The HTTP protocol

With this article we analyze the protocol that forms the core of the Web, or 'HTTP.

HTTP stands for Hyper Text Transfer Protocol and is one of the most important and dated application layer protocols.
Whenever a user requires any Web page using the HTTP protocol is to make the request to the server hosting the page is to receive data from the server in response.
It 'obvious, therefore, that the HTTP protocol is present both in the application layer and in the Client Server communication otherwise described above would not occur.

The request by the client is done through the browser that handles all communications on the screen and returns the resources requested by the user. The browser sees a web page as a set of objects related to each other through hyperlinks.
So definitely a web page consisting of a HTML body as other resources that may be scripts, images, Java applets and so on.
All resources on a server can be accessed through a URL path that refers to one specific object and. The structure of the URL is defined by a well-defined standards and consists of two main structures. Take for example the following resource:

 



 http://www.miosito.it/informazioni/curriculum.html

 

• www.miosito.it: identifies the host on which the resource is hosted we seek.
• / Info / curriculum.html: identifies the path to follow (within the host) to reach the resource sought. The path can be passed parameters (QueryString) to make queries to the server-side scripts (programs real bow).

There are two variations to the protocol: the 'HTTP/1.0 HTTP/1.1 more dated and that right now is that most Web browsers and servers by using the shell being more recent and more powerful than version 1.0.

The special feature of the HTTP protocol is to be defined as a Stateless Protocol which is a stateless protocol because the web server does not maintain any kind of information on clients who have requested a resource.

The HTTP protocol relies on the TCP transport layer to manage the transfer of data from the server to the client. The choice of TCP is due to the fact that TCP provides a reliable data transfer service, which does not necessarily another transport protocol is UDP.

The use TCP has the advantage - as we said - the reliable transfer of data, but the other involves a more wait time to receive the requested resource as TCP, before transmitting the data, must establish a connection operation that is called the handshake. If the reader wanted to investigate the operation and characteristics of TCP referring to an ' article of the present centre-equestre-lepuy.com.

HTTP is essential for the reliable transfer of data as if the whole body of an HTML web page to be transferred to the browser, due to some transmission error, the page request would be impossible to see or crippled in its content.

As mentioned above belongs to the HTTP application layer and the TCP is a transport-layer protocol. That said, how does the HTTP to exchange data with TCP?
This is possible thanks to the socket that represent the point of contact between the application layer and transport layer. Each application on a given host has a specific socket interface to the transport layer, so if for example, a user requests a web page while sending an e-mail that there will be a two-socket gestiscce data exchange between HTTP and transport layer and the other between the email protocols and the transport layer.

Assume now that a user requires two simultaneous web pages: you create two separate sockets? The answer is no, because the socket refers to a process (in this case HTTP) and will be responsible for managing quesst'ultimo, independently, the two received packets viewing web pages requested separately.

After this quick overview sull'HTTP in the next chapter we will enter into the heart of the discussion of the protocol explaining how the request is handled by a client and the consequent transfer of data.

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