A data connection is created each time a file is transferred between the client and the FTP server. The client controls the creation of a data connection by issuing the commands that require a data connection (such as FTP ls, dir or put commands).
Once a data connection is established, the file transfer type (ASCII or binary) is specified. Clients attempt to auto-negotiate a transfer type. The default transfer type depends on the client system. For example, UNIX might default to binary. To specify the transfer type, enter the bin or ascii command at the FTP prompt.