What does http mean?

HyperText Transfer Protocol (HTTP) is the most widely used network transmission protocol on the Internet. All WWW files must comply with this standard. The original purpose of designing HTTP was to provide a way to publish and receive HTML pages. The current application is mainly used to transmit hypertext data in addition to HTML web pages, such as: pictures, audio files (MP3, etc.), video files (rm, avi, etc.), compressed packages (zip, rar, etc.) basically as long as the file data Both can be transmitted using HTTP.

Web application layer protocol HTTP is the core of the Web. HTTP is implemented in the web client and server programs. Clients and server programs running on different end systems communicate with each other by exchanging HTTP messages. HTTP defines the structure of these messages and how the client and server exchange these messages. Before explaining HTTP in detail, let's review some of the terminology in the web.

A web page (also called a document) consists of multiple objects. An object is simply a file that can be addressed by a single URL, such as an HTML file, a JPG image, a GIF image, a JAVA applet, a voice clip, and the like. Most web pages consist of a single basic HIML file and several referenced objects. For example, if a web page contains HTML text and 5 JPEG images, it consists of 6 objects, a basic H1ML file plus 5 images. The base HTML file uses the corresponding URL to reference other objects on this page. Each URL consists of the server host name that holds the object and the path name of the object. For example, in the following URL:

www.45it.com/skin/new/logo.gif

www.45it.com is a pathname. A browser is a web user agent that displays the requested web page and provides a number of navigation and configuration features. The web browser also implements the HTTP client, so in the web context, we will use the terms browser and client interchangeably in the process sense. Popular web browsers include Netscape Communicator, Firefox and Microsoft's IE. The web server stores web objects that can be addressed by URLs. The web server also implements the server side of HTTP. Popular web servers are Apache, Microsoft's IIS, and Netscape Enterprise Server. Netcraft provides a summary of the web server [Netcrft 2000].

HTTP defines how a web client (ie, a browser) requests a web page from a web server and how the server delivers the web page to the client. The figure below shows this request response behavior. When a user requests a web page (such as clicking on a hyperlink), the browser sends an HTTP request message requesting each object in the page to the server. After the server receives the request, it responds by sending an HTTP response message containing these objects. By the end of 1997, essentially all browser and web server software implemented the HTTP/1.0 version defined in RFC 1945. In early 1998, some web server software and browser software began to implement the HTTP/1.1 version defined in RFC 2616. H1TP/1.1 is backward compatible with HTTP/1.0; a web server running version 1.1 can talk to a browser running version 1.0, and a browser running version 1.1 can also talk to a web server running version 1.0.

Both HTTP/1.0 and HTTP/1.1 use TCP as the underlying transport protocol. The HTTP client first initiates a TCP connection with the server. Once the connection is established, the browser process and the server process can access TCP through their respective sockets. As mentioned earlier, a client socket is the gate between a client process and a TCP connection, and a server-side socket is the gate between the server process and the same TCP connection. The client sends an HTTP request message to its own socket and also receives an HTTP response message from its own socket. Similarly, the server receives an HTTP request message from its own socket and also sends an HTTP response message to its own socket. Once a client or server sends a message to its own socket, the message falls completely under the control of TCP. TCP provides a reliable data transfer service to HTTP; this means that every HTTP request message sent by the client will eventually reach the server without loss, and each HTTP response message sent by the server will eventually reach the client without loss. We can see a clear advantage of a layered network architecture. HTTP doesn't have to worry about data being lost, nor does it need to care about how TCP recovers from data loss and misordering. These are the tasks of the lower protocol layers in TCP and protocol stacks.

TCP also uses a congestion control mechanism. This mechanism forces each new TCP connection to initially transmit data at a relatively slow rate, but as long as the network is not congested, each connection can quickly rise to a relatively high rate. The initial phase of this slow transfer is called a slow start.

It is important to note that the server does not store any status information about the client while it is sending the requested file. Even if a client requests the same object again in a few seconds, the server will not respond saying that it just sent it to it. Instead, the server resends this object because it has completely forgotten what it did earlier. Since the HTTP server does not maintain the client's state information, we say that HTTP is a stateless protocol.