Introduction to WWW [Ecommerce notes]

WWW : World Wide Wait ?  or World Wide Web ? Former one got famous during teething phase of www cloud due to bandwidth / technological constraints. To begin with, simple definition of WWW also known as web, " its global information space which people can communicate via computers connected to the Internet" . Some people use "internet" and "the web" interchangeably, even though the web is a service that operates over the internet. In this post, you will study about fundamentals of World Wide Web(WWW). The evolution of  WWW have been discussed in detail. Internet Basics including rise of internet, services provided by internet have been thoroughly discussed together with its technical bottle necks.  Topics covered: Understand fundaments of Word Wide Web Learn about the history of web and Internet Differentiate between WWW and Internet Understand how Internet Works Analyze the growth of Internet Understand web servers, web browser and various protocols that make Internet work  WORLD WIDE WEB FUNDAMENTALS   To begin with, simple definition of WWW also known as web, "WWW is a global information space where people can communicate via computers connected to the Internet". Some people use "internet" and "the web" interchangeably, even though the web is a service that operates over the internet. WWW is an acronym used for World Wide Web. Technically defining WWW can be understood as a system of Internet servers through which several Internet protocols can be accessed using a web browser. Precisely, WWW can be understood as the most commonly used services on the Internet.  Almost all protocols available on the Internet are available on the Web. This creates a convenient and user-friendly environment through which email, FTP, Telnet, Usenet News etc. can be accessed. Due to the ability of the Web to work with multimedia and advanced programming languages, the World Wide Web has been the fastest growing and the most interesting part of the Internet.   User uses a browser software like Internet Explorer, Netscape, Google chrome, mozilla, Firefox, etc to navigate the Web. WWW also makes valuable use of hypertext along with high quality graphics. As against text based services like FTP and telnet the Web is a graphic medium with most Web pages having some amount of images.Today we also have web pages that have sound and video embedded in them. WWW Protocol   Most famous and popular protocols on the web is the HyperText Transfer Protocol (HTTP). It is the application protocol that makes the web work.  It is an application level protocol as it just sits on top of the TCP layer in the protocol stack and is used by specific applications to talk to one another. In this case the applications are web browsers and web servers. These protocols are taken in detail in the discussions below.  Do not confuse HTTP with the Hypertext Markup Language (HTML). HTML is the scripting language used to create web pages. Many times web pages are called hyper text documents. Hyperit text documents are the document that contain links which connect them to other documents or files. The user can activate these links or 'hot spots' (through a mouse button click, for example) and the target document will then be transferred on to the client machine and if it is a web page, it would be displayed in the browser. These links can be placed on text, pictures etc in the hypertext document. A single HyperText document can contain many such hyperlinks. It is because of all this "linking" between the webpages a virtual web of connections is created.  Characteristics of HTTP HTTP is a connectionless text based protocol. Clients (web browsers) send requests to web servers for web elements such as web pages and images.  Before an HTTP request can be made by a client, a new connection must be made to the server.   After the request is serviced by a server, the connection between client and server across the Internet is disconnected. It is important to understand that a new connection is established between the client and the server each time when client makes a request. Note: Most protocols are connection oriented. This means that the two computers communicating with each other keep the connection open over the Internet. HTTP does not however. When you type a URL into a web browser HTTP will work as follows: 1. In case URL contains a domain name (like www.yahoo.com) the browser will first connect to a domain name server and retrieves the corresponding IP address for the web server.  URL can be understood as the   unique address of a file which can be accessed through internet.  Note:  URL has been taken in detail in a later sub-section. 2. The web browser connects to the web server and sends an HTTP request (via the protocol stack) for the desired web page. 3. The web server receives the request and checks for the desired page. If the page exists, the web server sends it. If the server cannot find the requested page, it will send an HTTP 404 error message. (404 mean 'Page Not Found' as anyone who has surfed the web probably knows.) 4. The web browser receives the page back and the connection is closed. The browser then parses through the page and looks for other page elements it needs to complete the web page. These usually include images, applets, etc. For each element needed, the browser makes additional connections and HTTP requests to the server for each element. Once the browser has finished loading all images, applets, etc. the page will be completely loaded in the browser window.   Internet Basics Basics dumb rule: No single person or entity owns internet, everyone uses internet! …there are millions of contributors and billions of users of Internet !! The Internet is a worldwide collection of computer networks. When user is surfing internet, he/she is part of a community of millions who use computers of communicate with one another and share ideas / information. Internet is also called as information superhighway or cyberspace. As you travel the highway, you will encounter many different information communities. Information and it's accessibility is actual treasure on the internet !! The Internet has revolutionized the computer and communications world like nothing before. The invention of the telegraph, telephone, radio, and computer set the stage for this unprecedented integration of capabilities. The Internet is at once a world-wide broadcasting capability, a mechanism for information dissemination, and a medium for collaboration and interaction between individuals and their computers without regard for geographic location. The Internet represents one of the most successful examples of the benefits of sustained investment and commitment to research and development of information infrastructure. Client/Server Model Internet is based upon client/server model. It basically contains two types of computers: Servers: Servers are computers which provide services or information required by other computers. Servers run special software called Web Server software to respond to client's request. You will learn about them in the later section of this unit.  