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?

The Basic Process

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://etechsupport.net/goodone.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:




Behind the Scenes

If you want to get into a bit more detail on the process of getting a Web page onto your computer screen, 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.etechsupport.net")
3. The file name ("goodone.htm")

  • The browser communicated with a name server to translate the server name "www.etechsupport.net" into an IP Address, which it uses to

    connect to the server machine.


  • 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. If you've never explored this process before, that's a lot of new vocabulary. To understand this whole process in detail, you need to learn about IP addresses, ports, protocols... etc


The Internet

So what is "the Internet"? The Internet is a gigantic collection of millions of computers, all linked together on a computer network. The network allows all of the computers to communicate with one another. A home computer may be linked to the Internet using a phone-line modem, DSL or cable modem that talks to an Internet service provider (ISP). A computer in a business or university will usually have a network interface card (NIC) that directly connects it to a local area network (LAN) inside the business. The business can then connect its LAN to an ISP using a high-speed phone line like a T1 line. A T1 line can handle approximately 1.5 million bits per second, while a normal phone line using a modem can typically handle 30,000 to 50,000 bits per second. ISPs then connect to larger ISPs, and the largest ISPs maintain fiber-optic "backbones" for an entire nation or region. Backbones around the world are connected through fiber-optic lines, undersea cables or satellite links. In this way, every computer on the Internet is connected to every other computer on the Internet.



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.

IP Addresses

To keep all of these machines straight, each machine on the Internet is assigned a unique address called an IP address. IP stands for Internet protocol, and these addresses are 32-bit numbers, normally expressed as four "octets" in a "dotted decimal number." A typical IP address looks like this: 66.94.234.13 The four numbers in an IP address are called octets because they can have values between 0 and 255, which is 28 possibilities per octet. Every machine on the Internet has a unique IP address. A server has a static IP address that does not change very often.

Domain Names

Because most people have trouble remembering the strings of numbers that make up IP addresses, and because IP addresses sometimes need to change, all servers on the Internet also have human-readable names, called domain names. For example, www.etechsupport.net is a permanent, human-readable name. It is easier for most of us to remember etechsupport.net than it is to remember 147.202.32.244

Name Servers

A set of servers called domain name servers (DNS) maps the human-readable names to the IP addresses. These servers are simple databases that map names to IP addresses, and they are distributed all over the Internet. Most individual companies, ISPs and universities maintain small name servers to map host names to IP addresses. If you type the URL http://etechsupport.net/goodone.htm" into your browser, your browser extracts the name "etechsupport.net," passes it to a domain name server, and the domain name server returns the correct IP address for etechsupport.net. A number of name servers may be involved to get the right IP address. For example, in the case of www.etechsupport.net, the name server for the "com" top-level domain will know the IP address for the name server that knows host names, and a separate query to that name server, operated by the etechsupport’s ISP, may deliver the actual IP address for the eTechSupport
server machine.

Hope this small explaination works for everybody.

Enjoy Learning ! ! !