control connection

         The communication path between the USER-PI and SERVER-PI for
         the exchange of commands and replies.  This connection follows
         the Telnet Protocol.

      data connection

         A full duplex connection over which data is transferred, in a
         specified mode and type. The data transferred may be a part of
         a file, an entire file or a number of files.  The path may be
         between a server-DTP and a user-DTP, or between two
         server-DTPs.

      data port

         The passive data transfer process "listens" on the data port
         for a connection from the active transfer process in order to
         open the data connection.