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# 1.2.1.10.1 Abstraction Model

How The Library Works

Files are transferred via the data connection. The control connection is used for the transfer of commands and the replies to these commands. Several commands are concerned with the transfer of data between hosts. These data transfer commands include the command which specify how the data is to be transmitted and the way in which the data is to be represented.

The mechanism of transferring data consists of setting up the data connection to the appropriate ports and choosing the parameters for the transfer.

The passive data transfer process shall "listen" on the data port prior to sending a transfer request command.

The FTP request command determines the direction of the data transfer. The server, upon receiving the transfer request, will initiate the data connection to the port. When the connection is established, the data

transfer begins between DTP’s, and the server-PI sends a confirming reply to the user-PI.

It is possible for the user to specify an alternate data port by use of the PORT command.

In general, it is the server’s responsibility to maintain the data connection, to initiate it and to close it.