Internet

I

Introduction

Internet, computer-based global information system. The Internet is composed of many interconnected computer networks. Each network may link tens, hundreds, or even thousands of computers, enabling them to share information and processing power. The Internet has made it possible for people all over the world to communicate with one another effectively and inexpensively. Unlike traditional broadcasting media, such as radio and television, the Internet does not have a centralized distribution system. Instead, an individual who has Internet access can communicate directly with anyone else on the Internet, post information for general consumption, retrieve information, use distant applications and services, or buy and sell products.

The Internet has brought new opportunities to government, business, and education. Governments use the Internet for internal communication, distribution of information, and automated tax processing. In addition to offering goods and services online to customers, businesses use the Internet to interact with other businesses. Many individuals use the Internet for communicating through electronic mail (e-mail), retrieving news, researching information, shopping, paying bills, banking, listening to music, watching videos, playing games, and making telephone calls. Educational institutions use the Internet for research and to deliver online courses and course material to students.

Use of the Internet has grown tremendously since its inception. The Internet’s success arises from its flexibility. Instead of restricting component networks to a particular manufacturer or particular type, Internet technology allows interconnection of any kind of computer network. No network is too large or too small, too fast or too slow to be interconnected. Thus, the Internet includes inexpensive networks that can only connect a few computers within a single room as well as expensive networks that can span a continent and connect thousands of computers. See Local Area Network.

Internet service providers (ISPs) provide Internet access to customers, usually for a monthly fee. A customer who subscribes to an ISP’s service uses the ISP’s network to access the Internet. The networks operated by ISPs are known as public access networks because they are offered to the general public. In the United Kingdom, as in many countries, ISPs are private companies; in countries where the telephone service is a government-regulated monopoly, the government often controls ISPs.

An organization that has many computers usually owns and operates a private network, called an intranet, which connects all the computers within the organization. To provide an Internet service, the organization connects its intranet to the Internet. Unlike public access networks, intranets are restricted to provide security. Only authorized computers at the organization can connect to the intranet, and the organization restricts communication between the intranet and the global Internet. The restrictions allow computers inside the organization to exchange information but keep the information confidential and protected from outsiders.

The Internet has doubled in size every 9 to 14 months since its inception in the late 1970s. In 1981 only 213 computers were connected to the Internet. By 2000 the number had grown to more than 400 million. By 2007 there were more than a billion Internet users worldwide.

II

Uses of the Internet

Before the Internet was created, the US army had developed and deployed communications networks, including a network known as ARPANET. Uses of the networks were restricted to army personnel and the researchers who developed the technology. Many people regard the ARPANET as the precursor of the Internet. From the 1970s until the late 1980s the Internet was a US government-funded communication and research tool restricted almost exclusively to academic and military uses. It was administered by the National Science Foundation (NSF). At universities, only a handful of researchers working on Internet research had access. In the 1980s the NSF developed an “acceptable use policy” that relaxed restrictions and allowed staff at universities to use the Internet for academic activities. However, the NSF policy prohibited all commercial use of the Internet. Under this policy advertising did not appear on the Internet, and people could not charge for access to content or sell products or services.

By 1995, however, the NSF had ceased its administration of the Internet. The Internet was privatized, and commercial use was permitted. This move coincided with the growth in popularity of the World Wide Web (WWW), which was developed by the British physicist and computer scientist Tim Berners-Lee. The Web replaced file transfer as the application used for most Internet traffic. The difference between the Internet and the Web is similar to the distinction between a road system and a courier delivery service that uses the roads to move cargo from one place to another: the Internet is the road system over which Web traffic and traffic from other applications move. The Web consists of programs running on many computers that allow a user to find and display multimedia documents (documents that contain a combination of text, photographs, graphics, audio, and video). Many analysts attribute the explosion in use and popularity of the Internet to the visual nature of Web documents, and Web traffic now dominates the Internet.

Companies, individuals, and institutions use the Internet in many ways. Companies use the Internet for electronic commerce, also called e-commerce, including advertising, selling, buying, distributing products, and providing customer service. In addition, companies use the Internet for business-to-business transactions, such as exchanging financial information and accessing complex databases. Businesses and institutions use the Internet for voice and video conferencing and other forms of communication that enable people to telecommute (work away from the office using a computer). The use of e-mail speeds communication between companies, among co-workers, and among other individuals. Media and entertainment companies run online news and weather services over the Internet, distribute music and films, and broadcast audio and video, including live radio and television programmes. File-sharing services let individuals swap music, films, photos, and applications. Online chat allows people to carry on discussions using written text. Instant messaging enables people to exchange text messages; share digital photo, video, and audio files; and play games in real time. Scientists and academics use the Internet to communicate with colleagues, perform research, distribute lecture notes and course materials to students, and publish papers and articles. Individuals use the Internet for communication, entertainment, finding information, and buying and selling goods and services.

