FTP Sequence Diagrams

The diagrams below trace an FTP session across the control (port 21) and data (port 20) connections.

Here we explore the sequence of interactions in a typical FTP (File Transfer Protocol) session. Individual sequence diagrams for interactions on Port 20 and 21 are also included.

The complete sequence diagram can be divided into the following steps:

• DNS Query to obtain the IP address for the FTP Server
• FTP Telnet connection setup and login. (USER and PASS commands)
• Obtaining a directory listing (PORT and LIST command)
• Changing directory (CWD command)
• Downloading a file using FTP get (PORT and RETR command)