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2.2.2 Nonpersistent and Persistent Connections
HTTP can use both nonpersistent connections and persistent connections. HTTP/1.0 uses nonpersistent connections. Conversely, use of persistent connections is the default mode for HTTP/1.1.
Nonpersistent Connections
Let us walk through the steps of transferring a Web page from server to client for the case of nonpersistent connections. Suppose the page consists of a base HTML file and 10 JPEG images, and that all 11 of these objects reside on the same server. Suppose the URL for the base HTML file is
www.someSchool.edu /someDepartment/home.index.
Here is what happens:
1. The HTTP client initiates a TCP connection to the server www.someSchool.edu. Port number 80 is used as the default port number at which the HTTP server will be listening for HTTP clients that want to retrieve documents using HTTP.
2. The HTTP client sends a HTTP request message to the server via the socket associated with the TCP connection that was established in step 1. The request message includes the path name/someDepartment/home.index.(We will discuss the HTTP message in some detail below.)
3. The HTTP server receives the request message via the socket associated with the connection that was established in step 1,retrieves the object/someDepartment/home.index from its storage(RAM or disk),encapsulates the object in an HTTP response message ,and sends the response message to the client via the socket.
4. The HTTP client receives the response message. The TCP connection (But TCP doesn’t actually terminate the connection until the client has received the response message intact.)
5. The HTTP client receives the response message .The TCP connection terminate. The message indicates that the encapsulated object is an HTML file .The client extracts the file from the response message, parses the HTML file, and finds references to the 10 JPEG objects.
6. The first four steps are then repeated for each of the referenced JPEG objects