Transcript Internet Infrastructure

Chapter 2:
Technology Infrastructure:
The Internet and the World
Wide Web
Objectives
In this chapter, you will learn about:
• The origin, growth, and current structure of the Internet
• How packet-switched networks are combined to form the
Internet
• How Internet protocols and Internet addressing work
• The history and use of markup languages on the Web,
including SGML, HTML, and XML
•
How HTML tags and links work on the World Wide Web
•
The differences among internets, intranets, and extranets
•
Options for connecting to the Internet, including cost and
bandwidth factors
•
Internet2 and the Semantic Web
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The Internet and the World
Wide Web
• Computer network
– Any technology that allows people to
connect computers to each other
• The Internet
– A large system of interconnected computer
networks spanning the globe
• World Wide Web
– A subset of computers on the Internet
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History of the Internet
• Wikipedia Internet History
• Early 1960s
– U.S. Department of Defense funded research to
explore creating a worldwide network
• In 1969
– Defense Department researchers connected four
computers into a network called ARPANET
• Throughout the 1970s and 1980s
– Academic researchers connected to ARPANET and
contributed to its technological developments
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New Uses for the Internet
• 1972
– E-mail was born
• Mailing list
– E-mail address that forwards any message
received to any user who has subscribed to
the list
•
Usenet
– Started by a group of students and
programmers at Duke University and the
University of North Carolina
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Growth of the Internet
• In 1991, the NSF:
– Eased restrictions on commercial Internet
activity
– Began implementing plans to privatize the
Internet
• Network access points (NAPs)
– Basis of the new structure of the Internet
• Network access providers
– Sell Internet access rights directly to larger
customers and indirectly to smaller firms
and individuals through ISPs
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Emergence of the World
Wide Web
• The Web
– Software that runs on computers connected to
the Internet
• Vannevar Bush speculated that engineers
would eventually build a memory
extension device (the Memex)
• In the 1960s, Ted Nelson described a
similar system called hypertext
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Emergence of the World
Wide Web
• Tim Berners-Lee developed code for a
hypertext server program
• Hypertext server:
– Stores files written in the hypertext markup
language
– Lets other computers connect to it and read
files
• Hypertext Markup Language (HTML)
– Includes a set of codes (or tags) attached to
text
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Routing Packets
• Routing computers
– Computers that decide how best to forward
packets
• Routing algorithms
– Rules contained in programs on router
computers that determine the best path on
which to send packets
– Programs apply their routing algorithms to
information they have stored in routing tables
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Internet Protocols
• Protocol
– Collection of rules for formatting, ordering, and errorchecking data sent across a network
• Rules for message handling include:
– Independent networks should not require any internal
changes to be connected to the network
– Packets that do not arrive at their destinations must
be retransmitted from their source network
– Router computers act as receive-and-forward devices
– No global control exists over the network
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TCP/IP
• TCP
– Controls disassembly of a message or a file
into packets before transmission over the
Internet
– Controls reassembly of packets into their
original formats when they reach their
destinations
• IP
– Specifies addressing details for each packet
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Domain Names
• A domain name is a set of words assigned
to a specific IP address
• Top-level domain (or TLD)
– Rightmost part of a domain name
• Internet Corporation for Assigned Names
and Numbers (ICANN)
– Responsible for managing domain names and
coordinating them with IP address registrars
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Web Page Request and
Delivery Protocols
• Web client computers
– Run software called Web client software or
Web browser software
• Web server computers
– Run software called Web server software
• The web uses a thin-client/server
architecture
– Combination of client computers running
Web client software and server computers
running Web server software
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Web Page Request and
Delivery Protocols
• Hypertext Transfer Protocol (HTTP)
– Set of rules for delivering Web page files over
the Internet
• Uniform Resource Locator (URL)
– Combination of the protocol name and domain
name
– Allows a user to locate a resource (the Web
page) on another computer (the Web server)
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Electronic Mail Protocols
• Electronic mail (e-mail)
– Must be formatted according to a common set
of rules
• E-mail server
– Computer devoted to handling e-mail
• E-mail client software
– Used to read and send e-mail
– Examples include Microsoft Outlook and
Netscape Messenger
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Electronic Mail Protocols
• Simple Mail Transfer Protocol (SMTP)
– Specifies the format of a mail message
• Post Office Protocol (POP)
– POP messages can tell the e-mail server to:
• Send mail to a user’s computer and delete it from the
e-mail server
• Send mail to a user’s computer and not delete it
• Simply ask whether new mail has arrived
– POP provides support for Multipurpose Internet
Mail Extensions (MIME)
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Markup Languages and the
Web
• Text markup language
– Specifies a set of tags that are inserted into
text
• Standard Generalized Markup
Language (SGML)
– Older and more complex text markup
language than HTML
– A meta language
• World Wide Web Consortium (W3C)
– Not-for-profit group that maintains standards
for the Web
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Standard Generalized
Markup Language
• Offers a system of marking up documents
that is independent of any software
application
• Nonproprietary and platform independent
• Offers user-defined tags
• Costly to set up and maintain
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Hypertext Markup
Language (HTML)
