Network Topology is the arrangement of computers or nodes in the network.it describes how nodes are connected to each other in a network.There are two basic categories of network topologies:
i)Physical topologies
ii)Logical topologies
Physical Topologies:-The shape of the cabling layout used to link devices in any network is referred to as physical topology of the network. This refers to the layout of cabling, the locations of nodes, and the interconnections between the nodes and the cabling.
Logical Topologies:-It is the way by which signals act on the network media, or data passes through the network from one device to the next without regard to the physical interconnection of the devices.
Various Physical Topologies are:
1)Bus Topology
In Bus topology each computer or server is connected to 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. If the machine address does not match the intended address for the data, the machine ignores the data. Alternatively, if the data matches the machine address, the data is accepted.Some features of this topology are:
i)Nodes are connected to single bus cable.
ii)Since it uses only single cable media ,therefore is inexpensive.
iii)Endpoints of the common transmission medium are normally terminated using 50 ohm resistor.
Disadvantages:
i)Failure of single cable bus will cause entire network failure.
ii)data transmission will fail if cable is not properly terminated on both ends.
2)Ring Topology
A network topology that is set up in a circular fashion in which data travels around the ring in one direction.in this topology each device on the right 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.
Some features of this Topology are:
i)Nodes are connected in ring like structure.
ii)Transfer rate is dependent on the data transfer rate of each node.iii)Single Media is used by all nodes.
Disadvantages:-
i)If any of the node fails the entire network fails.
ii)Chances of data collision are more.
3)Star Topology
In star topology each network host is connected to a central hub with a point-to-point connection.this central node is called hub or switch.Features of Star Topology are:
i)each node of network is connected to a central node that is called switch or hub.
ii)Switch acts as server and other nodes work as clients.
iii)Clients Communicate through centralized node only.
iv)Security checks can be easily implemented because each and every data passes through central hub.
v)failure of any client node causes no effect on rest of the nodes.
Disadvantages
i)Entire network fails if central node fails.
ii)Expensive ,since separate media is used for every node.
4) Mesh Topology
In Mesh Topology each and every node is connected to one another.There is point to point connection between nodes.Some Features of this topology are:
i)There is point to point connection between every node.
ii) This topology is used when there are only a small number of nodes to be interconnected.
iii)Data follows shortest path to reach destination.
iv)if any link fails,data is transferred through alternate line.
v)The number of connections in a full mesh = n(n – 1) / 2.
Disadvantages
i)It can be implemented in small networks because it is very expensive.reason behind this is that separate media is used for connecting each node.
ii) In case of failure or break in one of the links, network uses the remaining alternative paths to the destination. This requires that the nodes of the network possess some type of algorithm to determine the correct path.
i)Physical topologies
ii)Logical topologies
Physical Topologies:-The shape of the cabling layout used to link devices in any network is referred to as physical topology of the network. This refers to the layout of cabling, the locations of nodes, and the interconnections between the nodes and the cabling.
Logical Topologies:-It is the way by which signals act on the network media, or data passes through the network from one device to the next without regard to the physical interconnection of the devices.
Various Physical Topologies are:
1)Bus Topology
In Bus topology each computer or server is connected to 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. If the machine address does not match the intended address for the data, the machine ignores the data. Alternatively, if the data matches the machine address, the data is accepted.Some features of this topology are:
i)Nodes are connected to single bus cable.
ii)Since it uses only single cable media ,therefore is inexpensive.
iii)Endpoints of the common transmission medium are normally terminated using 50 ohm resistor.
i)Failure of single cable bus will cause entire network failure.
ii)data transmission will fail if cable is not properly terminated on both ends.
2)Ring Topology
A network topology that is set up in a circular fashion in which data travels around the ring in one direction.in this topology each device on the right 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.
Some features of this Topology are:
i)Nodes are connected in ring like structure.
ii)Transfer rate is dependent on the data transfer rate of each node.iii)Single Media is used by all nodes.
Disadvantages:-
i)If any of the node fails the entire network fails.
ii)Chances of data collision are more.
3)Star Topology
In star topology each network host is connected to a central hub with a point-to-point connection.this central node is called hub or switch.Features of Star Topology are:
i)each node of network is connected to a central node that is called switch or hub.
ii)Switch acts as server and other nodes work as clients.
iii)Clients Communicate through centralized node only.
iv)Security checks can be easily implemented because each and every data passes through central hub.
v)failure of any client node causes no effect on rest of the nodes.
Disadvantages
i)Entire network fails if central node fails.
ii)Expensive ,since separate media is used for every node.
4) Mesh Topology
In Mesh Topology each and every node is connected to one another.There is point to point connection between nodes.Some Features of this topology are:
i)There is point to point connection between every node.
ii) This topology is used when there are only a small number of nodes to be interconnected.
iii)Data follows shortest path to reach destination.
iv)if any link fails,data is transferred through alternate line.
v)The number of connections in a full mesh = n(n – 1) / 2.
Disadvantages
i)It can be implemented in small networks because it is very expensive.reason behind this is that separate media is used for connecting each node.
ii) In case of failure or break in one of the links, network uses the remaining alternative paths to the destination. This requires that the nodes of the network possess some type of algorithm to determine the correct path.
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