W orld W ide W eb Client/Server design using TCP/IP Incorporates Other Client/Server Systems –ftp –gopher –mail Server runs on port 80, named httpd, exchanges http Hyperlinks connect documents to other documents Documents can be linked to documents at other sites Graphical and text based info can be used HTML - Hypertext Markup Language for formatting URL - Universal Resource Locator indicates the type of resource being sought

Many servers can be accessed through the browser WWW Browser (client) INTERNET FTP (protocol) Server HTTPD Server (HTML documents) E.g., NETSCAPE or IE HTTP (protocol) HTML (format exchanged) FTP (protocol) Any file type

URL U niversal R esource L ocator Used in Hyperlinks Describes the protocol to be used to find the server and link the info to your screen A complete URL includes: –the protocol –the site at which the server is located –the path and filename in which the document can be found EXAMPLE: http protocol server sitepath and filename

HTML PRIMARY file format for web documents –text based –TAGS mark the intented use of the text –BEGIN/END type markers This could be the main heading Various versions supported as browsers evolve Describes the information to be in the document but leaves specific interpretation to the browser. –HTML file may show that a graphical image is to be displayed, but a text browser may print a message instead

HTML tags entire document document header info body of html doc </BODY. Example: header info Body, lists, pictures

More Tags Sample Course Syllabus Course Description Does in italics One Two Three DRJ LOGO IMAGE Course Description Does in italics One Two Three DRJ Sample Course Syllabus

Links on the Document... Figure 8.9 HTTP Server Web Pages Browser

Trying WWW on the net Either running –windows interface on DECs or Hunter Creech Suns –PPP connection to Suns In unix command shell type netscape & Open OR HAPPY SURFING! Use the “source” menu choice to view the text file and the associated html tags

Using WWW to view ftp site Try using ftp to log in and examine the directories on the department’s site: ftp.pcs.cnu.edu Make some notes about what you saw Run netscape as shown in the previous slide Access the ftp site via the netscape browser at ftp://ftp.pcs.cnu.edu Look for the same directories and file Can you look at and/or retrieve the file on either ?

HTML 3.0 Enhancements New Tags for text –Footnote, Margin,Abstract, Note, Role Inline Graphics –Allow text to wrap around either side Tables –Multi-column, multi-row tables mixing inline-graphics and text Forms –multiple submit buttons per form Document toolbars –creadted by the author to aide in navigation of long documents Validation without having to try it w/multiple browsers

Other enhancements Clickable images processed at client-side Cursor change when mouse hits a hot-spot Secure transactions –authenticity –confidentiality –check Info on html enhancements: –check

How Do Client/Servers Relate To the OSI model Physical Data Network Transport Browser (netscape) Physical Data Network Transport Httpd server Effective horizontal communication is using http. Actual vertical communication wraps it in TCP/IP. http Each client-server level interaction uses a different protocol: ftp, smtp(mail), or custom designed protocols

Dynamic Content? What if the page should look different on each day of the week? What if the page should reflect the currect day’s temperature, a customer’s balance, a student’s grade? Numerous Options exist! –CGI –Java –Java script –VB Script Later!