CHAPTER-4 : Internet Network

What is a Network?

When one or more devices connected with each other it makes a network 

A network is simply a group of computers that are so connected that resources can be shared and information can be exchanged.

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Need for Networking

i) Resource Sharing

make all programs, data and peripherals available to authorized users on the network.

ii) Reliability

Providing an alternative source of data available for use.

iii) Financial benefits

Small computers have a better price-to-performance ratio as compared to the large one.

iv) Better communication medium

It is possible to transfer any kind of information to any other

v) Access to Remote databases

form a remote place in any part of the world, a user can book an air ticket from one city to another.

Network Terminologies

Node

The PCs and the servers are known as network devices or network devices or network nodes.

In general, A device or node is connected directly to a network cable or data path.

Host

The term host refers to a microcomputer attached to a network device.

Workstation

A workstation is a powerful PC used as a node on a network primarily used to run application programs.

Bandwidth

Bandwidth refers to the difference between the highest and lowest frequencies of a transmission channel.

This term is sometimes also used to refer to the amount of information travelling through a single channel at any one point of time.

Types of Networking

i) Local Area Network (LAN)

ii) Metropolitan Area Network (MAN)

iii) Wide Area Network (WAN)

Local Area Network (LAN)

LAN is a group of computers located in the same room, on the same floor or in the same building that is connected to form a single network as to share resources such as data, printers, fax, etc.

Advantages of LAN

- It allows the sharing of expensive resources such as laser printers, software.

- LAN allows for a high-speed exchange of essential information.

- It contributes to increased productivity.

Disadvantages of LAN

- The financial cost of local area networking is still high.

- Local Area networking software requires memory space in each of the computers used on the network.

- Some control on the part of the user is lost.

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Metropolitan Area Network (MAN)

Man are networks spread over a city. It is a network that is utilized across multiple buildings. 

It is commonly used in the school campus, large universities and large companies.

Characteristics of MAN

- MAN can support both data and voice connectivity.

- It generally covers towns and cities (50kms)

- It is developed in the 1980s

- Optical Cabel is used. 

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Wide Area Network (WAN)

WANs are used to connect LANs and other types of networks together. 

So that Users and Computers in one location can communicate with Users and Computers in other Locations

Characteristics of WAN

- It generally covers a large distance.

- Communication medium used is Satellites.

- It may also enable LANs to communicate with each other.

Image Source: Google

Image Source: Google

Network Topologies

- Topology is the method is which networks are physically connected together.

- Topology determines the complexity of connecting computers and, therefore the cost of network cable installation.

- Topology also determines the strategy for physically expanding the network in future.

There are different topologies available, there are the following, 

i) Bus topology

ii) Ring topology

       a) Token ring

       b) FDDI

iii) Star Topology

iv) Mesh Topology

Bus Topology

In Bus Topology, all computer are connected by a single length of cable with a terminator at each end.

It is passive topology, which means only one computer at a time can send a message.

A computer must wait until the bus is free before it can transmit. 

The bus topology is the simplest and most widely used LAN design.

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Advantages of Bus topology

- It is simple, reliable and easy to be used in a small-sized LAN network.

- Less expensive than other cabling arrangements.

- If one computer on the bus fails, it does not affect the rest of the traffic on the bus.

Disadvantages of Bus topology

- In this topology, no two computers can transmit data at the same time.

- Terminators are required at both ends of the cable.

- Performance degrades as additional computers are added.

Ring Topology

- Ring Topology is also known as circular topology. 

- In this topology, computers are arranged in a circle. 

- Data travel around the ring in one direction.

- In this layout, each node is physically connected to only two other nodes.

- Each node passes information along to the next until it arrives at its intended destination. So each computer re-transmits what it received.

Image Source: Google

Advantages of Ring topology

- It creates a much larger network using a token ring.

- Because every compute given equal access to the token, no one computer can monopolize the network.

- It performs better under the heavy load.

- It does not require a network server to manage the connectivity between the computers.

Disadvantages of Ring topology

- Failure of one computer on the ring affects the whole computer network.

- It is difficult to troubleshoot a ring network.

- Adding or removing computers disrupts the whole networks.

Token Ring Topology

- Token ring works very differently from ring topologies.

- Each station in a ring topology has given an equal chance by getting a free token.

- A node received the token from its nearest active upstream neighbour and passes to its nearest downstream neighbour.

- The token and data are sent repeatedly until they reach their destination.

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How the token ring works

Token Ring passed a free token Ring around in the ring in one consistent direction.

if a station wants to send data to another station, It must receive the token and attached the data from it and send the token down the ring.

Fiber Distributed Data Interface (FDDI)

- FDDI is another ring-based network, and unlike the token ring, it is implemented without hubs.

- FDDI uses fibre-optic cables to implement very fast, reliable networks.

- FDDI cabling consists of two fibre rings, one transmitting clockwise and the other transmitting counterclockwise. If either one breaks, the other can be used as a backup.

Image Source: Google

How FDDI Works

- FDDI uses token-passing schemes to control network access, several FDDI devices can transmit data simultaneously.  

- Like a token ring, a token is passed around the ring and the possessor of the Token is allowed to transmit FDDI frames.

Star Topology

In the star topology, each computer on a network communicates with a central hub that resends the messages either to all computers or only to the destination computer.

An active hub regenerates the electrical signal and sends it to all the computers connected to it.

