13.1 Architecture

The architecture of the FTP protocol is as follows:

Figure 13.1: The FTP architecture

A user works with a user interface that is represented either by the command line of the FTP program, a GUI FTP utility, or an Internet browser.

The user interface is usually created according to the working of the operating system in which it is implemented. The user interface gives requests to the layer of the command interpreter. Then the command interpreter communicates with the server using commands defined by the FTP protocol. Section 13.4 contains an overview of these commands. However, the user can make use of an even richer range of commands since the command interpreter usually interprets several commands for working with the local file system of the client (for example, the lcd command that is used to set the current directory on the client side).

If both the client and the server layers of the command interpreter in the command channel agree on data transmission between the...