Transcript Ch.2 notes modified for 2005.

Introduction to the Web and Internet
Questions Answered in this Chapter:
– What is the internet ?
–
–
–
–
Modified for 2005
What are the characteristics of the internet that make it work?
What are the content types on the web?
How are websites created?
What is behind the growth of the web and Internet?
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Exhibit 2-1
Internet Adoption Rates Versus Other Media
Internet as Mass Medium — North American Adoption Curves
120
100
TV
80
Radio
North American 60
Users / Households
(MM)
50 Million Users /
Households
Cable
Commercial
Internet
40
20
0
Radio: 38 years
TV: 13 years
Cable*: 10 years
Commercial
Internet: 5 years
Years to Reach
50 MM Users
-20
1922 1926
1930
1934 1938
1942
1946
1950 1954 1958
1962
1966 1970
1974
1978
1982 1986
1990
1994 1998E
* Launch of HBO in 1976 used to estimate the beginning of cable as an entertainment / advertising medium
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The Original WWW
• Like the internet, radio began as a communication medium
• Early market medium known as wireless telegraphy or telephony;
radio’s point-to-point wireless messaging
• Demand for radio broadcasting surged in 1922 when it shifted from a
point-to-point communication tool to a broadcast medium
• During the 1920s, all 48 states in the US had at least one radio station
• By 1925, 27 of the original 48 stations were out of business
• Revenue sources such as programming subsides from radio-set sales,
radio taxes, generalized goodwill for corporate sponsors and
advertising emerged as new revenue generation models
• The pay for service revenue model allowed radio to compete with
telegraph and cut the price of telegraph by 30%
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Exhibit 2-2
Radio Stations Opened and Closed, 1921-24
100
Stations Opened
Stations Closed
75
50
25
0
21-Sep
22-Feb
22-Jul
22-Dec
23-May
23-Oct
24-Mar
24-Aug
Source: Hanson, Ward. “The Original WWW: Web Lessons from the Early Days of Radio. 7/15/96.
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Early networks
• Internet’s beginnings can be traced back to memos written in 1962 by
MIT’s Joseph Carl Robnett Licklider outlining the galactic networking
concept
• Great advances were made in network technology in 1960s
• To connect computers and permit transfer of information locally, many
organizations installed Local Area Networks
• LAN technology was limited by geographical distance
• To allow computer and networks separated by larger geographical
distance to communicate ARPA (Advanced Research Projects Agency)
developed a Wide Area Network (WAN) called the ARPANET
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Business Tasks Requiring Networks
APPLICATION
EXAMPLE
REQUIREMENT
ONLINE DATA ENTRY
INVENTORY CONTROL
DIRECT RESPONSE REQUIRED
ON-LINE TEXT RETRIEVAL
HOSPITAL INFO SYSTEM
LIBRARY SYSTEMS
HIGH VOLUME REAL TIME RESPONSE
INQUIRY / RESPONSE
POINT-OF SALES
AIRLINE RESERVATIONS
CREDIT CHECKING
RESPONSE WITHIN SECONDS
ADMINISTRATIVE MESSAGES
ELECTRONIC MAIL
SHORT RESPONSE / DELIVERY TIMES
PROCESS CONTROL
COMPUTER AIDED
MANUFACTURING : NUMERIC
MACHINE CONTROL
INTERCOMPUTER DATA
EXCHANGE
ELECTRONIC FUNDS TRANSFER
9.5Modified for 2005
CONTINUOUS INPUT / ONLINE
RESPONSES
BURST TRANSFER OF LARGE DATA
BLOCKS ON-LINE IMMEDIATE RESPONSE
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Analog Signal
• CONTINUOUS WAVEFORM
• PASSES THRU SYSTEM
• VOICE COMMUNICATIONS
*
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Digital Signal
• DISCRETE WAVEFORM
• TWO DISCRETE STATES:
– 1-BIT & 0-BIT
– ON / OFF PULSE
• DATA COMMUNICATION
*
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Ways to Transmit Signals
MEANS BY WHICH DATA ARE
TRANSMITTED:
• TWISTED PAIR (Copper Wires)
• COAXIAL CABLE: (Insulated Copper
Wires)
• FIBER-OPTIC CABLE
• WIRELESS (including radio signals)
*
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Wireless Spectrum (in Megahertz)
• 105 - 108: AM Radio; Short Wave; FM;
VHF-TV
• 108 - 1010: UHF-TV, Cellular Phones, RAM
Mobile, Data, Cordless Phone, Paging,
Narrow Band PCS, Industrial
• 1010 - 1012: Radar, Microwave
• 1013 - 1014: Infra Red, Remote Control,
Wireless
*
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9.12
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Wireless Spectrum (in megahertz)
• 1015 - 1016: Visible Light; Fiber Optics
• 1018 - 1022: X-Ray, Gamma, Cosmic,
Personal Communication Services (PCS)
*
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Speed of Media
MEDIUM
TWISTED PAIR
SPEED
300 BPS - 10 MBPS
MICROWAVE
256 KBPS - 100 MBPS
SATELLITE
