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The TCP/IP Guide  9  TCP/IP Application Layer Protocols, Services and Applications (OSI Layers 5, 6 and 7)       9  TCP/IP Key Applications and Application Protocols            9  TCP/IP File and Message Transfer Applications and Protocols (FTP, TFTP, Electronic Mail, USENET, HTTP/WWW, Gopher)                 9  TCP/IP General File Transfer Protocols (FTP and TFTP)                      9  File Transfer Protocol (FTP)                           9  FTP Concepts and General Operation

FTP Concepts and General Operation 1 2 3 4 FTP Control Connection Establishment, User Authentication and Anonymous FTP Access

Server-FTP Process Components

The Server-FTP Process contains these two protocol elements:

• Server Protocol Interpreter (Server-PI): The protocol interpreter responsible for managing the control connection on the server. It listens on the main reserved FTP port for incoming connection requests from users (clients). Once a connection is established, it receives commands from the User-PI, sends back replies, and manages the server data transfer process.
  
  
• Server Data Transfer Process (Server-DTP): The DTP on the server side, used to send or receive data to or from the User-DTP. The Server-DTP may either establish a data connection or listen for a data connection coming from the user. It interacts with the server's local file system to read and write files.

The User-FTP Process contains these three protocol elements:

• User Protocol Interpreter (User-PI): The protocol interpreter responsible for managing the control connection on the client. It initiates the FTP session by issuing a request to the Server-PI. Once a connection is established, it processes commands received from the user interface, sends them to the Server-PI, and receives back replies. It also manages the user data transfer process.
  
  
• User Data Transfer Process (User-DTP): The DTP on the user side, which sends or receives data to or from the Server-DTP. The User-DTP may either establish a data connection or listen for a data connection coming from the server. It interacts with the client device's local file system.
  
  
• User Interface: The user interface provides a more “friendly” FTP interface to a human user. It allows simpler user-oriented commands to be used for FTP functions rather than the somewhat cryptic internal FTP commands, and also allows results and information to be conveyed back to the person operating the FTP session.

FTP Concepts and General Operation 1 2 3 4 FTP Control Connection Establishment, User Authentication and Anonymous FTP Access