Transcript The World Wide Web


Internet: a network of network
 The internet consists of thousands of smaller
networks
 They may be educational, commercial, nonprofit,
military organizations, etc.
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
Internet History
 Began with 1969’s ARPANET for US Dept. of




Defense
62 computers in 1974
500 computers in 1983
28,000 computers in 1987
Early 1990s, multimedia (www) became available
on internet
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MAC-b
IP:B.6.b
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MAC-a
IP:B.6.a
PC-a
IP:B.1.a
ISP2/POP-1
IP:B.1.0
Amazon.com Server
IP: A.AS.0
ISP1/POP-2
IP:E.2.0
NAP-E
IP:E.0.0
PC-c
IP:E.2.c
MAC-a
IP:C.4.a
Udel-4
IP:C.4.0
PC-b
IP:E.2.b
PC-b
IP:C.4.b
NAP-C
IP:C.0.0
NAP-D
IP:D.0.0
Comcast/POP-3
IP:D.3.0
Comcast/POP-5
IP:D.5.0
PC-a
IP:E.2.a
PC-d
IP:E.2.d
MAC-d
IP:B.6.d
ISP2/POP-6
IP:B.6.0
NAP-B
IP: B.0.0
NAP-A
IP: A.0.0
MAC-c
IP:B.6.c
PC-a
IP:D.5.a
PC-b
IP:D.5.b
PC-b
IP:D.3.b
MAC-a
IP:D.3.a

NAP (Network Access Point): A routing computer at a point on
the internet where several connections come together
 Connects to the Internet Backbone (fast, expensive connection)

Router: A device that forwards data from one network to
another based on internal routing tables
 Routers read each packet’s destination IP address and decide how to
forward it.
IP Address: Internet Protocol Address – a unique address that
identifies every computer and device connected to the internet
 POP – Point of Presence – A local access point to the internet
 ISP: Internet Service Provider – A local, regional, or national
organization/company that provides access to the internet
 LAN – Local Area Network – a computer network that spans a
relatively small area

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
Protocols
 set of rules and encoding specifications for sending data
 Internet uses TCP/IP (Transfer Control Protocol/Internet
Protocol
▪ Used for all internet transactions

TCP – Deals with Transfer of Data – how it is broken up
and reassembled to be sent across the internet
 Packets
▪ Fixed-length blocks of data for transmission
▪ Data transmissions (files) are broken up into packets
▪ Not all packets from the same file will follow the same pathway
▪ Data must be reassembled at the other end
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

IP – Deals with the addressing and pathways the data
travels over the internet
IP Addresses
 Every device connected to the internet has an
address
 Each IP address uniquely identifies that device
 The address is four sets of 3-digit numbers
separated by periods
▪ Example: 95.160.10.240
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
The Internet is Distributed
 No centralized control of the internet
▪ If any one computer goes down, the internet can continue
to function
 Allows for expansion of the internet as well
 Can easily add new computers and networks to
the internet.
▪ Must assign unique IP addresses to computers connecting
to the internet and
▪ Must update Router Tables
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
Client/Server Model
 Client: a computer requesting data or services
 Server: a host computer, a central computer supplying data or services
requested of it
▪ Services can be requested over the internet
▪ E.g., Check your bank account
 A client program on your computer forwards your request to a server program at your
bank. The bank server sends the info back to your client program
 Often multiple clients share the services of one server
▪ Or Services can be local requests
▪ Maybe one computer on a local network has extra disk space and can hold a large database
▪ Clients on the network make requests from the local server and the server sends only the data
the client requests

Peer to Peer (P2P) Model
 Computers that both provide services to and receive services from each
other
▪ Services execute on a temporary basis
▪ E.g., Instant Messaging,
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
The World Wide Web:
 Browsers
▪ Software for web-surfing
▪ Examples: Internet Explorer, Netscape Navigator,
Mozilla FireFox, Opera, Apple Macintosh browser,
Safari
▪ Browsers do 2 key things:
▪ Locate web sites via unique addresses
▪ Read web pages and display them
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 Website
▪ A location on the web that has a unique address
and a set of interconnected web pages, usually on
the same server
▪ Example: www.barnesandnoble.com,
www.eecis.udel.edu
▪ The website could be anywhere
▪ not necessarily at company headquarters
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
Web Pages
 The documents and files on a website
 Can include text, pictures, sound, and video

