Definition, Bus, Ring, Star Topology

The computers on LAN can be physically connected with the wires in different manner as the requirement of an organization or office. The manner in which the computers on the LAN are connected is known as LAN Topology. So, network topology is the physical layout of cabling for connecting computers on the network. It can be defined as the arrangement or connection pattern of computers on a LAN. A LAN topology describes how the computers are physically connected and how do they communicate on the network. It determines the data paths that may be used between any pair of nodes of the network. There are three basic network topologies. They are Bus topology, Ring topology and Star topology.

BUS TOPOLOGY

In a bus topology computers are arranged in the linear format. So, it is called Linear Topology. In this topology, all nodes are connected directly to the common cable with the help of T-connectors. The common cable is also known as also known as a network bus or trunk. The network bus acts as a backbone to the network.Many different lengths of co-axial cables are used in this type of topology. On the both side of the network bus (i.e. coaxial cable), BNC (Bayonet Naur Connector) jacks are connected. A T-connector is used to join segments of cables and computers. The BNC jack on each side of network bus is connected to the T-connector i.e. top the T-connector is connected to the NIC card of a Computer. The T-connectors connected to the last computers on both sides are attached with terminators.

In this network topology, the position of the server is not fixed i.e. can be any where on the network. When any node sends the data, the data passes on both directions in the form of packets through the bus and reaches to all the nodes. Since each data packet contains the data bits and the destination address, only the destination node accepts the data packets. The terminators at both end sides absorb the packets or signals travelling on the bus to prevent the bouncing of the signals which causes interference.

ADVANTAGES

a. Since each small segments of cables are joined to form a trunk or network bus it is easy to setup computers on the bus.

b. Since nodes are arranged in the linear form, it requires the less amounts of cables.

c. The coaxial cables used for networking are inexpensive and joining connectors on the cables is also easy.

d. Failure of any node does not affect other nodes on the topology.

e. Well suited for temporary networks (quick set

up).

DISADVANTAGES

a. If the backbone cable i.e. network bus has problem then the entire network fails.

b. Finding fault on this topology is not easy.

c. It provides limited flexibility for change, so adding or removing nodes in between is not easy.

d. The performance degrades when the

number of computers is more on the. so, it is not suitable for big size network.

RING TOPOLOGY

In a ring topology, all nodes are arranged in the shape of a circle (ring). Both ends of a cable are connected to the nodes so there is no any point like a bus topology. Since the both ends are connected to the nodes there is no any terminator in this topology. In this topology, many different lengths of co-axial cables are used according to distance of computers. In this topology each computer acts like a repeater that boosts an incoming signal before passing it on to the next computer.

In this topology, data or messages are transmitted in one direction either clockwise or anticlockwise. When any node sends a message or data, the message or data reaches to the first node on the circle. If the first node in the circle is the destination node then it absorbs the data or message otherwise it regenerates the signal and passes to another node on the loop and so on. If the message or data is not absorbed by any node then it is absorbed by the sender node.

ADVANTAGES

a. Since each node on the ring acts as a repeater, no any external repeater is required to boost up the signals.

b. It supports high data transmission. Rate.

c. It is easy to setup.

DISADVANTAGES

a. If any node or connecting cable fails the entire network does not work.

b. The diagnosis of the fault is difficult.

c. Since data or message reaches on the node in sequence, so addition of few nodes increases the communication delays.

d. It provides limited flexibility for change,

so adding or removing nodes in between is not easy.

STAR TOPOLOGY

Star Topology is the most popular topology used to connect computers and other network devices on the network. In a star topology all nodes are connected through a centrally located device in the form of star. But the shape of arrangement of computers is not necessarily to be star. The device whic

h connects computers on the network is either a hub or a switch. A hub or a switch has connecting ports or slots where the wires running from each node are connected. A twisted pair cable (specially unshielded twisted pair cable) is used for connecting a computer and a hub or switch. Each segment of UTP cable is attached with RJ-45 jacks. And one side of the UTP cable is connected to the node and another side is connected to the hub or switch. When any node sends data or message, the data or message reaches to the hub or switch and then to the targeted computer on the network.

ADVANTAGES

a. Computers can be added or removed easily without affecting the network.

b. If any of the workstation or the connecting cable fails, it does not affect the remaining portion of the network.

c. Fault detection in the star topology is easy.

d. It is easy to extend so it is suitable for a large network.

e. It is one of the reliable network topology.

DISADVANTAGES

a. Since each node is required to connect with the centralized hub or switch more cables are needed which increases the cost of installation.

b. The entire network fails if there is any problem on the hub or switch.

c. In comparison to Linear and Ring topologies, it is little expensive as it requires more length of cables and other controlling devices.