Transcript internet-new - Computer Science and Engineering

Getting into the fast lane
on the
Information Superhighway
Objectives:
•Insights into the history and
architecture of the Internet
•A little lesson in html
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You already know how to use these
Communication tools. But how do
they work?
 E-Mail
 Newsgroups
 World
Wide Web
– Search Engines
– URLs, Domains, Extensions, Etc.
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Building Blocks of Data
Communication
 Architecture
– How the pieces fit together – Physical links
 Protocol
– Rules of communication observed between the
pieces
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The Simplest Network - Architecture
Handshaking
Computer <--> Modem <-->
–Transmission Media
<--> Modem <--> Computer
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Local Area Networks (LAN)
X
X
Backbone or truck


Ring
Do messages go from point A to B or are they sent to all
nodes (“broadcasting”)?
Who goes first?
– Synchronous time division allows a node to send only at a specific
time (you can use the phone only on even hours)
– Frequency signal division allows a node to send a signal over a
specified “part” of the bandwidth (tv signals sent to your TV)

What happens if a node goes down?
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Wide Area Networks (WAN)

Client-Server Architecture
– one to many relationship
– centralized processing, storage
– Protocol Issues
 What happens if server goes down?
X
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Birth of the Internet
In 1957 as a reaction to the Soviet launch of Sputnik the US
government funded the agency ARPA
Their fundamental charge was to create a way
authorities could communicate in the aftermath of a
Nuclear attack - computers were being used by the
military for logistics & communications, & weapons
systems
1957 Communication
networks used a chained
point to point approach
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Birth of the Internet
From 1962 -1969 some of the best technical minds explored the
idea of a “fishnet” structure of connecting computers and “packet
switching” to relay messages across this network.
– Major technical hurdles needed to be overcome:
 Hardware - Could packets be sent/received on many
different types of computers?
 Memory - Did current day systems have enough memory to
do this?
 Software and Protocols - How were packets to be received
and sent to the correct place?
Remember this is still prior to the introduction of the PC. Even the largest
computers of this time were less powerful than a typical PC.
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1969: The original ARPANET had 4 nodes
UCLA
UCSB
Stanford
Univ. of Utah
A message could start out at UCSB take many different routes to
get to Stanford
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Birth of the Internet
Between 1970 and and 1982 the Internet continued
to evolve
 Email was introduced
 The number of nodes grew to 213 in 1981
including US & European governments and
universities.
 Commercial versions were launched (Usenet,
Bitnet) allowing for the first newsgroups
The development of Personal Computers - the introduction of the IBM
PC’s was taking place toward the end of this period
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Birth of the Internet 1982 -1991 the Internet develops into the format we
have today




1982 the TCP/IP transfer protocols were adopted after
almost a decade of development & testing
1986 NSF funds the NSFNet which is the backbone of the
modern Internet. They also remove the commercial use
restriction.
1989 “Http” was introduced allowing for the use of text,
graphics and sound
1990 The first web browsers were introduced
(early 1990 was about the timeframe of Windows being marketed)
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The Growth of the Internet as Measured by
The Number of Nodes
140,000,000
Number of Nodes
120,000,000
100,000,000
80,000,000
60,000,000
40,000,000
20,000,000
69
71
77
81
84
86
87
89
95
97
98
99
00
01
Year
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Internet Architecture -Nodes
ISP - Internet Service Provider
– Collects and switches traffic
– For example, MCI, AOL, Iwaynet
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ISP
ISP
ISP
IPP
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Internet Architecture - Nodes
IPP - Internet
Presence Provider
– Virtual Real Estate
Landlord – stores our
html files, e-mail etc.
– Geocities & Yahoo,
cis.ohio-state.edu
ISP
ISP
IPP
ISP
For More: http://navigators.com/internet_architecture.html
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So how does my e-mail get from here to wherever?
Me
London
– Does my email get “broadcast” to every
computer in the world and the one with the
correct address reads it?
– In fact the internet ISP’s actually create direct
links and send the message on, one link at at
time. These are known as “routers”. Messages
are queued at either end by mail servers.
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So how does our e-mail get from here to wherever?
 Physically
the computers are
sending & receiving signals
(pulse, digital, optical, radio
etc.) over a transmission media
representing binary digits (0,1)
 How does the computer know
what they mean?
Me
0
1
1
0
London
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Internet Protocol Standards
A series of rules or “protocols” have been
developed and adopted by all in order that
messages, web text, images, files can be understood
 One of the challenges was to develop a method in
which the intermediary “routers” don’t actually
care what is being sent in order to transmit it to the
next stop (digital, optical, radio, etc).
 To solve this problem “Layers” of protocols were
established, each with a different function. Each
layer is independent of the previous layer.

