File Transfer

Transferring of data from one computer to the other is the one most common task in networking and inter-networking environment. As a matter of the fact, that greatest volume of data exchange in the Internet today is due to file transfer. We are going to discuss the most popular protocol on Internet that is File transfer Protocol.

File Transfer Protocol (FTP)

File transfer protocol (FTP) is the standard mechanism provided by the TCP/IP for copying file from one host to another. Although transferring file from one system to another is a simple straightforward, but some problems must be dealt with him. For example two systems may have different file name, they have different file directory and have different file format. These problems are solved very efficiently with the using of FTP. FTP is the very simple and elegant approach.

FTP is different from other client/server application it established two connection. In these two connections one is used for the data transfer and the other is used for the control information (command and response). That is for the complexity from the other side of the connection. Because of the variety of the data type that is transferred. However the complexity is only in the FTP level, not on TCP.

FTP uses the two well-known TCP ports: port 21 for the control information and the port 20 for the data information.

FTP uses the services of TCP. It needs two TCP connections

A well-known port 21 is used for control connection

And the other well-known port 20 is used for data connection

Communication over control connection

FTP uses the same approach as SMTP to communicate across the control connection. It uses the 7-bit ASCII character set. Communication is archived through commands and response. The simple method is used for the control connection. Each command and response is the short line. That’s why no need to check out the format of the document.

Communication over data connection

File transfer in FTP means one of the three things:

1. A file is to be copied from the server to the client. This is called retrieving a file. It is done under the supervision of the RETR command.  
2. A file is to be copied from the client to the server. This is called storing a file. It is done under the supervision of the STOR command.      
3. A list of directory or file names is to be sent from the server to the client. This is done under the supervision of the LIST command. Note that FTP treats a list of directory or file names as a file. It is sent over data connection.