Transcript W W W

INTERNET
A global network connecting millions of computers. More than
100 countries are linked into exchanges of data, news and
opinions.
There are a variety of ways to access the Internet
It is also possible to gain access through a commercial
Internet Service Provider (ISP).
HISTORY
In 1969,the Advanced Research Project Agency (ARPA) funded by US
department of Defense, created the first version of what we now term the
internet called as ARPANET. The first version linked four computer located in
US.
The first e-mail program was created by Ray Tomlinson of BBN in 1972.
ARPANET was currently using the Network Control Protocol or NCP to
transfer data. This allowed communications between hosts running on the
same network.
1973 Development began on the protocol later to be called TCP/IP, it was
developed by a group headed by Vinton Cerf from Stanford and Bob Kahn
from DARPA. This new protocol was to allow diverse computer networks to
interconnect and communicate with each other.
1976 Dr. Robert M. Metcalfe develops Ethernet, which allowed coaxial cable
to move data extremely fast. This was a crucial component to the
development of LANs.
In 1992 World-Wide Web released by Corporation for Research and
Educational Networking (CREN).
ISP

Internet Service Provider, a company that
provides access to the Internet. For a
monthly fee, the service provider gives you a
software package, username, password and
access phone number. Equipped with a
modem, you can then log on to the Internet ,
browse the World Wide Web and send and
receive e-mail.
MODEM

(mō´dem) (n.) Short for modulator-demodulator. A
modem is a device or program that enables a
computer to transmit data over, for example,
telephone or cable lines. Computer information is
stored digitally, whereas information transmitted over
telephone lines is transmitted in the form of analog
waves. A modem converts between these two forms.
Fortunately, there is one standard interface for
connecting external modems to computers called RS232.
Difference between Internet and WWW

The Internet and the Web are two separate but related things.

The Internet is a massive network of networks, a networking
infrastructure. It connects millions of computers together globally,
forming a network in which any computer can communicate with any
other computer as long as they are both connected to the Internet.

Information that travels over the Internet does so via a variety of
languages known as protocols.

The World Wide Web, or simply Web, is a way of accessing information
over the medium of the Internet.

The Web uses the HTTP protocol, only one of the languages spoken over
the Internet, to transmit data.

Web also utilizes browsers, such as Internet Explorer or Firefox, to
access Web documents called Web pages that are linked to each other
via hyperlinks. Web documents also contain graphics, sounds, text and
video.
PROTOCOLS
The protocol determines the following:
1.the type of error checking to be used
2.data compression method, if any
3.how the sending device will indicate that it
has finished sending a message
4.how the receiving device will indicate that it
has received a message
 The protocol can be implemented either in
hardware or in software.

WWW
A system of Internet servers that support specially formatted
documents. The documents are formatted in a markup
language called HTML (HyperText Markup Language) that
supports links to other documents, as well as graphics, audio,
and video files.
This means you can jump from one document to another
simply by clicking on hot spots.
BROWSER
Short for Web browser, a software
application used to locate and display Web
pages.
 The two most popular browsers are
Microsoft Internet Explorer and Firefox. Both
of these are graphical browsers, which
means that they can display graphics as well
as text.
 In addition, most modern browsers can
present multimedia information, including
sound and video, though they require plugins for some formats

URL
Abbreviation of Uniform Resource Locator, the global
address of documents and other resources on the World
Wide Web.
ftp://www.pcwebopedia.com/stuff.exe
http://www.pcwebopedia.com/index.html
The first part of the address is called a protocol identifier
and it indicates what protocol to use, and the second part is
called a resource name and it specifies the IP address or
the domain name where the resource is located. The
protocol identifier and the resource name are separated by
a colon and two forward slashes. For example, the two URLs
point to two different files at the domain pcwebopedia.com.
The first specifies an executable file that should be fetched
using the FTP protocol; the second specifies a Web page
that should be fetched using the HTTP protocol.
DOMAIN NAME


A name that identifies one or more IP addresses. For example,
the domain name microsoft.com represents about a dozen IP
addresses. Domain names are used in URLs to identify
particular Web pages. For example, in the URL
http://www.pcwebopedia.com/index.html, the domain name is
pcwebopedia.com.
Every domain name has a suffix that indicates which top level
domain (TLD) it belongs to. There are only a limited number of
such domains. For example:
gov - Government agencies
edu - Educational institutions
org - Organizations (nonprofit)
mil - Military
com - commercial business
net - Network organizations
ca - Canada
th - Thailand

Because the Internet is based on IP addresses, not domain
names, every Web server requires a Domain Name System
(DNS) server to translate domain names into IP addresses.
IP ADDRESS
The internet works by defining an address for each
resource attached to it. In the case of attached
computer and some devices , this is internet protocol
address. IP add it’s a 32 bit address.
 Eg : 158.162.131.2
The number break down to a country, to a specific
domain, right down to machine itself.
 of course we don’t use numbers to find resources and
machines – we use name like vesit.ce.edu
 The name will actually have an associate number, but
when a name is entered into a web browser ,the a web
browser ,the computer will use a special system called
Domain Name System (DNS) to look up the associate
number which it will then use to get in contact with the
desired server.

