FTP stands for File Transport Protocol, and it does what the name says, i.e. it helps in transferring files between two computers over a network.
This protocol works by using two connections between the user’s computer (client) and the server. One connection is called the command channel where only commands are sent from the client to the server. The other connection is called data channel which is used for transferring the actual data.
Typically a user-name and password is required for logging into the server and performing some operations. But, there may be some FTP servers where no user-name or password is required for interacting with the FTP server. Such servers are called Anonymous FTP servers.
FTP has 2 modes of working – Active & Passive. In active mode, the client initiates a connection via the command channel and the server initiates another connection back to the client via the data channel. Thus, the server participates actively. On the other hand, in the passive mode, the client initiates a connection via the command channel and the server sends details via the command channel itself to the client to open a data connection with the server. The benefit of passive channel over the active mode is that there is a chance that the connections from the server to the client may be blocked if there is a firewall in place.
Once this FTP connection is in place, the commands and data can be shared through the command and data channels. Once the file transmission is done, the connection is closed gracefully.
FTP is capable of transferring files between systems that are using different operating systems and different file-systems.
In recent times, FTP has been used along with SSH for transferring files through a secure connection over an insecure network. This has come to be known as SFTP (or SSH File Transfer Protocol).
For Wikipedia entry on FTP, click here.
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