecting to each other in the network. Network topologies can be classified into five basic types: mesh, star, bus, ring, and tree.
Mesh Topology
In mesh topology, every device is connected with every other device through a point-to-point link. The link is a dedicated one, i.e., the link carries traffic only between the two devices that are connected. This dedicated link ensures that each connection transports its own load of data. This helps avoid the traffic problems that would crop up if the links were shared by many devices. A mesh topology is a robust one. Even if a particular link becomes useless, it will not affect the entire system. This type of network ensures security and privacy. As the message or data is transported through a dedicated link, only the receiver can access it. The point-to-point links help in identifying faults easily and traffic can then be routed in such a way as to avoid suspect links. However, mesh topology has a limited use as it requires a huge amount of cabling and a number of I/O ports and it is difficult to install and reconfigure.
Star Topology
In star topology, each device is connected to a centrally located hub through a point-to-point link. There is no direct link between the devices. Star topology does not permit direct traffic between the devices. The hub acts as an intermediary between the devices. For example, if a computer wants to send data to another, it first sends the data to the hub, which in turn transmits the data to other devices.
Bus Topology
A bus topology has a multipoint configuration. All the devices in a bus topology are linked through a long cable. Drop lines and taps are used to connect the nodes of the devices to the cable. A drop line is a connection or link that runs between the main cable and the device, while a tap is a connector which joins the main cable or penetrates into the covering of the cable to make contact with the metallic core. When a signal travels along the backbone, some energy gets transformed into heat. Thus, the signal gets weaker and weaker along the distance it has to travel. A bus topology is easy to install, but difficult to reconfigure. It uses less cabling than the star, the tree, or the mesh topologies. Adding new devices is difficult in a bus topology as it requires modifications or replacement of the cable. Any puncture or break in the bus stops transmission.
Ring Topology
In a ring topology, each device is linked to two devices on either side of it through a dedicated point-to-point connection. Each device is physically linked to its immediate neighbors. Signals in a ring topology are passed in one direction from device to device till it reaches its destination. Each device has a repeater. The repeater regenerates the bits and passes them whenever a device receives a signal which is meant for another device. It is easy to install and reconfigure a network with a ring topology. A device can be easily added or deleted as it requires only two connections. Ring topologies, however, are subject to traffic and media constraints, i.e., the number of devices and the length of the ring. Another disadvantage is the direction of the traffic, which is unidirectional, that is, it flows in a single direction. Any small rupture in the ring would disable the whole network. However, this problem can be solved by using a switch for closing the rupture or a dual ring.
Tree Topology
In a tree topology, the nodes of some devices are linked to a centrally located hub. The other nodes are indirectly connected to the hub through a secondary hub, which in turn, is connected to the main hub. The central hub is called the active hub while the secondary hubs can be active or passive. The active hub has a hardware device called the repeater, which regenerates the bit patterns (which are received), before sending them out. This strengthens the transmission and increases the traveling distance of a signal. A passive hub gives a simple connection to the devices. Tree topologies have advantages similar to those of star topologies. The presence of a secondary hub allows more devices to be connected to the active hub and therefore increases the traveling distance between the devices. The secondary hub can also isolate or prioritize communications between different computers.
Hybrid Topologies
In hybrid topologies, different topologies can be used in a single network. For example, in a business organization, different departments can use different topologies. If one department uses a ring topology, while another uses a bus topology, a centrally located hub using star topology can be used to connect these two departments.
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