> Wouldn't FTP need three simplex connections - commands to server, responses from server, data transfer?
AFAICT, per RFC 114, responses from the server are considered a data type: when a user sends a command to the server, sometimes the response is a status update ('MKDIR successful'†) and sometimes the response is the requested file.
The data structure of the response has fields to say what's coming back on the data channel for the requested transaction.
† MKDIR was not a command, just using it as an modern example.
AFAICT, per RFC 114, responses from the server are considered a data type: when a user sends a command to the server, sometimes the response is a status update ('MKDIR successful'†) and sometimes the response is the requested file.
The data structure of the response has fields to say what's coming back on the data channel for the requested transaction.
† MKDIR was not a command, just using it as an modern example.