Introduction to WWWSlide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Introduction to WWWInstructor: Dr. Jerry Gao San Jose State Universityemail: [email protected]: http://www.engr.sjsu.edu/gaojerryIntroduction- What is the Internet?- History of the Internet- Internet Design Principles- Basic Internet protocols- Basic Internet tools- What is the World Wide Web- History of the World Wide Web- Basic concepts about WWW- Basic WWW protocols- Basic Web ToolsCopyright@1999. Jerry Gao, Ph.DCopyright@1999. Jerry Gao, Ph.DThe Internet: Development History- Grew out of a research network originally funded by U.S. Department of Defense. - Development of this network, known as the ARPAnet after the AdvancedResearch Projects Agency (ARPA), began in 1969.- As the network grew, it was used for applications beyond research, such aselectronic mail.In the early 1980s, the current versions of the core Internet protocols, TCP and IP, were introduced across the network.The term “Internet” comes from the word “inter-network” - an interconnected set of networks.In 1992, the Center for European Nuclear Research (CERN) released the first versions of World Wide Web software.- Subsequently, the number of Web servers has grown quickly.The Internet Properties:Key properties of the Internet:- The Internet is interoperable.- The Internet is global.- The Web makes it easy.- The costs of the network are shared across multiple applicationsand borne by the end users.The striking characteristic of the Internet --> heterogeneity.Copyright@1999. Jerry Gao, Ph.DInternetSmallcomputer networkThe Internet Layered Architecture:The Internet, as a network of connecting many small networks, consists of four layers:- Application Layer (HTTP, SMTP..)- Transport Layer (TCP, UDP)- Network Layer (IP)- Physical LayerCopyright@1999. Jerry Gao, Ph.DApplication layer (HTTP, SMTP)Transport Layer (TCP, UDP)Network Layer (IP)Physical Layer(e.g. Ethernet)The Internet: Design PrinciplesThe Internet has been successful because of some fundamental decisions aboutits design made early in its history.- Interoperability:Independent implementations of Internet protocols actually work together. Interoperability means that systems can be assembled using client and servercomputers and software from different vendors.In the context of Internet commerce, interoperability means that buyers and sellers do not have to buy and upgrade software simultaneously from the samevendors to conduct commerce.- Layering:Internet protocols are designed to work in layers,with each higher layer building on the facilities provided by lower layers.Copyright@1999. Jerry Gao, Ph.DThe Internet: Design Principles- Simplicity:One way to look at the layering of the Internet is that it grows both up and downfrom IP. IP is very simple, providing only addressing and formatting of packets.Below the level of IP, there is the complexity of many different kinds of networkhardware, topologies, and routers.IP hides that complexity from applications and insulates application developersfrom:- the complexities of different network devices- the complexities of implementing low-level network protocols.Above IP, higher-level protocols such as TCP offer service abstractions that areeasy for application programmers to understand and use.Copyright@1999. Jerry Gao, Ph.DThe Internet: Design Principles- Uniform naming and addressing:The IP layer offers a uniform addressing structure that assigns a 32-bit addressto each computer connected to the network. Domain name system (DNS) offers a uniform way to translate human-readablenames for computers, such as “www.openmarket.com” to the numeric addressfor that computer.- End-to-end:Internet is designed around end-to-end protocols. That is, the interpretation of the data happens on the sending and receiving systems, but nothing in the networkneeds to look at anything but the destination address for delivering the packet.End-to-end protocols have several advantages:- hide the internal structure of the network- provide simple abstractions to programmers- shielding them from such things as the messy details of recovering from lower-level errors.Copyright@1999. Jerry Gao, Ph.DThe Internet Protocols- FTP:(File transfer protocol)- One of the most oldest and probably the most popular protocol to be used to move files on the Internet.- TCP/IP:(Transmission Control Protocol and Internet Protocol)- The low-level communications protocol that holds the Internet together.- It provides means to allows two software on difference machines on the Internet find each other, rendezvous, and transfer data.- It provides the essential service of making sure that each piece of data is transferred in the correct sequence and without error.- SMTP: (the e-mail message protocol)- A protocol to allow two users to communicate through e-mail messagesover the Internet.- NNTP: (Net News Transfer Protocol)- A protocol, which can be used to access or transfer Usenet news over the Internet.- Telnet: - The traditional teletype-style communications protocol for communicating with text-based information services.Copyright@1999. Jerry Gao, Ph.DThe World Wide Web: History- March, 1989, Tim Berners-Lee of Geneva’s European Particle Physics Laboratory (CERN) circulated a proposal to develop “a hypertext system” for global information sharing in High Energy Physics community. (http://info.cern.ch/hypertext/WWW/TheProject.html)- The World Wide Web project began to take shape at the beginning of 1991.- October 1991, the gateway for WAIS search (a crucial development for the Web’s futureas search as well as a browsing tool), - Before the end of 1991, CERN announced the Web to the High Energy Physics community in general.- Essentially, 1992 was a developmental year. In March of 1993, WWW traffic clocked inat 0.1 percent of total Internet backbone traffic.- In July of 1994, CERN began to turn over the Web project to a new groupcalled the W3 organization, a joint venture between CERN and MIT to developthe Web further.Copyright@1999. Jerry Gao, Ph.DThe World Wide Web: HTMLHTML is a simplified derivative of SGML, or Standard Generalized Markuplanguage. - Its code can be used to make documents readable across a variety of platformsand software. - Like SGML, HTML operates through a series of codes placed within an ASCII doc. These codes are translated by a WWW client such as Lynx, Mosaic,Cello,