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 Formats

Clients 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 Browser
The 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/Ports
Standard Port Numbers
• FTP : 20, 21
• Telnet : 23
• SMTP (email) : 25
• HTTP : 80
On unix servers
• Port number below 1023 : root
• Port number above 1024 : normal user

Servers 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 files

File Types
• ASCII text files
** Letters number and punctuation
** View and edit with standard tools
** HTML
• Binary files
** Images
** Sound
** Programs

HTML Authoring Packages
• Netscape Composer
• Microsoft FrontPage
• Macromedia Dreamweaver
• Adobe PageMill
• Alaire Homesite

Image 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 photographs

Audio File Types
• WAV
** Windows
• AIFF
** Macintosh
• AU
** UNIX
• Modern browsers support all these and More

MIME
• 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/mpeg

Request 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 server

HTTP Status Code Categories
• Informational
• Success
• Redirection
• Client error
• Server error

FTP
• Copies files from one host to another
• Used to retrieve files from internet archieves
• Useful for binary and text files
• Log in identification

SSL
• Secure Sockets Layer
• Encrypts data in TCP/IP packets
** ordinary HTTP uses clear text
• Commercial web applications
• Web server support