1. Introduction

FTP stands for File Transfer Protocol.

FTP is an application-layer protocol used to transfer files between a client computer and a server over a TCP/IP network.

In simple words:

FTP is a protocol that allows users to upload files to a server and download files from a server.

For example, a website developer can use FTP to upload:

HTML files
Images
CSS files
JavaScript files
Documents
Other website files

2. Basic Idea of FTP

FTP follows a client-server architecture.

          FTP CLIENT
              │
              │
       Upload / Download
              │
              ↓
          FTP SERVER
              │
        ┌─────┼─────┐
        │     │     │
      Files Files  Files

FTP Client

The FTP client is the software used by the user to connect to an FTP server.

Examples include:

FileZilla
WinSCP
Command-line FTP client

FTP Server

The FTP server stores files and responds to requests from FTP clients.

3. Main Functions of FTP

FTP provides several file management functions:

Upload files
Download files
Delete files
Rename files
Create directories
Delete directories
List files and directories
Move between directories
Authenticate users

4. How FTP Works

The basic FTP process is:

User
  ↓
FTP Client
  ↓
Connection to FTP Server
  ↓
Login / Authentication
  ↓
File Operations
  ↓
Upload / Download
  ↓
Disconnect

Step 1: FTP Client

The user opens an FTP client.

Step 2: Connect to FTP Server

The client connects to the FTP server using the server’s hostname or IP address.

Example:

ftp.example.com

Step 3: Authentication

The server may ask for:

Username
Password

Some servers also support anonymous FTP, where limited access may be provided without a personal account.

Step 4: Directory Listing

After login, the user can view available directories and files.

Step 5: File Transfer

The user can:

Upload:
Client ─────────► Server

Download:
Client ◄───────── Server

Step 6: Connection Termination

After completing the work, the client closes the FTP session.

5. FTP Uses Two Connections

This is a very important point for exams.

Traditional FTP uses two separate TCP connections:

Control connection
Data connection

             FTP Client
             /        \
            /          \
     Control           Data
    Connection       Connection
        │                │
        ↓                ↓
     FTP Server       FTP Server

A. Control Connection

The control connection is used for commands and responses.

Examples:

Login
List directory
Change directory
Download request
Upload request

Traditional FTP uses TCP port 21 for the control connection.

B. Data Connection

The data connection is used for actual file data and directory listings.

For traditional FTP, the data connection uses a separate TCP connection.

The way this connection is established depends on whether FTP is operating in active mode or passive mode.

6. Active and Passive FTP

A. Active Mode

In active FTP, the server establishes the data connection back to the client.

Simplified:

Client ── Control ──► Server
Client ◄── Data ───── Server

A common issue with active mode is that firewalls or NAT devices on the client side may block the incoming data connection.

B. Passive Mode

In passive FTP, the client establishes both the control and data connections to the server.

Client ── Control ──► Server
Client ── Data ──────► Server

Passive mode is widely used because it works better with modern firewalls and NAT.

7. FTP Commands

FTP provides commands for performing different operations.

Command	Purpose
`USER`	Specifies username
`PASS`	Specifies password
`LIST`	Lists files/directories
`PWD`	Shows current directory
`CWD`	Changes directory
`RETR`	Downloads a file
`STOR`	Uploads/stores a file
`DELE`	Deletes a file
`MKD`	Creates a directory
`RMD`	Removes a directory
`QUIT`	Ends the FTP session

Example

If a user wants to download:

notes.pdf

the client can issue an FTP RETR command for that file.

8. File Transfer Modes

FTP supports different ways of representing transferred data.

1. ASCII Mode

Used mainly for text files.

Examples:

HTML
TXT
CSS
Source code

2. Binary Mode

Used for files where the exact bytes must be preserved.

Examples:

Images
Videos
PDF files
Executable files
ZIP files

For modern FTP clients, binary transfer is commonly used for non-text files.

9. Anonymous FTP

FTP can support anonymous access.

In anonymous FTP:

User
 ↓
FTP Server
 ↓
Anonymous Access

The server allows users to access selected public files without having a normal personal account.

Uses

Public software distribution
Public documents
Research data
Public archives

However, anonymous FTP access is normally restricted for security reasons.

10. FTP vs HTTP

Both FTP and HTTP can transfer files, but they have different purposes.

