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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Electronic Spreadsheet - LibreOffice Calc Analysis Tools

LibreOffice Calc: Analysis Tools

1. Goal Seek

Definition: Goal Seek helps find an unknown input when the output is predefined.

Example:

Find the interest rate required for a loan where the EMI is ₹5,000.

Steps:
1. Enter loan details (Principal ₹1,00,000, Interest Rate, EMI ₹5,000).
2. Go to Tools > Goal Seek.
3. Set "Target Cell" as EMI (₹5,000).
4. Set "Variable Cell" as Interest Rate.
5. Click OK to compute the interest rate.

2. Scenario Manager

Definition: Used for "What-If" analysis to compare different data conditions.

Example:

Comparing best-case, average-case, and worst-case sales scenarios.

Steps:
1. Enter sales data for different scenarios.
2. Go to Tools > Scenarios.
3. Add different values and name them (Best, Average, Worst).
4. Click OK and switch between scenarios.

3. Data Consolidation

Definition: Merges and summarizes data from multiple sources.

Example:

Combining sales data from multiple branches.

Steps:
1. Open multiple sheets with sales data.
2. Go to Data > Consolidate.
3. Select source data ranges.
4. Choose SUM to get total sales.
5. Click OK, and data will be merged.

4. Solver

Definition: Solver finds the best possible solution by adjusting variables under constraints.

Example:

Maximizing profit for a factory with limited resources.

Steps:
1. Enter profit per unit for chairs & tables.
2. Define constraints (budget, labor, materials).
3. Go to Tools > Solver.
4. Set "Target Cell" as profit (maximize).
5. Click Solve to compute the best combination.

Summary of Key Uses:

• Goal Seek: Find unknown inputs for a given output (e.g., EMI calculation).
• Scenario Manager: Compare different data conditions (e.g., best/worst sales cases).
• Data Consolidation: Merge multiple datasets (e.g., sales from different branches).
• Solver: Optimize decision-making (e.g., maximize profit under constraints).

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What is Workplace Safety?

Workplace Safety - Class 10

1. What is Workplace Safety?

Workplace Safety refers to measures and policies designed to prevent accidents, injuries, and hazards in a work environment.

2. Importance of Workplace Safety

• Reduces workplace injuries and accidents.
• Improves employee productivity and morale.
• Ensures legal compliance with safety laws.
• Prevents financial losses due to damages or medical expenses.

3. Common Workplace Hazards

Type of Hazard	Description
Physical Hazards	Unsafe equipment, slippery floors, fire risks.
Chemical Hazards	Exposure to harmful chemicals or gases.
Ergonomic Hazards	Poor posture, repetitive strain injuries.
Biological Hazards	Viruses, bacteria, or other health risks.
Electrical Hazards	Faulty wiring, overloaded circuits, electrocution.

4. Safety Measures in the Workplace

• Use Safety Equipment: Helmets, gloves, safety goggles, etc.
• Maintain Cleanliness: Keep the workplace free of hazards.
• Emergency Preparedness: Fire drills, emergency exits, first aid.
• Proper Electrical Safety: Avoid overloading circuits, inspect wires.
• Safe Handling of Chemicals: Store and label hazardous materials properly.
• Follow Safety Rules: Adhere to workplace safety guidelines.

5. First Aid Measures in the Workplace

• Cuts & Wounds: Clean the wound, apply a bandage.
• Burns: Cool with running water, apply burn ointment.
• Electric Shock: Turn off the power source, call for medical help.
• Fainting: Ensure fresh air, elevate the legs, seek medical help if needed.

✔ Stay safe and follow workplace safety rules! 🦺

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Database Management System - LibreOffice Base

LibreOffice Base: 4 Main Components

1. Tables 📊

Tables store data in rows (records) and columns (fields). Each field has a specific data type.

Example Table: "Students"

ID	Name	Age	Class
1	Rahul	14	10
2	Priya	15	10

2. Queries 🔍

Queries retrieve specific data using conditions.

Example SQL Query:

SELECT Name FROM Students WHERE Class = 10;

3. Forms 📝

Forms make data entry easy with a user-friendly interface.

Example: A student admission form to enter details like name, age, and class.

4. Reports 📄

Reports format data for professional presentation and printing.

Example: A student report card displaying marks and grades.

📌 Summary Table:

Component	Purpose
Tables	Store and organize raw data
Queries	Retrieve and filter specific data
Forms	Provide an easy interface for data entry
Reports	Format data for presentation and printing

✔ LibreOffice Base efficiently manages, analyzes, and presents data! 🚀

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Digital Documentation - LibreOffice Writer (Basic Overview)

LibreOffice Writer – Class 10 CBSE Notes

1. Features of LibreOffice Writer

• Document Formatting: Change font, size, color, and alignment.
• Tables & Images: Insert tables, images, and charts.
• Page Layout: Set margins, headers, footers, and columns.
• Spell Check & Grammar: Detects errors and suggests corrections.
• Mail Merge: Automates sending letters to multiple recipients.
• Export Options: Save as PDF, DOCX, ODT, etc.

2. Basic Components of LibreOffice Writer

• Title Bar: Displays the document name.
• Menu Bar: Contains options like File, Edit, View, Insert, etc.
• Toolbar: Provides shortcuts for common tasks.
• Ruler: Helps in adjusting margins and tab settings.

3. Text Formatting in LibreOffice Writer

Font Formatting: Change font type, size, and color.

Paragraph Formatting: Set alignment, adjust line spacing and indentation.

4. Page Formatting in LibreOffice Writer

• Margins & Page Size: Set from Format > Page Style.
• Headers & Footers: Insert repeating text at the top/bottom of pages.
• Page Breaks: Split content into different pages.

5. Inserting Tables, Images, and Charts

• Tables: Insert a table from Table > Insert Table.
• Images: Add images using Insert > Image.

6. Spell Check & AutoCorrect

Enable it from Tools > Spelling and Grammar.

7. Mail Merge (For Sending Bulk Letters)

1. Go to Tools > Mail Merge Wizard.
2. Select document type (letters, email, etc.).
3. Link to a data source (spreadsheet or database).
4. Insert placeholders (e.g., Name, Address).

8. Saving & Exporting Documents

• Save As (.odt): Default format for LibreOffice Writer.
• Save As (.docx): Compatible with Microsoft Word.
• Export as PDF: Convert documents into PDF format.

9. Keyboard Shortcuts in LibreOffice Writer

Action	Shortcut
Save File	Ctrl + S
Open File	Ctrl + O
Copy	Ctrl + C
Paste	Ctrl + V
Undo	Ctrl + Z
Bold	Ctrl + B
Italic	Ctrl + I

10. Advantages of LibreOffice Writer

• Free and open-source software.
• Supports multiple file formats.
• Provides advanced document formatting.

Conclusion

LibreOffice Writer is a powerful tool for creating, editing, and formatting documents.

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