256 KBPS - 100 MBPS
COAXIAL CABLE
56 KBPS - 200 MBPS
FIBER OPTICS
56 KBPS - 10 GBPS
BPS: BITS PER SECOND
KBPS: KILOBITS PER SECOND
MBPS: MEGABITS PER SECOND
GBPS:
PER
SECOND
Modified forGIGABITS
2005
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Exhibit 2-3
Wide Area and Local Area Networks
WAN
PC
PC
PC
PC
LAN
PC
LAN
PC
PC
PC
PC
PC
PC
LAN
3
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LANS: Multiple Access Methods
• Fixed assignment
– Partition channel so each node gets a slice of the bandwidth
– Essentially circuit switching – thus inefficient
– Examples: TDMA, FDMA, CDMA (all used in
wireless/cellular environments)
• Contention-based
– Nodes contends equally for bandwidth and recover from
collisions
– Examples: Aloha, Ethernet
• Token-based or reservation-based
– Take turns using the channel
– Examples: Token ring
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Ethernet
• History
– Developed by Bob Metcalfe and others at Xerox PARC in
mid-1970s
– Roots in Aloha packet-radio network
– Standardized by Xerox, DEC, and Intel in 1978
– LAN standards define MAC and physical layer connectivity
• IEEE 802.3 (CSMA/CD - Ethernet) standard – originally
2Mbps
• IEEE 802.3u standard for 100Mbps Ethernet
• IEEE 802.3z standard for 1,000Mbps Ethernet
• IEEE 802.11..n Wireless LAN (1999)
• IEEE 802.15 (wireless personal area net, ~2002,Bluetooth)
• CSMA/CD:
Ethernet’s
Media Access Control (MAC) policy 15
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Ethernet Overview (contd.)
• Ethernet by definition is a broadcast protocol
- Most popular packet-switched LAN technology
• Bandwidths: 10Mbps, 100Mbps, 1Gbps
• signal can be received by all hosts
– Switching enables individual hosts to communicate
• Network layer packets are transmitted over an
Ethernet by encapsulating
• Frame Format
64
48
48
16
Preamble
Dest
addr
Src
addr
Type
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Body
CRC
16
Internetworking Software is used to go between
discrete networks
• The two most well-known pieces of internetworking
software are the TCP and IP
• IP software set rules of data transfer over the network
• TCP software ensures the safe and reliable transfer of
data
• With open system nature of TCP/IP development, software
development and computer companies could more easily
build TCP/IP compliant software and hardware
• TCP/IP standard network protocol laid the groundwork
that enabled the deep internetworking that made internet
possible
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Paul Baran
1
-Worked for RAND from 1959.
-Must design a network to survive
nuclear attacks.
-Vulnerabilities were in the topology
-1964 three topology types
-suggests Packet Switching
- Military and AT&T reject the idea.
http://www.ibiblio.org/pioneers/baran.html
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J.C.R. Licklider
-He worked for several years at ARPA where
he set the stage for the creation of the ARPANET.
-He also worked at Bolt Beranek and Newman (BBN)
from 1957 to 1968, where he acquired 2 computers for BBN,
that would be developed into the first computers connected
on the ARPANET.
-From 1950 at MIT he had
worked on a Cold War project called SAGE designed
to create computer-based air defense systems
against Soviet bombers. Computing was batch processing
and took a lot of time.
In 1960, Licklider published his
groundbreaking work "Man Computer Symbiosis." , and
much of his work has lead to the developments in
Interactive processing.
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Early History of the ARPANET
• 1958Eisenhower forms the ARPA (Advance Research Projects Agency) in
response to the USSR's launch of the Sputnik.
• 1966 December: ARPA Computer Network (ARPANET) project begins.
• 1967 April: Suggested that the ARPANET utilize a separate computer between
the host and the network. This computer would perform the packet
switching/routing. This separate computer dubbed the Interface Message
Processor or IMP.
• 1968 December: Contract to build the IMPs is won by Bolt Beranek and
Newman Inc. (BBN)
• 1969 April: First specification for Host to IMP communication (BBN report
1822) is released. The discussion of the Host to Host Protocol begins with RFC
1. The Network Working Group (NWG) forms to deal with the task of HostHost layer communication protocols.
September: The first IMP is delivered and connected to a Sigma 7 computer at
UCLA. This IMP constitutes the first node of the ARPANET.
October: The second node of the ARPANET is installed at Stanford Research
Institute (SRI). The IMP is connected to an SDS 940 Computer. The first
message is sent across the network and received.