Feature	FTP	HTTP
Full form	File Transfer Protocol	HyperText Transfer Protocol
Main purpose	File transfer and file management	Web pages and web resources
Architecture	Client-server	Client-server
Traditional FTP control port	21	80
Secure version	FTPS / SFTP*	HTTPS
Directory management	Supported	Not a core feature
Upload/download	Yes	Yes
Common use	Server file management	Web browsing

Important: SFTP is SSH File Transfer Protocol, which is different from FTPS. SFTP is not simply “secure FTP”; it is a separate protocol that runs over SSH.

11. FTP vs SFTP

This is useful for practical understanding.

FTP	SFTP
File Transfer Protocol	SSH File Transfer Protocol
Traditionally unencrypted	Encrypted through SSH
Uses separate FTP control/data connections	Uses one SSH-based connection
Less secure for sensitive data	More secure
Traditional FTP control port: 21	Usually SSH port 22

For transferring sensitive files, SFTP is generally preferred over traditional FTP.

12. Advantages of FTP

1. Easy file transfer

Users can easily upload and download files.

2. Supports large files

FTP can be used to transfer large files.

3. File management

Users can create, delete, rename and organize files and directories, depending on permissions.

4. Authentication

FTP can use usernames and passwords to control access.

5. Resume capability

Many FTP clients can resume interrupted file transfers.

6. Useful for website management

Web developers can transfer website files between their computers and hosting servers.

13. Disadvantages of FTP

1. Traditional FTP is not encrypted

Usernames, passwords and transferred data can be exposed on an untrusted network.

2. Security risks

Traditional FTP is not suitable for transferring sensitive information over insecure networks.

3. Firewall/NAT issues

Active FTP can create connectivity problems with firewalls and NAT.

4. More complex than simple web downloads

FTP involves separate control and data connections.

5. Better secure alternatives exist

SFTP and FTPS provide stronger protection for secure file transfer.

14. Applications of FTP

FTP has been used extensively for:

1. Website development

Developers upload website files to web hosting servers.

Computer
   ↓
FTP
   ↓
Web Hosting Server

2. Software distribution

Files and software packages can be distributed through FTP servers.

3. Backup and file transfer

Organizations can transfer files between systems.

4. Sharing large files

FTP can be used to transfer large datasets and files.

5. Server administration

Administrators can manage files on remote servers when appropriate access is available.

15. FTP Working Example

Suppose you have created a website on your computer:

index.html
about.html
style.css
logo.png

You want to upload these files to your hosting server.

The process is:

          YOUR COMPUTER
              │
          FTP Client
              │
              │ FTP
              ↓
        HOSTING SERVER
              │
        ┌─────┼─────┐
        │     │     │
     index  about  style
      .html  .html  .css

After uploading, the web server can serve these files to visitors.

16. FTP Architecture Diagram

For a 10-mark answer, you can draw:

                 FTP SYSTEM

        ┌──────────────────┐
        │    FTP CLIENT    │
        │                  │
        │  User / Browser  │
        └────────┬─────────┘
                 │
          Control Connection
             TCP Port 21
                 │
                 ↓
        ┌──────────────────┐
        │    FTP SERVER    │
        │                  │
        │ Files/Directories│
        └────────┬─────────┘
                 ↑
                 │
           Data Connection
                 │
        File Upload/Download

17. Important FTP Terms

Term	Meaning
FTP	File Transfer Protocol
Client	Software/device requesting file services
Server	System providing file services
Upload	Client → Server
Download	Server → Client
Control Connection	Carries FTP commands/responses
Data Connection	Carries files/data
Port 21	Traditional FTP control connection
Active Mode	Server initiates data connection
Passive Mode	Client initiates data connection
Anonymous FTP	FTP access without a normal personal account
SFTP	SSH File Transfer Protocol
FTPS	FTP secured with TLS

18. Quick Revision

Remember these points:

FTP → File Transfer Protocol

Main purpose → Upload and download files

Architecture → Client-Server

Traditional control port → TCP 21

Two connections → Control + Data

Active FTP → Server establishes data connection

Passive FTP → Client establishes data connection

Traditional FTP → Not encrypted

SFTP → Secure file transfer over SSH

10-Mark Conclusion

File Transfer Protocol (FTP) is an application-layer protocol used to transfer files between a client and a server over a TCP/IP network. It supports operations such as uploading, downloading, renaming and deleting files. Traditional FTP uses a separate control connection, normally on TCP port 21, and a separate data connection for transferring files. FTP supports active and passive modes and can use authentication for controlled access. However, traditional FTP does not encrypt its communication, so secure alternatives such as SFTP or FTPS are preferred when security is important.