- ICT Note -: Network Topology

Network topology is defined as the interconnection of the various elements (links, nodes, etc.) of a computer network.^[1]^[2] Network Topologies can be physical or logical. Physical Topology means the physical design of a network including the devices, location and cable installation. Logical topology refers to the fact that how data actually transfers in a network as opposed to its physical design.

Topology can be considered as a virtual shape or structure of a network. This shape actually does not correspond to the actual physical design of the devices on the computer network. The computers on the home network can be arranged in a circle shape but it does not necessarily mean that it presents a ring topology.

Any particular network topology is determined only by the graphical mapping of the configuration of physical and/or logical connections between nodes. The study of network topology uses graph theory. Distances between nodes, physical interconnections, transmission rates, and/or signal types may differ in two networks and yet their topologies may be identical.

A Local Area Network (LAN) is one example of a network that exhibits both a physical topology and a logical topology. Any given node in the LAN has one or more links to one or more nodes in the network and the mapping of these links and nodes in a graph results in a geometrical shape that may be used to describe the physical topology of the network. Likewise, the mapping of the data flow between the nodes in the network determines the logical topology of the network. The physical and logical topologies may or may not be identical in any particular network.

Diagram of different network topologies

Basic topology types

The study of network topology recognizes five basic topologies:

Bus topology
Star topology
Ring topology
Tree topology
Mesh topology

Bus

In local area networks where bus topology is used, each machine is connected to a single cable. Each computer or server is connected to the single bus cable through some kind of connector. A terminator is required at each end of the bus cable to pr ev ent the signal from bouncing back and forth on the bus cable. A signal from the source travels in both directions to all machines connected on the bus cable until it finds the MAC add ress or IP address on the network that is the intended recipient. If the machine address does not match the intended address for the data, the machine ignores the data. Alternatively, if the data doe s match the machine address, the data is accepted. Sinc e the bus topology consists of only one wire, it is rather inexpensive to implement when compared t o other topologies. However, the low cost of implementing the technol ogy is offse t by the high cost of managing the network. Additionally, since only one cable is utilized, it can be the single point of failure. If the netw ork cable breaks, the e ntire network will be down.

Bus network topology

Star

In local area networks with a star topology, each network host is connected to a central hub. In contrast to the bus topology, the star topology connect s ea ch node to the hub with a point-to-point connection. All traffic that transverses the ne twork passes through the central hub. The hub acts as a signal booster or repeater. The star topology is considered the easiest topology to design and implement. An advantage of the star top ology is the simplicity of adding additional nodes. The primary disadvantage of the star topology is that the hub represents a single

Star network topology

Ring

In local area networks where the ring topology is used, each computer is connected to the network in a closed loop or ring. Each machine or computer has a unique address that is used for identification purposes. The signal passes throug h e ach machine or computer connected to the ring in one direction. Ring topologies typically utili ze a token passing scheme, used to control access to the network. By utilizing this scheme, only one machine can transmit on the network at a time. The machines or computers connected to the ring act as signal boosters or repeaters which strengthen the signals that transverse the network. The primary disadvantage of ring topology is the failure of one machine will cause the entire network to fail.^{[citation needed]}

Ring network topology

Tree

Also known as a hierarchical network.

The type of network topology in which a central 'root' node (the top level of the hierarchy) is connected to one or more other nodes that are one level lower in the hierarchy (i.e., the second level) with a point-to-point link between each of the

second level nodes and the top level central 'root' node, while each of the second level nodes that are connected to the top level central 'root' node will also have one or more other nodes that are o

ne level lower in the hierarchy (i.e., the third level) connected to it, also with a point-to-point link, the top level central 'root' node being the only node tha

t has no other node above it in the hierarchy (The hierarchy of the tree is symmetrical.) Each node in the network having a specific fixed number, of nodes connected to it at the next lower l

evel in the hierarchy, the number, being referred to as the 'branching factor' of the hierarchical tree.