The Internet. Networks - Overview Internet – a network of networks Overview of networks A network...

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