Digital Media
Dr. Jim Rowan
ITEC 2110
your browser
(Safari)(client)
DHCP:
your computer
webpages
and
other stuff
yahoo.com
(server)
235.01.30.240
walmart.com
(server)
100.43.153.07
The Internet
Domain Name System (DNS)
your browser
(Safari)(client)
DHCP: 135.10.34.222
your computer
ISP
webpages
and
other stuff
yahoo.com
(server)
235.01.30.240
walmart.com
(server)
100.43.153.07
The Internet
Domain Name System (DNS)
your browser
(Safari)(client) http://www.yahoo.com
DHCP: 135.10.34.220
your computer
webpages
and
other stuff
yahoo.com
(server)
235.01.30.240
walmart.com
(server)
100.43.153.07
The Internet
Domain Name System (DNS)
http://www.yahoo.com =
235.01.30.240
your browser /index.html
(Safari)(client) http://www.yahoo.com
DHCP: 135.10.34.222
your computer
webpages
and
other stuff
yahoo.com
(server)
235.01.30.240
walmart.com
(server)
100.43.153.07
The Internet
Domain Name System (DNS)
http://www.yahoo.com =
235.01.30.240
IPv4 & IPv6
How many computers?
• IPv4
http://en.wikipedia.org/wiki/Internet_Protocol_version_4
FF:FF:FF:FF
255.255.255.255
256 ** 4 = 4,294,967,296 computers
• IPv6
http://en.wikipedia.org/wiki/IPv6_address
FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF
65536:65536:65536:65536:65536:65536:65536:65536
65536 ** 8 = 3.4e+38 computers: how big is that?==>
How big is that?
Circumference of the earth = 25,000 miles
25,000 x 5280 x 12 = 1,584,000,000 inches
Circumference = pi x diameter
Circumference of the earth = pi x 2 x radius
1584000000 = 3.14 x 2 x radius
radius =252,229,299 inches
Surface area of the earth = 4 x pi x radius**2
Surface area of the earth = 4 x 3.14 x 252,229,299**2
Surface area of the earth = 7.99e+17 sq inches
3.4e+38 computers / 7.99e+17 sq inches = 4.255e+20
So…
that’s 4.255e+20 computers per square inch of surface area
That should cover it!
Web Protocols
• Protocols define the rules to be followed in a
conversation
–
–
–
–
who talks first
what is acceptable to request
what are acceptable responses to a request
syntax is the actual form of each interaction
• HTTP - Hyper Text Transfer Protocol
– identifies it as a web page request
• FTP - File Transfer Protocol
– identifies it as a file that needs to be downloaded
• SMTP - Simple Mail Transport Protocol
– identifies it as pertaining to email
•
Parts of the
Uniform Resource Locator
URL
Three parts:
– Specifies the protocol to use
• HTTP
• FTP
• SMTP
– The Domain Name
• www.ggc.edu
– Directory information used by the server to find the
file to transmit
– This can be
• directory and pages
• data to be handed to a program
How to start your own website
• You have to buy a Domain Name from a
Domain Name supplier
– register.com
– godaddy.com
• The Domain Name supplier
– pay by the year
– set up domain-name-to-IP mapping
– may provide some storage space for your web
pages using their IP
…or to start a website
• You could have your own server
– Macs come with servers built in
• You must have a FIXED IP from your ISP
– not really but it makes life MUCH simpler
• You still need a Domain Name from a Domain Name
Supplier
– pay by the year
– set up domain-name-to-IP mapping
Looking up URLs and IPs
• whois IP and Domain lookups http://iplookup.net/
• look up pondliner.com domain name to get IP
• connect to pondliner.com using the IP address
• see who owns pondliner.com
• http://www.register.com/whois.rcmx
WebCrawlers
• Once looked and collected email addresses to
sell to spammers
• Simple to do
– request a page
– look through the text of the page for something @
something.something
• Can be defeated by using unfriendly-to-robotcode like: jrowan (at) GGC (dot) USG (dot) EDU
– humans can read this just fine!
Search Engines
• Web crawlers look through the web looking
for keywords
• Then they build a catalog of keywords
– You enter a keyword in the engine
– It looks at its table
– It sends you the URLs associated with the
keyword
• GOOGLE extends this by including the
number of links that point to that particular
page
And now for a little history...
A brief history
• Ward Cunningham
– invented the WikiWikiWeb
– www pages quickly editable by its users
– Wiki is Hawaiian for “fast”
A brief history
• Tim Berners-Lee
–
–
–
–
invented the World Wide Web
1980 built the first web server
mid 1980s worked with hypertext
1988- “I just had to take the hypertext idea and connect
it to the TCP and DNS ideas and ta-da! the World Wide
Web!”
– wrote the first web browser (the client)
Randy Pausch
HCI pioneer
Disney Imagineering
CMU: Entertainment
Technology Center
Creator of the Alice language
Randy Pausch
The Last Lecture:
Really Achieving Your Childhood
Dreams
http://www.youtube.com/watch?v=ji5_MqicxSo
And now…
Alan Kay
• Alan Kay’s 1968 vision of how computing
COULD be: The Dynabook
Before Alan Kay at XEROX PARC…
The command driven computer interface:
Remember the Disk Operating System? (probably not!)
• Alan Kay’s 1970’s XEROX PARC work
• The Graphical User Interface GUI
• But Xerox corporate didn’t think it was important
• which opens the door for Steven Jobs
– Macintosh 1984
– …and personal computing as we know it is born