Please Whitelist This Site?
I know everyone hates ads. But please understand that I am providing premium content for free that takes hundreds of hours of time to research and write. I don't want to go to a pay-only model like some sites, but when more and more people block ads, I end up working for free. And I have a family to support, just like you. :)
If you like The TCP/IP Guide, please consider the download version. It's priced very economically and you can read all of it in a convenient format without ads.
If you want to use this site for free, I'd be grateful if you could add the site to the whitelist for Adblock. To do so, just open the Adblock menu and select "Disable on tcpipguide.com". Or go to the Tools menu and select "Adblock Plus Preferences...". Then click "Add Filter..." at the bottom, and add this string: "@@||tcpipguide.com^$document". Then just click OK.
Thanks for your understanding!
Sincerely, Charles Kozierok
Author and Publisher, The TCP/IP Guide
NOTE: Using software to mass-download the site degrades the server and is prohibited.
If you want to read The TCP/IP Guide offline, please consider licensing it. Thank you.
FTP Operational Model, Protocol Components and Key Terminology
(Page 1 of 4)
The standards that define the File
Transfer Protocol (FTP) describe its overall operation using a simple
conceptual tool called the FTP model. This model defines the
roles of the devices that participate in a file transfer, and the two
communication channels that are established between them. It also describes
the components of FTP that manage these channels, and defines the terminology
used for the components. This makes it an ideal place for us to see
how FTP works in broad terms.
The Server-FTP Process and User-FTP Process
FTP is a classical client/server
protocol, as I mentioned in the overview.
However, the client is not called by that name but rather is called
the user. The name comes from the fact that the human user that
issues FTP commands works on the client machine. The full set of FTP
software operating on a device is called a process. The FTP software
on the server is called the Server-FTP Process, while the software
on the client is the User-FTP Process.
Key Concept: The FTP client is sometimes called the user device, since the human user interacts with the client directly. The FTP client software is called the User-FTP Process; the FTP server software, the Server-FTP Process.
FTP Control Connection and Data Connection
A critical concept in understanding
FTP is that while it uses TCP like many other applications, it does
not use just one TCP connection for all communication
the way most protocols do. The FTP model is designed around two
logical channels of communication between the server and user FTP processes:
- Control Connection: This is the main logical
TCP connection that is created when an FTP session is established. It
is maintained throughout the FTP session and is used only for passing
control information, such as FTP commands and replies. It is not used
to send files.
- Data Connection: Each time that data is
sent from the server to the client or vice-versa, a distinct TCP data
connection is established between them. Data is transferred over this
connection. When the file transfer is complete, the connection is terminated.
The reason for having these separate
channels is that it provides flexibility in how the protocol is used,
as we will see later in this section. It does, however, add complexity
Key Concept: Unlike most protocols, FTP does not use a single TCP connection. When a session is set up, a permanent control connection is established using TCP, for passing commands and replies. When files or other data are to be sent, they are passed over separate TCP data connections that are created and then dismantled as needed.
|If you find The TCP/IP Guide useful, please consider making a small Paypal donation to help the site, using one of the buttons below. You can also donate a custom amount using the far right button (not less than $1 please, or PayPal gets most/all of your money!) In lieu of a larger donation, you may wish to consider purchasing a download license of The TCP/IP Guide. Thanks for your support!|
Table Of Contents - Contact Us
The TCP/IP Guide (http://www.TCPIPGuide.com)
Version 3.0 - Version Date: September 20, 2005
© Copyright 2001-2005 Charles M. Kozierok. All Rights Reserved.
Not responsible for any loss resulting from the use of this site.