2.3 The Network: Information Transfer 2.4 Hosting a web site
2.1 Internet Architecture: The Life Cycle Approach
A worldwide system of interconnected computer networks. The origins of the Internet can be traced to the creation of ARPANET (Advanced Research Projects Agency Network) as a network of computers under the auspices of the U.S.
Department of Defense in 1969. Today, the Internet connects millions of computers around the world in a nonhierarchical manner unprecedented in the history of communications. The Internet is a product of the convergence of media, computers, and telecommunications. It is not merely a technological development but the product of social and political processes, involving both the academic world and the government (the Department of Defense). From its origins in a nonindustrial, non- corporate environment and in a purely scientific culture, it has quickly diffused into the world of commerce.
The Internet is a combination of several media technologies and an electronic version of newspapers, magazines, books, catalogs, bulletin boards, and much more. This versatility gives the Internet its power.
Technological features
The Internet 'Ls technological success depends on its principal communication tools, the Transmission Control Protocol (TCP) and the Internet Protocol (IP). They are referred to frequently as TCP/IP. A protocol is an agreed-upon set of conventions that defines the rules of communication. TCP breaks down and reassembles packets, whereas IP is responsible for ensuring that the packets are sent to the right destination.
Data travels across the Internet through several levels of networks until it reaches its destination.
E-mail messages arrive at the mail server (similar to the local post office) from a remote personal computer connected by a modem, or a node on a local-area network. From the server, the messages pass through a router, a special purpose computer ensuring that each message is sent to
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its correct destination. A message may pass through several networks to reach its destination.
Each network has its own router that determines how best to move the message closer to its destination, taking into account the traffic on the network. A message passes from one network to the next, until it arrives at the destination network, from where it can be sent to the recipient, who has a mailbox on that network.
TCP/IP
TCP/IP is a set of protocols developed to allow cooperating computers to share resources across the networks. The TCP/IP establishes the standards and rules by which messages are sent through the networks. The most important traditional TCP/IP services are file transfer, remote login, and mail transfer.
The file transfer protocol (FTP) allows a user on any computer to get files from another computer, or to send files to another computer. Security is handled by requiring the user to specify a user name and password for the other computer.
The network terminal protocol (TELNET) allows a user to log in on any other computer on the network. The user starts a remote session by specifying a computer to connect to. From that time until the end of the session, anything the user types is sent to the other computer. Mail transfer allows a user to send messages to users on other computers.
Originally, people tended to use only one or two specific computers. They would maintain ―mail files‖ on those machines. The computer mail system is simply a way for a user to add a message to another user's mail file.
Other services have also become important: resource sharing, diskless workstations, computer conferencing, transaction processing, security, multimedia access, and directory services.
TCP is responsible for breaking up the message into datagrams, reassembling the datagrams at the other end, resending anything that gets lost, and putting things back in the right order. IP is responsible for routing individual datagrams. The datagrams are individually identified by a unique sequence number to facilitate reassembly in the correct order. The whole process of transmission is done through the use of routers. Routing is the process by which two communication stations find and use the optimum path across any network of any complexity.
Routers must support fragmentation, the ability to subdivide received information into smaller units where this is required to match the underlying network technology. Routers operate by
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recognizing that a particular network number relates to a specific area within the interconnected networks. They keep track of the numbers throughout the entire process.
Domain Name System
The addressing system on the Internet generates IP addresses, which are usually indicated by numbers such as 128.201.86.290. Since such numbers are difficult to remember, a user-friendly system has been created known as the Domain Name System (DNS). This system provides the mnemonic equivalent of a numeric IP address and further ensures that every site on the Internet has a unique address. For example, an Internet address might appear as crito.uci.edu. If this address is accessed through a Web browser, it is referred to as a URL (Uniform Resource Locator), and the full URL will appear as http://www.crito.uci.edu.
The Domain Name System divides the Internet into a series of component networks called domains that enable e-mail (and other files) to be sent across the entire Internet. Each site attached to the Internet belongs to one of the domains.
Universities, for example, belong to the ―edu‖ domain. Other domains are gov (government), com (commercial organizations), mil (military), net (network service providers), and org (nonprofit organizations).
World Wide Web
The World Wide Web (WWW) is based on technology called hypertext. The Web may be thought of as a very large subset of the Internet, consisting of hypertext and hypermedia documents. A hypertext document is a document that has a reference (or link) to another hypertext document, which may be on the same computer or in a different computer that may be located anywhere in the world. Hypermedia is a similar concept except that it provides links to graphic, sound, and video files in addition to text files.
