UNIT 6 – DATA COMMUNICATION & NETWORKING GCE A/L Sri Lanka Notes Online Classes

 

🔷 6.1 DATA COMMUNICATION BASICS

📘 Definition

Data Communication is the process of transmitting data between two or more devices.

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🧠 Basic Components

1. Sender

Device that sends data
👉 Example: Your phone sending a WhatsApp message

2. Receiver

Device that receives data
👉 Example: Friend’s phone

3. Transmission Medium

Path used to send data
👉 Example:

• Cable
• Wi-Fi

4. Protocol

Rules for communication
👉 Example:

• Language in conversation

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🎯 Teaching Analogy

Sending a letter:

• Sender → You
• Receiver → Friend
• Medium → Postal service
• Protocol → Address format

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🔷 Data vs Signal

Data	Signal
Raw information	Form used to transmit
Digital	Analog/Digital

👉 Example:

• Data = “HELLO”
• Signal = electrical pulses carrying it

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🔷 Analog vs Digital Signals

Analog

• Continuous
  👉 Example: Radio waves

Digital

• Discrete (0 & 1)
  👉 Example: Computer data

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🔷 Transmission Modes

Simplex

One direction only
👉 Example: TV broadcast

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Half Duplex

Both ways, but one at a time
👉 Example: Walkie-talkie

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Full Duplex

Both ways simultaneously
👉 Example: Phone call

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🔷 6.2 TRANSMISSION MEDIA

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📘 Definition

Path through which data travels

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🔌 Guided Media (Wired)

1. Twisted Pair Cable

👉 Used in LAN
👉 Example: Ethernet cable

✔ Cheap
❌ More noise

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2. Coaxial Cable

👉 Used in cable TV

✔ Better shielding

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3. Fiber Optic Cable

👉 Uses light

✔ Very fast
✔ Long distance
❌ Expensive

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📡 Unguided Media (Wireless)

1. Radio Waves

👉 Wi-Fi, Bluetooth

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2. Microwaves

👉 Satellite communication

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3. Infrared

👉 TV remote

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🎯 Comparison Teaching Tip

Ask students:

• Which is fastest? → Fiber
• Cheapest? → Twisted pair

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🔷 6.3 NETWORK FUNDAMENTALS

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📘 Definition

A network is a collection of connected devices.

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🌐 Types of Networks

LAN (Local Area Network)

👉 Small area
Example: School lab

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MAN (Metropolitan Area Network)

👉 City level

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WAN (Wide Area Network)

👉 Large/global
Example: Internet

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🔷 Network Topologies

1. Bus

Single backbone cable

✔ Cheap
❌ Failure affects all

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2. Star

All devices connected to central hub

✔ Easy management
❌ Hub failure = network down

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3. Ring

Connected in circle

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4. Mesh

All connected to each other

✔ Reliable
❌ Expensive

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🎯 Teaching Tip

Draw diagrams — very important for exams

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🔷 6.4 NETWORK DEVICES

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🔌 Hub

• Broadcasts to all

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🔀 Switch

• Sends data to correct device

👉 Example:
Like a smart postman

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🌐 Router

• Connects networks

👉 Example:
Home router connects to internet

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🔗 Bridge

• Connects similar networks

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🔄 Gateway

• Connects different systems

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📶 Access Point

• Provides Wi-Fi

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📞 Modem

• Converts digital ↔ analog

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🔷 6.5 OSI MODEL (VERY IMPORTANT 🔥)

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📘 Definition

A 7-layer model for network communication

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🧠 Layers & Explanation

1. Physical

Transmission of bits
👉 Example: cables

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2. Data Link

Error detection

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3. Network

Routing

👉 Example: IP

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4. Transport

Reliable delivery

👉 Example: TCP

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5. Session

Session control

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6. Presentation

Data format

👉 Example:
Encryption

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7. Application

User interface

👉 Example:
Web browser

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🎯 Easy Memory Trick

“Please Do Not Throw Sausage Pizza Away”

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🔷 6.6 TCP/IP MODEL

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Layers:

1. Network Interface
2. Internet
3. Transport
4. Application

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🧠 Key Point

OSI = theoretical
TCP/IP = practical

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🔷 6.7 IP ADDRESSING

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📘 Definition

Unique identifier for devices

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🧠 IPv4 Format

Example:

192.168.1.1

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🔢 Classes

Class	Range
A	1–126
B	128–191
C	192–223

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🧠 Network ID vs Host ID

• Network → identifies network
• Host → identifies device

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🔷 6.8 SUBNETTING (VERY IMPORTANT 🔥)

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📘 Definition

Dividing network into smaller parts

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🧠 Example

Network:

192.168.1.0/24

👉 Can divide into:

• 2 subnets
• 4 subnets

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🎯 Teaching Analogy

Like dividing a classroom into groups

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🔷 6.9 DATA TRANSMISSION CONCEPTS

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📊 Bandwidth

Maximum capacity

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⚡ Bit Rate

Speed of data

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⏱ Latency

Delay

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📦 Throughput

Actual data transferred

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🔍 Error Detection

Parity Bit

Checks errors

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🔷 6.10 NETWORK SECURITY

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⚠ Threats

• Hacking
• Sniffing
• Spoofing

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🔐 Protection Methods

Firewall

Blocks unwanted access

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Encryption

Converts data into secret form

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VPN

Secure connection

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🔷 6.11 NETWORK PROTOCOLS

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🌐 HTTP / HTTPS

Web browsing

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📁 FTP

File transfer

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📧 SMTP

Sending emails

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📥 POP3 / IMAP

Receiving emails

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🌍 DNS

Converts domain → IP

👉 Example:
google.com → IP address

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📡 DHCP

Assigns IP automatically

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🎯 HOW TO TEACH UNIT 6 EFFECTIVELY

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✅ Use Real-Life Examples

• Wi-Fi
• Mobile data
• Internet

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✅ Focus on Diagrams

• Topologies
• OSI model

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✅ Practice Problems

• IP addressing
• Subnetting

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🔥 EXAM STRATEGY

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HIGH PRIORITY

✔ OSI Model
✔ Subnetting
✔ IP Addressing
✔ Network devices

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MEDIUM PRIORITY

✔ Transmission media
✔ Protocols

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LOW PRIORITY

✔ Basic definitions