Transcript Chapter 1 Intro to Computers and the Internet

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 150.108.64.52.
• 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:
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E-mail (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
request
response
Internet
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 (www.w3c.org) 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.
© 2004, Robert K. Moniot