Contents Data Communications Applications File print serving Mail

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Contents • Data Communications Applications – File & print serving – Mail – Domain

Contents • Data Communications Applications – File & print serving – Mail – Domain Name Server – Telnet – File Transfer Protocol – World Wide Web • Multi-media Applications – Voice – Images Postacademic Interuniversity Course in Information Technology – Module C 1 p 1

World Wide Web • Uniform hypertext based, user friendly interface for distributed databases. •

World Wide Web • Uniform hypertext based, user friendly interface for distributed databases. • Inexpensive, high quality, browsers available for almost all computers. • Sophisticated and application specific user’s interactivity by downloading programs to be executed on client’s workstation (Java applets). • Already over 500, 000 pages available worldwide, mainly for public relations, publicity and, to some extent, electronic commerce. • Electronic commerce still restrained by security concerns. Postacademic Interuniversity Course in Information Technology – Module C 1 p 2

WWW page example Postacademic Interuniversity Course in Information Technology – Module C 1 p

WWW page example Postacademic Interuniversity Course in Information Technology – Module C 1 p 3

Search Engines • Finding information becomes more and more difficult due to the amount

Search Engines • Finding information becomes more and more difficult due to the amount of information. • Automated indexing services, searching all available databases on the Internet and setting up keyword databases are very popular. • Good ranking of keywords can be purchased from indexing services. • Many sites use tricks to be favorably presented by search engines Postacademic Interuniversity Course in Information Technology – Module C 1 p 4

Technically, what is it ? The WEB = Internet + HTML + URL +

Technically, what is it ? The WEB = Internet + HTML + URL + HTTP HTML : hypertext Markup Language. – Hypertext = multimedia information(containing even executable programs) with references to other pieces of hypertexts. URL : Universal Resource Locator. – The address where a piece of hypertext (or other resources) can be obtained HTTP : Hypertext Transfer Protocol. - Conventions to transfer hypertexts between computers Postacademic Interuniversity Course in Information Technology – Module C 1 p 5

Technically, what is it ? The WEB = Internet + HTML + URL +

Technically, what is it ? The WEB = Internet + HTML + URL + HTTP HTML : hypertext Markup Language. – Hypertext = multimedia information(containing even executable programs) with references to other pieces of hypertexts. URL : Universal Resource Locator. – The address where a piece of hypertext (or other resources) can be obtained HTTP : Hypertext Transfer Protocol. - Conventions to transfer hypertexts between computers Postacademic Interuniversity Course in Information Technology – Module C 1 p 6

HTML Hyper. Text Markup Language • Hypertext – Multimedia document • Normal text •

HTML Hyper. Text Markup Language • Hypertext – Multimedia document • Normal text • Graphics and images (stored in separate files) • Sound (stored in separate files) • Executable programs ( = applets in Java code) – References to other hypertext documents (“Anchors”) • “clickable” normal text or image (icon) • address (URL) where the corresponding document can be found Postacademic Interuniversity Course in Information Technology – Module C 1 p 7

HTML Hyper. Text Markup Language • Physical Markup (used for textprocessors, not in “pure”

HTML Hyper. Text Markup Language • Physical Markup (used for textprocessors, not in “pure” HTML) – Functional role of contents is not mentioned – Describes how the document should look “new page”; “use font ‘Times-Roman 24’ “ “Print ‘Teleprocessing’ page-centered” – Presentation imposed by author of document – What You See Is What You Get (WYSIWYG) Postacademic Interuniversity Course in Information Technology – Module C 1 p 8

HTML Hyper. Text Markup Language • Semantic Markup (used in original HTML) – Functional

HTML Hyper. Text Markup Language • Semantic Markup (used in original HTML) – Functional role of contents is described “Main Title ‘Teleprocessing’ “ – Presentation defined by interpreter settings Text only / graphics , Black & white / color, . . . Braille. – What You Get Is What You Meant (WYGIWYM) Postacademic Interuniversity Course in Information Technology – Module C 1 p 9

