Computer networks

MG5CCRBCA300 Computer Networks — Full Notes

UNIT 1: Overview of Computer Networks

1. Definition of a Computer Network

A computer network is a group of computers and devices that are connected to each other so they can talk to each other and share things.

These devices are connected through communication links [paths that carry data — like wires or wireless signals].

Each computer can still work on its own, but when connected in a network, they can share resources [useful things like files, printers, and internet] with each other.

Data [information saved on a computer] can be sent quickly and easily between different computers using a network.

2. Objectives [Goals] of a Computer Network

1. Resource Sharing People can share things like printers, storage devices [devices used to save data, like hard disks], and software [computer programs] — so not everyone needs to buy their own.

2. Information Sharing People can send and receive data and information between computers quickly and easily.

3. Communication Networks let people communicate [talk or message each other] through email, chat messages, voice calls, and video calls.

4. Reliability [Dependability — being able to trust that something will work] If one computer fails, data saved as a backup [a copy saved somewhere else] on another computer can still be accessed. This makes the system more dependable.

5. Cost Reduction When many people share the same resources, the cost of buying hardware [physical devices like printers] and software goes down.

6. Remote Access [Using something from far away] People can access [open and use] their files and services from a different location, not just from one fixed place.

7. Improved Performance Work can be divided [split up] among many computers, so tasks get done faster and more efficiently [without wasting time or effort].

3. Applications [Uses] of Computer Networks

1. Internet The Internet is the biggest computer network in the world. It connects millions of computers and lets people browse [look through] websites, send emails, and communicate online.

2. Business Companies use networks so that employees [workers] can share files, use the same software, and communicate with each other easily.

3. Education Schools and colleges use networks for online classes, sharing study materials, using digital libraries [collections of books and resources available online], and managing student records.

4. Banking Banks use networks for online transactions [money transfers done through the internet], ATM services, and safe communication between different bank branches [smaller offices of the same bank in different locations].

5. Healthcare [Medical Services] Hospitals use networks to store patient records [files with a patient's medical history], share medical information between doctors, and provide online health services.

6. E-commerce [Online Shopping] Shopping websites use networks to connect buyers, sellers, and payment systems so people can buy and sell things online.

7. Cloud Computing [Storing and using things over the internet] Instead of saving everything on your own computer, networks let you store data and use software on remote servers [powerful computers located somewhere far away that you access through the internet].

8. Communication Services Apps like video calling, instant messaging [sending and receiving text messages in real time], and social media [websites like Facebook and Instagram] all work because of computer networks.

4. Types of Computer Networks

Networks are grouped in two ways:

• Based on geographical area [how large an area the network covers]

• Based on communication method [how data is sent between devices]

Based on Geographical Area

A. PAN — Personal Area Network

A PAN is the smallest type of network. It connects your own personal devices [devices you personally own and use] within a very short distance — just a few meters.

Devices it connects: mobile phones, laptops, tablets, smartwatches.

Example: When you connect your phone to your Bluetooth [a short-range wireless technology used to connect nearby devices] earphones, that is a PAN.

B. LAN — Local Area Network

A LAN connects computers within a small area like a home, office, classroom, or one building.

Computers in a LAN connect using:

• Ethernet cables [physical wires that carry data between devices] for wired connection

• Wi-Fi [wireless internet] for wireless connection

They connect through devices like:

• Switch [a device that connects multiple computers in a network and sends data to the right computer]

• Router [a device that connects your local network to the internet or to other networks]

• Access point [a device that provides Wi-Fi connection to devices nearby]

A LAN is usually privately owned [owned and managed by one person or organization, not the public].

One computer in the LAN can be made a server [a powerful computer that stores files and programs that other computers in the network can use]. The other computers are called clients [computers that use what the server provides].

Data transfer speeds in LAN are normally 100 or 1000 Mbps [Megabits per second — a unit that measures how fast data travels].

Main Features of LAN:

• Covers a small area like a room, building, or campus [the grounds of a school or college]

• Owned by one person or organization

• Very fast communication

• Data stays within the local [nearby] area

• Easy to manage and maintain [keep in good working condition]

Example: A college computer lab where 50 computers are all connected to one switch and share a printer and internet connection.

C. MAN — Metropolitan Area Network

A MAN connects multiple LANs [more than one LAN] across a city or large area. It is bigger than a LAN but smaller than a WAN.

The main purpose is to connect different buildings or offices of the same organization across a city.

Example: A university that has its main campus, engineering college, office, and research centre in different parts of a city — all connected together — is using a MAN.

Technologies [methods/tools] used:

• Fiber optic cables [very thin cables made of glass that carry data as light — very fast]

• Leased lines [private communication lines rented from a telecom company]

• Microwave links [wireless data sent using microwave radio signals through the air]

• Metro Ethernet [a fast network technology used to connect places across a city]

Managed by:

• Large organizations

• Telecom companies [companies that provide long-distance communication services]

• Internet service providers [companies that give you internet access]

Example: A bank with many branches across a city all connected through a fast network is using a MAN.

D. WAN — Wide Area Network

A WAN connects networks across very large distances — like between different cities, countries, or even continents [very large areas of land like Asia or Europe].

WANs connect multiple LANs and MANs using long-distance communication links.

Because the distances are so large, WANs depend on telecommunication providers [companies that manage long-distance communication systems like phone and internet companies].