How computer links to internet
Email
server
web
DNS
Internet
Internet Service Provider
81.155.138.148
Router/Gateway
192.168.1.1
192.168.1.2
192.168.1.3
192.168.1.4

Any communication that takes place on the
internet uses the TCP/IP suite. This is a set
of communication protocols for dialogs
between computers and devices.

These protocols implements a stack ,each
layer of which solve problems relating to the
transmission of data , as well providing
services to higher layers than itself. Higher
layers are logically closer to the user.
M2-Internet
H. Fauconnier
DNS: DOMAIN NAME SYSTEM
People: many identifiers:

SSN, name, passport #
Domain Name System:

Internet hosts, routers:


IP address (32 bit) - used for
addressing datagrams
“name”, e.g., ww.yahoo.com used by humans
Q: map between IP addresses
and name ?

distributed database
implemented in hierarchy of
many name servers
application-layer protocol host,
routers, name servers to
communicate to resolve names
(address/name translation)
 note: core Internet function,
implemented as applicationlayer protocol
 complexity at network’s
“edge”
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M2-Internet
H. Fauconnier
DISTRIBUTED, HIERARCHICAL DATABASE
Root DNS Servers
com DNS servers
yahoo.com
amazon.com
DNS servers DNS servers
org DNS servers
pbs.org
DNS servers
edu DNS servers
poly.edu
umass.edu
DNS serversDNS servers
Client wants IP for www.amazon.com; 1st approx:
 client queries a root server to find com DNS server
 client queries com DNS server to get amazon.com DNS
server
 client queries amazon.com DNS server to get IP address
for www.amazon.com
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M2-Internet
H. Fauconnier
DNS
DNS services
 hostname to IP address
translation
 host aliasing



Canonical, alias names
mail server aliasing
load distribution

Why not centralize DNS?
 single point of failure
 traffic volume
 distant centralized database
 maintenance
doesn’t scale!
replicated Web servers:
set of IP addresses for one
canonical name
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M2-Internet
H. Fauconnier
LOCAL NAME SERVER
does not strictly belong to hierarchy
 each ISP (residential ISP, company, university)
has one.

 also

called “default name server”
when host makes DNS query, query is sent to
its local DNS server
 acts
as proxy, forwards query into hierarchy
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M2-Internet
DNS NAME
RESOLUTION EXAMPLE
H. Fauconnier
root DNS server
2

3
Host at cis.poly.edu
wants IP address for
gaia.cs.umass.edu
iterated query:
 contacted server
replies with name of
server to contact
 “I don’t know this
name, but ask this
server”
TLD DNS server
4
5
local DNS server
dns.poly.edu
1
8
requesting host
7
6
authoritative DNS server
dns.cs.umass.edu
cis.poly.edu
gaia.cs.umass.edu
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M2-Internet
DNS NAME
RESOLUTION EXAMPLE
recursive query:
 puts burden of name
resolution on
contacted name
server
 heavy load?
H. Fauconnier
root DNS server
2
3
7
6
TLD DNS server
local DNS server
dns.poly.edu
1
5
4
8
requesting host
authoritative DNS server
dns.cs.umass.edu
cis.poly.edu
gaia.cs.umass.edu
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

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
Layer 7: The application layer ...This is the layer at which communication
partners are identified, quality of service is identified, user authentication and
privacy are considered, and any constraints on data syntax are identified. (This
layer is not the application itself, although some applications may perform
application layer functions.)
Layer 6: The presentation layer ...This is a layer, usually part of an operating
system, that converts incoming and outgoing data from one presentation format
to another (for example, from a text stream into a popup window with the newly
arrived text). Sometimes called the syntax layer.
Layer 5: The session layer ...This layer sets up, coordinates, and terminates
conversations, exchanges, and dialogs between the applications at each end. It
deals with session and connection coordination.
Layer 4: The transport layer ...This layer manages the end-to-end control (for
example, determining whether all packets have arrived) and error-checking. It
ensures complete data transfer.
Layer 3: The network layer ...This layer handles the routing of the data (sending it
in the right direction to the right destination on outgoing transmissions and
receiving incoming transmissions at the packet level). The network layer does
routing and forwarding.
Layer 2: The data-link layer ...This layer provides synchronization for the physical
level and does bit-stuffing for strings of 1's in excess of 5. It furnishes
transmission protocol knowledge and management.
Layer 1: The physical layer ...This layer conveys the bit stream through the
network at the electrical and mechanical level. It provides the hardware means
of sending and receiving data on a carrier.
WEB PAGE
A document on the World Wide Web. Every Web
page is identified by a unique URL .
 Main protocol used for communication between a
browser and a web server is HTTP. This protocol
was designed to enable documents to be
transferred but can be used with other type of
data too.
 For web documents the http protocol works by
sending command over a TCP connection.

192.168.18.32
Port 80
Server
client
GET index.html
HTTP /1.1
http://www.mysports.com/index.html
DSN
192.168.18.32
HTTP/ 1.1 200 OK
Client
server
Contents of document
Client side prog.
Server side prog.
HTML
DHTML
XHTML
CSS
XML
Java script, VB script
ASP
Servlet
JSP