TECHNOLOGY INFRASTRUCTURE:
THE INTERNET & THE WORLD WIDE WEB
The Internet & 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
Packet-Switched Networks
*Local area network (LAN)
– Network of computers located close together
*Wide area networks (WANs)
– Networks of computers connected over greater distances
*Circuit
– Combination of telephone lines and closed switches that connect them to each other
*Circuit switching
– Centrally controlled, single-connection model
*Packets
– Files and e-mail messages on a packetswitched network are broken down into small pieces, called packets
– Travel from computer to computer along the interconnected networks until they reach their destinations
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
Router-Based Architecture of the Internet
Internet Protocols
*Protocol
– Collection of rules for formatting, ordering, and error-checking 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
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
IP Addressing
*Internet Protocol version 4 (IPv4)
– Uses a 32-bit number to identify computers connected to the Internet
*Base 2 (binary) number system
– Used by computers to perform internal calculations
*Subnetting
– Use of reserved private IP addresseswithin LANs and WANs to provide additional address space
*Private IP addresses
– Series of IP numbers not permitted on packets that travel on the Internet
*Network Address Translation (NAT) Device
– Used in subnetting to convert private IP addresses into normal IP addresses
*Internet Protocol version 6 (IPv6)
– Protocol that will replace IPv4
– Uses a 128-bit number for addresses
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
Top-Level Domain Names
Web Page Requests & Delivery Protocols
*Web client computers
– Run software called Web client software or Web browser software
*Web server computers
– Run software called Web server software
*Client/server architecture
– Combination of client computers running Web client software and server computers running Web server software
*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)
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
*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:
a. Send mail to a user’s computer and delete it from the e-mail server
b. Send mail to a user’s computer and not delete it
c. Simply ask whether new mail has arrived
– POP provides support for Multipurpose Internet Mail Extensions (MIME)
Markup Languages & 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
Development of Markup Languages
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
Hypertext Markup Language
*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
*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
Extensible Markup Language
*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
Processing A Request for an XML Page
Intranets & 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
Public & 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
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
*VPN software
– Must be installed on the computers at both ends of the transmission
VPN Architecture Example
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
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
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
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
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
*Ultra Wideband (UWB)
– Developed for short-range secure communications in military during the 1960s
– Are expected to be used in the future personal area networking applications, such as home media centers and linking mobile phone to the Internet
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 & other devices
– Has a potential bandwidth of 11 Mbps and a range of about 300 feet
– Devices are capable of roaming
*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
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 shortrange
transceivers
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
Internet2 & The Semantic Web
*Internet2
– Experimental test bed for new networking technologies
– Has achieved bandwidths of 10 Gbps and more on parts of its network
– Used by universities to conduct large collaborative research projects
*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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