Web Server Part 1

How documents are published on the WWW?How computers on the Internet talk to each other?How Web pages get from a Web server to a browser?The underlying technology :• The communication protocols• Network terminology• Document FormatsClients and Servers• A Client is a piece of hardware or software used to communicate with a data provider (server)• A server is usually a large computer capable of providing data to many clients at the same time.• The word ‘Server’ can mean the physical computer or piece of hardware, or it can refer to the actual server software or daemon running on that machine.• Server accepts requests from clients, processes the requests and returns the results to the requesting client.• A Web Server is a spesific type of server that knows how to communicate with clients using HTTP.• On the Web, the clients are Web browsers (applications especially well suited for displaying HTML content).History of a Web Server• The European Laboratory for Particle Physics (CERN) produced one of the first Web Servers.• The World Wide Web Consortium (W3C) supports a java-based server known as jigsaw.• CERN HTTPD was dificult to configure and not available for many platforms, so the National Center for Supercomputing Applications (NCSA) wrote their own version.• Apache is a popular server based on the NCSA implementation.The First Web BrowserThe first real HTML browser, NCSA Mosaic, came into being in early 1993.• It was free• It was available for all major platforms : UNIX, Macint0osh, and MS Windows.• It was easy to create content.TCP/IP Network Connections/PortsStandard Port Numbers• FTP : 20, 21• Telnet : 23• SMTP (email) : 25• HTTP : 80On unix servers• Port number below 1023 : root• Port number above 1024 : normal userServers and Browsers• The main goal of any Web server is to provide documents to clients.• The purpose of a Web browser is to retrieve and display information from a Web server by using HTTP.• Browsers have evolved, adding features that far extend the capabilities of browsers that once displayed only basic HTML.Browsers Plug-Ins• Extends browser capability• More than just HTML• RealPlayer live audio and video• Shockwave animations• Acrobat Reader view PDF filesFile Types• ASCII text files** Letters number and punctuation** View and edit with standard tools** HTML• Binary files** Images** Sound** ProgramsHTML Authoring Packages• Netscape Composer• Microsoft FrontPage• Macromedia Dreamweaver• Adobe PageMill• Alaire HomesiteImage File Types• GIF (Graphics Interchange Format)** 256 colours** Lossless compression** Transparency** Can be animated** Good for illustrations** Proprietary (patent)• PNG (Portable Network Graphic)** As GIF, except** more colours** no animation** not proprietary• JPEG (Joint Photographic Experts Group)** Millions of colours** Lossy compression** Good for photographsAudio File Types• WAV** Windows• AIFF** Macintosh• AU** UNIX• Modern browsers support all these and MoreMIME• Multipurpose internet mail extensions• MIME are a set of rules that allow multimedia documents to be exchanged among many different computer systems.• MIME was originaly designed for sending attachments in e-mail.• MIME uses media types and subtypes to describe the format of a file.MIME Types• Application** application/excel• Audio** audio/midi• Image** image/jpeg• Message** message/news• Multipart** multipart/digest• Text** text/html• Video** video/mpegRequest Methods• GET** Typical way of getting a resource from a server** Can be used to pass data to the server• HEAD** Server returns only header data** Use to verify the existence of a resource• POST** Used to send data to the server** Typically- send HTML form data to the serverHTTP Status Code Categories• Informational• Success• Redirection• Client error• Server errorFTP• Copies files from one host to another• Used to retrieve files from internet archieves• Useful for binary and text files• Log in identificationSSL• Secure Sockets Layer• Encrypts data in TCP/IP packets** ordinary HTTP uses clear text• Commercial web applications• Web server support