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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)

FTP Overview, History and Standards 1 FTP Operational Model, Protocol Components and Key Terminology

The developers of the File Transfer Protocol (FTP) had to balance the need for a rich set of functionality with the desire for a protocol that was as simple and easy to implement as possible. FTP is therefore not nearly as simple as its “little brother”, the Trivial File Transfer Protocol (TFTP), but given what the protocol can do, it's much less complicated than one might expect. The operation of the protocol can in fact be broken down into a number of rather straight-forward elements that work together to establish connections and pass commands and data.

In this section I describe the most important concepts behind the File Transfer Protocol and explain its operation in general terms. I begin with a discussion of the FTP communication and operational model, which shows the internal components of the protocol and how they communicate over the internetwork. I describe the process by which FTP control connections are established, and how user authentication is performed. I explain the two main methods of creating data connections (normal and passive) and discuss the issues that pertain to when each is used. I then describe how FTP communication works in general and the various transmission modes. I conclude with a discussion of the different options for data representation used for files sent with FTP.

FTP Overview, History and Standards 1 FTP Operational Model, Protocol Components and Key Terminology