• File Transfer Protocol (FTP) is the standard mechanism provided by TCP/IP for copying a file from one host to another.

• Although transferring files from one system to another seems simple and straightforward, some problems must be dealt with first.

• For example, two systems may use different file name conventions. Two systems may have different ways to represent text and data.

• Two systems may have different directory structures. All these problems have been solved by FTP in a very simple and elegant approach.

• FTP differs from other client/server applications in that it establishes two connections between the hosts. One connection is used for data transfer, the other for control information (commands and responses).

• Separation of commands and data transfer makes FTP more efficient. The control connection uses very simple rules of communication.

• Wc need to transfer only a line of command or a line of response at a time. The data connection, on the other hand, needs more complex rules due to the variety of data types transferred. However, the difference in complexity is at the FTP level, not TCP.

• For TCP, both connections are treated the same. FTP uses two well-known TCP ports: Port 21 is used for the control connection, and port 20 is used for the data connection.

FTP uses the services of TCP. It needs two TCP connections. The well-known port 21 is used for the control connection and the well-known port 20 for the data connection

• Figure shows the basic model of FTP.

• The client has three components: user interface, client control process, and the client data transfer process.

• The server has two components: the server control process and the server data transfer process.

• The control connection is made between the control processes. The data connection is made between the data transfer processes.

• The control connection remains connected during the entire interactive FTP session.

• The data connection is opened and then closed for each file transferred. It opens each time commands that involve transferring files are used, and it closes when the file is transferred.

• In other words, when a user starts an FTP session, the control connection opens. While the control connection is open, the data connection can be opened and closed multiple times if several files are transferred.