November: The third node of the ARPANET is installed at UCSB.
December: The fourth node of the ARPANET is installed at The University of
Utah.
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and internet
What is the Internet?
• The internet is a collection of wires, protocols and
hardware that allows the electronic transmission of data
over TCP/IP
• Any data can be transferred over the net, e.g., email,
faxes,video,voice & web pages
• Technically www (web) and the net are not the same.The
web is an application for the net
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BBN
• Bolt, Beranek and Newman (now called BBN Technologies) is a
technology company that provides research and development services. BBN
is based in Cambridge, Massachusetts. It is also a defense contractor.
• Founded in 1947 by Leo Beranek and Richard Bolt, both professors at MIT,
with Bolt's former student Robert Newman, Bolt, Beranek and Newman
started life as an acoustical consulting company. Their first contract was
consultation for the design of the acoustics of the United Nations Assembly
Hall in New York.
• Work in acoustics then required substantial calculations which led to an
interest and later business opportunities in computing. Although BBN still
has a substantial interest in acoustics, it is now better known for its activities
in computing.
• Some of BBN's developments of note are the implementation and
operation of the ARPANET, the first person-to-person network email
sent, the invention of the @ sign in an email address, the first router and
the development of the TCP protocol.
• BBN creates large multi-processor systems for warfare simulation for the
U.S. Navy.
• http://www.bbn.com
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How the internet works
Characteristics that allow shared access of data in a network :
1.
Unique identification of each computer on the network
Internet is a network of millions of computers and thousands of
networks intertwined together. Thus it was important that each
computer can be uniquely identified by assigning a specific Internet
Protocol(IP) address. (16 bit in V4. 128 bit in V6.)
e.g.,198.108.95.145
2.
Human-friendly addressing
Domain Name System(DNS) gave each computer on the network an
address comprising an easily recognizable letters and words
instead of an IP address.
e.g., www.philanthropy.com
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How the internet works(cont’d)
3.
Packet Switching
To remedy delays associated with unequally sized data transfers,
instead of transferring files in their entirety, whole files are broken
up into data packets before being transferred over the network.
4.
Routing
Routers are dedicated, special-purpose computers which serve as
an intermediary between networks. They route packets efficiently
through networks. Routers are building blocks of the internet.
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Switching Networks
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Circuit Switching – Basics
• Dedicated communication path between two
stations
• Three phases
– Circuit establishment
– Data transfer
– Circuit disconnect
• Developed for voice traffic (phone)
• Once connected, transfer is transparent
• Inefficient
– Channel capacity dedicated for duration of connection
– If no data, capacity wasted
– Set up (connection)
takes time
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Circuit Switching – Routing
• Requirements:
– Efficiency
– Resilience
• Static routing uses the same approach all the
time
• Dynamic routing allows for changes in
routing depending on traffic
• Alternate routing allows different sets of
routes may be used at different times
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Circuit Switching –Alternate Routing Example
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Packet-Switching – Basics
Longer messages split into packets, data transmitted in small packets.
In each switching node, packets are received, stored briefly, and
passed on to the next node.
Advantages: Line efficiency, no busy conditions, priorities, ...
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Packet Switching – Datagram
•
•
•
•
•
Each packet treated independently
Packets can take any practical route
Packets may arrive out of order
Packets may go missing
Up to receiver to re-order packets and
recover from missing packets
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•
•
•
•
•
•
Packet Switching –Virtual Circuit
Preplanned route established before any
packets sent
Call request and call accept packets establish
connection (handshake)
Each packet contains a virtual circuit
identifier instead of destination address
No routing decisions required for each
packet
Clear request to drop circuit
Not a dedicated path
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Packet Switching –
Virtual Circuit v Datagram
• Virtual circuit
– Network can provide sequencing and error control
– Packets are forwarded more quickly
• No routing decisions to make
– Less reliable
• Loss of a node looses all circuits through that node
• Datagram
– No call setup phase
• Better if few packets
– More flexible
• Routing can be used to avoid congested parts of the
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and internet
Routing – Requirements
•
•
•
•
•
•
•
Correctness
Simplicity
Robustness
Stability
Fairness
Optimality
Efficiency
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Exhibit 2-6
Routers
WAN
Router
Router
Router
Router
Router
Router
Large Organization
PC
PC
LAN
PC
PC
PC
Router
Router
LAN
PC
PC
PC
PC
PC
PC
LAN
6
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How the internet works (cont’d)
5. Reliability and Transmission control Protocol
IP software handles packet deliveries and TCP handles safe delivery of
packages.
6. Standardization
Without the TCP/IP standardization, there would have been many
negative tradeoffs, such as inflexibility and increased functional and
switching costs.