In order for the Web to work, every client must be able to display every document from any server. This is accomplished by imposing a set of standards known as a protocol to govern the way that data are transmitted across the Web.
Thus data travel from client to server and back through a protocol known as the HyperText Transfer Protocol (http). In order to access the documents that are transmitted through this protocol, a special program known as a browser is required, which browses the Web. See also
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World Wide Web.
Commerce on the Internet
Commerce on the Internet is known by a few other names, such as e-business, Etailing (electronic retailing), and e-commerce. The strengths of e-business depend on the strengths of the Internet. Internet commerce is divided into two major segments, companies that have started their businesses on the Internet, and others that have existed previously and are now transitioning into the Internet world. Some products and services, such as books, compact disks (CDs), computer software, and airline tickets, seem to be particularly suited for online business.
World Wide Web : A major service on the Internet. To understand exactly how the Web relates to the Internet, see Web vs. Internet. The World Wide Web is made up of "Web servers" that store and disseminate "Web pages," which are "rich" documents that contain text, graphics, animations and videos to anyone with an Internet connection.
The heart of the Web technology is the hyperlink, which connects each document to each other by its "URL" address, whether locally or in another country.
"Click here" caused the Web to explode in the mid-1990s, turning the Internet into the largest shopping mall and information source in the world. It also enabled the concept of a "global server" that provides a source for all applications and data.
The Browser
Web pages are accessed by the user via a Web browser application such as Internet Explorer, Netscape, Safari, Opera and Firefox. The browser renders the pages on screen, executes embedded scripts and automatically invokes additional software as needed. For example, animations and special effects are provided by browser plug-ins, and audio and video are played by media player software that either comes with the operating system or from a third party.
HTML Is the Format
A Web page is a text document embedded with HTML tags that define how the text is rendered on screen. Web pages can be created with any text editor or word processor. They are also created in HTML authoring programs that provide a graphical interface for designing the layout.
Authoring programs generate the HTML tags behind the scenes, but the tags can be edited if required. Many applications export documents directly to HTML, thus basic Web pages can be
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created in numerous ways without HTML coding. The ease of page creation helped fuel the Web's growth. A collection of Web pages makes up a Web site. Very large organizations deploy their Web sites on in-house servers or on their own servers co-located in a third party facility that provides power and Internet access. Small to medium sites are generally hosted by Internet service providers (ISPs). Millions of people have developed their own mini Web sites as ISPs typically host a small number of personal Web pages at no extra cost to individual customers.
The public Web spawned the private "intranet," an inhouse Web site for employees. Protected via a firewall that lets employees access the Internet, the firewall restricts uninvited users from coming in and viewing internal information.
There is no difference in intranet and Web architectures. It has only to do with who has access.
HTTP Can Deliver Anything HTML pages are transmitted to the user via the HTTP protocol. A Web server stores HTML pages for a Web site, but it can also be a storehouse for any kind of file delivered to a client application via HTTP. For example, the Windows version of this Encyclopedia is available as an HTTP application. The text and images are hosted on The Computer Language Company's Web server and delivered to the Windows client in the user's PC. The Windows client is an HTTP-enabled version of the popular interface first introduced in 1996 for stand-alone PCs and client/server LANs.
Where It Came From - Where It's Going
The World Wide Web was developed at the European Organization for Nuclear Research (CERN) in Geneva from a proposal by Tim Berners-Lee in 1989. It was created to share research information on nuclear physics. In 1991, the first command line browser was introduced. By the start of 1993, there were 50 Web servers, and the Voila X Window browser provided the first graphical capability. In that same year,
CERN introduced its Macintosh browser, and the National Center for Supercomputing Applications (NCSA) in Chicago introduced the X Window version of Mosaic. Mosaic was developed by Marc Andreessen, who later became world famous as a principal at Netscape.
By 1994, there were approximately 500 Web sites, and, by the start of 1995, nearly 10,000. By the turn of the century, there were more than 30 million registered domain names. Many believe the Web signified the real beginning of the information age. However, those people who still use
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analog dial-up modems consider it the "World Wide Wait."
Everyone has some interest in the Web. ISPs, cable and telephone companies want to give you connectivity. Webmasters want more visitors. IT managers want more security. The publishing industry wants to preserve its copyrights. Hardware and software vendors want to make every product Web accessible. Nothing in the computer/communications field ever came onto the scene with such intensity. Even with the dot-com crash of 2000/2001, the future of the Web is going to be very exciting. Stay tuned! See Web 2.0, Internet, HTTP, HTML, World Wide Wait and Wild Wooly Web.