Transcript Chapter 7 - The Internet, Intranets, and Extranets

Chapter 7
The Internet, Intranets, and
Extranets
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The Internet
 The internet
 A network of networks
 The internet transmits data from one computer
(called a host) to another
 Internet networks
 Linked networks that work much the same
way -- they pass data around in packets, each
of which carries the addresses of its sender and
receiver
Schematic
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Internet ‘Discussion’ (1)
A global network connecting millions of computers. As of 1999, the
Internet has more than 200 million users worldwide, and that number
is growing rapidly. More than 100 countries are linked into
exchanges of data, news and opinions.
Unlike online services, which are centrally controlled, the Internet is
decentralized by design. Each Internet computer, called a host, is
independent. Its operators can choose which Internet services to
use and which local services to make available to the global Internet
community. Remarkably, this anarchy by design works exceedingly
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Internet ‘Discussion’ (2)
well.
There are a variety of ways to access the Internet. Most online
services, such as America Online, offer access to some Internet
services. It is also possible to gain access through a commercial
Internet Service Provider (ISP).
Note: York University’s CCS (Computer and Communications
Services) is an ISP.
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How the Internet Works
 Transport control protocol (TCP)
 A protocol that operates at the transport layer and is


used in combination with IP by most Internet
applications
Backbone
 An Internet high-speed, long distance communications
links (like a bus; wire that connects nodes)
Uniform resource locator (URL)
 An assigned address on the Internet for each computer
 E.g., http://www.yorku.ca/
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Domain Affiliations
Domain
arts
com
edu
firm
gov
info
mil
nom
net
org
rec
store
web
net
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Affiliations
cultural and entertainment activities
business organizations
educational sites
businesses and firms
government sites
information service providers
military sites
individuals
networking organizations
organizations
recreational activities
businesses offering goods for purchase
entities related to World Wide Web activities
networking organizations
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Access to the Internet
 LAN servers
• Local servers can provide access to the Internet through
normal connections (e.g., Ethernet)
 Serial line internet protocol (SLIP) and
Point-to-point protocol (PPP)
• Communications protocol software that transmits packets over
telephone lines, allowing dial-up access to the Internet
 Connection via an on-line service
• Examples are America Online and Microsoft Network. These
services usually require sign-up procedures
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Three Ways to Access the
Internet
Schematic
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Internet Service Providers
 Internet service provider (ISP)
 Any company that provides individuals or
companies with access to the Internet
 Thousands of providers including large
communications companies
 Need an account with the ISP and software that
links with TCP/IP
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ISP Examples
Internet Service Provider
Web Address
AT&T WorldNet Service
www.att.com
Digex, Inc.
www.digex.net
GTE Internetworking
www.gte.net
IBM Internet Connection
www.ibm.net
MCI Internet
www.mci2000.com
NetCom On-Line Communication www.netcom.com
Services
www.psinet.com
PSINet, Inc.
Sprint Internet Services
www.sprint.net
Uunet Technologies, Inc.
www.us.uu.net
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Internet Services
 E-mail
 Telnet
 FTP
 Usenet and newsgroups
 Chat rooms
 Internet phone
 Internet videoconferencing
 Content streaming
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Selected Usenet Groups
alt.fan.addams.family
alt.pets
alt.autos.camaro
alt.cloning
alt.fan.u2
alt.sports.baseball.cinci-red
alt.politics.socialism
alt.sports.soccer.european.uk
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alt.life.itself
alt.fan.bevis-n-butthead
alt.fan.leonardo-dicaprio
alt.history
alt.music.blues
alt.music.zz-top
alt.sports.college.sec
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Internet Services
 Internet telephony
 Also called voice-over-IP (VOIP)
• Technology that enables network managers to route
phone calls and fax transmissions over the same
network they use for data
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VOIP ‘Discussion’
Internet telephony is a category of hardware and software that
enables people to use the Internet as the transmission medium for
telephone calls. For users who have free, or fixed-price, Internet
access, Internet telephony software essentially provides free
telephone calls anywhere in the world. To date, however, Internet
telephony does not offer the same quality of telephone service as
direct telephone connections.