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TCP Standardization
•
•
Networking technologies are not inherently compatible.
Before the development of internetworking technology
an organization with networks had two options:
One Alternative- allow groups to have network
technology best suited to them, which was not flexible
Other alternative – have a standard
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Functions of TCP/IP
•
•
•
•
•
Prevents loss of data
Checks packets
Eliminates duplicate packets
Sends confirmation when the packet is received
If confirmation is not received, then the packet is
retransmitted
• Enables reliable and error-free communication over the net
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What Web pages are made of
• The entire Web is built upon three concepts: web pages
(documents seen on the browser), links (connecting one
web page to another), and servers (storing and transmitting
the information to the browsers for display)
• No special software is required to create a web page
• Majority of pages are created using Hyper Text MarkUp
Language(HTML).
• There is a growing use of XHTML and XML.
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Exhibit 2-7
WorldWideWeb - The First Graphical Web Browser (1993 version running on a NeXT PC)
7
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Contents of the web
• Links
– Internal Anchor Links:
Internal anchors are used to connect with other locations within
the same document.
– Page Links:
Page links allow users to link to other web pages.
– Mail-to Links:
Mail links are used to let users send feedback and questions
directly to them.
• Forms
Forms are basically web pages where the user can enter information
on the fields provided on the page.Forms are useful in getting highly
structured feedback.
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Contents of the web(cont’d)
• Images
The most supported image formats on the Web are Graphic Image
Format (GIF) and Joint Picture Encoding Group(JPEG).
• Multimedia
Web supports multimedia file type such as images, audio and video.
• Capturing contents and compressing data
Printed images can be captured with low cost scanners and photos can
be downloaded with digital video cameras.
• Audio
Sounds can be captured, compressed and stored for use on the web.
• Video (Streaming Technologies)
Video capture cards allow users to capture the analog video output of
camcorders, VCRs and DVD players.
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How are Web Sites Created?
1.
2.
3.
4.
A Web page can be made by adding text-based codes called Hyper
Text Markup Language (HTML) to a text file.Text editor allows to
create WebPages and gives more flexibility and control over design
and layout.
Document conversion tools enable existing documents and new
documents to be created and posted with minimal investment in
learning markup language.
Several web authoring tools are available; e.g., Microsoft FrontPage
lets users add multimedia objects such as sound and animation to
their web pages.
High-end Web authoring tools such as Dreamweaver and Adobe
GoLive offer more powerful site creation and management features,
and allow expanded features such as database integration to be built
in a web site.
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Exhibit 2-8
Browser View and Source View of a Web Page
8
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Behind the Scenes
•
•
Browsers make the retrieval process transparent
Uniform Resource Locator tells the browser several things about
how to access the desired content:
1. The transmission protocol to access the content.
e.g., Hyper Text Transfer Protocol for Web Pages, File
Transfer Protocol (FTP) for transmission of files and the
extended S-HTTP for a higher degree of security.
2. The name of the computer where the content can be found
3. The directory on the computer where content is stored and
the name of the file containing the content.
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Exhibit 2-9
Sharing a cable or DSL modem
Client
DSL or Cable Modem
Host
Internet
ISP Computer
Client
Ethernet HUB
9
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Exhibit 2-10
Components of a URL
The
Thename
nameof
ofthe
thecomputer
computer
being
accessed
(could
being accessed (couldalso
alsouse
use
this
computer’s
IP
address
this computer’s IP address
which
whichisis 208.178.40.89)
208.178.40.89)
The
Thename
nameof
ofthe
the
file
you
want
to
file you want toview
view
http://www.monitor.com/cgi-bin/templates/index.html
Indicates
Indicatesbrowser
browsershould
shoulduse
use
HyperText
Transfer
HyperText TransferProtocol
Protocol
for
forserver
serveraccess
access
The
Thedirectory
directory
that
contains
that containsthe
thefile
file you
you want
want
to
view
to view
Adapted from Comer fig. 22.7, p. 203
1
0
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INTERNET ADDRESS
[email protected]
INDIVIDUAL OR
ORGANIZATION NAME
HOST
COMPUTER
DOMAIN
LOCATION
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WWW ADDRESS
http//www.datamation.com
GO TO WEB
WEB SITE
NAME
TYPE OF
ORGANIZATION
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Factors behind the growth of the net
•
•
•
•
•
•
•
Ease of content consumption
Browser versatility and convenience
Speed
Easy to download
Platform independence
Ease of content creation
Standards
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Exhibit 2-11
Drivers of Internet Growth
Standards
Standards
Ease
Ease of
of Content
Content
Creation
Creation
Internet
Internet Growth
Growth
Ease
Ease of
of Content
Content
Consumption
Consumption
Browser
Browser
Versatility
Versatility and
and
Convenience
Convenience
1
1
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