Understanding Web Applications and Internet Services
Web Applications and Internet Services
The Internet World
Definition: The Internet is a global network of shared devices (PCs, printers, hard drives, etc.) that communicate using a common language (protocol) to exchange information.
History: The Internet originated with ARPANET in the USA.
Connecting to the Internet: You connect through an ISP (Internet Service Provider).
Internet Services
Web Navigation
Accessing web pages located on websites. The first page you see is the home page (index, home, rate...). Web pages have extensions like .html, .asp, .aspx, and .php.
Each site has a URL (Universal Resource Locator) which corresponds to a public IP address.
Browsers and Plugins
Use a browser (like Explorer, Mozilla, Netscape, Opera, Safari, or Chrome) along with plugins for Flash and PDF support.
Modems and Routers
- Connections: RJ45 (8 wires), RJ11 (4 wires), Wi-Fi (WEP/WPA)
- Accessible via Web/Telnet (Open Ports)
- Technologies: RTB, ADSL, Cable (Fiber Optic)
Functioning of the Internet
Communication is possible because devices use the same language (protocol).
Protocol Definition: A set of rules that allows different devices to communicate.
Examples:
- PPP: Point-to-Point Protocol (analog modems)
- TCP/IP: Transfer Control Protocol / Internet Protocol
- IPX (Novell)
- AppleTalk (Apple)
- UDP (Emule, P2P, etc.)
How TCP/IP Works
- Information is divided into chunks (packets).
- Packets travel on the network (different paths).
- Packets are reassembled at the destination.
Site Navigation
Accessing a site:
- Enter the URL into the browser.
- Click on hyperlinks (links).
- Redirection (HTML, JavaScript).
The browser interprets HTML (with JavaScript) using HTTP (Hypertext Transfer Protocol) over port 80 (or 8080).
Electronic Mail (E-mail)
Allows sending and receiving text messages, images, and attachments.
Accessing Email
- Web page (webmail): Hotmail, Yahoo, Gmail, etc.
- Email client programs: Microsoft Outlook, Eudora Mail, Mozilla Thunderbird
Email Client Configuration
- Email address (name@domain)
- Username
- Password
- SMTP server (smtp.maquina.xxx) [SMTP = Simple Mail Transfer Protocol]
- POP server (pop[3].maquina.xxx) [POP = Post Office Protocol]
Examples:
- Hotmail: smtp.live.com / pop3.live.com
- Yahoo: smtp.correo.yahoo.es / pop.correo.yahoo.es
- Gmail: smtp.gmail.com / pop.gmail.com
Note: IMAP (Internet Message Access Protocol) is another protocol, a mix of webmail and program-client.
Unsafe!
Other Services
FTP (File Transfer Protocol)
Allows inserting/extracting information from a web server.
Access
- FTP client program (anonymous or identified)
- Browser using a URL:
ftp://
Instant Messaging
Examples: Messenger, AOL…
Chats and Forums
- Forum: Reading and writing on various topics.
- Chat: Real-time chat (e.g., IRC – Internet Relay Chat).
Newsgroups
News Groups using NNTP (Network News Transfer Protocol). Allows reading (and writing) on a particular theme.
Access
- Specific software (X-News)
- Email clients (Outlook)
Downloads headlines first, then the body of the news that interests you.
RSS
Evolved to:
- Rich Site Summary (RSS 0.91)
- RDF Site Summary (RSS 0.9 and 1.0)
- Really Simple Syndication (RSS 2.0)
Subscription system that allows you to receive information.
Telephony IP (VOIP)
Allows telephone conversations over the Internet.
Usage
- Software (Skype)
- Hardware
Telnet (HyperTerminal)
Allows remote access to a computer using its IP address or name. The source and target OS is not important (Windows to Linux, etc.). It’s a text-mode tool, but graphical alternatives exist.
Graphical Alternatives
- Remote Access Windows
- Radmin
- Net Support