There are many Internet telephony applications available. Some,
like CoolTalk and NetMeeting, come bundled with popular Web
browsers. Others are stand-alone products. Internet telephony
products are sometimes called IP telephony, Voice over the Internet
(VOI) or Voice over IP (VOIP) products.
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Content Streaming
 Content streaming
• A method for transferring multimedia files over the
•
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Internet so that the data stream of voice and pictures
plays continuously, without a break, or very few of
them
It also enables users to browse large files in real
time
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The World Wide Web
 World Wide Web
• A collection of tens of thousands of independentlyowned computers that work together as one in an
Internet service
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WWW Terminology
 Home page
• The cover page for a Web site that has graphics,
titles, coloured text, etc.
 Hypermedia
• Tools that connect the data on Web pages, allowing
users to access topics in whatever order they wish
 Hypertext markup language (HTML)
• The standard page description language for Web
pages
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Some Interesting Web Sites
Library of Congress
PointCast
In-Box Direct
Online Career Center
New York Times
Project Gutenberg
Sportsline USA
White House
MIT Lab for Computer Science
The Wall Street Journal
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http://lcweb.loc.gov
http://www.pointcast.com
http://www.netscape.com
http://occ.com
http://www.nytimes.com
http://www.gutenberg.org
http://www.sportsline.com
http://www.whitehouse.gov
http://www.lcs.mit.edu
http://www.wsj.com
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WWW Terminology
 Web browser
• Software that creates a unique hypermedia-based
menu on your computer screen and provides a
graphical interface to the Web
 Web page
• A screen of information sent to a requesting user
and presented through a browser
 Applet
• A small program embedded in Web pages
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HTML
 “The” language of WWW pages
 Need we say more!!!
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Search Engines
 Search engines
 A search tool for the Web (like card catalogs in
libraries)
 E.g., Altavista
Excite
Galaxy
Hotbot
Infoseek
Lycos
Webcrawler
Yahoo!
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http://www.altavista.digital.com
http://www.excite.com
http://www.einet.net
http://www.hotbot.com
http://www.infoseek.com
http://www.lycos.com
http://www.webcrawler.com
http://www.yahoo.com
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Java
 Java
 An object-oriented programming language
 Developed by Sun Microsystems
 Based on C++
 Allows small programs -- applets -- to be
embedded within an HTML document
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Applets
 Applets are small java programs that are
downloaded from the server to the local
machine
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Push Technology
 Push technology
• Technology that enables users to automatically
receive information over the Internet rather than
searching for it using a browser
Also called Webcasting
•
 E.g.,
• PointCast
• InterMind
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Webcasting ‘Discussion’
Using the Internet, and the World Wide Web in particular, to
broadcast information. Unlike typical surfing, which relies on a pull
method of transferring Web pages, webcasting uses push
technologies.
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Push ‘Discussion’ (1)
In client/server applications, to send data to a client without
the client requesting it. The World Wide Web is based on a pull
technology where the client browser must request a Web page
before it is sent. Broadcast media, on the other hand, are push
technologies because they send information out regardless of
whether anyone is tuned in.
Increasingly, companies are using the Internet to deliver information
push-style. One of the most successful examples of this is
PointCast, which delivers customized news to users' desktops.
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Push ‘Discussion’ (2)
Probably the oldest and most widely used push technology is e-mail.
This is a push technology because you receive mail whether you ask
for it or not -- that is, the sender pushes the message to the
receiver.
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Business Use of the Web
 Uses:
 Applications, E-mail, Product Display, Catalogs, Order
placement
 Products people are likely to buy on the Web
Software
Books
CDs
Computer hardware
Airline tickets
Magazine subscriptions
Concert/theater tickets
Flowers
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77%
67%
64%
63%
61%
53%
48%
45%
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Intranets and Extranets
 Intranet
• An internal corporate network built using Internet
and World Wide Web standards and products that
allows employees of an organization to gain access
to corporate information
 Extranet
• A network based on Web technologies that links
selected resources of the intranet of a company with
its customers, suppliers, or other business partners
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Intranet ‘Discussion’
A network based on TCP/IP protocols (an internet) belonging to an
organization, usually a corporation, accessible only by the
organization's members, employees, or others with authorization. An
intranet's Web sites look and act just like any other Web sites, but
the firewall surrounding an intranet fends off unauthorized access.