• Prevalent markup language used to
create documents on the Web today
• HTML tags are interpreted by a Web
browser and are used by it to format the
display of the text
• HTML links can be structured as:
– Linear hyperlink structures
– Hierarchical hyperlink structures
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Hypertext Markup Language
(HTML))
• The most common scripting languages
include JavaScript, JScript, Perl, and
VBScript
• Cascading Style Sheets (CSS) are sets of
instructions that give Web developers more
control over the format of displayed pages
– Style sheet is:
• Usually stored in a separate file
• Referenced using the HTML style tag
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Extensible Markup Language
(XML)
• XML uses paired start and stop tags
• It includes data management capabilities
that HTML cannot provide
• Differences between XML and HTML:
– XML is not a markup language with defined
tags
– XML tags do not specify how text appears on a
Web page
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Intranets and Extranets
• Intranet
– Interconnected network that does not extend
beyond the organization that created it
• Extranet
– Intranet extended to include entities outside
the boundaries of an organization
– Connects companies with suppliers, business
partners, or other authorized users
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Public and Private
Networks
• Public network
– Any computer network or
telecommunications network available to the
public
• Private network
– A private, leased-line connection between
two companies that physically connects their
intranets
• Leased line
– Permanent telephone connection between
two points
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Virtual Private Network (VPN)
• VPN
– An extranet that uses public networks and their
protocols
• IP tunneling
– Effectively creates a private passageway
through the public Internet
• Encapsulation
– Process used by VPN software
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Internet Connection Options
• Bandwidth
– Amount of data that can travel through a
communication line per unit of time
• Net bandwidth
– Actual speed that information travels
• Symmetric connections
– Provide the same bandwidth in both
directions
• Asymmetric connections
– Provide different bandwidths for each
direction
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Voice-Grade Telephone
Connections
• POTS, or plain old telephone service
– Uses existing telephone lines and an analog
modem
– Provides bandwidth between 28 and 56 Kbps
• Digital Subscriber Line (DSL)
– Connection methods that do not use a modem
• Integrated Services Digital Network
(ISDN)
– Bandwidths between 128 Kbps and 256 Kbps
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Broadband Connections
• Broadband connections operate at speeds
of greater than 200 Kbps
• Asymmetric digital subscriber line (ADSL)
– Transmission bandwidth is from 100 to 640
Kbps upstream and from 1.5 to 9 Mbps
downstream
• Cable modems
– Provide transmission speeds between 300 Kbps
and 1 Mbps
• DSL
– Private line with no competing traffic
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Leased-Line Connections
• DS0 (digital signal zero)
– Telephone line designed to carry one digital signal
• T1 line (also called a DS1)
– Carries 24 DS0 lines and operates at 1.544 Mbps
• Fractional T1
– Provides service speeds of 128 Kbps and upward in
128-Kbps increments
• T3 service (also called DS3)
– Offers 44.736 Mbps
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Wireless Connections
• Bluetooth
– Designed for personal use over short distances
– Low-bandwidth technology, with speeds of up
to 722 Kbps
– Networks are called personal area networks
(PANs) or piconets
– Consumes very little power
– Devices can discover each other and
exchange information automatically
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Wireless Ethernet (Wi-Fi)
• Wireless Ethernet (Wi-Fi or 802.11b) is
the most common wireless connection
technology for use on LANs
• Wireless access point (WAP)
– Device that transmits network packets
between Wi-Fi-equipped computers and other
devices
• Has a potential bandwidth of 11 Mbps and
a range of about 300 feet
• Devices are capable of roaming
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Wireless Ethernet (Wi-Fi)
(continued)
• 802.11a protocol
– Capable of transmitting data at speeds up to
54 Mbps
• 802.11g protocol
– Has 54 Mbps speed of 802.11a
– Compatible with 802.11b devices
• 802.11n
– Expected to offer speeds up to 320 Mbps
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Fixed-Point Wireless
• One version of fixed-point wireless uses a
system of repeaters to forward a radio
signal from an ISP to customers
• Repeaters
– Transmitter-receiver devices (transceivers)
• Mesh routing
– Directly transmits Wi-Fi packets through
hundreds, or even thousands, of short-range
transceivers
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Cellular Telephone
Networks
• Third-generation (3G) cell phones
– Combine the latest technologies available today
• Short message service (SMS)
– Protocol used to send and receive short text
messages
• Mobile commerce (m-commerce)
– Describes the kinds of resources people might
want to access using wireless devices
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Internet2 and the Semantic
Web
• Internet2
– Experimental test bed for new
networking technologies
– Includes bandwidths of 10 Gbps and
more on parts of its network
– Used by universities to conduct large
collaborative research projects
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Internet2 and the Semantic
Web (continued)
• Semantic Web
– Project by Tim Berners-Lee
– If successful, it would result in words on Web
pages being tagged (using XML) with their
meanings
• Resource description framework (RDF)
– Set of standards for XML syntax
• Ontology
– Set of standards that defines relationships
among RDF standards and specific XML tags
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Summary
• TCP/IP
– Protocol suite used to create and transport
information packets across the Internet
• POP, SMTP, and IMAP
– Protocols that help manage e-mail
• Languages derived from SGML
– Hypertext Markup Language (HTML)
– Extensible Markup Language (XML)
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Summary (continued)
• Intranets
– Private internal networks
• Extranet
– Used when companies want to collaborate
with suppliers, partners, or customers
• Internet2
– Experimental network built by a consortium of
research universities and businesses
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