Technologies used:

• Fiber optic cables

• Undersea cables [cables placed under the ocean to connect countries across the sea]

• Satellite communication [sending data through satellites [man-made objects orbiting Earth] in space]

• Leased communication lines

• Internet connections

Example: The Internet is the largest WAN. A company with offices in India, USA, and Europe that connects all its offices together is using a WAN.

Comparison Table: PAN vs LAN vs MAN vs WAN

Based on Communication Method

A. Point-to-Point Network

This is a network where a direct link [a connection made only between two devices] exists between exactly two devices.

Data travels directly from one device to the other through their own dedicated [private, reserved only for them] connection.

Example: Two computers connected directly to each other with a cable.

B. Broadcast Network [Send to Everyone]

In this type, all devices share one common channel [one shared path for sending data]. When one device sends data, every device receives it — but only the device it was meant for will actually read and use it.

Example: Many LANs use broadcast communication.

Broadcast works well in small networks. But in large networks like the Internet, point-to-point links are used because sending data directly to the right device is faster and less wasteful.

UNIT 2: Network Topologies

What is Network Topology?

Network topology is the arrangement [the way things are laid out or organized] of devices and connections in a network.

It shows how computers and devices are connected and how data moves between them.

Devices in a network are called nodes [individual computers or devices connected in a network].

The connections between them are called links [the wires or wireless paths that carry data between devices].

Choosing the right topology is important because it affects:

• Performance [how fast and well the network works]

• Cost [how much money is needed to set it up]

• Reliability [how dependable the network is]

• Security [how safe the network is from outsiders or attacks]

Physical vs Logical Topology

Physical Topology

Physical topology is the actual physical layout [the real arrangement you can see — where the cables go and where the devices are placed] of the network.

It describes how devices are physically connected using real cables and hardware [physical equipment].

Example: The actual cables and switches you can see in a computer lab show the physical topology.

Common physical topologies: Star, Bus, Ring, Mesh, Hybrid.

Logical Topology

Logical topology describes how data actually travels inside the network — not how the cables look, but the path data takes to get from one device to another.

Example: Computers may be physically arranged in a star shape, but data might flow [travel] in a ring-like pattern inside. The way data moves is the logical topology.

Common logical topologies: Logical Bus, Logical Ring.

Common Network Topologies

1. Star Topology

In a star topology, every computer connects to one central device in the middle — usually a switch [a smart device that receives data and sends it only to the correct computer] or hub [a simpler device that sends data to all connected computers].

No computer connects directly to another. All data passes through the central device first.

How it works: If Computer A wants to send data to Computer D, the data first goes to the switch. The switch then sends it to Computer D only.

Structure:

      Computer A
           |
Computer B --- Switch --- Computer C
           |
      Computer D

Advantages [Good things about it]:

Disadvantages [Problems with it]:

Example: A college computer lab where all computers connect to one central switch.

2. Bus Topology

In a bus topology, all computers connect to one single long cable called the backbone cable [the main cable that runs through the whole network carrying all data].

When any computer sends data, it travels along this cable and reaches every computer — but only the computer it was meant for will accept and read it.

Structure:

Computer 1 -- Computer 2 -- Computer 3 -- Computer 4
|______________________________________________|
                  Backbone Cable

Advantages:

Disadvantages:

Example: Older Ethernet networks used bus topology.

3. Ring Topology

In a ring topology, each computer connects to exactly two other computers — one on its left and one on its right — forming a circle [a closed loop with no beginning or end].

The last computer connects back to the first, completing the ring.

Data travels around the ring in one direction [like going around a roundabout] from one computer to the next until it reaches the right destination [the computer it was meant for].

Every computer checks if the data is meant for it. If not, it passes the data on to the next computer.

Token Passing: A special signal called a token [a tiny packet [small unit of data] that gives permission to send data] goes around the ring. A computer can only send data when it has the token. This stops two computers from sending data at the same time, which prevents collisions [data clashing].

Structure:

Computer 1 → Computer 2 → Computer 3 → Computer 4
↑                                            ↓
└────────────────────────────────────────────┘

Advantages:

Disadvantages:

What happens when one computer fails:

Normal:  A → B → C → D → E → A
C fails: A → B     D → E → A   ← the ring breaks, communication stops

4. Mesh Topology

In a mesh topology, each device connects directly to one or more other devices.

In a full mesh [where every device is connected to every other device], every single computer has its own direct connection to all other computers.

This means there are many paths [multiple routes data can take] for data to travel.

Structure:

Computer 1 -------- Computer 2
        \          /
         \        /
          \      /
          Computer 3

Advantages:

Disadvantages:

Example: Military [army and defence] communication systems and backbone networks [the main high-speed internet connections that carry huge amounts of data].

5. Hybrid Topology

A hybrid topology is a mix of two or more different topologies [network layouts] like star, bus, ring, or mesh combined together.

It is designed to use the good features of each topology and avoid [stay away from] their weaknesses.

Example: A large company might use star topology inside each department [a section of a company], and then connect all departments together using a bus or mesh connection.

Structure:

        Computer
            |
Computer - Switch - Computer
            |
        Computer
            |
============================
       Backbone Cable
============================
            |
          Switch
         /  |  \
        PC  PC  PC

Advantages:

Disadvantages:

Example: Large companies and universities often use hybrid topology.

Final Summary Table — All Topologies