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.
C Network Names and Addresses
To be connected to the Internet, a computer must be assigned a unique number, known as its IP (Internet Protocol) address. Each packet sent over the Internet contains the IP address of the computer to which it is being sent. Intermediate routers use the address to determine how to forward the packet. Users almost never need to enter or view IP addresses directly. Instead, to make it easier for users, each computer is also assigned a domain name; protocol software automatically translates domain names into IP addresses. See Domain Name System.
Users encounter domain names when they use applications such as the World Wide Web. Each page of information on the Web is assigned a URL (Uniform Resource Locator) that includes the domain name of the computer on which the page is located. Other items in the URL give further details about the page. For example, the string http specifies that a browser should use the http protocol, one of many TCP/IP protocols, to fetch the item.
D Client/Server Architecture
Internet applications, such as the Web, are based on the concept of client/server architecture. In client/server architecture, some application programs act as information providers (servers), while other application programs act as information receivers (clients). The client/server architecture is not one-to-one. That is, a single client can access many different servers, and a single server can be accessed by a number of different clients. Usually, a user runs a client application, such as a Web browser, that contacts one server at a time to obtain information. Client software can run on almost any computer, including small handheld devices such as personal organizers and mobile phones, because it only needs to access one server at a time. To supply information to others, a computer must run a server application. Although server software can run on any computer, most companies choose large, powerful computers to run server software because the company expects many clients to be in contact with its server at any given time. A faster computer enables the server program to return information with less delay.
E Electronic Mail
Electronic mail, or e-mail, is a widely used Internet application that enables individuals or groups of individuals to exchange messages quickly, even if they are separated by long distances. A user creates an e-mail message and specifies a recipient using an e-mail address, which is a string consisting of the recipient’s login name followed by an @ (at) sign and then a domain name. E-mail software transfers the message across the Internet to the recipient’s computer, or to a remote server, where it is placed in the specified mailbox. The recipient uses an e-mail application to view and reply to the message, as well as to save or delete it. E-mail is a convenient and inexpensive form of communication, which has dramatically improved personal and business communication.
In its original form, e-mail could only be sent to recipients named by the sender, and only text messages could be sent. E-mail has been extended in two ways, and is now a much more powerful tool. Software has been invented that can automatically propagate to multiple recipients a message sent to a single address. Known as a mail gateway or list server, such software allows individuals to join or leave a mail list at any time. Such software can be used to create lists of individuals who will receive announcements about a product or service or to create online discussion groups.
E-mail software has also been extended to allow the transfer of non-text documents, such as photographs and other images, executable computer programs, and pre-recorded audio. Such documents, appended to an e-mail message, are called attachments. The standard used for encoding attachments is known as Multipurpose Internet Mail Extensions (MIME). Since the Internet e-mail system only transfers printable text, MIME software encodes each document using printable letters and digits before sending it and then decodes the item when e-mail arrives. Most significantly, MIME allows a single message to contain multiple items, enabling a sender to include more than one attachment.
F Other Internet Applications
Although the World Wide Web is the most popular application, some older Internet applications are still used. For example, the Telnet application enables a user to access a remote computer interactively. Telnet gives the appearance that the user’s keyboard and monitor are connected directly to the remote computer. For example, a businessperson who is visiting a location that has Internet access can use Telnet to contact an office-based computer. Doing so is faster and less expensive than using a dial-up modem.
Another application, known as the File Transfer Protocol (FTP), is used to download files from an Internet site to a user’s computer. The FTP application is often automatically invoked when a user downloads an updated version of a piece of software. Applications such as FTP have been integrated with the World Wide Web, making them transparent so that they run automatically without requiring users to open them. When a Web browser encounters a URL that begins with ftp:// it automatically uses FTP to access the item.
Network News discussion groups (newsgroups), originally part of the Usenet network, are another form of online discussion. Thousands of newsgroups exist, on an extremely wide range of subjects. Messages to a newsgroup are not sent directly to each user. Instead, an ordered list is disseminated to computers around the world that run news server software. Newsgroup application software allows a user to obtain a copy of selected articles from a local news server or to use e-mail to post a new message to the newsgroup. The system makes newsgroup discussions available worldwide.
A service known as Voice Over IP (VoIP) allows individuals and businesses to make phone calls over the Internet. Low-cost services (some of them free) often transfer calls via personal computers (PCs) equipped with microphones and speakers instead of the traditional telephone handset. A growing number of services operate outside the PC, making calls via a special adapter that connects to a traditional telephone handset. The calls still travel over the Internet, but the person using the special adapter never has to turn on his or her computer. Thousands now use such VoIP services in lieu of traditional phone service. VoIP services are not subject to the same government regulation as traditional phone service. Thus, they are often less expensive.
