1Computer Sciences Department

Web Design 3Computer Sciences Department

Internet History and Protocols Domain Name System Client and Server Web server Document root Uniform Resource Locator Hypertext Transfer Protocol Computer Sciences Department4 Objectives

5 Internet History Origins – ARPAnet - late 1960s and early 1970s Network reliability For ARPA-funded research organizations BITnet, CSnet - late 1970s & early 1980s and file transfer for other institutions – NSFnet Originally for non-DOD funded places Initially connected five supercomputer centers By 1990, it had replaced ARPAnet for non-military uses Soon became the network for all (by the early 1990s) - NSFnet eventually became known as the Internet Computer Sciences Department

6 What the Internet is: A world-wide network of computer networks At the lowest level, since 1982, all connections use TCP/IP TCP/IP hides the differences among devices connected to the Internet Computer Sciences Department

7 Internet Protocols Internet Protocol (IP) Addresses – Every node has a unique numeric address – Form: 32-bit binary number – New standard, IPv6, has 128 bits (1998) Organizations are assigned groups of IPs for their computers By the mid-1980s, several different protocols had been invented and were being used on the Internet, all with different user interfaces (Telnet, FTP, Usenet, mailto Computer Sciences Department

8 Internet Protocols What Is a 'Domain Name System '? Domain Name System, or “DNS”, is the recognized system for assigning addresses to Internet web servers.  The domain names keep the real technical IP address invisible to most viewers. Example: Internet domain names  Domain names are organized right to left, with general descriptors to the right, and specific descriptors to the left. “These descriptors are called "domains”  The "top level domains" (TLD, or parent domain ) is to the far right of a domain name. Mid level domains (children and grandchildren) are in the middle. The machine name, often "www", is to the far left. Levels of domains are separated by periods ("dots"). Computer Sciences Department

9 Domain name conversion Computer Sciences Department

10 Client and Server Clients and Servers are programs that communicate with each other over the Internet A Server runs continuously, waiting to be contacted by a Client – Each Server provides certain services – Services include providing web pages A Client will send a message to a Server requesting the service provided by that server – The client will usually provide some information, parameters, with the request Computer Sciences Department

11 The World-Wide Web Web or Internet?  The Web uses one of the protocols, http, that runs on the Internet. The internet is a collection of computers……….etc Web Browsers:  Browsers are clients - always initiate, servers react (although sometimes servers require responses). Most requests are for existing documents, using HyperText Transfer Protocol (HTTP) Web Servers:  Provide responses to browser requests, either existing documents or dynamically built documents. Browser-server connection is now maintained through more than one request- response cycle. All communications between browsers and servers use Hypertext Transfer Protocol (HTTP) Computer Sciences Department

12 Web Server Operation Details Web servers have two main directories: 1.Document root (servable documents) 2.Server root (server system software) Document root “is accessed indirectly by clients”, “localHost” – The document root is the folder where the website files for a domain name are stored. Example: “C:\wamp\www” – Virtual document root “VirtualHost” run multiple independent websites on the same machine – Instead of typing every time to view our site. just type and it works Computer Sciences Department Browsers :

Computer Sciences Department13 Proxy servers Web servers now support other Internet protocols as ftp…etc

Web Server Web Server Operation : Apache (open source, fast, reliable) Web Server Operation : IIS Operation is maintained through a program with a GUI interface 14Computer Sciences Department

URL 15 General form: scheme:object-address  The scheme is the communication protocol.  These protocols include - http, ftp, telnet, mailto.  Different schemes use different object addresses.  HTTP uses an object address of the following form: //fully-qualified-domain-name/path-to-document // Computer Sciences Department

16 URLs Host name may include a port number, as in :80 (80 is the default) URLs cannot include spaces or any of a collection of other special characters (semicolons, colons,...) The doc path may be abbreviated as a partial path – The rest is furnished by the server configuration If the doc path ends with a slash, it means it is a directory Example: URL path  Computer Sciences Department