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Internet Protocol Standards
Application Layer: Specific to application – HTTP, FTP,
SMTP (decoding)
Transmission Layer: Creates packets for transmission,
requests transmission connection, verifies transmission
receipt (receiving)
Network Layer: Handles Routing & addressing (routing)
Physical or Link Layer: Transmits the signal for a
specific connection (transmitting)
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The Application Layer
The Application protocol attaches information to be sent
with a transmission listing parameters the receiving
computer will need to interpret the information. The
length and order of this data is determined by the
protocol type:
– FTP - File Transfer Protocol
– HTTP - Hypertext Transfer Protocol
– SMTP – Simple Mail Transfer Protocol
Application layer adds tag - #Bytes
This is my
& order of the tag are determined by
email message
protocol type
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The Transmission Layer
•The transmission layer breaks
up the message into smaller
packets. Then it adds a tag
onto each packet.
• The transmission layer works with the Network
layer to translate the destination IP address
• Common transmission protocols include:
• TCP – protocol designed to create a verifiable
transmission (transfer control protocol)
• UDP – protocol designed to create an unverified
transmission (user datagram protocol)
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The Transmission Layer - Packet
Transmission layer tag#Bytes &
order determined by protocol type
Application Part of
layer tag
email
The transmission header includes information in a
specific format. Each protocol has its own set of rules.
This information may include:
•Source and destination ports (Application type)
•Total number of packets
•Size of this packet
•Checks information for verification that data was
correctly received (TCP protocol)
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The Network Layer
The Network layer takes each packet and again adds
a tag that includes information in a pre-set order &
size. This is the IP protocol tag, 320 bites in length.
Byte lengths:
4
version
4
4
priority
Pay load length
4
4
4
flow label
next header
4
4
hop limit
128 bites source address
128 bites destination address
Network layer tag
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Transmission
layer tag
Application Part of
layer tag
email
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What is an IP address?
• In general we use domain names to address our email
or locate a web page. The routers use an IP address
system. Each “node” has a unique 64 bit IP address.
• The domain osu.edu IP address is 164.107.23.1 this
translates to 10100010.01101011.00010111.00000001
• The Transmission layer protocols working with lower
levels, match the domain name to an IP address. Using
a hieratical search, the computer first looks for stored
names. If there is no match the computer contacts a
DNS (domain name service) to search their indices.
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Matching the domain name to an IP address
The TCP protocol first tries to match the domain name
to a stored IP addresses on the node. If there is no match
it goes “out” to find the information, until a match is
found.
Domain Name Service
.uk
.com
.org
.gov
.edu
.osu
.cis
.uc
164.107.23.1
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The Physical or Link Layer
Thus far we have this “packet” of our data addressed with
all the information needed to send it on its way and
translate it at the other end. The Physical or Link Layer is
responsible for transmitting this series of bits (0’s & 1’s)
on its way- including:
• Preparing
the bit stream for transmission
• Bits are added to identify to the receiver that a new packet is
coming and where the data starts & ends. Bits are also added
to breakup large chunks of repeated signals to avoid
transmission errors.
•
Receiving, storing and interpreting the signals
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The Physical or Link Layer
Each packet is sent from the ISP to the next node onwards
until it reaches its destination. Router’s match the IP
address to a constantly updated list and pass the packet
along.
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Packet
Transmission
Email
Application
layer
Transmission
layer
•A packet of data is prepared and
transmitted
•At each router stop, the signals are
interpreted and sent to the network
Email
layer in order to read the IP address
and determine the next appropriate
Application
stop.
layer
•The packet then goes back to the
physical layer for re-transmission. Transmission
layer
Network
layer
Network
layer
Network
layer
Network
layer
Physical layer
Physical layer
Physical layer
Physical layer
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Packet transmission is only one “piece” :
Host computer
requests link
ISP responds & Link
established
Host
Sends packets
Link closed
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Destination host
receives packets
and acknowledges
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How fast can information be transmitted?
Transmission Rates are only as fast as the slowest pipe
– Personal connections in bytes per second:
Standard telephone lines 14.4 kbps to 33.6 kbps
 Leased lines 56 kbps
 500-30,000 kbsp – TV cable

