Working with Internet does not mean just browsing www and sending and receiving e-mails. The Basic Structure of the Internet was developed through last 30 years of existence of the Internet. The Internet is a heterogeneous worldwide network consisting of a large number of host computers and local area networks. The Internet uses the TCP/IP suite of protocols. This allows the integration of a large number of different computers into one single network with highly efficient communication between them. This way, the user can access information on all kinds of host computers from a desktop PC, Macintosh, or whatever he/she has available.

TCP/IP, the communication standard underlying the Internet, originates from work done at the US-Department of Defense in the late 1960s. The first version of the Internet was built in 1969 and consisted of just four computers. In 1982 a set of specifications and protocols have been implemented, which became known as TCP/IP in reference to their two major elements, the “Transmission Control Protocol” and the “Internet Protocol”. The development and implementation of TCP/IP stimulated a massive growth process for the Internet. “By late 1987 it was estimated that the growth had reached 15% per month and remained high for the following two years.

By 1990, the connected Internet included over 3,000 active networks, over 3,000 active networks, and over 200,000 computers. By January 1992 the number of hosts on the Internet was 727,000, doubling about every 7 months. Various groups of users are connected to the Internet: universities and other educational institutions, government agencies, the military, and at an increasing number private businesses. The most fundamental function of the Internet is to pass electronic information from one computer to another. A 32 bit Internet Address or IP-Number identifies every computer on the network.

This number is commonly represented as four numbers joined by periods. The Internet uses these numbers to guide information through the network. This is called routing. For human users, however, such numbers are usually difficult to keep in mind. Therefore, computers are also identified by Domain Names, which are to some extent similar to mailing addresses. Special programs, called name servers, translate domain names into IP-Addresses. Internet services can be divided into two groups, communication services, and information services.

In the first group, the Internet mediates in the communication between two or more individuals. In the second group, the user turns to the Internet-service in search for some particular information. Communication services can roughly be compared to a telephone call, information services to a dictionary . The most important communication services on the Internet are electronic mail, Netnews and some derived services. Major information services are terminal emulation and file transfer, Gopher, WAIS, and World Wide Web. Electronic mail is the most popular and widely used network service.

It can be viewed as the electronic equivalent to a regular mail letter. When one user wants to send a message to another Internet user, he types the message into a special computer program, adds the e-mail address of the recipient, and sends the message off through the network. Typically, the message reaches its destination almost immediately, even when it is on another continent. Practically all gateways between the Internet and other computer networks can handle e-mail messages. Therefore, many more people can be reached by e-mail than are connected to the Internet via TCP/IP.

The major advantage of e-mail over regular mail is that an e- mail message comes in electronic form. Therefore, it can easily be handled and interpreted by a computer program. This feature is use by electronic discussion lists. They operate a database of subscribers and each incoming e-mail message is automatically distributed to each subscriber. Listserv, the most popular program for managing discussion lists also handles subscription via mail messages, archives incoming messages, and allows users to retrieve these and other archived files. Thousands of discussion lists focusing on all kinds of topics exist on the Internet.

Topics range from various hobbies, political discussions to operational aspects of different computer systems and research questions. For the user, discussion lists are an easy way to identify and contact a large number of people with similar interests. A discussion list can also be considered as a worldwide forum for expressing views and discussing opinions. While messages are automatically sent to all subscribed users in the case of a discussion list and one has to be subscribed in order to receive the messages, messages in Netnews are distributed between a net of servers.

Messages are organized in a hierarchy of newsgroups. Incoming messages are stored for a particular period in a publicly accessible area. Each user can connect to this area, browse through the stored messages, and respond to any one of them. This way Netnews allows for a better overview of ongoing discussions but requires the user to actively connect to the respective area. One of the reasons for the creation of a computer network like the Internet was to give users access to remote computers and to allow them to transfer files to and from this machine. These are typical demands for Telnet and FTP for file transfer protocol.

In both services, the user specifies a specific remote host through its IP-number or domain-name that he wants to access. When the user has an account on this remote host, he can work there just like on a local machine. With telnet available, increasingly Internet-sites allowed outside users to access some of their information services. Typical examples are electronic library card catalogs, campus information systems, and other database applications. Today, the electronic card catalogs of practically all-major libraries and many university libraries in Europe are publicly accessible through the Internet.

Many sites run large specialized information systems for the network community. A similar type of anonymous access is available through FTP. Many Internet sites allow users to log in as anonymous through FTP. The way the sites can make files publicly available. This system has led to a huge supply of freeware- and shareware-software that is distributed through this channel. Practically all network software is available in this way. In addition, information files specifications of network standards; research papers, multimedia files, and even the complete texts of classical books can be accessed through anonymous FTP.

When using an FTP client program to download files, assure yourself, that it is giving a bogus password, like [email protected] com, not your real one. If your browser lets you, turn off the feature that sends your e-mail address as a password for anonymous FTP sessions. The File Transfer Protocol, as its name states, is a set of rules that dictates how files should be transferred over the TCP/IP protocol. A basic FTP connection consists of a client and a server. The client gets a file by opening a connection to the server. Usually, the server is run on port 21, however, the system administrator can change this if he or she wishes.

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