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- 25 January, 2012 -
- beginner -
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How the Internet Works
Take a look at the diagram below and read through the notes so you understand how the internet works. (Note that “Client” refers to the computer where the web page is viewed…)
Servers
The Server is where the web site files live. The web server software runs on the server machine, responding to client requests by sending files back to the client. The server also processes CGI (Common Gateway Interface) requests, runs programs, and accesses databases.
- Server software runs on the server machine
- The web site files are on a hard disk attached to the server
- The server software formats and delivers each web page element based on HTTP requests
- Elements are delivered to many clients at the same time
- A “hit” indicates that one element (not a page!) was delivered (e.g. an image)
- A web page is composed of many elements, therefore each page accessed generates many hits
- Hits vs. page visits vs. site visit
Clients
The client is the computer where the web page is viewed. The browser software runs on the Client computer and sends requests to the Server computer. When the client receives files from the server, the Client assembles the web page and displays it.
- The web browser runs on the client
- The client requests elements from the server
- It receives and “parses” the elements delivered by the server
- First reads the HTML
- Formats the page, and displays the text
- Gets additional elements (images, audio, etc.) specified in the HTML
- Displays additional elements
- Manages the interactions with the user (e.g. forms, scrolling, image maps, etc.), minimizing the amount of work the server has to do
- Runs client-side software (JavaScript, Java, plug-ins)
Composition of a web page
A web page is composed of the following elements:
- The HTML file, which describes the page layout, defines links to other web pages, and contains the text for the page
- Elements that come from the same server where the HTML files is, or from a different server
- Image files (.gif, .jpg, .png)
- Audio files (.mp3, .au, .ram, .mov)
- Other multimedia objects (QuickTime movies, Flash, Real, etc.)
- JavaScript
See the links to the directories below for examples. Take a look and note the various elements that comprise the web pages. Notice all the HTML files. (.htm and .shtml files are also HTML files).
- Can you find the .jpg and .gifs images? Where are they located?
- What about the Flash files… they end in .swf and only one of the directories below contain Flash files. Do you know which one?
- Do you know what a .css file is? A CSS file stands for”Cascading Style Sheet” and we will talk about these later in the semester.
