FTP is a standardized network protocol and probably the quickest as well as easiest option available when a large chunk of data is to be transferred, from one host to another, over a TCP-based network. FTP defines a client-server architecture which uses two separate ‘well-known’ ports, for data (port no. 20, used for data transfer) and control (port no. 21, used for authentication) connections, in order to establish connectivity between the server and the client.

Source: How To : Set up a FTPS (FTP over SSL) Server on Linux ~ Your Own Linux..!