Data Communication

🧠 MENTAL PICTURE

Imagine two people talking through a telephone:

Person A
(Sender)
   ↓
Message
   ↓
Telephone Network
(Medium)
   ↓
Person B
(Receiver)

Both must follow
the same rules
   ↓
Protocol

Now convert that into computers:

COMPUTER A
  Sender
    ↓
   Data
    ↓
Transmission Medium
    ↓
COMPUTER B
 Receiver

The entire chapter can be reduced to:

               DATA COMMUNICATION
                      |
      ┌───────────────┼────────────────┐
      ↓               ↓                ↓
  Who sends?      How travels?      What rules?
    Sender           Medium          Protocol
      ↓
   Receiver

11.1 Concept of Communication

Communication means:

Sending or receiving data.

Data can be:

Text
Image
Audio
Video
Multimedia

Example:

Phone A
  ↓
"Hello"
  ↓
Mobile network
  ↓
Phone B

Memory

Data Communication = Exchange of data between connected devices.

Now expand only this picture:

DATA COMMUNICATION
│
├── Components
│   ├── Sender
│   ├── Receiver
│   ├── Message
│   ├── Medium
│   └── Protocol
│
├── Capacity
│   ├── Bandwidth → Hz
│   └── Data Rate → bps
│
├── Direction
│   ├── Simplex       → A ──→ B
│   ├── Half Duplex   → A ←→ B, one at a time
│   └── Full Duplex   → A ⇄ B, simultaneously
│
├── Switching
│   ├── Circuit → dedicated path
│   └── Packet  → break message into packets
│
├── Transmission
│   ├── Wired
│   │   ├── Twisted Pair
│   │   ├── Coaxial
│   │   └── Optical Fibre
│   │
│   └── Wireless
│       ├── Radio
│       ├── Microwave
│       └── Infrared
│
├── Mobile
│   └── 1G → 2G → 3G → 4G → 5G
│
└── Protocol
    ├── HTTP → Web
    ├── FTP  → File transfer
    └── PPP  → Point-to-point

11.4 Types of Data Communication

Simplex
Half-duplex
Full-duplex

## Simplex

One-way communication.

```text
A ─────────→ B
Sender      Receiver

Examples

Keyboard → computer
Computer → speaker

Memory:

Simplex = only one direction

Half-Duplex

Both sides can communicate, but not simultaneously.

A ─────→ B

then
A ←───── B

Example:

Walkie-talkie

When one person talks, the other listens. NCERT

Memory:

Half-duplex = both directions, one at a time.

Full-Duplex

Both sides communicate at the same time.

A ⇄ B

Chapter 12 — Security Aspects

🧠 MENTAL PICTURE

Imagine your computer as a house:

COMPUTER
                  ┌─────────┐
 Internet ───────→│ FIREWALL│
                  │         │
 Malware ────────→│ANTIVIRUS│
                  │         │
 Hacker ─────────→│SECURITY │
                  └─────────┘

You want to protect:

DEVICE
+
DATA
+
NETWORK

12.2 Malware

Malware means:

MALicious softWARE

It is software intentionally designed to damage systems, steal data or cause other trouble. NCERT

Important types:

Virus
Worm
Ransomware
Trojan
Spyware
Adware
Keylogger

Virus

A virus inserts/copies malicious code into another program or executable.

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It normally becomes active when the infected file is executed. NCERT

Mental:

Host Program
    +
 Virus code
    ↓
Infected program

Worm

A worm:

Does NOT require a host program
Can work independently
Can self-replicate
Can spread through networks

### Virus vs Worm

Virus
→ needs host/infected file
→ typically user triggering

Worm
→ standalone
→ self-replicates

Ransomware

Mental:

Your Files
   ↓
LOCK / ENCRYPT
   ↓
"Pay money"
   ↓
Ransomware

The chapter uses WannaCry as an example and notes its 2017 global outbreak.

Trojan

Looks legitimate:

Normal-looking program
        ↓
Install it
        ↓
Malicious behaviour

Unlike a worm, a Trojan does not self-replicate; it relies on user interaction such as opening/downloading it.

Spyware

Secretly collects information.

Examples of targeted information include:

Internet usage
Passwords
Bank information
Identity information

Keylogger

Records keys pressed by the user.

Mental:

You type:
PASSWORD123
     ↓
Keylogger records keys
     ↓
Sensitive information leaked

12.6 Firewall

Imagine a security guard at a gate:

Internet
   ↓
┌──────────┐
│ FIREWALL │
│   GUARD  │
└──────────┘
   ↓
Private Network

A firewall monitors and controls incoming and outgoing network traffic according to security rules.

12.7 Cookies

A cookie is a small piece of information a website uses to remember information associated with a user’s browsing/session.

Examples:

Login/authentication

Session timeout

Remembering information

🔥 FOLLOW-UP QUESTIONS — Security

Virus vs Worm?

Virus
→ requires a host
→ usually triggered by user

Worm
→ standalone
→ self-replicates

Trojan?

Malware disguised as legitimate software

Ransomware?

Blocks/encrypts data
→ demands ransom

Antivirus?

Detects/prevents/removes malware

HTTP vs HTTPS?

HTTP → unencrypted textbook model
HTTPS → encrypted communication

Firewall?

Filters network traffic

White vs Black Hat?

White → ethical
Black → malicious/unethical

DoS vs DDoS?

DoS → denial attack
DDoS → distributed attack using many systems

Malware
→ malicious software

Virus
→ malicious code requiring host/infected file

Worm
→ standalone self-replicating malware

Ransomware
→ locks/encrypts data for ransom

Trojan
→ malicious software disguised as legitimate

Firewall
→ network traffic filter

HTTPS
→ encrypted web communication

White Hat
→ ethical hacker

DoS
→ deny service by overwhelming resource

DDoS
→ distributed DoS from many machines

Snooping
→ secret traffic capture/analysis

Eavesdropping
→ real-time interception

                   DATA COMMUNICATION
                           |
             ┌─────────────┼─────────────┐
             ↓             ↓             ↓
        COMPONENTS       MEDIA        PROTOCOLS
             |             |             |
     Sender/Receiver    Wired         HTTP
     Message            Wireless      FTP
     Medium                           PPP
     Protocol
             |
      Communication Type
      /       |        \
 Simplex   Half       Full


                       SECURITY
                          |
         ┌────────────────┼────────────────┐
         ↓                ↓                ↓
      MALWARE          PROTECTION       THREATS
         |                |                |
 Virus/Worm           Antivirus          DoS
 Ransomware           Firewall           DDoS
 Trojan               HTTPS              Intrusion
 Spyware              Updates            Snooping
 Keylogger            Backup             Eavesdropping