Test: File Transfer Protocol (FTP) - Computer Science Engineering (CSE) MCQ

The PASS command, preceded by the username, completes the user’s identification for access control in an FTP session. Without the valid password, the user won’t be able to initiate the FTP connection.

An FTP connection includes a Server and a Client which wish to share a number of data files. The server can transfer files with multiple clients at the same time while the client communicates with only one server at a time.

The correct response code for the message “Can’t open data connection” is 425. Response code 452 is sent usually when the connection is suddenly closed.

FTP is out-of-band because the data connection is done separately through port 20 and control connection is done separately through port 21.

FTP server maintains state information of every control connection to keep track of the active and inactive connections in the session. This helps the server decide which connection to terminate, in case the connection is inactive for too long.

File Transfer Protocol is an application layer protocol used to share “files” between a server and a client. The protocol uses two separate ports for data and control connections: port 20 for data and port 21 for control.

Control connection using FTP port: 21, and data connection using FTP port: 20. The FTP session is started or ended using port 21 and the actual data i.e. files are sent through port 20.

The client would first initiate the TCP control connection through port 21. Then for every file transfer, a separate connection would be made through port 20. Now, since we have five files to be transferred, 1 control connection + 5 data connections = 6 total TCP connections.

FTP was designed to transmit commands only in English characters that are possible with just 7 bits in ASCII. Even the media has to be converted to ASCII before transmission.

Stream mode is the default mode of FTP, in which the TCP transforms/fragments the data into segments, and then after the transmission is completed, converts it back to stream of bytes.