© 2004, Robert K. Moniot Chapter 1 Introduction to Computers and the Internet

© 2004, Robert K. Moniot The Internet Developed beginning in the 1960s, sponsored by ARPA (Dept. of Defense Advanced Research Projects Agency). Protocol for communication between computers is called TCP/IP: Transmission Control Protocol / Internet Protocol. Information is transmitted by packet switching: data is broken up into packets, which are then passed from one computer to the next until they reach their destination. This is in contrast to the phone system, which creates a temporary direct link between communicating parties. Packet switching is robust since it can route around disabled nodes and use multiple paths. But there is no guarantee packets will be delivered within any given time.

© 2004, Robert K. Moniot The Internet IP requires each connected computer to have a unique address: a number such as Clients such as home computers are generally assigned IP addresses dynamically (by DHCP) from a pool of available numbers upon connecting to the Internet. Server computers have static IP addresses. Computers can also be identified by names. Domain Name Service (DNS) translates between name and number. Internet names have two parts: a host name (the first component) and a domain (everything else). Example: erdos.dsm.fordham.edu

© 2004, Robert K. Moniot The Internet Various protocols are built on top of TCP/IP: – (SMTP) –File Transfer Protocol (FTP) –Drive and printer sharing protocols, e.g. NetBIOS –Network Time Protocol (NTP) for setting computers' clocks. –Hypertext Transport Protocol (HTTP): the World-Wide Web TCP requires computers to connect via numbered ports defined by the network software applications. Each protocol uses a different port. For instance, Web transactions usually use port 80. Note that the Web is just one of many protocols using the Internet.

© 2004, Robert K. Moniot The World-Wide Web Invented around 1990 by Tim Berners-Lee, a programmer at CERN (a physics lab in Geneva) to simplify sharing of information between research groups. Designed to be easy to program, easy to use, flexible and decentralized. Based on client-server model: –client computer runs a browser (e.g. Internet Explorer or Netscape) that requests information from a server –server computer runs a web server (e.g. Microsoft Internet Information Server or Apache Web Server) that listens for requests and sends back information

© 2004, Robert K. Moniot Client-Server Model Internet request response Server Client

© 2004, Robert K. Moniot Web Programming Elements HTML: Hyper-Text Markup Language. Provides formatting of text and graphics, as well as links between documents. CSS: Cascading Style Sheets. Provide more powerful and detailed control of style and formatting. JavaScript: a programming language for client-side scripting, to provide dynamically changing content. Java: a more powerful programming language for web applications on the client that can also run independently of the browser. Server-side scripting and programming (SHTML, ASP, PHP, CGI). These permit access to databases and other information located on the server.

© 2004, Robert K. Moniot Compatibility Unfortunately, competition between software companies has often resulted in the introduction of incompatible features so that web pages that work on one browser do not look right on a different one. The World-Wide Web Consortium ( exists to develop and define standards for HTML, CSS, etc. However, compliance with these standards is only partial at best. –Stick to features known to be compatible –Test your web pages on as many different browsers and platforms as possible.