Topology 

Network topology refers to the layout of a network, how different nodes are connected to each other and how the communication is stabilised in a network.

Types of topology:

1) Bus topology

2)Ring topology

3)Star topology

4)Mesh topology

5)Tree topology

6) Hybrid topology

1) Bus topology:- 

• In Bus Topology every computer and network device is connected by a single length of a cable with a terminator at each end.
• It is also called linear bus topology. 
• It is passive topology which means only one  computer can send messages at a time.
• The data signal is available to all computers that are connected in the network .
• It carries the address of the destination computer and it is good for connecting 15 to 20 computers in a network.

Advantage of Bus Topology:-

• Bus Topology is simple, reliable and best suited for small LAN.
• Bus Topology required the less amount of Cable therefore less expensive.
• It is easy to stand on a bus.
• easy to connect or peripheral device to a Bus topology.

Disadvantages of Bus topology:-

• If a wire breaks from any place, the entire Network is shut down. 
• Heavy traffic can slow down a bus. 
• collisions are the problem in the bus Topology.
• There is a limit on central cable length and number of nodes that can be connected.
• Security is very low because all the computers receive the sent signal from the source.

Ethernet:-

• Ethernet was invented by Bob Metcalfe.
• It was based on IEEE standard 802.3, CSMA/CD.

CSMA/CD:- 

• In the term of networking, collision happens when two computers attempt to transmit data on the same wire at the same time, this creates a conflict .
• The CSMA/CD protocol holds one data packet to prevent the collision . 
• This is when only one data packet is transmitted at a time to prevent data collision.

Ring topology:-

• In ring topology all the nodes are connected in a circular manner.
• Data travel in around the ring in one direction.
• It does not have terminated ends, data signals travel in a circle .
• Ring networks typically use a token passing protocol.

Token ring:-

• It is also called IEEE standard 802.5.
• It is based on ring topology .
• It has a free packet called a token that moves around the ring.
• The computer that receives a free token can send its data.
• This token gives equal chance to every node and moves to the next node after a fixed interval.

Advantage:-

• Easy to install and maintain.
• Every computer is given access to the token.
• Reduce the chance of data collision.

Disadvantage:-

• Failure of one computer on the ring affects the whole network.
• Adding or removing devices to the networks disturb all other nodes.

FDDI ( Fiber distributed data interface) :- FDDI is another ring based network unlike token ring one transmitting data clockwise and another transmitting data anticlockwise.

Star topology:-

• In star topology every computer is connected to a central hub or switch. 
• It can be used with twisted pair, coaxial cable and fibre optic cable.
• * In star topology for casting device hubs are not recommended because in hubs the data transmission is half duplex.

Advantage:-

• A single computer failure does not break down the whole network.
• It is easier to modify the network without disturbing it.
• Easy to diagnose network fault.

Disadvantage:-

• If the central hub fails its result is to fail the whole network.
• Its cabling cost is high because each computer has its individual wire.

Mesh topology:-

• In this topology, every node has a point to point connection to the other node.
• All the computer systems interconnected to each other in a network.
• It is fast , expensive and complex topology.

Advantage:

• This network is very reliable.
• If any link breaks, it will not affect the other connected computer .
• It is very fast communication between the nodes.

Disadvantage:

• This type of mesh topology is very expensive.
• The installation process is difficult.

Tree Topology:-

• It has a root node and all other nodes are connected to it. 
• It is also called hierarchical topology. 
• It should have at least three levels of hierarchy. 
• It combined characteristics of bus and star topology.

Advantage:

• It is easy to add a computer.
• Fast expansion of nodes.
• Easy to find errors.

Disadvantage:

• Failure in the main bus cable will damage the overall network.
• If any faults occur, it is difficult too.

Hybrid Topology:-

It is the combination of two or more topologies.