Multipurpose Internet Mail Extensions (MIME) read only 17Computer Sciences Department

18 HTTP request and respond phase  The client will initiate the communication by: -sending a request (HTTP Request) and -the HTTP Server (or Web Server) will respond back by sending a response (HTTP Response).  Every time a client needs to send the request, it first establishes a TCP reliable connection with the Web Server and then transfer the request via this connection.  The same happens in case a Web Server needs to send back an HTTP Response to a client.  Any of the two parties - the client or the server can prematurely stop the transfer by terminating the TCP connection. Client Server - Cookies are key/value pairs used by websites to store state information on the browser - client-side cookies are often used to remember data that is not relevant to the server - UI stuff; which check boxes have been checked; past login info; etc.

The Hypertext Transfer Protocol  The protocol used by ALL Web communications  Request Phase  Form: HTTP method domain part of URL HTTP ver. Header fields blank line Message body  An example of the first line of a request: GET /degrees.html HTTP/1.1 19Computer Sciences Department

The Hypertext Transfer Protocol: Methods  GET - Fetch a document  HEAD - Fetch just the header of the document  POST - Execute the document, using the data in body  PUT - Store a new document on the server  DELETE - Remove a document from the server 20Computer Sciences Department

HTTP Request Methods 21Computer Sciences Department

HTTP Headers 22Computer Sciences Department HTTP header fields are components of the header section of request and response messages in the Hypertext Transfer Protocol (HTTP). They define the operating parameters of an HTTP transaction “both sender and recipient refer to either the client or the server, depending on who sends and who receives the entity” The Accept request-header field can be used to specify certain media types which are acceptable for the response Accept: text/plain Accept: text/* If no Accept header field is present, then it is assumed that the client accepts all media types

 The asterisk "*" character is used to group media types into ranges, with "*/*" indicating all media types and "type/*" indicating all subtypes of that type. Computer Sciences Department23 Media types

24Computer Sciences Department HTTP Response is in the form of- status line:

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Web Security 27Computer Sciences Department

XHTML  To describe the general form and layout of documents  An XHTML document is a mix of content and controls  Controls are tags and their attributes  Tags often delimit content and specify something about how the content should be arranged in the document  Attributes provide additional information about the content of a tag 28Computer Sciences Department

Creating XHTML documents  XHTML editors - make document creation easier  Shortcuts to typing tag names, spell-checker,  WYSIWYG XHTML editors  What you see is what you get (MS FrontPage) 29Computer Sciences Department

Plug-ins and Filters  Plug-ins  Integrated into tools like word processors, effectively converting them to WYSIWYG XHTML editors.  Filters  Convert documents from X formats to XHTML 30Computer Sciences Department

 To control the style and layout of multiple Web pages all at once. Computer Sciences Department31 CSS

Plug-ins and Filters: Advantages and Disadvantages  Advantages of both filters and plug-ins:  Existing documents produced with other tools can be converted to XHTML documents.  Use a tool you already know to produce XHTML  Disadvantages of both filters and plug-ins:  XHTML output of both is not perfect - must be fine tuned  XHTML may be non-standard  You have two versions of the document, which are difficult to synchronize 32Computer Sciences Department

JavaScript  A client-side HTML-embedded scripting language  Only related to Java through syntax  Dynamically typed and not object-oriented  Provides a way to access elements of HTML documents and dynamically change them 33Computer Sciences Department

XML  A meta-markup language  Used to create a new markup language for a particular purpose or area.  Because the tags are designed for a specific area, they can be meaningful.  No presentation details.  A simple and universal way of representing data of any textual kind. 34Computer Sciences Department

PHP  A server-side scripting language  An alternative to CGI  Similar to JavaScript  Great for form processing and database access through the Web 35Computer Sciences Department

Java  General purpose object-oriented programming language  Based on C++, but simpler and safer  Focuses on applets, servlets, and JSP 36Computer Sciences Department

ASP.NET 37Computer Sciences Department

Perl, Ruby, Rails and Ajax no need 38Computer Sciences Department