Technically, what is it ? The WEB = Internet + HTML + URL +

Technically, what is it ? The WEB = Internet + HTML + URL + HTTP HTML : hypertext Markup Language. – Hypertext = multimedia information(containing even executable programs) with references to other pieces of hypertexts. URL : Universal Resource Locator. – The address where a piece of hypertext (or other resources) can be obtained HTTP : Hypertext Transfer Protocol. - Conventions to transfer hypertexts between computers Postacademic Interuniversity Course in Information Technology – Module C 1 p 10

URL Universal Resource Locator http: //www. info. vub. ac. be: 80 /webpages/info. html •

URL Universal Resource Locator http: //www. info. vub. ac. be: 80 /webpages/info. html • Protocol used to communicate with resource (each protocol further defines URL format) • Internet Resource Address – Domain name • Internet Protocol address of machine (134. 121. 023. 001) • Domain Server Name of machine (infoweb. vub. ac. be) – Port number on machine • Optional : Each protocol has a default port number • Resource details (protocol specific) (i. e. directory and filename of an HTML page) Postacademic Interuniversity Course in Information Technology – Module C 1 p 11

Technically, what is it ? The WEB = Internet + HTML + URL +

Technically, what is it ? The WEB = Internet + HTML + URL + HTTP HTML : hypertext Markup Language. – Hypertext = multimedia information(containing even executable programs) with references to other pieces of hypertexts. URL : Universal Resource Locator. – The address where a piece of hypertext (or other resources) can be obtained HTTP : Hypertext Transfer Protocol. - Conventions to transfer hypertexts between computers Postacademic Interuniversity Course in Information Technology – Module C 1 p 12

HTTP : Hyper. Text Transfer Protocol. – HTTP Client : a Web Browser •

HTTP : Hyper. Text Transfer Protocol. – HTTP Client : a Web Browser • Presenting information encoded in HTML. • Translating user interactions into the HTTP. – HTTP Server : a process interpreting client requests • Sending pieces of hypertext stored in HTML • Translating information available in other formats • acquiring information from outside the Web. Postacademic Interuniversity Course in Information Technology – Module C 1 p 13

Inside the Web HTTP Server HTTP Client (Web Browser) HTTP Server HTTP Link transporting

Inside the Web HTTP Server HTTP Client (Web Browser) HTTP Server HTTP Link transporting HTMLencoded hypertext HTTP Server Other Server Postacademic Interuniversity Course in Information Technology – Module C 1 Other Data Link p 14

HTTP Hypertext Transfer Protocol • Stateless (connectionless) communication protocol • Uses a connection oriented

HTTP Hypertext Transfer Protocol • Stateless (connectionless) communication protocol • Uses a connection oriented transport protocol. • Typical HTTP 1. 0 transaction: 1 Client HTTP entity opens transport connection with specified Server HTTP entity. 2 Client makes the request to the server. 3 Server sends response. 4 Server closes transport connection. • Some HTTP implementations allow looping through steps 2 and 3 (Keep-alive) to transfer entire hypertext pages with images and sound in one HTTP transaction. Postacademic Interuniversity Course in Information Technology – Module C 1 p 15

HTTP Web Server Browser Client HTTP Connectionless protocol Server HTTP Transport entity Connection oriented

HTTP Web Server Browser Client HTTP Connectionless protocol Server HTTP Transport entity Connection oriented protocol Transport entity Network Service Postacademic Interuniversity Course in Information Technology – Module C 1 p 16

HTTP is a Stateless Protocol • Benefit : performance of server • Penalty :

HTTP is a Stateless Protocol • Benefit : performance of server • Penalty : Server can not keep information about user. Browser Client HTTP > show me my bank transactions Give your name and password < > XYZ, ****** OK, what do you want < > show me my bank transactions Give your name and password <. . Connectionless protocol Postacademic Interuniversity Course in Information Technology – Module C 1 Web Server HTTP p 17

HTTP Adding state to a Stateless Protocol The state is kept in the messages

HTTP Adding state to a Stateless Protocol The state is kept in the messages traveling between server and browser !!! Browser Client HTTP > I want to log into the server Give your name and password < > XYZ, ****** OK, here is your key 478 < > show me my bank records, my key is 478. Here are your bank records < $$$$$ < If you need more use key 953 < Connectionless protocol Postacademic Interuniversity Course in Information Technology – Module C 1 Web Server HTTP p 18