III

How the Internet Works

A

Internet Access

The term Internet access refers to the communication between a residence or a business and an ISP that connects to the Internet. Access falls into three broad categories: dedicated, dial-up, and wireless. With dedicated access, a subscriber’s computer remains directly connected to the Internet at all times through a permanent, physical connection. Most large businesses have high-capacity dedicated connections; small businesses or individuals that desire dedicated access choose technologies such as digital subscriber line (DSL) or cable modems, which both use existing wiring to lower cost. A DSL sends data across the same wires that the telephone service uses, and cable modems use the same wiring as cable television. In each case, the electronic devices that are used to send data employ separate frequencies or channels that do not interfere with other signals on the wires. Thus, a DSL Internet connection can send data over a pair of wires while the wires are being used simultaneously for a telephone call, and cable modems can send data via a cable that is already being used to receive television signals. Another, less-popular option is satellite Internet access, in which a computer grabs an Internet signal from orbiting satellites via an outdoor satellite dish. The user usually pays a fixed monthly fee for a dedicated connection. In exchange, the company providing the connection agrees to relay data between the user’s computer and the Internet.

Dial-up is the least expensive access technology, but it is also the least convenient. To use dial-up access, a subscriber must have a telephone modem, a device that connects a computer to the telephone system and is capable of converting data into sounds and sounds back into data. The user’s ISP provides software that controls the modem. To access the Internet, the user opens the software application, which causes the dial-up modem to place a telephone call to the ISP. A modem at the ISP answers the call, and the two modems use audible tones to send data in both directions. When one of the modems is given data to send, the modem converts the data from the digital values used by computers—numbers stored as a sequence of 1s and 0s—into tones. The receiving side converts the tones back into digital values. Unlike dedicated access technologies, a dial-up modem does not use separate frequencies, so the telephone line cannot be used for voice calls while the dial-up modem is sending data.

B

How Information Travels Over the Internet

All information is transmitted across the Internet in small units of data called packets. Software on the sending computer divides a large document into many packets for transmission; software on the receiving computer regroups incoming packets into the original document. Similar to a postcard, each packet has two parts: a packet header specifying the computer to which the packet should be delivered, and a packet payload containing the data being sent. The header also specifies how the data in the packet should be combined with the data in other packets by recording which piece of a document is contained in the packet.

A series of rules known as computer communication protocols specify how packet headers are formed and how packets are processed. The set of protocols used for the Internet is named TCP/IP after the two most important protocols in the set: the Transmission Control Protocol and the Internet Protocol. TCP/IP protocols enable the Internet to detect and correct transmission problems automatically. For example, if any network or device malfunctions, protocols detect the failure and automatically find an alternative path for packets in order to avoid the malfunction. Protocol software also ensures that data arrives complete and intact. If any packets are missing or damaged, protocol software on the receiving computer requests for the source to resend them. Only when the data has arrived correctly does the protocol software make it available to the receiving application program, and therefore to the user.

Hardware devices that connect networks over the Internet are called IP routers because they follow the IP protocol when forwarding packets. A router examines the header in each packet that arrives to determine the packet’s destination. The router either delivers the packet to the destination computer across a local network or forwards the packet to another router that is closer to the final destination. Thus, a packet travels from router to router as it passes through the Internet. In some cases, a router can deliver packets across a local area wireless network, allowing desktop and laptop computers to access the Internet without the use of cables or wires. Today’s business and home wireless local area networks (LANs), which operate according to a family of wireless protocols known as Wi-Fi, are fast enough to deliver Internet feeds as quickly as wired LANs.

Increasingly, mobile phone and handheld computer users are also accessing the Internet through wireless cellular telephone networks. Although handheld devices, equipped with much smaller screens and displays, are more difficult to use than full-sized computers, with wide area wireless, users can access the Internet on the go and in places where access is otherwise impossible. Initially such wide area wireless access was much slower than high-capacity dedicated, or broadband, access, or dial-up access. However, third generation (3G) cellular networks, first introduced in Japan in 2001, provide wide area Internet access at DSL-like speeds.