The Internet is a vast network connecting computers

üThe Internet is a vast network connecting computers all over the world üThe original plans for the Internet grew out of a series of memos written by J. C. R. Licklider of the Massachusetts Institute of Technology (MIT) in August 1962 discussing his concept of a “Galactic Network” üLicklider envisioned a global computer network through which users could access data and programs from any site on the network

üAccessing cross-referenced documents, known as hypertext linking, is probably the most important aspect of the Web because it allows you to quickly open other Web pages üA hypertext link, or hyperlink, contains a reference to a specific Web page that you can click to quickly open that Web page

üInternet developed in the 1960 s by the Advanced Research Projects Agency (ARPA) of the U. S. Department of Defense to connect the main computer systems of various universities and research institutions that were funded by ARPA üIn 1990 and 1991, Tim Berners-Lee created what would become the World Wide Web (WWW), or the Web, at the European Laboratory for Particle Physics (CERN) in Geneva, Switzerland, as a way to easily access cross-referenced documents that existed on the CERN computer network

üA document on the Web is called a Web page, identified by a unique address called the Uniform Resource Locator, or URL üURL commonly referred to as a Web address üA URL is a type of Uniform Resource Identifier (URI), which is a generic term for many types of names and addresses on the World Wide Web üA Web site refers to the location on the Internet of the Web pages and related files (such as graphic files) that belong to a company, organization, or individual

Internet Protocols TCP/IP http: // ftp: // telnet: mailto: Transfer Control Protocol/Internet Protocol World Wide Web File Transfer Protocol Telnet E-mail address

When Computers Communicate • When two or more computers communicate, they must have a common way in which to communicate. • To do this computers use protocols • A protocol is an agreement by which two or more computers can communicate. • Transfer Control Protocol/Internet Protocol is the underlying protocol for the Internet.

How TCP/IP Works 1) Transfer Control Protocol (TCP) breaks data into small pieces of no bigger than 1500 characters each. These “pieces” are called packets.

How TCP/IP Works 2) Each packet is inserted into different Internet Protocol (IP) “envelopes. ” Each contains the address of the intended recipient and has the exact same header as all other envelopes.

How TCP/IP Works • A router receives the packets and then determines the most efficient way to send the packets to the recipient. • After traveling along a series of routers, the packets arrive at their destination. (Router)

How TCP/IP Works • Upon arrival at their destination, TCP checks the data for corruption against the header included in each packet. If TCP finds a bad packet, it sends a request that the packet be retransmitted.

IP Addresses • Since computers process numbers more efficiently and quickly than characters, each machine directly connected to the Internet is given an IP Address • An IP address is a 32 -bit address comprised of four 8 -bit numbers (28) separated by periods. Each of the four numbers has a value between 0 and 255

IP Addresses • Example of an IP Address: http: //134. 68. 140. 1/ The IP Address of the Computer Science Department’s Web Server

IP Addresses vs. URLs • While numeric IP addresses work very well for computers, most humans find it difficult to remember long patterns of numbers. • Instead, humans identify computers using Uniform Resource Locators (URLs), a. k. a. “Web Addresses”.

IP Addresses vs. URLs • When a human types a URL into a browser, the request is sent to a Domain Name Server (DNS), which then translates the URL to an IP address understood by computers. • The DNS acts like a phonebook.

Anatomy of a URL http: //www. cs. iupui. edu/inde x. html protocol sub-sub domain machine name domain name sub domai n file name

Top Level Domain Names In the 1980 s, seven g. TLDs (. com, . edu, . gov, . int, . mil, . net, and. org) were created. Domain names may be registered in three of these (. com, . net, and. org) without restriction; the other four have limited purposes . com. net. org. edu. gov. mil. int Commercial Entity Internet Service Provider Non-Profit Organization Educational Institution Governmental Agency Military Entity Internet Assigned Numbers Authority http: //www. icann. org/faq/ Internet Corporation For Assigned Names and Numbers

Country codes. JP. IT. FR. DK. AU. DE. CN. ES Japan Italy France Denmark Australia Germany China Spain Top Level Domain Names and Country Codes http: //www. thrall. org/domains. htm