Like the Internet itself, intranets are used to share information.
Secure intranets are now the fastest-growing segment of the
Internet because they are much less expensive to build and manage
than private networks based on proprietary protocols.
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Extranet ‘Discussion’
A new buzzword that refers to an intranet that is partially
accessible to authorized outsiders. Whereas an intranet resides
behind a firewall and is accessible only to people who are members
of the same company or organization, an extranet provides various
levels of accessibility to outsiders. You can access an extranet only
if you have a valid username and password, and your identity
determines which parts of the extranet you can view.
Extranets are becoming a very popular means for business partners
to exchange information.
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Virtual Private Network (VPN)
 Virtual Private Network (VPN)
• A secure connection between two points across the
Internet
 Tunneling
• The process by which VPNs transfer information by
encapsulating traffic in IP packets and sending the
packets over the Internet
Schematic
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VPN ‘Discussion’
Short for virtual private network, a network that is constructed by
using public wires to connect nodes. For example, there are a
number of systems that enable you to create networks using the
Internet as the medium for transporting data. These systems use
encryption and other security mechanisms to ensure that only
authorized users can access the network and that the data cannot
be intercepted.
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Tunneling ‘Discussion’
A technology that enables one network to send its data via another
network's connections. Tunneling works by encapsulating a network
protocol within packets carried by the second network. For example,
Microsoft's PPTP technology enables organizations to use the
Internet to transmit data across a virtual private network (VPN). It
does this by embedding its own network protocol within the TCP/IP
packets carried by the Internet. (Note: PPTP = point-to-point tunneling
protocol)
Tunneling is also called encapsulation.
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Internet Issues
 Management issues
 No centralized governing body for the Internet
 Service bottlenecks
 Phenomenal growth has left a service void
 Providers underestimating computing power
needed
 Reconciling router addresses needed to
transverse the network
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Privacy & Security
 Cryptography
• The process of converting a message into a secret code and
changing the encoded message back to regular text
 Encryption
• The original conversion of a message into a secret code
 Digital Signature
• An encryption technique used for online financial transactions
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Have a
nice day…
Encryption
software
running on
sending
computer
E%$&:”}{|…
Decryption
software
running on
Receiving
computer
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Have a
nice day…
Firewalls
 Firewalls
• A method of preventing unauthorized access
between a company’s computers and the Internet
(looks at the header of a packet)
 Assured pipeline
• An Internet security method that looks at the entire
request for data and then determines whether the
request is valid
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Firewall ‘Discussion’ (1)
A system designed to prevent unauthorized access to or from a
private network. Firewalls can be implemented in both hardware and
software, or a combination of both. Firewalls are frequently used to
prevent unauthorized Internet users from accessing private
networks connected to the Internet, especially intranets. All
messages entering or leaving the intranet pass through the firewall,
which examines each message and blocks those that do not meet
the specified security criteria.
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Firewall ‘Discussion’ (2)
There are several types of firewall techniques:
 Packet filter: Looks at each packet entering or leaving the network and



accepts or rejects it based on user-defined rules. Packet filtering is fairly
effective and transparent to users, but it is difficult to configure. In addition, it
is susceptible to IP spoofing.
Application gateway: Applies security mechanisms to specific applications,
such as FTP and Telnet servers. This is very effective, but can impose a
performance degradation.
Circuit-level gateway: Applies security mechanisms when a TCP or UDP
connection is established. Once the connection has been made, packets can
flow between the hosts without further checking.
Proxy server: Intercepts all messages entering and leaving the network. The
proxy server effectively hides the true network addresses.
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Firewall ‘Discussion’ (3)
In practice, many firewalls use two or more of these techniques in
concert.
A firewall is considered a first line of defense in protecting private
information. For greater security, data can be encrypted.
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End of Chapter 7
Chapter 8
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