Transcript Book Title - St. Francis Xavier University

CSCI-235
Micro-Computer Applications
The Internet
 Communications
and Networking
LAN (Local Area Network)
WAN (Wide Area Network)

The Internet is a global, interconnected computer
network in which every computer connected to it can
exchange data with any other connected computer

 History
of Internet
The ARPANet (precursor to the Internet) became a
reality in 1969

• Advanced Research Project Agency (ARPA)
• Intended to connect only military installations and
universities participating in government projects
• It employed dedicated cables, buried underground
• The data transfer was 56K bits/sec, roughly the same
as dial-up services today
By 1980, close to 100 sites were connected to the
ARPANet

• Satellite connections provided links to select cities
outside the continental U.S.
 Internet
Growth
A Quick Timeline
 http://www.internet-story.com/index.htm
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The Future of the Internet
 Key
changes in the Internet need to take
place to handle the growing number of
users and the speed of the connections
 Future changes include:

More bandwidth
• Internet 2 (I2) is being developed and tested to
establish gigabits per second Points of Presence
(gigaPOP)
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The Internet and Web: What’s
the Difference?

The Internet is the physical connection of
millions of networks
 The Web uses the Internet for its existence
 The Web consists of hypertext embedded on
Web pages that are hosted on Web sites
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Web Site
A
Web site is a
collection of related
Web documents that
are made available to
the public
 The index page, or
home page, is the first
page of a Web site
 Web pages are
individual Web
documents
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Tim Berners-Lee

Worked at CERN lab in Geneva





Thought his work would be easier if he
could link to colleagues’ computers
Envisioned a network of computers
much like a spider web
Used links to transfer data from one site
to another location
CERN site considered the
birthplace of the World Wide Web
http://en.wikipedia.org/wiki/Tim_Ber
ners-Lee
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Marc Andreessen

Developed the first graphical
browser


Called Mosaic
Led to Netscape Navigator
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Web Browsers and Servers

Web browsers display a Web document and
enable users to link to other Web pages



The first browsers were text-only
Mosaic was the first graphical browser
Web servers respond to the requests of
browsers. They find and send requested
resources back to the browser
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Architecture of WWW
Browser
Web Addresses (URLs)

Web addresses are an addressing system
that identifies where a Web resource is
located
 The uniform resource locator (URL) is the
standard used to identify Web resources
 The URL consists of:
Protocol
identifies
the means
of access
Server contains
the domain
name of the
Web server
Path
identifies the
location of the
document
Resource
specifies the
filename of the
resource
URL http://www.yahoo.com/ help/shop/ shop-01.html
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Web Page Design
HTML
Document

Authors use a markup language called
Hypertext Markup Language (HTML) to create
Web pages
 The markup language consists of codes that
identify portions and special effects in the
document
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PageDocument
Created
HTML
Click again
Click to view an HTML document and the page that it
creates.
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IP Addresses

IP address – Each computer connected to the
Internet is given an address composed of
numbers and periods. Example: 209.234.456.8

Every machine on the Internet has a unique IP
address

Windows command WINIPCFG.EXE
(IPCONFIG.EXE for Windows 2000/XP)

http://www.whatismyip.com/
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Dotted-decimal notation and binary notation for an IPv4 address
19.19
Example
Find the error, if any, in the following IPv4 addresses.
Solution
a. There must be no leading zero (045).
b. There can be no more than four numbers.
c. Each number needs to be less than or equal to 255.
d. A mixture of binary notation and dotted-decimal
notation is not allowed.
Finding the classes in binary and dotted-decimal notation
Example
Find the class of each address.
a. 00000001 00001011 00001011 11101111
b. 11000001 10000011 00011011 11111111
c. 14.23.120.8
d. 252.5.15.111
Solution
a. The first bit is 0. This is a class A address.
b. The first 2 bits are 1; the third bit is 0. This is a class C
address.
c. The first byte is 14; the class is A.
d. The first byte is 252; the class is E.
Default masks for classful addressing
19.23
Two levels of hierarchy in an IPv4 address
A frame in a character-oriented protocol
Domain Names
Domain Name

Domain Name System (DNS) – Enables users to
type names of Web sites and Web pages as well
as IP addresses

UNIX command nslookup

http://www.iana.org
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Port addresses
Ports

Any server machine makes its services available
to the Internet using numbered ports, one for
each service that is available on the server

Clients connect to a service at a specific IP
address and on a specific port

If a firewall is not protecting the port, you can
connect to the port from anywhere on the
Internet and use the service
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Ports

If you were to set up your own machine and load
Web server software on it, you could put the
Web server on port 918, or any other unused
port, if you wanted to

Then, if your machine were known as
xxx.yyy.com, someone on the Internet could
connect to your server with the URL
http://xxx.yyy.com:918. The ":918" explicitly
specifies the port number

When no port is specified, the browser simply
assumes that the server is using the well-known
port 80
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HTTP Protocol

Every Web server on the Internet conforms to the
HTTP protocol, summarized nicely in The Original
HTTP as defined in 1991

The most basic form of the protocol understood by
an HTTP server involves just one command: GET

"GET filename," the server will respond by
sending you the contents of the named file and
then disconnecting

telnet www.cnn.com 80
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Putting It All Together

http://www.stfx.ca/athletics/schedules.html

The browser breaks the URL into three parts:
 The protocol ("http")
 The server name ("www.stfx.ca")
 The file name (“athletics/schedules.html")

The browser communicates with a name server
to translate the server name, "www.stfx.ca," into
an IP address, which it uses to connect to that
server machine
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Putting It All Together

The browser then forms a connection to the Web
server at that IP address on port 80

Following the HTTP protocol, the browser sends
a GET request to the server, asking for the file

The server sends the HTML text for the Web
page to the browser

The browser reads the HTML tags and formats
the page onto your screen
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Static document
Dynamic document using CGI
Dynamic document using server-site script
Active document using Java applet
Active document using client-site script
Electronic Mail (E-mail)
 E-mail
is sending messages via computer
 Business is using more e-mail and fax
 To access you must have a mail server
and software
 Each person has a username and
password
 All mail programs allow you to Send,
Compose, Reply and Forward, Delete
Internet Address
[email protected]
Highest-level
domain
Next-level domain
Username
Host Computer
A valid Internet Address must contain the @ symbol
E-mail Protocols
POP Client --Post Office Protocol
•Mail is read composed and stored locally
•Can work off-line
IMAP --Messages stored remotely
•Stored on a server
•Download for local storage
SMTP --Simple Mail Transfer Protocol
•The protocol required to send mail
messages through the Internet