the internet. networks - overview internet – a network of networks overview of networks a network...
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The Internet
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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
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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
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Networks – Benefits
Benefits of networks Convenience Resource sharing Facilitates communication Saves money Reliability Scalability
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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
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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)
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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
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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)
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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
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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
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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
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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
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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
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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
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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
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IP Address (con’t) Vital in packet switching Internet Assigned Numbers Authority (IANA)
Operating unit of Internet Corporation for Assigned Names and Numbers (ICANN) – http://www.icann.org/index.html
Assigns and manages IP addresses IP address to domain names
Resolver converts symbolic name to IP address Programs convert IP addresses to symbolic
names (vice versa) nslookup (UNIX-based systems)
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IP Address (con’t)
Static IP address Permanent Connection through router
Dynamic IP address Changes with each Internet connection Connection through ISP
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IP Address (con’t)
IPv6 or IPng - latest version of Internet Protocol (IP or IPv4)
Major changes: More addresses
IP address size from 32 bits to 128 bits IPv4 supports 232 addresses; IPv6 supports 2128
addresses Simplified IP headers
Reduction of header fields in IP packet Added security features
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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
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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
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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
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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
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Issues and Predictions Intranets
Isolated, private network with an internal Web 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
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Internet Culture
Critical Evaluation of Information Freedom of Expression Communication Mechanisms Advertising Societal Impact
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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
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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
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Societal Impact Advertising
Clickable images Revolving advertisements Spam
Internet related jobs Information and communication
Weather, news, stock prices, travel information How we shop / bank / invest (spend $)
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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
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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
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Collaborative ComputingCollaborative Computing
Applications that allow sharing of information and resources between people World Wide Web
Collaborative computing platform supporting HTML Groupware
Collaborative computing platform software on networked computer system
E-mail Intelligent form Version control Videoconferencing