514.2 TCP/IP, FTP, and SFTP

Explore how web data is structured for transmission, and how file transfer protocols operate at different layers of the internet.

Overview

In this topic, we explore the TCP/IP model, which defines how data travels across the internet, from a user's browser to a web server and back again. Students also investigate file transfer protocols—FTP and SFTP—and learn how they function at different layers of the stack. This topic builds the foundation for understanding encryption, ports, and secure communication later in the module.

Targets

In this topic, students learn to:

• Describe the four layers of the TCP/IP model and their responsibilities

• Explain the difference between TCP and IP protocols

• Define what a port is and how protocols use them

• Compare FTP and SFTP, including their use cases and security features

• Understand how file transfer occurs between client and server

Syllabus references

Programming for the web

Data transmission using the web

• Investigate and describe the function of web protocols

  • TCP/IP

  • FTP, SFTP

The TCP/IP model

The TCP/IP model is a conceptual framework used to explain how data moves across networks. It consists of four layers:

Layer	Description
Application (5-7)	Interfaces with software like browsers and email clients (e.g. HTTP, FTP)
Transport (4)	Manages communication between devices and ensures complete delivery (e.g. TCP)
Network (3)	Routes packets across networks using IP addresses (e.g. IP)
Network Access (1-2)	Handles the physical transmission of data over wires or wireless signals

Each layer adds its own information to the packet, forming an encapsulation system that enables reliable communication. The table above includes numbers that represent the more detailed layers shown in the diagram below.

Each layer in the TCP/IP model handles a specific part of communication. Data is encapsulated at each step and unwrapped in reverse at the destination.

What is TCP?

TCP (Transmission Control Protocol) ensures that:

• Data is broken into packets

• Packets arrive in the correct order

• Lost or corrupted packets are resent

TCP is reliable and connection-oriented, used by most common applications like websites, email, and streaming.

What is IP?

IP (Internet Protocol) is responsible for:

• Addressing each device with an IP address

• Routing data between networks

• Making sure packets reach the correct destination

Together, TCP/IP makes the internet function.

What are ports?

Ports are numbered endpoints used to identify specific services running on a device.

• Port 80 is commonly used for HTTP

• Port 443 is used for HTTPS

• Port 21 is used for FTP

• Port 22 is used for SFTP and SSH

When a browser or client sends data to a server, it includes both the IP address and the port number so the server knows which application should receive the data. The combination of a port and an IP address is known as a socket. They ensure that server requests are received by the sending application on the client when several browser sessions or TCP/IP apps are running at once on the client.

File transfer protocols

FTP (File Transfer Protocol)

FTP is used to upload or download files between computers. It is:

• Easy to set up

• Useful for public file distribution

• Not secure – passwords and data are sent in plain text

SFTP (SSH File Transfer Protocol)

SFTP adds encryption and authentication. It:

• Uses the secure SSH protocol

• Encrypts all communication, including login credentials

• Is recommended for secure file handling over the internet

Unlike FTP, SFTP encrypts data and login credentials during transfer, making it safer for transmitting sensitive files.

Summary

The TCP/IP model explains how web communication works in layered steps, from software to network cable. It supports all major web protocols, including file transfer protocols like FTP and SFTP. While FTP is insecure, SFTP provides encrypted file handling and is better suited to modern secure systems.