Information requested by a client program by means of the X protocol is sent back to the client with a ``reply.'' Both events and replies are multiplexed on the same connection. Most requests do not generate replies. Some requests generate multiple replies.
an acknowledgement (positive or negative) sent from server to user via the TELNET connections in response to FTP commands
an acknowledgment (positive or negative) sent from receiver to sender via the control connection in response to a MTP command