– Networks

Apple Talk, Ethernet, IBM token ring range 4000-100,000 kbps
– Long Haul lines
T3 or DS3 44,736 kbps
 OC12 622,000 kbps

?
?
ISP
ISP
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ISP
?
ISP
?
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Caution: Viruses
Viruses are little programs that attach themselves to
your computer system with potential for harm.
Be suspicious of any unsolicited email, even from
friends. ( for more info - http://www.symantec.com/avcenter/vinfodb.html)
– attachments may contain viruses (e.g. Happy99, Lovebug).
– Some viruses exploit security “holes” in popular email
packages (e.g. Melissa)
Most
people who transmit viruses in email don’t even
know that their system is infected.
Virus detection software only protects you from
KNOWN viruses and security “holes”.
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How are we able to view the same web
page on different browsers?
Transmission Protocols allow us to transmit
information without regard to what is being
transmitted.
 The web similarly specifies a set of protocols that
allow us to interpret textual, graphic and sound
and video data, independent of the “browser”
software we use. Browsers read a common
language known as HTML.

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What is HTML?
 HTML (HyperText
Markup Language) is
the language used to write Web pages.
 You can view HTML pages in two ways:
– One view is their appearance on a Web
browser
colors, different text sizes, graphics.
– The other view is called "HTML Code"
 this
is the code that tells the browser what to do.
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HTML Code
The Simplest Web Page
<html>
<head>
<title> Simple Page </title>
</head>
<body>
<h1><b> This is my first web
page </b></h1>
<h2> It is pretty simple </h2>
<hr>
Someday I will be able to put
more on this page.
But, for now I am done.
</body>
</html>
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What you see from the Browser
Simple Page
My first web page
It is pretty simple
Someday I will be able to put
more on this page.
But for now I am done
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What is a tag?

A tag tells the browser what to do.
– change the appearance of text, show a graphic, or
to make a link to another page.
The tags you write are not visible, but their
effects are.
 Tags begin with "<" and end with ">".
 Tags usually come in pairs but not always

– <b> starts printing bold text.
</b> stops printing bold text.
– <hr> create a line
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What each tag does:
<html> Cues the browser to start interpreting tags
<head> </head> Cues the browser to place text in the
header bar of browser window
<title> </title> Places the text in the title format
<body> </body> Begins &ends the body of the web
page
<h1> </h1> Begins & ends a Predefined Header 1 format
<b> </b> Begins & ends bolding all text after this tag
<h2> </h2> Begins & ends header 2 format
<hr> Draws a line
</html> Cues the browser to stop interpreting tags
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Here are some common tags
HTML Code
Browser Display
I want to <I>italicize</I> this!
I want to italicize this!
I want to <U>underline</U>
this!
I want to underline this!
I want to <B>emphasize</B>
this!
I want to emphasize this!
I want <FONT
COLOR=”red”>RED!</FONT>
I want RED!
I want <FONT
I want BLUE!
COLOR=”blue”>BLUE!</FONT
>
I want <FONT
I want GREEN!
COLOR=”green”>GREEN!
</FONT>
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Putting the hyper into hypertext.
HTML allows us to create pages that reference other
documents and images residing in different directories,
and computers. We can use these links to display an
image that resides in another file, or to actually send
our browser to another URL.
– A "link" is a pointer to somewhere else.
– An "anchor" is a link that sends your browser
to another location.
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Hypertext link
<a href=”http://www.microsoft.com”> Go to Microsoft</a>
A hypertext link sends the browser to the link's
destination. To create a hypertext link use the anchor tag.
The Anchor Tag has three parts:
 <a href=“url”> tells the browser where to go, if
selected.
 linked text tells the user what the link is for
 </a> tells the browser to stop linking text
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Another use for an Anchor tag is to send
email to a specified address

Use a anchor tag to launch your default email
program. In Netscape it will bring up a composer
window with the address specified in the link.
<a href=“mailto:[email protected]”>
Send john smith email</a>
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Linking to Graphic images
An <IMG> tag requests that an image file be
inserted at this point on the current web page.
 Notice this is not an anchor, the browser does not
jump to another location.