Clients: Computers that request information from the server are called Clients. History In 1969, the department of Defence (DoD) of United States started a network called ARPANET (Advacnced Research Project Administration Network). It was an experiement carried out to reveal whether networking could be reliable. This network was setup for military to ensure that communication did not break down in the events of war.The DoD wanted to maintain contacts with military research contractors and universities in the event of war. The DoD also wanted these agencies to share software and hardware resources that they could not afford. Later, the military allowed universities to join the network. Students at these universities caught on to the network and developed much of the software that its present shape. APARNET quickly agree to emcompass the entire American continent and became a big success. Every university in the country wanted to be part of this cloud. To strcuture out things, network was diversified MILNET for managing military sites and APARNET for managing non military sites. Henceforth, it evolved into a huge network which is presently known as Internet. Growth of Internet •          Internet doubles each year •          Reasons for success: •          Decisions not politically based •          Internet is distributed in operations •          Open standards, free (or inexpensive) software •           Easy to operate Internet Protocols Internet Protocols (set of instructions) are used to transfer files or data from one machine to the other. All computers on the Internet communicate with each other using the Transmission Control Protocol / Internet Protocol (TCP/IP). Thus, data is sent from the server to the client (and vice-versa) using TCP/IP. Typically, the client is your browser and the server is a program running on a different computer. You use the browser on your computer (called the client machine in Internet lingo) to access the information on another computer (called the server machine). This server machine can be located thousands of miles from your workplace. There are many other protocols such as the File Transfer Protocol (FTP) used in FTP applications and the HyperText Transfer Protocol (HTTP) employed on the World Wide Web.   The File Transfer Protocol(FTP)   The File Transfer Protocol is an excellent method to transfer (download and send) files from one computer to the other on the Internet. Though you can transfer files using email, it is not a good choice especially when the file size is large or when you need to transfer several files. The objectives of FTP are to: ·             promote file (programs or data) sharing ·             efficiently transfer data from one computer to another ·             encourage indirect or implicit use of remote computers ·             provide a common platform for file storages among different hosts The HTTP - HyperText Transfer Protocol The HTTP provides a set of instructions for accurate information exchange. The communication between the client (your browser) and the server (a software located on a remote computer) involves requests sent by the client and responses from the server. The Telnet Protocol The Telnet protocol allows you to connect to another machine. Once connected, your computer behaves like a terminal of the distant machine and you can utilize all the resources on the remote system if you have the required permissions. Some older Internet protocols Protocols such as Gopher, Archie etc. were used extensively on the Internet. But now they have faded into oblivion; why? Thanks to the WWW. The Email Protocol Email is the most used application on the Internet. Emails allow users to communicate with each other almost instantly. Each email message consists of a header and a body. The header contains the following information: ·             Recipient email address ·             Senders email address ·             Email address of the people to whom a carbon copy (Cc) and blind carbon copy (Bcc) has been      sent. ·             The subject line ·             The main text message resides in the email body. The Way Internet Works The most peculiar thing about the Internet is the way data is transferred from one computer to another.   This is what happens to a piece of data (e.g. a Web page) when it is transferred over the Internet: It is broken up into a whole lot of same-sized pieces (called packets). A header is added to each packet. This header explains the source and destination of the packet. Also how it will fit among the rest of the packets. Each packet is sent from computer to computer until it finds its way to its destination. Each computer along the way decides where next to send the packet. This could depend on number of things like how busy the other computers are when the packet was received. It is quite possible that packets may not all take the same route. At the destination, the packets are examined. In case any packet is missing or damaged, a message is sent asking for those packets to be resent. This continues until all the packets have been received intact. The packets are reassembled into their original form.    Working of Internet Internet uses TCP/IP protocol for communication. TCP/IP (Transmission Control Protocol/Internet Protocol) specifies how computers connect, send, and receive information where as IP specifies how packets are routed between two computers. Message is split into IP packets which contain following information: •          Pieces of message •          Information about sender •          Information about receiver •          Sequence number •          Error checking information When the packet has been received by destination computer, it reassembles the message. In case any packet gets corrupted receiving computer sends request for corrupt packets back to the sender. Advantages of using packets can be summarized as follows: •          Error recovery •          Load distribution •          Flexibility