UNIT1 Web Essentials History of the Internet and

UNIT-1 Web Essentials

History of the Internet and World Wide Web Outline History of the Internet Personal Computing History of the World Wide Web Consortium (W 3 C)

History of the Internet Contd… *ARPANET Implemented in late 1960’s by ARPA (Advanced Research Projects Agency of DOD) * Networked computer systems of a dozen universities and institutions with 56 KB communications lines * ARPA’s goals: Allow multiple users to send and receive info at same time. Network operated packet switching technique. Digital data sent in small packages called packets * Packets contained data, address info, error-control info and sequencing info Greatly reduced transmission costs of dedicated communications lines * Network designed to be operated without centralized control. If portion of network fails, remaining portions still able to route packets

History of the Internet Contd… * Transmission Control Protocol (TCP)Name of protocols for communicating over ARPAnet * Ensured that messages were properly routed and that they arrived intact Organizations implemented own networks Used both for intraorganization and communication * Huge variety of networking hardware and software appeared ARPA achieved inter-communication between all platforms with development of the IPInternetworking Protocol * The Internet. Limited to universities and research institutions Military became big user. Next, government decided to access Internet for commercial purposes

History of the Internet Contd… * Internet traffic grew. Businesses spent heavily to improve Internet Better service their clients * Fierce competition among communications carriers and hardware and software suppliers * Bandwidth (info carrying capacity) of Internet increased tremendously * Costs plummeted

History of the World Wide Web * WWW Allows computer users to locate and view multimedia-based documents * Introduced in 1990 by Tim Berners-Lee * Internet today Mixes computing and communications technologies Makes information constantly and instantly available to anyone with a connection

World Wide Web Consortium (W 3 C) * W 3 CFounded in 1994 by Tim Berners-Lee Devoted to developing nonproprietary and interoperable technologies for the World Wide Web and making the Web universally accessible * Standardization. W 3 C Recommendations: technologies standardized by W 3 Cinclude Extensible Hyper. Text Markup Language (XHTML), Cascading Style Sheets (CSS) and the Extensible Markup Language (XML) * Document must pass through Working Draft, Candidate Recommendation and Proposed Recommendation phases before considered for W 3 C Recommendation

Protocols * Protocols are agreed formats for transmitting data between devices * The protocol determines : The error checking required * Data compression method used * The way the end of a message is signaled T * The way the device indicates that it has received the message There are many protocols used by the Internet and the WWW, including TCP/IP. - HTTP - FTP - Electronic mail protocols IMAP - POP

TCP/IP * The Internet uses two main protocols (developed by Vicent Cerf and Robert Kahn)Transmission control protocol (TCP)Controls disassembly of message into packets at the origin * Reassembles at the destination * Internet protocol (IP)Specifies the addressing details for each packet Each packet is labeled with its origin and destination

Hypertext Transfer Protocol (HTTP) * The hypertext transfer protocol (HTTP) was developed by Tim Berners. Lee in 1991 * HTTP was designed to transfer pages between machines * The client (or Web browser) makes a request for a given page and the Server is responsible for finding it and returning it to the client * The browser connects and requests a page from the server The server reads the page from the file system, sends it to the client and terminates the connection

Electronic Mail Protocols * Electronic mail uses the client/server model * The organization has an email server devoted to handling email Stores and forwards email messages * Individuals use email client software to read and send email (e. g. Microsoft Outlook, or Netscape Messenger) * Simple Mail Transfer Protocol (SMTP)Specifies format of mail messages * Post Office Protocol (POP) tells the email server to: Send mail to the user’s computer and delete it from the server * Send mail to the user’s computer and do not delete it from the server Ask whether new mail has arrived

Electronic Mail Protocols Cont’d * Interactive Mail Access Protocol (IMAP)Newer than POP, provides similar functions with additional features e. g. can send specific messages to the client rather than all the messages * A user can view email message headers and the sender’s name before downloading the entire message * Allows users to delete and search mailboxes held on the email server * The disadvantage of POP You can only access messages from one PC * The disadvantage of IMAP Since email is stored on the email server, there is a need for more and more expensive (high speed) storage space

MIME - Multi-purpose Internet Mail Extensions The MIME protocol lets SMTP transmit multimedia files including voice, audio, and binary data across TCP/IP networks.

HTML Hypertext Markup Language

Markup: * The markup provides instructions to the software used for viewing a webpage (web browser) on how the page should look and work. * Markup language essentially means a language that when you write something up in the language, the attributes and settings you write will be displayed visually. Hypertext: * Hypertext is text displayed on a computer display or other electronic device with references (hyperlinks) to other text that the reader can immediately access, usually by a mouse click, keypress sequence or by touching the screen. * It enables an easy-to-use and flexible connection and sharing of information over the Internet.

Basic Definitions Web Page: A web page is a document or resource of information that is suitable for the World Wide Web and can be accessed through a web browser. Website: A collection of pages on the World Wide Web that are accessible from the same URL and typically residing on the same server Browser: A web browser is a software application for retrieving, presenting, and traversing information resources on the World Wide Web URL: Uniform Resource Locator, the unique address which identifies a resource on the Internet for routing purposes

HTTP: A protocol to transfer hypertext requests and information between servers and browsers Hypertext: Hypertext is text, displayed on a computer, with references (hyperlinks) to other text that the reader can immediately follow, usually by a mouse Web server: software that delivers Web pages and other documents to browsers using the HTTP protocol