File Transfer Protocol (FTP): Working, Types, Modes, Advantages & Applications

Introduction

File Transfer Protocol (FTP) is a standard communication protocol used to transfer files between a client and a server over a computer network. FTP works on a client–server model and uses separate control and data connections. Users authenticate using a username and password, although anonymous access is also possible if allowed by the server.

FTP can be secured using SSL/TLS (FTPS) or replaced by SFTP (SSH File Transfer Protocol), which encrypts both credentials and content. Early FTP clients were command-line tools, still available on Windows, Linux, and Unix systems. Today, many graphical FTP clients, mobile applications, server tools, and automation utilities are widely used. FTP is also integrated into file managers and HTML editors.

Types of File Transfer Protocol

1. HTTP

HTTP (Hypertext Transfer Protocol) is widely used for transferring files, especially in client-to-server and client-to-client communication. However, HTTP does not offer strong security and is unsuitable for sensitive data.

2. FTPS

FTPS (FTP Secure) is similar to HTTPS and uses TLS/SSL for encryption. It ensures secure communication between businesses, partners, and customers. Client certificates and server authentication enhance its reliability.

3. HTTPS

HTTPS (Hypertext Transfer Protocol Secure) is commonly used for encrypted communication between websites and browsers. It is essential for transferring sensitive information such as bank or healthcare data.

4. SFTP

SFTP (SSH File Transfer Protocol) runs over SSH and provides strong encryption, authentication, and integrity protection. It has largely replaced FTP and FTPS due to its simplicity and enhanced security.

5. SCP

SCP (Secure Copy Protocol) is an older SSH-based file transfer method. It is used mainly for compatibility with legacy SSH servers, as SFTP offers more features.

6. WebDAVS

WebDAVS is a secure version of WebDAV that uses HTTPS. It inherits SSL-based security features for safe data transfer.

7. TFTP

TFTP (Trivial File Transfer Protocol) is used for network management tasks such as booting devices, backing up configurations, and installing operating systems. It is lightweight but not secure.

8. AS2

AS2 (Applicability Statement 2) is used for secure Electronic Data Interchange (EDI) in industries like manufacturing, retail, and healthcare.

9. OFTP

OFTP (Odette File Transfer Protocol) is widely used in Europe for secure EDI-based B2B transactions. It supports electronic delivery receipts and high security.

10. AFTP

AFTP (Accelerated File Transfer Protocol) improves transfer speeds over high-latency networks. It can achieve speeds up to 100 times faster than FTP.

How FTP Works?

An FTP connection is established between two systems over a network. Users authenticate using credentials or anonymous login.

Two types of channels are created:

• Command Channel: For sending commands and receiving responses (uses port 21).
• Data Channel: For actual file transfer (uses port 20).

FTP uses NVT ASCII for control communication, similar to SMTP and TELNET. Once authentication is successful, the client can upload, download, list, or manage files on the server.

Control Connection

The control connection handles user authentication, directory navigation, and commands. It remains open throughout the session.

• Uses server port 21
• Allows one command and one response at a time
• Connects control processes of client and server

Data Connection

The data connection handles the actual transfer of files. It is opened and closed for each file being transferred.

• Uses server port 20
• Transfers file data based on commands sent via the control connection
• Requires specification of file type, structure, and transmission mode

FTP Transmission Modes

FTP supports three transmission modes:

1. Stream Mode

Default mode. Data is sent as a continuous stream of bytes. TCP handles segmentation. The connection closes automatically when all data is transferred.

2. Block Mode

Data is sent in blocks, each with a 3-byte header. Useful for structured data transfers.

3. Compressed Mode

Used for large file transfers where data compression reduces file size and improves transfer efficiency.

Advantages of FTP

• High speed – One of the fastest methods of transferring files.
• Efficient – Reduces overhead by simplifying file operations.
• Secure (when using credentials) – Username and password provide access control.
• Supports two-way transfer – Files can be uploaded and downloaded easily.

Disadvantages of FTP

• Not all FTP providers offer encryption; this must be ensured manually.
• Maximum file size supported is typically 2GB.
• Passwords and file contents in basic FTP are sent in clear text.
• Susceptible to brute-force attacks without strong security.
• Not compatible with all operating systems.

Applications of FTP

• Used for daily business file transfers (B2B, peer-to-peer)
• File sharing across branches and remote offices
• Secure file transfers between teams and clients
• IT teams use it for backup and disaster recovery operations
• Web developers use FTP to upload website content
• Used in industries such as construction, engineering, media, consulting, and finance