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Introduction to Computer Networks
Today the world scenario is changing. Data Communication and network have changed the way business and other daily affair works. Now, they rely on computer networks and internetwork. A set of devices often mentioned as nodes connected by media link is called a Network. A node can be a device which is capable of sending or receiving data generated by other nodes on the network like a computer, printer etc. These links connecting the devices are called Communication channels.
Computer network is a telecommunication channel through which we can share our data. It is also called data network. The best example of computer network is Internet. Computer network does not mean a system with control unit and other systems as its slave. It is called a distributed system
A network must be able to meet certain criteria, these are mentioned below:
- Performance
- Reliability
- Scalability
Performance
It can be measured in following ways :
- Transit time : It is the time taken to travel a message from one device to another.
- Response time : It is defined as the time elapsed between enquiry and response.
Other ways to measure performance are :
- Efficiency of software
- Number of users
- Capability of connected hardware
Reliability
It decides the frequency at which network failure take place. More the failures are, less is the network's reliability.
Security
It refers to the protection of data from the unauthorised user or access. While travelling through network, data passes many layers of network, and data can be traced if attempted. Hence security is also a very important characteristic for Networks.
Properties of Good Network
- Interpersonal Communication : We can communicate with each other efficiently and easily example emails, chat rooms, video conferencing etc.
- Resources can be shared : We can use the resources provided by network such as printers etc.
- Sharing files, data : Authorised users are allowed to share the files on the network.
Basic Communication Model
Communication model is used to exchange data between two parties. For example communication between a computer, server and telephone (through modem).
Source
Data to be transmitted is generated by this device, example: telephones, personal computers etc.
Transmitter
The data generated by the source system are not directly transmitted in the form they are generated. The transmitter transforms and encodes the information in such a form to produce electromagnetic waves or signals.
Transmission System
A transmission system can be a single transmission line or a complex network connecting source and destination.
Receiver
Receiver accepts the signal from the transmission system and converts it to a form which is easily managed by the destination device.
Destination
Destination receives the incoming data from the receiver.
Data Communication
The exchange of data between two devices through a transmission medium is Data Communication. The data is exchanged in the form of 0’s and 1’s. The transmission medium used is wire cable. For data communication to occur, the communication device must be part of a communication system. Data Communication has two types Local and Remote which are discussed below :
Local :
Local communication takes place when the communicating devices are in the same geographical area, same building, face-to-face between individuals etc.
Examples of simplex Mode is loudspeaker, television broadcasting, television and remote, keyboard and monitor etc.
HALF DUPLEX Mode
In half duplex system we can send data in both directions but it is done one at a time that is when the sender is sending the data then at that time we can’t send the sender our message. The data is sent in one direction.
Example of half duplex is a walkie- talkie in which message is sent one at a time and messages are sent in both the directions.
FULL DUPLEX Mode
In full duplex system we can send data in both directions as it is bidirectional. Data can be sent in both directions simultaneously. We can send as well as we receive the data.
Example of Full Duplex is a Telephone Network in which there is communication between two persons by a telephone line, through which both can talk and listen at the same time.
In full duplex system there can be two lines one for sending the data and the other for receiving data.
Line Configuration in Computer Networks
Network is a connection made through connection links between two or more devices. Devices can be a computer, printer or any other device that is capable to send and receive data. There are two ways to connect the devices :
- Point-to-Point connection
- Multipoint connection
Point-To-Point Connection
It is a protocol which is used as a communication link between two devices. It is simple to establish. The most common example for Point-to-Point connection (PPP) is a computer connected by telephone line. We can connect the two devices by means of a pair of wires or using a microwave or satellite link.
Example: Point-to-Point connection between remote control and Television for changing the channels.
Local Area Network (LAN)
It is also called LAN and designed for small physical areas such as an office, group of buildings or a factory. LANs are used widely as it is easy to design and to troubleshoot. Personal computers and workstations are connected to each other through LANs. We can use different types of topologies through LAN, these are Star, Ring, Bus, Tree etc.
