📌 Data
Transmission Basics
Whenever we send data
over a network using TCP or UDP, the data is divided into small units called packets.
These packets travel
across the network separately and are later combined again at the receiver’s
side.
This packet-based
communication makes internet communication fast and efficient.
 |
| Visual explanation of TCP vs UDP protocols, how data packets travel across networks, and how packet sniffing works in cybersecurity. |
📦 Example: How
Packets Work
Imagine Person 1 sends a video to Person 2.
The system will:
1. Break
the video into many small packets.
2. Assign
a number to each packet.
3. Send
packets through the network.
4. The
receiver rearranges packets in correct order.
5. The
original video becomes playable again.
Example received order:
3, 4, 5, 2, 1
Rearranged as:
1, 2, 3, 4, 5
🔹 UDP
(User Datagram Protocol)
In UDP, packets are sent without establishing a connection.
✔
Faster transmission
✔ No confirmation required
❌ Packets may arrive out of order or be lost
Example uses:
·
Video streaming
·
Online gaming
·
Voice calls (VoIP)
·
Video chats (Skype, IMO)
UDP focuses on speed over reliability.
🔹 TCP
(Transmission Control Protocol)
In TCP, a connection must be established
before data transfer.
Process:
1. Sender
sends Packet 1.
2. Receiver
confirms receipt.
3. Sender
sends Packet 2.
4. Process
continues sequentially.
✔
Reliable communication
✔ Ordered delivery
✔ Error checking
Used by:
·
Websites (Google, Facebook)
·
Email services
·
File downloads
TCP focuses on accuracy and reliability.
🕵️ What
is Packet Sniffing?
Packet sniffing means capturing and
analyzing network data packets.
Programs used:
·
Wireshark
·
Kali Linux sniffing tools
A sniffer monitors
network traffic and collects packets passing through the network.
⚠️ Educational Example
If two users are
connected to the same Wi-Fi network:
·
A sniffer can capture packets moving across the
network.
·
If a website uses HTTP (not HTTPS), data may travel as plaintext.
·
Login credentials could potentially be visible.
👉
Modern websites use HTTPS encryption,
which protects data from sniffing attacks.
Important: Packet sniffing should only
be used for learning, security testing,
or authorized network analysis.
📑 What
is a Packet Header?
Each data packet
carries extra information called a header.
Headers contain details
needed for transmission, such as:
·
Source address
·
Destination address
·
Sequence information
·
Error checking data
🔵 TCP
Header Structure
A TCP header contains 11 required fields (20 bytes):
1. Source
Port (2 bytes)
2. Destination
Port (2 bytes)
3. Sequence
Number (4 bytes)
4. Acknowledgment
Number (4 bytes)
5. Data
Offset
6. Reserved
Bits
7. Control
Flags
8. Window
Size
9. Checksum
10. Urgent
Pointer
11. Optional
Data (0–40 bytes)
🟢 UDP Header Structure
UDP headers are simpler
and only 8 bytes long.
Fields include:
1. Source
Port Number (2 bytes)
2. Destination
Port Number (2 bytes)
3. Length
Field (2 bytes)
4. Checksum
(2 bytes)
UDP is lightweight
because it does not manage connection reliability.
🤝 TCP Three-Way Handshake
Before sending data,
TCP creates a connection using a Three-Way
Handshake.
Steps:
1️⃣ Client sends SYN (request connection)
2️⃣ Server replies with SYN + ACK (accept request)
3️⃣ Client sends ACK (confirmation)
✅
Connection established.
Control Flags Meaning
·
URG
– Urgent data present
·
ACK
– Acknowledgment received
·
PSH
– Push data immediately
·
RST
– Reset connection
·
SYN
– Start connection
·
FIN
– End connection
❓ Why
Handshake is Needed?
Both devices must
confirm:
·
They can send data
·
They can receive data
·
Communication path is reliable
Only after verification
does data transfer begin.
🌐 TCP vs
UDP Examples
|
Protocol |
Used
For |
|
TCP ----- |
Websites,
Email, File Transfer |
|
UDP ----- |
Video
Calls, Streaming, Gaming |
✅
Summary
·
Data travels across networks as packets.
·
TCP provides reliable, ordered communication.
·
UDP provides faster but less reliable
transmission.
·
Packet sniffing captures network traffic for
analysis.
·
HTTPS encryption protects users from data
interception.
·
TCP handshake ensures secure communication
setup.
Also Read:
Introduction Of Virus, warms, intruders, insiders, criminal organizations, cyber terrorist, security attacks, phishing attack and SQL injection?
What is Security Attacks? What is Active and Passive Attack??
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