Transcript The World Wide Web - Clemson University

Internet and the WWW
Dr. Jim Martin
[email protected]
Copyright 2007 Jim Martin
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History of the Internet
ARPANET
Goal:
To allow scientists
at different
locations to share
information
Networking project by
Pentagon’s Advanced
Research Projects
Agency (ARPA)
Goal:
To function if
part of network
were disabled
Became
functional
September 1969
Copyright 2007 Jim Martin
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History of the Internet
Today
More than 400 million host nodes
1984
More than 1,000 host nodes
1969
Four host nodes
Copyright 2007 Jim Martin
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Who controls the Internet?


No one — it is a public, cooperative, and
independent network
Several organizations set standards
c
c
World Wide Web
Consortium (W3C)
 Oversees research, sets
standards and guidelines
 Tim Berners-Lee, director
Internet2 (I2)
 Internet-related research and
development project
 Develops and tests advanced
Internet technologies
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Internet names and addresses

The Internet Protocol (IP) defines many of the rules that make the
Internet work.

IP requires all computers on the Internet have an IP address.


A 32 bit (4 bytes) quantity
Every computer must have a different IP address.

You might here about an IP address shortage…

There are only 4,294,967,296 unique IP addresses (according to
http://www.ibiblio.org/lunarbin/worldpop there are just over 6.6 billion
people- so everyone can not have their own IP address)
To find the IP address of a Windows machine,
Go to start, control panel, network and Internet
connections, network connections and click the right
Button on the Local Area network connection and
Select status. You will see this panel of information.
The default gateway is the IP address of a machine
Nearby that helps your machine connect to the
Internet.
Copyright 2007 Jim Martin
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Internet names and addresses



The Internet Protocol (IP) defines many of the rules that make the
Internet work.
All computers on the Internet have an IP address
What is a IP address?


Number that uniquely identifies
each computer or device
connected to Internet
Some computers have a domain name that is mapped to the
computers IP address



Domain Name: www.google.com
Address in dotted decimal format: 216.239.39.99
Address in binary:
11011000 11101111 00101001 01100011
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Internet names and addresses


Names are organized in a hierarchy
Clemson’s Internet Names


Educational Institution - .edu
 Clemson University – clemson.edu
 Clemson’s Web Server – www.clemson.edu
 Computer Science – cs.clemson.edu
Other Top-Level Domains



.com – commercial
.org – non profit organization
.gov – government sites
Copyright 2007 Jim Martin
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Web browsers and servers
Internet Explorer,
FireFox
BellSouth
Internet
www.usatoday.com
HTTP GET COMMAND: "GET /~jmarty/index.html HTTP/1.0"
Returns the web object. File size ranges
From 20 bytes to gigabytes
Copyright 2007 Jim Martin
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Web browsers and servers
Internet Explorer,
FireFox
BellSouth
Internet
www.usatoday.com
Data sent between computers is packaged in packets.
TCP/IP refers to the set of protocols that defines the rules for
sending and receiving packets
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Web browsers and servers
Internet Explorer,
FireFox
BellSouth
Internet
www.usatoday.com
The time from when
the browser
Sends the message
until when all
The data is received is
the
response time.
HTTP GET COMMAND: "GET /~jmarty/index.html HTTP/1.0"
Returns the web object. File size ranges
From 20 bytes to gigabytes
Copyright 2007 Jim Martin
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Where do the delays come
from?

Transmission time: time to transmit the
message over a link.

T-t : message size in bits / link speed
(bits)

bits per second
Propagation delay : Time for the bit to
propagate over the physical medium.

Electro-Magnetic energy travels at the speed of
light.

E.g., propagation delay from NY to LA is about .003
seconds.
Copyright 2007 Jim Martin
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Ping program

Ping is an Internet program that tests if a machine is
alive.


Also lets us test the round trip time (RTT) and the loss rate
between two machines.
All computers have the ping program. However not
all computers will reply.
Ping request msg
Ping reply msg
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Ping: RTT calculation



Two computers connected by a 64000 bps link.
The one – way propagation delay over the link is
.003 seconds.
What RTT would you expect if a 64 byte message is
sent and echoed back?
RTT= 2 * transmission delay + 2 * propagation delay
= 2 * ( (64 * 8) / 64000) + 2 * (.003)
= 2 * (.008) + 2 * (.003) = .022 seconds
Copyright 2007 Jim Martin
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Assessing application
performance

When downloading a file throughput is
used to assess performance:

Throughput: how much data is sent in a
given time.


Download a 10,000 byte file in .060 seconds
Throughput = 10,000 * 8 / .060 = 1.33
megabits per second (1.33 Mbps)
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