Transcript Stair Principles-Chapter 7 - University of Illinois at Chicago

Chapter 7
The Internet
and
Intranets
The Internet
The world’s largest computer network
Consists of
ARPANET:
thousands of interconnected networks
Ancestor of the Internet
Started by the Department of Defense to link DOD &
military research contractors
Split into two networks
MILNET: all military sites
Reduced ARPANET: non-military sites
The Internet
[Figure 7.1]
How the Internet Works
The Internet
transmits data
from one
computer (host)
to another.
 [Figure 7.2]
continued...
How the Internet Works
Messages are routed through the multiple
networks that make up the Internet by using
special protocols.
Internet Protocol (IP)
The set of conventions used to pass packets from one host to
another
Transport Control Protocol (TCP)
Used in connection with IP
Operates at the transport layer
How the Internet Works
Each computer on the Internet has an assigned
address to identify it from other hosts (e.g.,
123.45.67.89).
Most also have names, which are much easier to
remember than the numbers (e.g,
flash.acme.com).
Internet Zones
 com: commercial sites
 edu: educational sites
 mil: military sites
 gov: government sites
 net: networking organizations
 org: organizations
 firm: businesses/firms
 store: businesses offering goods
for purchase
 info:




information service
providers
web: entities related to World
Wide Web activities
arts: cultural and
entertainment activities
rec: recreational activities
nom: individuals
Three Ways
to Access the Internet
Connect via LAN server
Connect via SLIP/PPP
Connect via an on-line service
Three Ways
to Access the Internet
[Figure 7.3]
Requirements for
Connecting via LAN Server
Network adapter card
Open Datalink Interface (ODI) or Network
Driver Interface Specification (NDIS)
Communications stack
Software that provides a set of communications protocols
that perform the complete functions of the seven layers of
the OSI communications model
A Communications Stack for
Accessing the Internet
[Figure 7.4]
Requirements for
Connecting via SLIP/PPP
Modem and the TCP/IP protocols
Serial Line Internet Protocol (SLIP) or Point to
Point Protocol (PPP) software (communications
protocols that transmit packets over telephone
lines, allowing dial-up access to the Internet)
Requirements for Connecting
via an On-Line Service
Modem
Standard communications software
On-line information service account
Internet Services
[Table 7.2]
Electronic Mail (E-Mail)
A way of sending an electronic message between
individuals or computers
Often called a store and forward system
Allows e-mail to be stored until it can be forwarded to the
next computer
Electronic Mail (E-Mail)
Typical e-mail message includes:
“From” line
“To” line
“Subject” line
“Message”
Usenet and Newsgroups
Usenet
A system closely allied with the Internet that uses e-mail to
provide a centralized news service
Newsgroup
An on-line discussion group that focuses on a particular
topic
Sample Newsgroup:
Sewing Newsgroup
[Sewing Newsgroup]
Finding Information and
Downloading Files
Telnet
A terminal emulation protocol that lets a user log on to
another computer on the Internet to gain access to publicly
available files
File Transfer Protocol (FTP)
Describes the file transfer process between a host and a
remote computer
Internet Phone and
Videoconferencing Services
Internet phone service
Enables users to communicate with other Internet users
around the world who have compatible equipment and
software
Internet videoconferencing
Supports both voice and visual communications
An emerging service
World Wide Web
Involves over 30,000 independently owned
computers that work together as one in an
Internet Service
Also known as the Web, WWW, or W3
A menu-based system that uses the client/server
model
continued...
World Wide Web
Data exists on the Web as:
ASCII characters
Word processing files
Audio files
Graphic images
Any other sort of data that is stored in a computer file
continued...
World Wide Web
A web site is like a magazine, with a cover page
(home page) that has graphics, titles, and black
and blue text.
Hypertext:
Blue, underlined type which links the onscreen page to other documents or Web sites
Hypermedia
Connects data on pages, allowing users to access topics in
any order
continued...
World Wide Web
Uniform Resource Locators (URLs)
A standard way of coding the location of the Hypertext
Markup Language (HTML) documents
Hypertext Transfer Protocol (HTTP)
A set of rules that allows the Web user to retrieves a
document
World Wide Web
 Hypertext Markup
Language (HTML)
 Standard page
description language for
Web pages
 HTML tags
 Codes that let the
browser know how to
format the text
[Figure 7.5]
Business Uses of the Web
In 1991, the Commercial Internet Exchange
(CIX) Association was established to allow
businesses to fully connect to the Internet.
Now businesses use the Internet for many
applications: E-mail, customer information web
sites, advertising direct sales web sites, on-line
shopping.
Web Browsers
A Web tool that creates a unique, hypermediabased menu as a graphical interface to the Web
Applets
Small programs embedded in Web pages
Search Engines
Web search tools that help users find the
information they seek
Two types of Web search tools
Directories: List of Web sites classified by topic
Indexes: Allow users to find specific documents through
keyword searches
Developing Web Content
Web authors work with several standards to
create their pages.
Two main problems limit creativity.
Confusing HTML standards
Slow communications speeds
Virtual Reality Modeling Language (VRML)
A language for creating 3-D scenes on the Internet
Java
Object-oriented program language from Sun
Microsystems based on C++
Allows small programs (applets) to be embedded
within an HTML document
Downloading an Applet
from a Web Server
[Figure 7.6]
Intranets
Internal corporate networks built using
Internet and World Wide Web standards and
products
Most companies have the foundation for an
intranet: a network that uses the Internet’s
TCP/IP.
Next stage of intranet usage: Interactive
transaction-based applications
Common Intranet Uses
[Table 7.7]
Managing the Internet
and Intranets
Although the Internet is a huge, global network, it
is managed at the local level; no centralized
governing body controls the Internet.
The Internet Society and the Internet Activities
Board (IAB) are the closest things to centralized
governing bodies.
Service Bottlenecks
Primary cause:
phenomenal growth in traffic
Other causes
More than half of Web users have slow modems (14.4
Kbps or less)
Inefficient software and software glitches
Cryptography
The process of converting a message into a secret
code and changing the encoded message back into
regular text
Digital Signature
A technique used to meet security needs for the processing
of on-line financial transactions
Cryptography
[Figure 7.8]
Firewalls
A device that sits between the internal network
and the outside Internet
Purpose: To limit access into and out of a
network based on an organization’s access policy
Can be set up to allow access from specific hosts
and networks or to prevent access from specific
hosts