Home page
 The main entry point for the website
 Contains links to other pages on the website
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(URL)

 A string of
(unique)
 URL =
 It consists of
▪
▪
▪
▪
▪
that points to a specific
on the web
The web protocol The
of the web server
The directory or
on that server
The file within the directory, including optional extension
http://www.imageek.com/girlgeek/java.htm
protocol
domain name
directory
file name . extension
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
 Must be unique
 Identify the
▪ www.whitehouse.
www.whitehouse.
▪ .gov ,.org, .edu, etc.
, and the type of
it is
is NOT the same as
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
 The
 Stands for
used to access the World Wide Web

 The
version of

 The language used in writing and publishing
 The set of tags used to specify document structure,
formatting, and links to other documents on the web
 NOT a programming language (but it can contain
programming code)

connect one web document to another
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
 Organizations that maintain
accessible through
on the internet
to locate
websites to help you find
 Users can ask questions or use
information
 Examples: Google, Ask Jeeves, and Gigablast

are compiled using software programs
called
▪
crawl through the World Wide Web
▪ Follow links from one page to another
▪
the words on that site
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
There is no
internet sites
 Should you

that verifies all
information you find online?
Guidelines to evaluate Web Resources
 Does the information appear on a
maintained by a
 Does the website
legitimate?
 Is the website
and
?
?
appear to be
,
,
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
Email Program
 Examples: Microsoft’s Outlook Express, Mozilla’s
Thunderbird, Apple’s Apple Mail
 Enables you to send email by running email
software on your computer that interacts with an
email
(usually at your
)

mail is stored on the
in
an electronic mailbox
 Upon
, mail is sent to your
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
Using email
1. Get an
, following the format
[email protected]
User Name
Domain name
2. Type addresses carefully, including capitalization,
underscores, and periods
3. Use the
to avoid addressing mistakes
4. Use the
to store email
addresses
5. Sort your email into
or use
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
2
for transferring mail from the
to the
:

I

1
for transferring mail from

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
–
(NOT to be
confused with Point of Presence!)
 How this works:
1.
2.
3.
4.
5.

– holds your mail
– logs on and requests mail
– downloads all mail to the client (your computer)
– removes your mail
can disconnect – you’ve got all your mail now!
Advantages:
▪
▪
▪
Don’t need to stay
to the
are used minimally
More software is currently available for
for long
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
 How this works:
1.
2.
3.
– holds your mail
– logs on
– downloads email headings
(subject) only
▪
▪
▪
reads mail on the
chooses which mail to
Mail remains on
and
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
Advantages:
▪
▪
▪
▪
▪
You can
your
any computer
Faster
time (not
email files)
Good for
Ability to handle
messages)
can act like
superset of
anywhere, from
all your
(e.g., MIME
– functionally is a
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
:
 Your
 You use
limits your
read your email
 You can only stay
limited amount of time
 Your server has

and
to the
only to
for a
:
 You travel or check your
 You get a lot of
to your computer
 You want
 You can maintain a
 You have a lot of
from more than one
and don’t want to
it all
to your messages
to your
on your
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

used to transfer data from one
to another
 Uses
 Think of it this way: When you send an email
message out, it uses
to travel to
. When you want to read an
email, you use
or
to get the
email message from the
.
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
 Any user on a given email system can send a
message and have it pop up instantly on the
screen of anyone logged into that system

 Participants have a typed discussion while online
at the same time

is one-on-one, but
participants
has a list of
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
 A software standard for transferring
between computers with different Operating Systems

 A giant electronic discussion board
 Usenet is the
the internet www.usenet.com
 To participate you need a
of servers on

 An email-based
 Uses an automatic
that sends
to subscribers on selected topics
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

Internet Telephony
 Uses the internet to make
 Long-distance calls are either very inexpensive or free
 Currently
to normal phone connections
 Programs that scour the web and pull together


from several
to one place
 Short for
, a diary-style web page
 Have become popular, both privately and in politics
 Recording internet radio or similar internet audio programs
 Some radio stations
their audio programs
over the internet
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
 Conducting business activities online

is business-to-business ecommerce

now involves online banking,
stock trading online, and e-money such as PayPal
 Online
link buyers with sellers
▪
is the most well-known example of personto-person
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