The correct answer is File Transfer Protocol.File Transfer Protocol:The File Transfer Protocol (FTP) is a standard communication protocol used for the transfer of computer files from a server to a client on a computer network.FTP is built on a client“server model architecture using separate control and data connections between the client and the server.FTP users may authenticate themselves with a clear-text sign-in protocol, normally in the form of a username and password, but can connect anonymously if the server is configured to allow it.For secure transmission that protects the username and password, and encrypts the content, FTP is often secured with SSL/TLS (FTPS) or replaced with SSH File Transfer Protocol (SFTP).Additional InformationFTP may run in active or passive mode, which determines how the data connection is established.This sense of "mode" is different from that of the MODE command in the FTP protocol, and corresponds to the PORT/PASV/EPSV commands instead.In both cases, the client creates a TCP control connection from a random, usually an unprivileged, port N to the FTP server command port 21.In active mode, the client starts listening for incoming data connections from the server on port M.It sends the FTP command PORT M to inform the server on which port it is listening.The server then initiates a data channel to the client from its port 20, the FTP server data port.In situations where the client is behind a firewall and unable to accept incoming TCP connections, passive mode may be used.In this mode, the client uses the control connection to send a PASV command to the server and then receives a server IP address and server port number from the server, which the client then uses to open a data connection from an arbitrary client port to the server IP address and server port number received.Both modes were updated in September 1998 to support IPv6.Further changes were introduced to the passive mode at that time, updating it to extended passive mode.