Active hubs and switches require electrical power to run. Passive hubs do not require electrical power to run.

Image Source: Google

Advantages of Star Topology

i) It is more reliable.

ii) It is easy to replace, install or remove the device

iii) It has good performance.

Disadvantages of Star Topology

i) It is Expensive to install

ii) centre node dependency, if the central hub fails, the entire network fails to operate.

iii) It costs more to cable a star network since it requires all the network cables to be pulled to one central point, requiring more cable length.

Mesh Topology

Mesh Topology is a type of network where each computer and Network devices are interconnected with one another, allowing most transmissions to be distributed, even one of the connection breaks down.

A mesh topology is used in large networks, this topology is expansive because it has a redundant (Duplicate) connection to every computer.

Image Source: Google

Hybrid Topology

The term hybrid is referred to combination, hybrid Topology is an interconnection between several local area networks with no. of different topologies.

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Transmission Media

Transmission media refers to the physical channel through which data can be sent from one point to another.

Media differ in the capability to support high data rate and long-distance transmission. The reasons for this are -

i) Noise Absorption

ii) Radiation

iii) Attenuation

iv) Bandwidth

Noise Absorption

Adding the external Noise that can cause the main signal speed will be reduced.

Radiation

Leakage of the signal from the main signal.

Attenuation

decrease the magnitude of signal with distance due to the absorption of energy by the media (surface).

Bandwidth

Bandwidth refers to the difference between the highest and lowest frequencies of a transmission channel.

bandwidth is directly proportional to frequency and transfer rate

Guided Media

- Guided Media provides the physical connection between two devices. 

- A signal travelling through guided media is directed and contained within the physical limits of the medium.

 Twisted Pair Wire

- A twisted pair wire consists of two insulated copper wire typically 1mm thick.

- The wires are twisted together, the purpose of twisting the wire is two reduce noise Absorption.

- Twisted together in helical shape look like a DNA molecule.

- transfer the data over 1 km distance.

- Use in Local telephone Communication.

Advantages of Twisted Pair Wire

- Being the oldest media repairment and service of this media are easily available.

- This media can be used for both analog and digital transmission.

- The bandwidth depends on the thickness of the wire and distance travelled.

- It is the least expansive media of transmission for networking.

Disadvantages of Twisted Pair Wire

- Twisted pair cable easily pickup noise signal which results in higher rates of errors.

- Being thin in size it is likely to break easily.

Image Source: Google

Co-axial Cabel

- Co-axial cable consists of thick copper wire as the core, surrounded by a plastic insulator material. 

- The Insulator is encased by a cylinder conductor often as a closely woven braided mesh.

- The outer conductor is covered in a plastic protective jacket. The signal is transmitted by the inner copper conductor and it is protected by outer metals sleave.

- Co-axial cable can support the high rate data transfer even when the distance is increased.

- Co-axial cable is difficult to connect the network devices.

- Many Co-axial cables require the connectors on the main cable to be attached directly to the adaptor on the personal computer.

Advantages of Co-axial cable

- It has better shielding against electromagnetic interface than twisted-pair cable.

- It can be used for both analog and digital data transmissions.

- It is inexpensive as compared to twisted-pair wires.

Image Source: Google

 Fibre Optical Cable

- It is the newest form of Guided media.

- Fibre Optical Cable is superior in data handling and security characteristics.

- Each fibre has an inner core of glass or plastic that conducts light.

- There are two types of light sources for which fibre cables are available. These are 

   a) LEDs

   b) Lasers

Image Source: Google

Image Source: Google

Characteristics of fibre-optic Cable

- Fibre optic cable is more expensive than copper cable.

- Fibre-optic cable is difficult to install than copper cable.

- Because it uses light, which has a higher frequency than electrical signals.

- Fibre optic cables have much lower attenuation than copper wires, mainly because the light is not radiated in the way electricity is radiated from copper cables.

- Fibre optic channels are half-duplex, which means that light signals can only move in one direction at a time.

- The fibre cable is lighter than copper cable.

- Fibres do not leak light and quite difficult to tap.

Unguided Media

Unguided media is used for transmitting the signal without any physical media. It transports electromagnetic waves and called wireless communication.

i) Radio waves

ii) Microwaves

iii) Infra-red waves

Radio waves

- having the frequency between 10 kHz to 1Ghz.

- radio waves can be generated Omni-directional or Unidirectional.

- They can travel long distances

- They can pass through a solid object, So they are widely used for indoor and outdoor communication.

- Radio waves are Omni-directional. It means they can travel in all directions from the source so that sending unit and receiving unit does not have to carefully align physically.

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Microwave Signal

- Microwaves signals are transmitted at the frequency rate above 100Mhz to Maximum of 10Ghz.

- These signals are uni-directional broadcasted.

- The waves travel in a straight line and can, therefore, normally focus concentrating all the energy into a small being using a parabolic antina (like Satellite, dish antina).

- Microwaves give higher signals less noise in long-distance transmission, they can travel 25 to 30 km between the transmitter and receiver station.

- Microwaves do not pass through buildings. Microwaves transmission also depend upon on whether and frequency.

- Microwaves communication widely used for long-distance telephone communication, several telephones and television distributions.

Image Source: Google

Infrared Signals

- It is widely used for short-range communication.

- Used for data communication in indoor wireless networking and controlling electronic home appliances.

- They are relatively direction or bydirection but do not pass any solid object.

- No Government licensing to operate an inferred communication system.

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