1. HTTP and Abstraction on the Internet
Lesson 2-11
AP Computer Science Principles

2. Objectives Students will be able to:
Explain how layers of protocols allow the Internet to function.
Identify abstractions used in the development of Internet protocols.
Use developer tools in a modern browser to explore the HTTP traffic associated with visiting common websites.

3. Layers of the Internet The Internet is composed of many layers.
TCP defines how a large message is divided into many packets, which can be sent along different channels and reconstructed into the original message on arrival.
TCP
IP defines how packets of information are addressed and routed from one computer to another.
On the lowest level, the Internet is a physical network of copper wire, fiber-optic cable, and radio signals. IP
Physical Layer

4. Layers of the Internet
Each layer relies on those below it, but uses them "abstractly." To put it differently, higher- level layers depend on the functionality of lower- level layers, without worrying about precisely how those layers work.

5. HTTP
Today we will focus our attention on the next layer of protocols on the Internet.
They define how computers "talk" to one another on the Internet, allowing us to access web pages, images, music, and video.

6. HTTP
Remarkably, the conversations had by computers are conducted entirely in ASCII-text, which can easily be read by humans.
Thanks to the power of abstraction, they can rely on TCP/IP and the physical Internet to handle the details of this problem, and assume only that there is some reliable way for computers to send text back and forth.

7. Video
The Internet: HTML and HTTP Overview

8. Activity
Today we are going to investigate one of the protocols covered in this video, HTTP.
In order to see the way this system operates more clearly, we are going to actually watch the traffic of HTTP messages being sent by our web browsers.
This is a lot like reading the conversation between our computers and the computers that host the websites we all use.

9. Definitions - Static vs. Dynamic Web Pages
A static web page is a web page that is delivered to the user exactly as stored.
Static web page displays the same information for all users, from all contexts.
A dynamic web page is generated by a web application
Content varies by user.

10. Activity – Developer Tools - Chrome
On the top right…
Then click Network

11. Activity – Developer Tools - IE
On the top right…
Then click Network

12. Activity Guide
Complete the Worksheet - HTTP in Action

13. Stage 11
Complete Stage 11