The Hypertext Transfer Protocol , the Web's （/）protocol , is at the heart of the Web. HTTP is implemented in two programs : a（ ） program and a server program . The client program and server program, executing on different end systems , talk to each other by（/）HTTP messages . HTTP defines how Web clients request Web pages from servers and how servers transfer web pages to clients . when a user （/） a web page , the browser sends HTTP request messages for the objects in the page to the server . The server （/） the requests and responds with HTTP response messages that contain the objects .