Can FTP have multiple TCP connection for multiple

问题:

While reading the FTP protocol specification from : (http://www.pcvr.nl/tcpip/ftp_file.htm). I came across this "FTP differs from the other applications that we've described because it uses two TCP connections to transfer a file". My question is, can FTP have multiple TCP connection for multiple parallel file transfer, for example can I transfer two files in parallel over two TCP connections, is this a matter of customization or standardization?

回答1:

While it would be theoretically possible to make an FTP server support multiple, concurrent transfers, it's not supported by the RFC or any known implementation.

The block is a simple one in that the control connection, after receiving a transfer request, does not return a final status or accept new commands until the data transfer is completed. Thus, though you could queue up another transfer request it wouldn't actually be processed by the server until the current one completes.

If you want multiple file transfers, just log into the FTP server multiple times using different programs or command-line windows and have each initiate a transfer.

回答2:

No it can't. FTP uses a control connection for sending commands and a data connection that exists for the duration of the file transfer or directory listing retrieval, that's it.

For more information you can consult RFC 959, which defines the specs of the FTP protocol.