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Browsing Basics

Browsing Basics

 

When you type in a URL (Uniform Resource Locater)/web address into your browser, and instruct your browser to display the content that URL points to, a few things occur before the page shows up on your screen.  There are two scenarios to look at.

1.)  Cached - Your computer (using TCP/IP) queries the ISP's DNS Server(s) basically asking "What is the IP address associated with www.yahoo.com?".  The DNS server returns the requested IP address to your computer, which then contacts the supplied IP address, downloads the content located at that IP address, and displays it in your browser (illustrated below).

2.) Un-Cached - Your computer queries the ISP's DNS Server(s) asking the same question.  In this scenario, the DNS server doesn't have a correct record of what IP address(es) associate to www.yahoo.com, so it queries a Root Server (a server that maintains a database listing of domain names, and IP addresses associate with those domain names) for the information.  The Root server returns the requested data to the DNS server, which then contacts www.yahoo.com, and pulls more information directly (zone information, mx info, etc.).  Once that is done, the DNS server then returns your computer's query, the site's IP is contacted, and browsing continues as normal.

 



URL Breakdown

 

URL stands for Uniform Resource Locater. The URL specifies the Internet address of a file stored on a host computer connected to the Internet. Every file on the Internet, no matter what its access protocol, has a unique URL. Web browsers use the URL to retrieve the file from the host computer and the specific directory in which it resides. This file is downloaded to the user's client computer and displayed on the monitor connected to the machine.

URLs are translated into numeric addresses using the Domain Name System (DNS). The DNS is a worldwide system of servers that stores location pointers to Web sites. The numeric address, called the IP (Internet Protocol) address, is actually the "real" URL. Since numeric strings are difficult for humans to use, alphneumeric addresses are employed by end users. Once the translation is made by the DNS, the browser can contact the Web server and ask for a specific file located on its site.

It's important, at this point, to note that, on the ensim servers, web content is stored in a wwwroot folder on the server.  This can be illustrated by the following example:  When you browse to http://tomg.ruraltel.net , The server hosting the site (in this case, ensim2) loads the index.html file located in the wwwroot directory for tomg.  To further illustrate this in reference to URL's, browsing to http://tomg.ruraltel.net/idesk will result in the server accessing first the wwwroot directory for tomg to make sure that the idesk subdirectory exists, then it will query the idesk directory for an index.html, default.html, or other web content.

Anatomy of a URL

This is the format of a typical URL:

protocol://host/path/filename.extension

For example, this is a URL on the website of the U.S. House of Representatives:

http://www.house.gov/house/2004_House_Calendar.html

 

The structure of this URL is as follows:

  1. Protocol: http
  2. Host computer name: www
  3. Second-level domain name: house
  4. Top-level domain name: gov
  5. Directory name: house
  6. File name: 2004_House_Calendar.html

Note how much information about the content of the file is present in this well-constructed URL.

Other examples:

telnet://locis.loc.gov - the catalog of the Library of Congress

ftp://ftp.sunsite.auc.dk/projects/cgfa/picasso/p-picasso11.jpg  - a file on an ftp site.

Several top-level domains (TLDs) are common in the United States :

com

commercial enterprise

edu

educational institution

gov

U.S. government entity

mil

U.S. military entity

net

network access provider

org

usually non-profit organizations

New domain names were approved in November 2000 by the Internet Corporation for Assigned Names and Numbers (ICANN): .biz, .museum, .info, .pro (for professionals) .name (for individuals), .aero (for the aerospace industry), and .coop (for cooperatives). ICANN continues to investigate proposals for addding additional domain names, for example, .mobi for sites designed for mobile devices, and .jobs for the human resources community.

In addition, dozens of domain names have been assigned to identify and locate files stored on host computers in countries around the world. These are referred to as two-letter Internet country codes, and have been standardized by the International Standards Organization as ISO 3166. For example:

ch

Switzerland

de

Germany

jp

Japan

uk

United Kingdom

As the technology of the Web evolves, URLs have become more complex. This is especially the case when content is retrieved from databases and served onto Web pages. The resulting URLs can have a variety of elaborate structures, for example,

http://spills.incidentnews.gov/incidentnews/FMPro?-db=images&-Format=maps.htm&SpillLink=8&Subj
ect=Waterway%20Closure%20Map&-SortField=EntryDate&-SortOrder=descend&-SortField=EntryTime&
-SortOrder= descend &-Token=8&-Max=20&-Find

The first part of this URL looks familiar. What follows are search elements that query the database and determine the order of the results. As a growing number of databases serve content to the Web, these types of URLs will appear more commonly in your browser's address window.