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FTP runs exclusively through TCP. The servers of FTP by default listen to port 21 for incoming connections from the clients of FTP. From FTP client, a connection to this port forms the control stream on which the commands are passed from the FTP client to the FTP server, and on certain occasions from the FTP server to the FTP client. It uses out-of-band control. This means that it uses a separate connection for data and control. Therefore, a different connection is required for the actual file transfer to take place, which is called the data stream. The process of setting up the data stream is different depending on the transfer mode.