Transcript The Internet

The Internet
Networks - Overview


Internet – a network of networks
Overview of networks


A network consists of two or more computers
connected together
Common components include:
 Client computers
 Server computers
 Shared devices
 Cables, hubs, and routers that provide the network
connections
Networks – Overview (con’t)

One way to describe networks is by their size:



LAN (Local Area Network) – single building, relatively short
distance
WAN (Wide Area Network) – spans a large geographic
area; Internet can be considered a large WAN
Also:




MAN (Metropolitan Area Network) – spans a distance larger
than a LAN but smaller than a WAN
WLAN (Wireless Local Area Network) – uses WiFi wireless
network technology
PAN (Personal Area Network) – organized around an
individual; can involve cell phone, PDA, mobile computer, etc.
CAN (Campus Area Network) – spans multiple LANs but
smaller than a MAN; used on a college campus
Networks – Benefits

Benefits of networks
 Convenience
 Resource sharing
 Facilitates communication
 Saves money
 Reliability
 Scalability
Internet Growth


433+ million computers linked as of 01/2007
(http://www.isc.org/index.pl)
Reasons for success:
 Decisions not politically based
 Internet is distributed operation
 Homogeneity of language and outlook
 Inherently interested people
 Free (or inexpensive) software
Internet Protocols

Protocols – rules that describe how computers
communicate; some common protocols:
 FTP (File Transfer Protocol)
 Email protocols – SMTP, POP, IMAP
 HTTP (HyperText Transfer Protocol)
 TCP/IP (Transmission Control Protocol/Internet
Protocol)
TCP/IP

TCP/IP (Transmission Control Protocol/Internet
Protocol):






How computers connect, send, and receive information
TCP permits communication between computers
IP specifies how data is routed to and from computers
TCP and IP are primary protocols but TCP/IP refers to
a whole suite of protocols
Called “language of the Internet”
Mandated in 1983 for all ARPANET hosts
TCP/IP (con’t)


Example 1: Sending an e-mail message
 Formatted according to Simple Mail Transfer
Protocol (SMTP)
Example 2: Requesting a Web page
 Formatted according to Hyper Text Transfer
Protocol (HTTP)
TCP/IP (con’t)

TCP is responsible for splitting the message into
IP packets; each packet contains:





Piece of message
Information about sender
Information about receiver
Sequence number
Error checking information
TCP/IP (con’t)


IP is responsible for routing the packets to the
correct destination address
At destination (receiving) computer TCP is
responsible for:



Reassembling message
Sending requests for corrupt packets to be resent
Advantages of packets:



Error recovery
Load distribution
Flexibility
Physical Components



Servers
 Answer service requests
Routers
 Direct data packets
Networks
 Transport packets
 Copper wires, fiber-optic cables, radio waves,
microwaves, infrared light, and visible light
Types of Internet Connections



Analog – regular dial-up - up to 56 Kbps
ISDN (Integrated Services Digital Network) –up
to 128 Kbps
Broadband connections – faster than analog and
ISDN:


xDSL (Digital Subscriber Line) – permanent
connection that uses phone line but does not tie up
your connection; 128 Kbps to 8 Mbps
Cable – permanent connection that operates over
cable TV lines; 512 Kbps to 20 Mbps
Types of Internet Connections (con’t)

Other types of connections:




Wireless Internet connections – uses radio frequency
bands instead of telephone or cable networks (newer
technology)
T-1 lines – leased line option; used by businesses
connecting to Internet and by ISPs connecting to the
Internet backbone. Dedicated phone connection that
supports data rates of 1.544 Mbps
T-3 lines – used to connect to backbone and for the
backbone itself. 43 to 45 Mbps
IoS – Internet over Satellite; access via satellite
ISPs, NSPs


Internet Service Provider (ISP)
Network Service Provider (NSP)
Local ISPs can connect to NSPs
 Leased-lines from local telephone companies provide
part of the network
 Transmit data at 1.54 megabits (Mbps)
Backbone Provider – organization that supplies
access to high-speed transmission lines used to connect
to the Internet; some providers include: MCI, Sprint,
UUNET, AGIS, BBN


IP Address



Unique numerical name identifying each
computer on Internet
vs. Domain Name
 People-oriented unique name using symbols;
e.g., www.amazon.com
32 bits (four bytes) – 1 byte can represent the
numbers 0 thru 255
 Four natural numbers separated by dots
(i.e., 72.21.203.1)
 Network component and host component
IP Address (con’t)


