Chapter 7 The Internet and Intranets
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Chapter 7
The Internet
and Intranets
The Internet
The world’s largest computer networkConsists of thousands of interconnected networks
ARPANET: Ancestor of the InternetStarted by the Department of Defense to link DOD &
military research contractorsSplit into two networks
MILNET: all military sitesReduced 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 IPOperates 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 forConnecting via LAN Server
Network adapter cardOpen 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 forConnecting 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 systemAllows 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
UsenetA system closely allied with the Internet that uses e-mail
to provide a centralized news service
NewsgroupAn on-line discussion group that focuses on a particular
topic
Sample Newsgroup:Sewing Newsgroup
[Sewing Newsgroup]
Finding Information and Downloading Files
TelnetA 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 serviceEnables users to communicate with other Internet users
around the world who have compatible equipment and software
Internet videoconferencingSupports both voice and visual communicationsAn 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 charactersWord processing filesAudio filesGraphic imagesAny 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 on-
screen page to other documents or Web sites
HypermediaConnects 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 tagsCodes 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, hypermedia-based menu as a graphical interface to the Web
AppletsSmall programs embedded in Web pages
Search Engines
Web search tools that help users find the information they seek
Two types of Web search toolsDirectories: List of Web sites classified by topicIndexes: 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 standardsSlow 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 Internetand 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 causesMore 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 SignatureA 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
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