Web Page Delivery

Have you ever wondered about the mechanisms that delivered this page to you? Chances are you are sitting at a computer right now, viewing this page in a browser -- so when you clicked on the link for this page, or typed in its URL (uniform resource locator), what happened behind the scenes to bring this page onto your screen?

Let's say that you are sitting at your computer, surfing the Web, and you get a call from a friend who says, "I just read a great article! Type in this URL and check it out! It's at http://computer.howstuffworks.com/web-server.htm." So you type that URL into your browser and press return. And magically, no matter where in the world that URL lives, the page pops up on your screen!

At the most basic level possible, the following diagram shows the steps that brought that page to your screen:

Your browser formed a connection to a Web server, requested a page and received it. If you want to get into a bit more detail, here are the basic steps that occurred behind the scenes:

• The browser broke the URL into three parts:
1. The protocol ("http")
2. The server name ("www.howstuffworks.com")
3. The file name ("web-server.htm")
• The browser communicated with a name server to translate the server name "www.howstuffworks.com" into an IP Address, which it uses to connect to the server machine.
• The browser then formed a connection to the server at that IP address on port 80. (We'll discuss ports later in this article.)
• Following the HTTP protocol, the browser sent a GET request to the server, asking for the file "http://computer.howstuffworks.com/web-server.htm." (Note that cookies may be sent from browser to server with the GET request). The server then sent the HTML text for the Web page to the browser. (Cookies may also be sent from server to browser in the header for the page.)
• The browser read the HTML tags and formatted the page onto your screen.

Clients and Servers
In general, all of the machines on the Internet can be categorized as two types: servers and clients. Those machines that provide services (like Web servers or FTP servers) to other machines are servers. And the machines that are used to connect to those services are clients. When you connect to Yahoo! at www.yahoo.com to read a page, Yahoo! is providing a machine (probably a cluster of very large machines), for use on the Internet, to service your request. Yahoo! is providing a server. Your machine, on the other hand, is probably providing no services to anyone else on the Internet. Therefore, it is a user machine, also known as a client. It is possible and common for a machine to be both a server and a client, but for our purposes here you can think of most machines as one or the other.

A server machine may provide one or more services on the Internet. For example, a server machine might have software running on it that allows it to act as a Web server, an e-mail server and an FTP server. Clients that come to a server machine do so with a specific intent, so clients direct their requests to a specific software server running on the overall server machine. For example, if you are running a Web browser on your machine, it will most likely want to talk to the Web server on the server machine. Your Telnet application will want to talk to the Telnet server, your e-mail application will talk to the e-mail server, and so on...

Questions:

1. What does URL stand for and where would you type it in to bring up a web site?

2. What do you have to connect to through your browser at home to receive the information for a website?

3. What three parts does the web server break the URL into?

4. What does the browser have to do to the server name to connect to the server machine?

5. What type of request does the browser have to send the server to get the file from the server and what can be sent to the server from the browser with this request?

6. What are the general names for the two type of computers used on the internet?

7. How do these computers interact with each other?

8. When providers such as Yahoo! have a server, does it consist of just one server or many servers, why?

9. How do you think web servers will change and advance in the future?