Computer Network 1 Class 12 CBSE Notes

Computer Networking Devices

Class 12 Computer Science (CBSE)

Networking Devices

1. NIC (Network Interface Card)

NIC connects a computer to the network. It converts computer data into network signals and provides a unique MAC address.

2. Hub

A Hub connects multiple computers in a network and sends incoming data to all connected devices.

3. Switch

A Switch connects computers in a LAN and forwards data only to the intended device using the MAC address.

4. Bridge

A Bridge connects two LAN segments and forwards data only when required, reducing network traffic.

5. Router

A Router connects different networks and forwards data packets using IP addresses.

6. Modem

A Modem converts digital signals into analog signals and vice versa to connect the network to the Internet.

7. Gateway

A Gateway connects different networks using different communication protocols and acts as a translator.

Stages of Establishing a Network Connection

Stage 1 – Computer → NIC

The computer sends data to the Network Interface Card (NIC). The NIC converts the data into network signals and assigns a unique MAC address.

Stage 2 – NIC → Switch

The Switch receives the frame, checks the destination MAC address, and forwards it only to the correct device within the Local Area Network (LAN).

Stage 3 – Switch → Bridge

If the destination device is located in another LAN segment, the Bridge forwards the frame to that segment while reducing unnecessary network traffic.

Stage 4 – Bridge → Router

The Router reads the destination IP address and determines the best route to send the packet to another network.

Stage 5 – Router → Modem

The Modem converts digital signals into analog signals (or vice versa) and transmits them to the Internet Service Provider (ISP).

Stage 6 – ISP → Gateway

When communication occurs between networks using different protocols, the Gateway translates the data into the required format before forwarding it.

Stage 7 – Gateway → Internet → Destination Server

The packet travels through the Internet to the destination server. The server processes the request and returns the response through the same path.

Overall Flow of Network Communication

Computer
⬇
NIC
⬇
Switch
⬇
Bridge (If Required)
⬇
Router
⬇
Modem
⬇
Internet Service Provider (ISP)
⬇
Gateway (If Required)
⬇
Internet
⬇
Destination Server

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Computer Networks 2 of Class 12 CBSE code 083

Computer Networks

CBSE Class 12 Computer Science (083)

80/20 Rule in Networking

Definition

The 80/20 Rule states that nearly 80% of network traffic remains inside the Local Area Network (LAN) while only 20% travels outside through routers to other networks or the Internet.

Explanation

• 80% Local Traffic – File sharing, printer access, local servers.
• 20% External Traffic – Internet browsing, cloud services and communication with remote networks.

Advantages

• Improves network performance.
• Reduces congestion.
• Efficient bandwidth utilization.
• Less network delay.
• Reliable communication.

Computer
⬇
NIC
⬇
Switch
⬇
Bridge (If Needed)
⬇
Router
⬇
Modem
⬇
ISP
⬇
Gateway (If Needed)
⬇
Internet

Communication Media and Devices

Scenario	Media	Device	Reason
Home Network	Wi-Fi / UTP	Modem, Router	Internet Connection
School Lab	UTP Cable	Switch	Fast LAN
Office	Optical Fiber	Switch, Router	Department Communication
Bank	Optical Fiber	Router, Gateway	Secure Network
Hospital	Fiber / UTP	Router, Switch	Medical Records
University	Fiber + Wi-Fi	Router, Access Point	Campus Network
Mobile Network	Microwave	Cell Tower	Wireless Communication
Satellite	Microwave	Satellite, Modem	Remote Communication
TV Broadcast	Radio Wave	Broadcast Tower	Signal Transmission
Video Conference	Fiber / Wi-Fi	Router	High Speed Data

Communication Media Selection

Requirement	Media
Short Distance	UTP Cable
Long Distance	Optical Fiber
Wireless	Wi-Fi
Mobile Communication	Microwave
Satellite Communication	Microwave
TV Broadcasting	Radio Waves

Networking Device Selection

Requirement	Device
Connect LAN	Switch
Connect Networks	Router
Internet	Modem
Extend Signal	Repeater
Connect LAN Segments	Bridge
Different Protocols	Gateway
Connect Computer	NIC
Wireless Access	Access Point
Broadcast Data	Hub

CBSE Scenario-Based Questions

1. School Computer Lab

Media: UTP Cable
Device: Switch

2. Bank Branch

Media: Optical Fiber
Device: Router + Gateway

3. Home Wi-Fi

Media: Wi-Fi
Device: Modem + Wireless Router

4. TV Broadcasting

Media: Radio Waves
Device: Broadcasting Tower

5. Remote Village Internet

Media: Microwave
Device: Satellite Dish + Modem

Exam Tip

1. Identify the distance.
2. Select suitable communication media.
3. Choose the correct networking device.
4. Write one reason.

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Chapter- Cyber Safety

Cyber Safety 

Cyber safety refers to the responsible and secure use of the internet, digital devices, and online services to protect data, privacy, and systems from cyber threats.

Need for Cyber Safety

With the rapid growth of the internet, users face risks such as hacking, identity theft, malware, phishing, and cyberbullying. Cyber safety helps in preventing data loss, financial fraud, and misuse of personal information

Identity Theft

Identity theft is a cyber crime in which a criminal steals someone’s personal or financial information and uses it without permission to commit fraud or illegal activities..

Tracking Using IP Address

An IP (Internet Protocol) address is a unique number assigned to a device connected to the internet.

How IP tracking works:

• When a user visits a website, the server automatically records the IP address.

• The IP address reveals:

  1. Country and city (approximate location)

  2. Internet Service Provider (ISP

  3. Type of network

Uses:

• Detecting user location

• Preventing fraud

• Monitoring unusual activity

Example:

A website can identify that a user is accessing it from India using the IP address.

---

2. Tracking Using Cookies

Cookies are small text files stored on a user’s device by websites.

How cookie tracking works:

• Cookies store information such as:

  • Login details

  • User preferences

  • Browsing history

• When the user revisits the website, cookies are read by the browser.

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