Computers store all information as binary numbers. The binary number system uses two binary digits, 0 and 1, which are called bits. The amount of data that a computer network can transfer in a certain amount of time is called the bandwidth of the network and is measured in kilobits per second (kbps) or megabits per second (mbps). A kilobit is 1 thousand bits; a megabit is 1 million bits. A dial-up telephone modem can transfer data at rates up to 56 kbps; DSL and cable modem connections are much faster and can transfer at mbps. The Internet connections used by businesses can operate at 45 mbps or more, and connections between routers in the heart of the Internet may operate at rates from 2,488 to 9,953 mbps (9.953 gigabits per second). The terms wideband or broadband are used to characterize networks with high capacity, such as DSL and cable, and to distinguish them from narrowband networks, such as dial-up modems, which have low capacity.
Research on dividing information into packets and switching them from computer to computer began in the 1960s. The US Department of Defense Advanced Research Projects Agency (ARPA) funded a research project that created a packet switching network known as the ARPANET. ARPA also funded research projects that produced two satellite networks. In the 1970s ARPA was faced with a dilemma: each of its networks had advantages for some situations, but each network was incompatible with the others. ARPA focused research on ways that networks could be interconnected, and the Internet was envisioned and created to be an interconnection of networks that use TCP/IP protocols. In the early 1980s a group of academic computer scientists formed the Computer Science NETwork, which used TCP/IP protocols. Other US government agencies extended the role of TCP/IP by applying it to their networks: the Department of Energy’s Magnetic Fusion Energy Network (MFENet), the High Energy Physics NETwork (HEPNET), and the National Science Foundation NETwork (NSFNET).
In the 1980s, as large commercial companies began to use TCP/IP to build private internets, ARPA investigated transmission of multimedia—audio, video, and graphics—across the Internet. Other groups investigated hypertext and created tools such as Gopher that allowed users to browse menus, which are lists of possible options. In 1989 many of these technologies were combined to create the World Wide Web. Initially designed to aid communication among physicists who worked in widely separated locations, the Web became immensely popular and eventually replaced other tools. Also during the late 1980s, the US government began to lift restrictions on who could use the Internet, and commercialization of the Internet began. In the early 1990s, with users no longer restricted to the scientific or military communities, the Internet quickly expanded to include universities, companies, libraries, schools, government, individuals, and families.
A The Future of the Internet
Several technical challenges must be overcome if the Internet is to continue to grow exponentially. The primary challenge is to create enough capacity to accommodate increases in traffic. Internet traffic is increasing as more people become Internet users and existing users send greater amounts of data. If the volume of traffic increases faster than the capacity of the network increases, congestion will occur, similar to the congestion that occurs when too many cars attempt to use a road. To avoid congestion, researchers have developed technologies, such as Dense Wave Division Multiplexing (DWDM), that transfer more bits per second across an optical fibre. The speed of routers and other packet-handling equipment must also increase to accommodate growth. In the short term, researchers are developing faster electronic processors; in the long term, new technologies will be required.
Another challenge involves IP addresses. Although the original protocol design provided addresses for up to 4.29 billion individual computers, the addresses have begun to run out because they were assigned in blocks. Researchers developed technologies, such as Network Address Translation (NAT), to conserve addresses. NAT allows multiple computers at a residence to “share” a single Internet address. Engineers have also planned a next-generation of IP, called IPv6, which will handle many more addresses than the current version.
Short, easy-to-remember domain names were once in short supply. Many domain names that used the simple format http://www.[word].com, where [word] is a common noun or verb, and .com referred to a for-profit business were mostly taken by 2001. Until 2001, only a few endings were allowed, such as .com, .org, and .net. By 2002, however, additional endings began to be used, such as .biz for businesses and .info for informational sites. This greatly expanded the number of possible URLs.
Other important questions concerning Internet growth relate to government controls, especially taxation and censorship. The rapid growth of the Internet has meant that governments have had little time to pass laws to control its deployment and use, impose taxes on Internet commerce, or otherwise regulate content. The introduction of censorship laws has been rigorously opposed in the United States by Internet users who regard such regulation as an infringement of their constitutional right to free speech.
Increasing commercial use of the Internet has heightened security and privacy concerns. With a credit or debit card, an Internet user can order almost anything from an Internet site and have it delivered to their home or office. Companies doing business over the Internet need sophisticated security measures to protect credit card, bank account, and national insurance numbers from unauthorized access as they pass across the Internet (see Computer Security). Any organization that connects its intranet to the global Internet must carefully control the access point to ensure that outsiders cannot disrupt the organization’s internal networks or gain unauthorized access to the organization’s computer systems and data.