the internet. networks - overview internet – a network of networks overview of networks a network...
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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)
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)
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
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
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
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
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
Clickable images Revolving advertisements Spam
Internet related jobs Information and communication
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 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