In the last few years, an explosive growth in computer telecommunications has been brought about by advances in computer technology and by the emergence of commercial and noncommercial providers of online computer access. One of the most visible and widespread developments has been the Internet, a worldwide web of interconnected computer networks. At the beginning of 1995, the Internet linked nearly 5 million computers on more than 46 000 computer networks. Many of these computers, perhaps 20 000 to 30 000, offer free information and services to the general public. These resources range from the trivial and entertaining to the scientific and technical. Academic institutions, medical centers, and government agencies are some of the organizations on the Internet that provide material of interest to the medical community. The amount of medical information available is extensive and growing rapidly, and a comprehensive review of this material is not possible. I highlight selected topics and briefly describe the Internet and ways to access its medical resources. The Internet The Internet began as a series of small-scale networking experiments that gradually expanded in scope. Persons developing these experiments had no clear idea that a nationwide, let alone worldwide, network of computers would result. The Internet is usually considered to have originated as a networking experiment funded by the Advanced Research Projects Agency (ARPA) of the Department of Defense, which interconnected computers at four academic institutions in California and Utah [1]. This network, ARPANET, became operational in 1969; soon, other academic institutions started connecting their networks to ARPANET. This interconnected series of networks began to be referred to as the Internet. In 1986, the National Science Foundation created NSFNET, an administrative and funding agency that supported the development of regional academic computer networks. This agency funded a private corporation, Advanced Network and Services, Inc. (ANS), to develop and operate a high-speed nationwide network, ANSNET, that interconnected the regional networks in all parts of the United States [2] (Figure 1). In early 1995, NSFNET terminated funding to ANS and awarded grants to the regional networks so that they could purchase their own Internet connections [3]. Currently, Sprint and MCI provide most of the long-distance Internet connectivity in the United States. Other countries, primarily Canada and countries in Western Europe, were developing nationwide computer networks at the same time as the United States. The interconnection of these national networks resulted in the globalization of the Internet. Figure 1.
The principal National Science Foundation network (NSFNET) in the United States. Internet Access The Internet can be accessed in many different ways. Most large academic, research, and medical institutions in the United States are connected to the Internet. Each institution determines the types of access and the services available to its members. Because these organizations typically have high-speed connections to the Internet and employ staff that can maintain computer hardware and software, persons at these organizations often have the best access to the Internet. For many users, the Internet is most conveniently accessed through a personal computer and a modem connected to standard telephone lines. In general, three things are needed to use Internet resources: 1) an access provider that supplies the physical links to the Internet, 2) networking software (TCP/IP [transmission control protocol/Internet protocol] software) for connecting to the Internet, and 3) application programs for accessing resources on remote computers. Several Internet access providers now sell various services and access methods to individual users. It is beyond the scope of this article to describe these vendors, but lists of vendors and their products and services can be found in current books and articles about the Internet [4-8] and in advertisements in many computer magazines. A list may also be obtained by sending an electronic mail (e-mail) message to [email protected]. No subject is required, and the text should be send pdial (without the quotes). An interesting new development is the ability to connect personal computers to the Internet through television cables.
Television cables can transmit data at 3 to 10 million bits of data per second, more than 100 times faster than the fastest modems [9]. At these speeds, many new applications are possible, such as real-time video. This technology is being tested in restricted areas throughout the United States and should be available in 1996. This service is described on the World Wide Web (WWW) at http://www.home.net (see below). From a user’s point of view, the simplest way to connect to the Internet is through a dial-up connection to an Internet access provider using a modem and standard communication software. For this type of access, called a shell account, all the network (TCP/IP) software and Internet application programs are on the provider’s computer, and the user accesses these programs from a remote location. The main drawback of this type of access is that users cannot run programs that display graphics or video and cannot directly download files from the Internet to their computers. Users may decide to run the networking software and Internet applications programs on their own computers and purchase just an Internet access program (SLIP [serial line Internet protocol] or PPP [point-to-point protocol] access) from a commercial vendor. This method of access allows users to run graphic-based programs, such as Mosaic and Netscape (described below) and to download files from the Internet directly to their computers. Much Internet software can be purchased or obtained free from the Internet. Commercial Internet software can be purchased as stand-alone products or as part of larger packages.
Microsoft, IBM, and Apple now offer Internet software as part of their current operating systems. All the major on-line computer services CompuServe, America Online, and Prodigyand some Internet access providers, such as MCI, PSI (Performance Systems International), and Netcom Online Communications, offer complete Internet packages consisting of an Internet connection, network software, and application programs. Internet Services The resources of the Internet are accessed by using application programs (often called Internet services) that connect to remote computers by various methods and perform different functions [4, 5, 10, 11]. The most commonly used services are FTP (file transfer protocol), telnet, gopher, and the WWW. All Internet services function in a type of computer interaction called the client-server model. An Internet resource on a remote computer is provided by a program called a server. A user runs a program on the local computer (the client) and supplies it with the name or address of the remote computer running the server. After the local computer is connected to the remote computer, the client passes a user’s request for information to the server. The server returns the information to the client program, which then displays the results on the local computer. Thus, for example, a user runs a telnet client program to access a remote computer that runs a telnet server. In practice, the terms client and server are not often used, the meaning being derived from the context. Computers on the Internet are identified by names and numbers. The computer naming system is called the domain name system. Computer names are strings of characters separated by periods that identify a computer and the networks it is connected to in a hierarchical fashion. Computer networks are grouped into categories called top-level domains. In the United States, seven top-level domains are used (Table 1 and Figure 2). Outside of the United States, top-level domains are countries and are specified by two-letter codes. Computers actually communicate in terms of numbers called IP addresses. Computer names are automatically converted to their corresponding IP addresses when a name is specified in an application program (Figure 2). Table 1. Top-Level Domains for Computer Networks in the United States Figure 2. Naming and numbering scheme for Internet computers. Many different client software programs are available for Internet services, but they can be grouped into two general categories: graphic-based user interfaces and text-based interfaces. Graphic-based user interfaces present a full-screen display from which commands or options can be chosen with a mouse. Complex graphic images can be displayed with these programs. Apple computers and the Microsoft Windows operating system for personal computers can be used to run these types of programs. Text-based interfaces use operating systems such as DOS and Unix and require that a user type commands or choose items from a menu. Software programs for all Internet services are available in both graphic-based and text-based formats, but much of the functionality of the WWW is lost when the text-based programs are used. In the following paragraphs on the main Internet services, examples of communication between the user and the remote computer are given in the text-based Unix format. Unix is the most widely used operating system on the Internet, and commands in other text-based systems are similar. In the examples below, messages or prompts from the remote computer appear as ordinary text, and user input appears in bold text. The last character of the user input must be followed by a hard-carriage return. Telnet The telnet service allows a user to log onto a remote computer and use its resources. At public sites, a login name is usually required and a password is occasionally needed.
