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Topology- definition and types of topology

A Topology of the network defines the manner in which the network devices are arranged and connected to each other in a network. It defines the shape of communication network. There are five common types of network Topologies.
  1. Bus Topology
  2. Ring Topology
  3. Star Topology
  4. Tree Topology
  5. Mesh Topology
Bus Topology/ Linear Topology
In a bus topology a single main cable connects each node (computers) which allows single line of computers accessing it from end-to-end. each node is connected to two others except those in end. The network operating system keeps track of  a unique electronic address for each node in the network, and manages the flow of data based on this addressing scheme. This topology is often found in a client / server systems, where one of the machines on the network is designated as file server.

In linear bus topology, all computers are connected by a single length of cabling with a terminator at each end. the bus topology is the simplest and most widely used network design.
Bus networks are the most common LANs. they have no switches, and in their simplest form, no repeaters, but simply share a common linear communication medium. Each station requires a tap (hardware for attachment to the medium), which must be capable of delivering the signal to all stations in the bus.
 The data is sent in packets, and each station hears all the transmissions, picking up those addressed to it.

Advantages of Bus Topology
  • Most bus networks have the advantage of being passive i.e all the active components are in the stations or nodes, and a failure affects only that one node.
  • It does not require all the computers to be up and running in order for network to function.
Disadvantages of Bus Topology
  • Because single cable is dedicated to all the computers the performance can suffer at time because of heavy traffic.
  • There is a distance limitation in bus topology. After certain length of cable the  performance of the Bus network degrades.
Ring Topology/ Circular Topology
In ring topology the computers are arranged in a circle. Data travels around the ring in one direction, with each devise on the ring acting as a repeater. Ring Networks typically use a Token Passing Protocol.
The layout is similar to linear bus, except that the nodes are connected in a circle using cable segments. In this layout, each node is connected to only two others. Each node passes information along to the next, until it reaches at its intended destination.
The ring topology is usually found in  peer-to-peer (PCs connected in pairs) networks, in which each machine manages both information processing and distribution of data files.

In ring topology type LAN architecture a series of devices are connected to one another by unidirectional transmission links to form a single closed loop. Both token ring/ IEEE 8019.5 and FDDI networks implement a ring topology.

Advantages of ring topology
  • Performance is good because each portion of cabling system is handling the data flow between two nodes (machines) only.
  • They do not have distance limitations as in Bus topology (difference between Bus and ring topology).
  • They can take advantages of fiber optic cables to speed up the performance, because only two machines are involved in packet exchange at a time.
Disadvantages of Ring Topology
  • Since all the nodes or computers are involved in data transfer, the failure of single node can bring whole network to the halt.
  • The ring control mechanism required to determine as to who should start up the ring, to determine that the packets are not corrupt, and to prevent the same packet to go around the ring because of network fault. Some Ring LANs need to deploy special computer to monitor this issue.
STAR Topology
In Star Topology, all the cables run from the computers to a central location, where they are connected by a hub. Hub is a device used to extend a network so that additional work stations can be attached.

In Star topology each node is connected to single centrally located server, using its own dedicated segment of cable. A star topology is a LAN architecture in which endpoints on the network are connected to a common central hub, or switch, by dedicated links. In this topology each node is connected to a centralised switch by a dedicated physical link. The switch provides a path between any two devices wishing to communicate, either physically in a circuit switch or logically in a packet switch.

Advantages Of star topology
  • This topology has the advantage of minimum data traffic along the cables (node to server only)., thus providing optimum performance.
  • The main advantage of star LAN are that the access to the network i.e decision on when a station can or cannot transmit, is under central control.
Disadvantages of Star Topology
  • Because single central machine must coordinate all communications, this topology requires an extremely powerful server. Hence Star Topology is expensive.
  • Speed is generally limited and central switch is an obvious potential source of catastrophic failure i.e if centralised server fails, whole topology fails.
Tree Topology
This is a network topology containing zero or more nodes/computers linked together in a hierarchical fashion. The topmost node is called the root. The root may have zero or more child nodes, connected by edges (links); the root is the parent root to its children. Each node can have in turn zero or more nodes of its own. Nodes sharing the same parents is called siblings. Every node in the tree has exactly one parent node (except root which has no parents), and all nodes in the tree are descendants of the root node. These relationships ensure that there is one and only one path from one node to any other node in the tree.
 A tree topology LAN architecture is identical to BUS topology network, except that branches with multiple nodes are possible in this case.
The advantages and disadvantages of Tree topology are same as that of Bus Topology.

Mesh Topology/ Graph Topology
In this topology, two or more nodes are connected together in an arbitrary fashion. Any two nodes in a Mesh or Graph may or may not be connected by a link. Not all the nodes need to be connected in a graph, but if the path can be traced between any two nodes, the graph is a connected one.
A Mesh Topology is a Mixture of BUS topology, STAR Topology, Ring and Tree Topology, with no restriction of connection among all the nodes in a network.

2 comments:

  1. hi..Im student from Informatics engineering, this article is very informative, thanks for sharing :)

    ReplyDelete