ASHIMA KALRA IMPORTANT TERMS

 WWW WWW  URL URL  HTTP PROTOCOL HTTP PROTOCOL  PROXIES PROXIES

 The World Wide Web, abbreviated as WWW or W3 and commonly known as the Web, is a system of interlinked hypertext documents accessed via the Internet. With a web browser, one can view web pages that may contain text, images, videos, and other multimedia and navigate between them via hyperlinks.  An official description of WWW is:An Internet-wide distributed hypermedia information retrieval system which provides access to a large universe of documents'' BACK

 It is based on a client/server protocol. There are several clients (WWW browsers) available; the most commonly used are the Netscape Navigator (NN) and the Microsoft Internet Explorer (MSIE) both discussed in the remainder of this section. BACK

 A Universal Resource Locator (URL) is a kind of address which contains not only the exact location of a certain resource on the Internet but also the protocol used to retrieve it, and, if necessary, additional information like a search query.  URL:  The first part of the address is called a protocol identifier and it indicates what protocol to use, and the second part is called a resource name and it specifies the IP address or the domain name where the resource is located. The protocol identifier and the resource name are separated by a colon and two forward slashes. BACK

 The substring after the port (/pub/WWW/History.html) shows the location of the resource in the hierarchically structured WWW server.  If the URL does not contain a filename, the server will retrieve the ``default index'' of the directory, which can be a file or a list of the files in the directory.  A URL can contain additional information for internal purposes, mostly separated by a question mark or a semi colon.  e.g: BACK

 HTTP stands for Hypertext Transfer Protocol. It is an TCP/IP based communication protocol which is used to deliver virtually all files and other data, collectively called resources, on the World Wide Web. These resources could be HTML files, image files, query results, or anything else.  A browser is works as an HTTP client because it sends requests to an HTTP server which is called Web server. The Web Server then sends responses back to the client. The standard and default port for HTTP servers to listen on is 80 but it can be changed to any other port like 8080 etc. BACK

 There are important things about HTTP of which you should be aware  HTTP is connectionless: After a request is made, the client disconnects from the server and waits for a response. The server must re-establish the connection after it process the request.  HTTP is stateless: This is a direct result of HTTP's being connectionless. The server and client are aware of each other only during a request. Afterwards, each forgets the other. For this reason neither the client nor the browser can retain information between different request across the web pages.  BACK

 In communications, a proxy is something that acts as a server, but when given requests from clients, acts itself as a client to the real servers. Analogy: Consider talking to somebody who speaks a foreign language through a translator. You talk to the translator, who receives your statements, then regenerates something else completely to the other end. The translator serves as your proxy. BACK

 The communication terminates at the proxy. In other words, the proxy doesn't forward data so much as it tears it completely apart. For example, an HTTP proxy doesn't forward every request sent through it. Instead, it first examines if it already has the requested web page in its cache. If so, then it returns that page without sending another request to the destination server. Because proxies completely terminate the communication channel, they are considered a more secure firewall technology than packet filters, because they dramatically increase the isolation between the networks. BACK