Arguably, the most popular TCP/IP application today is the web browser. Many major software vendors either have already changed or are changing their software to support access from a web browser. And thankfully, using a web browser is easy—you start a web browser on your computer and select a web site by typing in the name of the web site, and the web page appears.
What really happens to allow that web page to appear on your web browser? These next few sections take a high-level look at what happens behind the scene.
Imagine that Bob opens his browser. His browser has been configured to automatically ask for web server Larry’s default web page, or home page.
So what really happened? Bob’s initial request actually asks Larry to send his home page back to Bob. Larry’s web server software has been configured to know that Larry’s default web page is contained in a file called home.htm. Bob receives the file from Larry and displays the contents of the file in the web browser window.
Taking a closer look, this example uses two TCP/IP application layer protocols. First, the request for the file and the actual transfer of the file are performed according to the Hypertext Transfer Protocol (HTTP). Many of you have probably noticed that most web sites’ URLs (Universal Resource Locators, the text that identifies a web server and a particular web page) begin with the letters “http,” to imply that HTTP will be used to transfer the web pages.
The other protocol used is the Hypertext Markup Language (HTML). HTML defines how Bob’s web browser should interpret the text inside the file he just received. For instance, the file might contain directions about making certain text be a certain size, color, and so on. In most cases, it also includes directions about other files that Bob’s web browser should get— things such as graphics images and animation. HTTP would then be used to get those additional files from Larry, the web server.
What really happens to allow that web page to appear on your web browser? These next few sections take a high-level look at what happens behind the scene.
Imagine that Bob opens his browser. His browser has been configured to automatically ask for web server Larry’s default web page, or home page.
So what really happened? Bob’s initial request actually asks Larry to send his home page back to Bob. Larry’s web server software has been configured to know that Larry’s default web page is contained in a file called home.htm. Bob receives the file from Larry and displays the contents of the file in the web browser window.
Taking a closer look, this example uses two TCP/IP application layer protocols. First, the request for the file and the actual transfer of the file are performed according to the Hypertext Transfer Protocol (HTTP). Many of you have probably noticed that most web sites’ URLs (Universal Resource Locators, the text that identifies a web server and a particular web page) begin with the letters “http,” to imply that HTTP will be used to transfer the web pages.
The other protocol used is the Hypertext Markup Language (HTML). HTML defines how Bob’s web browser should interpret the text inside the file he just received. For instance, the file might contain directions about making certain text be a certain size, color, and so on. In most cases, it also includes directions about other files that Bob’s web browser should get— things such as graphics images and animation. HTTP would then be used to get those additional files from Larry, the web server.