File Transfer Protocol (FTP) is a protocol to transport files via a reliable TCP connection between a client and a server. FTP uses two reliable TCP connections to transfer files: a simple TCP connection (usually referred to as the Control Channel) to transfer control information and a secondary TCP connection (usually referred to as the Data Channel) to perform the data transfer. It uses a command/response based approach, i.e. the client issues a command and the server responds with a 3-digit status code and associated status information in text format. The Data Channel can be initiated either from the client or the server; the Control Channel is always started from the client.

The client is required to authenticate itself before other commands can be issued. This is performed using the USER and PASS commands specifying username and password, respectively.