<img src=“http://www.123clipart.com/misc/misc12.gif”>
Browser display
Notice that the <IMG> tag is an
unpaired HTML tag.
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Link Addresses
• Be careful to always use the correct address
for your links and graphics spellig UPPER
or lower case. Remember to use standard
graphic files.
• There a two types of link addresses which
can be used:
• Absolute link – addresses the link to a fixed URL or file
• Relative link – addresses the link to a file path/name
which is relative to your current file path
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Absolute URLs

Fully expressed path <img src=
“http://www.yahoo.com/images/jones/mypic.gif”
This link will retrieve the image file
from the computer host
www.yahoo.com (specific IP address).
Once connected to this server it will
link to the images directory, then to
the jones subdirectory and finally to
the file mypic.gif.
A
C:\WWW\images\mypic.gif
IP: 204.71.200.33
Domain: yahoo.com
No matter where you link from, the web
page will always insert this image.
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Relative URL
Incomplete path, depends on referrer’s current
directory. <img src= “/images/mypic.gif”>.
 Protocol and network parts are not included. The
path starts from the directory of the current
document.
 From different computers this would refer to
different image files. Frequently when the image is
not displayed, a relative URL has been used but the
desired file does not reside in the directory path of
the referencing computer.

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Relative URL
Starting from network A and B the tag
<img src= “/images/mypic.gif”> may result in
different images.
IP: 204.71.200.33
Domain: yahoo.com
A
C:\WWW\images\mypic.gif
B
164.107.114.99
cis.ohio-state.edu
Z:\WWW\~jones\200\mypic.gif
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Using Relative vs. Absolute Reference
When Writing Your Own Web Pages
•Relative link references have the advantage of
portability.
• Works even if you change hosts as long as all files are
also moved to new host maintaining the same directory
paths.
•Absolute link references have the advantage of
that you can link to files on other hosts.
• No matter where your file is moved to, the links will not
change. You are not required to store these files on your
own server.
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Creating Your Own Web Pages
The
easiest way is to use a software package capable
of translating the information into HTML
– MS Word - the use the file-save as html option
– Netscape - use menu option File | Open or New and choose as a
Composer document
– Many other software packages that allow you to create your web page
and save in html format
These
packages will assist you in formatting text,
inserting graphics and links.
– Each software package has a different way of allowing you to perform
each function. Experiment and read the on-line help. You should know
how to write text, incorporate a graphics file, setup a hyperlink to
another web page and a hyperlink to send email..
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Enhancing Your Web Pages

Copy a page or graphics from another web page
– Use FILE | SAVE AS on your browser to save interesting
pages locally. Then open the pages with your HTML editor
to tailor them. You can also directly copy the HTML code
from the source using VIEW | PAGE SOURCE.

Write a web page using HTML directly
– Learn to use HTML tags and write your page from scratch
with a text editor. Make sure your file is saved as type TEXT
and that the file name uses .htm or .html as a file extension.
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Doing more with your web page
 HTML editors
are not very good at handling
advanced HTML features like:
– frames
– forms
– java applets or animation
 To
get these features you need to be able to
write your own HTML tags.
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Caution:
Do not copy text and/or images from websites
that are copyrighted  !!
–
Some sites allow you to use the copyrighted
images/text for educational purposes. Be sure to
observe their stipulations
 prior
notification
 citation
 no direct links to their ISP
There are stiff penalties for violating copyright laws
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Publishing Your web Page onto the CIS IPP

To publish a web page you need the following:
– An Internet Presence Provider (cis.ohio-state.edu,)
– Save your file(s) to the correct file directory on the
Provider’s system (W:\WWW)
– Name the file(s) to match the default name of your web
site and give any files you link to the correct
paths/filenames as well (index.html)
– Set permissions so others can view your file – but not
change them (Everyone – read only)
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Publishing Your web Page onto the CIS IPP
You
will now should be able to find your web page at:
www.cis.ohio-state.edu/~yourloginname
If
at any point after this you edit your page either from the
original source (index.html file) or from the composer
you’ve used - you will have to reset the permissions again.
Note: This
page will be deleted from the server at the end of the
quarter. Yahoo.com and geocities.com and other commercial IPP
provide free web page services.
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Cautions:
With every wonderful new technology - there always
seem to be ways of abusing it. Just because its on
the internet doesn’t make it correct or legitimate.
– Use the same criteria as you would for any
printed document.
 Is
the source reputable?
 Does it make sense?
 Is it recommended by credentialed experts?
– Beware of hoaxes - selling, warning or
promising things. Deal only with reputable
companies. (for more info: http://www.snopes.com/spoons/faxlore/)
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