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FTP Operational Model, Protocol Components and Key Terminology
(Page 2 of 4)
FTP Process Components and Terminology
Since the control and data functions
are communicated using distinct channels, the FTP model divides the
software on each device into two logical protocol components that are
responsible for each channel. The protocol interpreter (PI) is
a piece of software that is charged with managing the control connection,
issuing and receiving commands and replies. The data transfer process
(DTP) is responsible for actually sending and receiving data between
the client and server. In addition to these two elements, the user FTP
process includes a third component, a user interface, that interacts
with the human FTP user; it is not present on the server side.
Thus, there are two server process
components and three client (user) process components in FTP. These
components are referred to in the FTP model by specific names, which
are used in the standard to describe the detailed operation of the protocol.
I plan to do the same in this section, so I will now describe more fully
the components in each device of this model, which are illustrated in
Figure 288: File Transfer Protocol (FTP) Operational Model
FTP is a client/server protocol, with communication taking place between the User-FTP Process on the client and the Server-FTP Process on the server. Commands, replies and status information are passed between the User-PI and Server-PI over the control connection, which is established once and maintained for the session. Data is moved between devices over data connections that are set up for each transfer.
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Version 3.0 - Version Date: September 20, 2005
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