Introduction to the Web Application Development Environment

Transmission, or How the Web Works

After the user has submitted whatever information they need to submit into whatever GUI you have designed, it is time to get that information from the web browser to the web server.

To do this, the information has to pass through the Communication Layer.

As you might imagine, there are a host of technologies which all poke their way into the Communication Layer. You'll hear terms like TCP/IP, OSI/ISO, HTTP, HTTP-S, SSL, etc. You'll also hear about technologies that modify the data in transmission such as encryption.

Whichever the case, the main idea that you should get used to when thinking about the Communication Layer is that information needs to get from one place to another and that data needs to get there in one piece, in the right order, and with no parts of that data changed or corrupted. In addition, the information could/should be transferred securely. That is, it should go from one place to another without anyone being able to read it, change it, or fake authorship of it.

When we say that information must go from one place to another, we mean specifically, from one computer to another computer and more specifically, from one software program on one computer to another software program on another computer.

Since there are so many types of computers and so many software packages that must communicate, you can imagine that it all just works out to a mass of blabber.

Well, to prevent such chaos, and to make the web work, everyone (software and hardware) is required to follow very rigorous standards of communications called protocols. Protocols guarantee that each participant of the discussion can understand the other.

For the purposes of the web, there are three types of communications protocols we care about:

• Computer to computer communication - This is handled by the IP protocol.
• Encryption of plain text over the wires - This is handled by a motley of technologies but most commonly involve some form of public key encryption.
• Software to software communication - Generally, TCP will move data from the hardware level to the software level. Once the data has been moved to the software level, the software packages themselves will provide their own protocols for communication. In the realm of web serves and browsers, this is usually handled by HTTP or SSL in the case of encrypted communication.

Consider the following diagram in which hardware hosts open a TCP/IP connection to exchange data between software programs. Once the TCP/IP connection is opened, the software communicates via HTTP or SSL. The actual data exchanged may or may not be encrypted.

Let's take a deeper look into each of these basic technologies.

Contents:

The Basics of TCP/IP
Internet Protocol (IP)
Transmission Control Protocol (TCP)
HTTP
Additional Resources

Summing up
Introduction to the Web Application Development Environment (Tools)
The Basics of TCP/IP