Vital in packet switching
Internet Assigned Numbers Authority (IANA)



IP address to domain names


Operating unit of Internet Corporation for Assigned
Names and Numbers (ICANN) –
http://www.icann.org/index.html
Assigns and manages IP addresses
Resolver converts symbolic name to IP address
Programs convert IP addresses to symbolic
names (vice versa)

nslookup (UNIX-based systems)
IP Address (con’t)

Static IP address



Permanent
Connection through router
Dynamic IP address


Changes with each Internet connection
Connection through ISP
IP Address (con’t)


IPv6 or IPng - latest version of Internet Protocol
(IP or IPv4)
Major changes:

More addresses



Simplified IP headers


IP address size from 32 bits to 128 bits
32
128
IPv4 supports 2 addresses; IPv6 supports 2
addresses
Reduction of header fields in IP packet
Added security features
Web Page Retrieval
Enter a URL
(how://where/what)
(1) Browser determines URL using “how” part
(2) Browser queries the DNS for IP address using
“where” part
(3) DNS responds with IP address (e.g. 172.132.173.2)
(4) Browser establishes TCP connection to above
(5) Browser sends a request for “what” portion
Web Page Retrieval (con’t)
Enter a URL (con’t)
(6) Server services request by sending back the
“what” part
(7) TCP connection closed
(8) Browser renders text portion of HTML
(9) Browser repeats steps for in-line image files
(10) Browser displays images as retrieved
World Wide Wait



Congestion issues and delays caused
frustration
Resulted from popularity
Reasons:


Increase in Internet users - why?
Elaborate Web pages contain images, sounds,
video clips
World Wide Wait (con’t)

World Wide Web Consortium (W3C) issues:





“Save the Internet from the Web”
Improving process of connecting
New techniques to expedite Web page requests
Refining how URL resolved
Web page design suggestions:



Avoid unnecessary graphics
Cascading Style Sheets (CSS)
PNG instead of GIF
Issues and Predictions

Intranets


Cost
Inexpensive – time to charge more?
Internet2 - http://www.internet2.edu
 Networking consortium that facilitates the
development, deployment and use of revolutionary
Internet technologies.
 For schools, libraries, universities, researchers
 Much higher speeds – Abilene network backbone
supports transfer rates 100 to 1000 times faster than
typical broadband connections


Isolated, private network with an internal Web
Internet Culture





Critical Evaluation of Information
Freedom of Expression
Communication Mechanisms
Advertising
Societal Impact
Freedom of Expression





Lack of regulation
Blue ribbon graphic
Obscene or offensive material
Censorship
Platform for Internet Content Selection (PICS)
 Set of technical specifications for designating
labels
 Works with vendor-supplied filtering software
Communication Mechanisms








E-mail and mailing lists
Internet Relay Chat (IRC)
Instant Messaging (AOL’s IM and ICQ)
Blogs
Newsgroups
Videoconferencing
Emoticons and shorthand
Flaming and SHOUTING
Societal Impact

Advertising





Internet related jobs
Information and communication


Clickable images
Revolving advertisements
Spam
Weather, news, stock prices, travel information
How we shop / bank / invest (spend $)
On-line Businesses


Types: Advertising, marketing, partnership, retail,
service, software, subscription
On-line business hurdles:
 Privacy and security
 Cookies - http://www.cookiecentral.com


File (on your disk) containing data about you
Created while on-line




Filling out a form/registering
Encrypted
Setting a cookie
Persistent cookie
Business and Safety/Security



Secure payment (credit cards); Secure Electronic
Transactions (SET); Electronic money
Legal Environment
 New and uncharted territory
 Taxes and tariffs
President Clinton (July 1997) - Framework for the Global
Electronic Commerce
 Policy on Global Information Infrastructure (GII)
 Principles:
 Encourage self-regulation of Internet
 Should not restrict e-commerce
 Provide legal environment
 Acknowledge uniqueness
 Promote globally
Collaborative Computing

Applications that allow sharing of information
and resources between people

World Wide Web


Groupware





Collaborative computing platform supporting HTML
Collaborative computing platform software on networked
computer system
E-mail
Intelligent form
Version control
Videoconferencing