Internet Basics | EFF Surveillance Self-Defense Project

The Internet is a global network of many individual computer networks, all speaking the same computer language, the Internet Protocol (IP). Every computer connected to the Internet has an IP address, a unique numeric identifier that can be "static", i.e. unchanging, or may be "dynamically" assigned by your ISP, such that your computer’s address changes with each new Internet session.

More sophisticated networking protocols may be "layered" on top of the IP protocol, enabling different types of Internet communications. For instance, World Wide Web (Web) communications are transmitted via the HyperText Transfer Protocol (HTTP) and e-mails via the Simple Mail Transport Protocol (SMTP).

These additional protocols use their own types of addresses, apart from IP addresses. For example, to download a Web page, you need its Web address, known as a Uniform Resource Locator (URL) (e.g., http://www.eff.org). To exchange e-mails, both the sender and recipient need e-mail addresses (e.g., user@emailprovider.com).

Computers that offer files for download over the Internet are called servers or hosts. For example, a computer that offers Web pages for download is called an HTTP server or Web host. Any computer may be server, client, or both, depending on the communication. The amount of data in an Internet communication is measured in bytes.

Communications to and from an Internet-connected computer occur through 65,536 different computer software "ports." Many networking protocols have been assigned to particular port numbers by the Internet Engineering Task Force. For example, HTTP (Web) is assigned to port 80 and SMTP (e-mail) is assigned to port 25. However, any port can be used for any application, and these are only conventions.

If you want to learn more, the website How Stuff Works publishes a popular series of "Internet Basics" articles that answer questions about the nuts and bolts of the Internet.

via ssd.eff.org