2. Computer Network
Collection of computers and devices connected by communications channels that facilitates communications among users and allows users to share resources with other users
Computer network is an interconnected collection of autonomous computers.
Two computers are said to be interconnected if they are able to exchange information through transmission media.
Any type of data i.e. text, picture, audio and video can be transmitted by using network.

3. Advantages or Need Resource Sharing Simultaneous Access
High Reliability due to alternative sources of data
Reduced Costs
Easier Backup
Communication Medium
Access to Remote Information
Person -to- person
Communication
Interactive Entertainment

4. Network Topology
Network topology is the physical interconnections of the elements (links, nodes, etc.) of a computer network
The physical and logical topologies may or may not be identical in any particular network.
The path taken by data from sender to receiver computer mainly depends upon the topology of the network.

5. Selection of a Topology
Availability of physical communication line
Reliability of the entire system
Number of cables required
Expandability of the system
Transmission delays
Maximum distance
Maximum number of nodes
Cost

6. Bus Topology
A single cable acts as a backbone of the network and all the nodes or computers are attached to it by using T connectors .
Each node on the network
has a direct connection with
the backbone cable.
When one computer sends a
signal up the cable, all nodes
receive the information ,but the one with the address in the message, accepts the information while all other reject .
Slow as the computer must wait until the bus is free.
Requires a proper termination at both the ends of
the cable.

7. Advantages and Disadvantages
Less number of cable required.
Easy to understand
Nodes can be added without disturbing the rest of network
Easy to understand and install
If the communication lines fail, the entire system breaks down
It is very difficult to repair the fault in this topology
Heavy network traffic slows down the speed

8. Star Topology Each network host is connected to a central hub.
Connects each node to the hub with a point-to-point connection.
All traffic that transverses the network passes through the central hub.
The hub acts as a signal booster or repeater.
E.g. .Telephone Network

9. Advantages and Disadvantages
Cheaper media of networking
Less number of cables required
Transmission delays do not increase by adding nodes
If any node fails, the remaining portion of the network is unaffected
Hub offers limited number of connections
Hub represents a single point of failure.
Cabling cost is more

10. Ring Topology
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 through each machine or computer connected to the ring in one direction.
A token passing scheme is used to control access to the network.
By utilizing this scheme, only one machine can transmit on the network at a time.

11. Advantages and Disadvantages
Shorter cable length required
Delivers fast and efficient performance
Suitable for high speed networks
The failure of one machine will cause the entire network to fail.
Addition of new node increases the communication delays
Difficult to reach at the fault
Difficult to add, remove or reconfigure the nodes in the network

12. Mesh Topology
Each node is connected to more than one nodes of the system
There exist multiple paths between two nodes
In case of failure of one path, the other path can be followed
Generally too costly and complex for practical networks,
Used when there are only a small number of nodes to be interconnected