PI - Protocol Interpreter

DTP - Data Transfer Process

FTP: An application protocol for the most efficient and secure means of transferring files from one computer to another over the Internet.

FTP is the standard for file transfer over the internet. It copies files from one system to another.

FTP uses two TCP connections in order to transfer a file:

One connection is the control connection. It is used to send commands, which we'll discuss later.

The control connection is established as in client-server model when the client starts to communicate with the server, and ends only at the end of FTP.

The client sends FTP commands via control connection, and receives replies from the server.

The second connection is the data connection, which is created each time a file needs to be transferred in each direction, or when we would like to send a listing of files or directories from the server to the client.