LAN can be a simple network like connecting two computers, to share files and network among each other while it can also be as complex as interconnecting an entire building.
LAN networks are also widely used to share resources like printers, shared hard-drive etc.
Applications of LAN
- One of the computer in a network can become a server serving all the remaining computers called clients. Software can be stored on the server and it can be used by the remaining clients.
- Connecting Locally all the workstations in a building to let them communicate with each other locally without any internet access.
- Sharing common resources like printers etc are some common applications of LAN.
Metropolitan Area Network (MAN)
It is basically a bigger version of LAN. It is also called MAN and uses the similar technology as LAN. It is designed to extend over the entire city. It can be means to connecting a number of LANs into a larger network or it can be a single cable. It is mainly hold and operated by single private company or a public company.
Wide Area Network (WAN)
It is also called WAN. WAN can be private or it can be public leased network. It is used for the network that covers large distance such as cover states of a country. It is not easy to design and maintain. Communication medium used by WAN are PSTN or Satellite links. WAN operates on low data rates.
Wireless Network
It is the fastest growing segment of computer. They are becoming very important in our daily life because wind connections are not possible in cars or aeroplane. We can access Internet at any
Types of Network Topology
Network Topology is the schematic description of a network arrangement, connecting various nodes(sender and receiver) through lines of connection.
BUS Topology
Bus topology is a network type in where every computer and network device is connected to single cable.
Features of Bus Topology
- It transmits data only in one direction.
- Every device is connected to a single cable
Advantages of Bus Topology
- It is cost effective.
- Cable required is least compared to other network topology.
- Used in small networks.
- It is easy to understand.
- Easy to expand joining two cables together.
Disadvantages of Bus Topology
- Cables fails then whole network fails.
- If network traffic is heavy or nodes are more the performance of the network decreases.
- Cable has a limited length.
- It is slower than the ring topology.
RING Topology
It is called ring topology because it forms a ring as each computer is connected to another computer, with the last one connected to the first. Exactly two neighbours for each device.
Features of Ring Topology
- A number of repeaters are used and the transmission is unidirectional.
- Date is transferred in a sequential manner that is bit by bit.
- Easy to setup and modify.
- Only that node is affected which has failed rest of the nodes can work smoothly.
Disadvantages of Star Topology
- Cost of installation is high.
- Expensive to use.
- If the hub is affected then the whole network is stopped because all the nodes depend on the hub.
- Performance is based on the hub that is it depends on its capacity
MESH Topology
It is a point-to-point connection to other nodes or devices. Traffic is carried only between two devices or nodes to which it is connected. Mesh has n (n-2)/2 physical channels to link hn devices.
Types of Mesh Topology
- Partial Mesh Topology : In this topology some of the systems are connected in the same fashion as mesh topology but some devices are only connected to two or three devices.
- Full Mesh Topology : Each and every nodes or devices are connected to each other.
Features of Mesh Topology
- Fully connected.
- Robust.
- Not flexible.
Advantages of Mesh Topology
- Each connection can carry its own data load.
- It is robust.
- Fault is diagnosed easily.
- Provides security and privacy.
Disadvantages of Mesh Topology
- Installation and configuration is difficult.
- Cabling cost is more.
- (^) Bulk wiring is required.
TREE Topology
It has a root node and all other nodes are connected to it forming a hierarchy. It is also called hierarchical topology. It should at least have three levels to the hierarchy.
Features of Tree Topology
- Ideal if workstations are located in groups.
- Used in Wide Area Network.
Advantages of Tree Topology
- Extension of bus and star topologies.
- Expansion of nodes is possible and easy.
- Easily managed and maintained.
- Error detection is easily done.
Disadvantages of Tree Topology
- Heavily cabled.
- (^) Costly.
- If more nodes are added maintenance is difficult.
- Central hub fails, network fails.
HYBRID Topology
