The Internet What does it mean to be connected to the internet? I.e. What does the internet do?? What do you need to connect your computer to the internet as opposed to any other network? The Internet More than Just WWW The internet is a world-wide computer network that runs some very specific services The best known of these services are: Electronic mail File transfer World Wide Web Voice Over IP (VoIP) Others Telnet: allows you to connect to remote computers with your computer acting as a dumb client Newsgroups (now done on the WWW) Etc Connecting to the internet Role of the ISP What do you need? 1. Install the appropriate networking protocol used by the internet. i.e. TCP/IP 2. An ISP (internet service provider) to act as your gateway to the internet Examples of ISPs: Comcast, AT&T, Verizon, etc Who is online? Estimated to be about 1.5 billion people as of January 2009 Only around 200 million are in the U.S. Soon China will have more Internet users than the US Taken Internet users by country Taken from Wikipedia 1
Types of broadband connections DSL Service Newer, faster, and cheaper than ISDN Can share phone line with voice traffic Cable Modem Connection Allows Internet connections using shared TV cables Can exceed DSL speeds Carries increased privacy and security risks Satellite Connection Provides connection using satellite dishes Wireless Connection Allows multiple computers to connect to a base station using radio waves. Internet Services Each of the main services available on the internet is governed by a series of rules and instructions, i.e. a protocol. E-mail (simple mail transfer protocol - SMTP) File Transfer (file transfer protocol) World Wide Web (hypertext transfer protocol - HTTP) Telnet (telnet communication protocol) Copyright 2008 M J Davidson E-mail Protocol used: SMTP (simple mail transfer protocol) SMTP E-mail server A computer connected to the internet, has TCP/IP installed, also has mail-server software installed The mail server software knows how to speak SMTP SMTP defines the rules and methods to send, receive, store, and route e-mails Any organization that supplies e-mail addresses to its customers, employees, etc will have its own e-mail server E.g. Comcast, the White House, DePaul, etc Anatomy of an e-mail address BobSmith@condor.depaul.edu Mr. Smith s account is located on DePaul s depaul.edu domain DePaul has a computer on the domain named condor that holds Mr. Smith s e-mail account The computer named condor runs SMTP server software (see later) Mr. Smith s e-mail mailbox is a folder/account on condor named BobSmith Internet Services Each of the main services available on the internet is governed by a series of rules and instructions, i.e. a protocol. E-mail (simple mail transfer protocol - SMTP) File Transfer (file transfer protocol) World Wide Web (hypertext transfer protocol - HTTP) Telnet (telnet communication protocol) 2
File transfer Protocol - FTP Internet Services File transfer protocol (FTP) allows users to transfer files between different computers on the internet Upload files to remote computers (e.g. from your local PC to a web server) Download files from remote servers to their computers As with e-mail servers, web servers, etc, you need to have a computer with appropriate FTP-server software installed if you want users to be able to FTP files to and from your server. Each of the main services available on the internet is governed by a series of rules and instructions, i.e. a protocol. E-mail (simple mail transfer protocol - SMTP) File Transfer (file transfer protocol) World Wide Web (hypertext transfer protocol - HTTP) Telnet (telnet communication protocol) W W W A large network of computers that can support specially formatted (i.e. HTTP-formatted) documents Internet World Wide Web o Internet o a collection of interconnected computer networks, linked by copper wires, fiber-optic cables, wireless connections etc.; o World Wide Web o a collection of interconnected documents, linked by hyperlinks and URLs o accessible using the Internet. 3
Hypertext in a computer environment, ability to move directly from one part of a document to another or from one document to another through internal connections among these documents (called "hyperlinks"); Resource Identifiers On a computer network the ability to locate a particular resource computer document other resource on the network through a unique identifier URL Uniform Resource Locator naming scheme allows every information resource on the Internet to be referred to using a uniform resource locator, or URL. URL Format Top-Level Domains Domain Name http:// weatherunderground.com/ Protocol for Web pages Resource File satellite/vis/1k/ US.html Path Common top-level domains include:.edu - educational sites.com - commercial sites.gov - government sites.mil - military sites.net - network administration sites.org - nonprofit organizations Many others (see below) List of top-level domains http://en.wikipedia.org/wiki/list_of_internet_toplevel_domains 4
Client-server Model client software or a client computer makes requests of server software or a server computer that provides the client with resources or services, such as data or files Web Server Stores web pages (and othe documents) Sends requested pages to HTTP clients (i.e. web browsers) Must run web-server software (e.g. Apache, Tomcat, IIS) Web Client E.g. Internet Explorer, Firefox, Safari, Chrome, etc Knows how to send requests for files to web servers Knows how to interpret and display responses (e.g. HTML pages) characters or codes embedded in text Markup Language indicate to a computer how to print or display the text, e.g. as in italics or bold type or font. 5
HTML HTML Mark-up Language All WWW documents are created in a markup language called HTML (HyperText Markup Language) HTML supports links to other documents, as well as graphics, audio, and video files. You can jump from one document to another simply by clicking on hot spots. Developing Web Pages Web Hosting Services Code HTML page Publish page to the Web by copying it onto a web server o Provide a place to post web pages and other material (usually for a fee, beware free Web space offers) o May provide other services (help in obtaining rights to a domain name) HTTP Clients web browsers Web browser software was built for viewing documents Web Browsers parse HTML and display the content with the appropriate markup in the browser window Plug-ins Handles/de-codes files that browsers can t Windows Media Player QuickTime Shockwave/Flash RealPlayer Adobe Reader and Acrobat (Adobe) 6