Web Application Development - Lecture 2

Web Technology

We need to answer…
…How is the Internet organized?
…How do we find and retrieve pages on the Internet?
…How is this data (web pages, etc) transmitted over the Internet?
…How is what we see in the browser window defined as a collection of data?

The Web is a client/server application: Web browsers are clients which send requests to Web servers, which send responses back.

Fetching Pages over the Internet

Architecturally, the Internet consists of a collection of layers, each one providing services for the one above it:
The Internet Layer gets packets to their destinations;
The Transport Layer sends streams of data;
The Application Layer provides high-level services to applications such as Web browsers.

HTTP

HTTP makes use of TCP to open connections between clients and servers and to pass the requests and responses between them.
When a user clicks a link or types a web address:
A TCP connection is opened between browser and server
Then requests and responses are sent back and forth using HTTP
HTTP is a stateless protocol, meaning each request for data is dealt with in isolation; once the server sends the response, it forgets everything about the original request.