File Transfer Protocol (FTP)

What Is FTP and Why Do You Need It?

The part of the TCP/IP protocol set that includes rules for formatting, ordering, and error-checking files
sent across a network.

Download and Upload
Download: The process of getting a file or data from a computer connected to the Internet and saving
the file or data on your PC.
Upload: The process of sending a file from a PC to another, usually larger, computer on connected to the Internet.

FTP server and FTP client

FTP server
A program that receives file transfer requests from your FTP client program and then acts on those commands.

FTP client
A program residing on your PC that facilitates transferring files between your PC and a computer connected to the Internet.

Examples of FTP Clients:

• Command line ftp clients for Windows and UNIX
• GUI (Graphical User Interface) clients:
• (WS_FTP LE (for the PC) and Fetch (for the MAC) are good free client programs but not secure
• SSH Secure File Transfer is a freeware secure (encrypted) client
• All browsers (I.E., Netscape, Mozilla, come with an integrated ftp client

Let's introduce FTP using the command line because it unveils some of its confusing aspects related to so called "anonymous" or "privileged" logging.

Command-line FTP
An FTP interface in which you enter a series of one-line commands to connect to an FTP site.
An ftp program is built in to Windows: to start it click Start, then Run, then type in ftp and press Enter

You can also Telnet to hills.ccsf.edu and at the $ type in ftp

Common FTP Commands

ascii binary cd directory close get filename help lcd directory ls or dir open remote put filename quit or bye

sets transfer mode to ASCII sets transfer mode to binary changes remote directory to directory disconnects from remote computer downloads filename from remote computer shows a help message changes local current directory to directory lists folders and filenames in the current remote directory connects to a remote FTP server uploads filename to a remote computer exits the FTP program and logs off the remote server

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Example FTP Session Anonymous login and Full-Privilege FTP
Anonymous login

Logging on to one of the many publicly accessible remote computers by specifying the user name anonymous and your e-mail address as the password. (see the example above with sol.ccsf.edu (alias ftp.ccsf.edu)

In the example above , I Telnetted to hills and I typed at the $ prompt the command: ftp sol.ccsf.edu

.Full-privilege FTP
Logging on to a computer on which you have an account, including a username and password, and using it to send
and receive files.

In the example below, at the command line of my PC (Start/Run/cmd), I typed: ftp hills.ccsf.edu

FTP session
The time period between when you log on to another computer anonymously or with full privilede and
when you log off. During that time, FTP transfers files to and from another computer connected to the Internet.

Anonymous FTP Using a Web Browser

Note that, if in the URL the the protocol type (ftp://) is followed immediately by the ftp host name,
the browser is programmed to send in the word anonymous as login and some e-mail address as password.

Named FTP using the Web Browser

On the other hand, if you have an account on a server running ftp, you have to follow the
"protocol type" ftp:// by your login and the browser will then prompt you for your password, as shown below

Desirable FTP Client Features
Multipane display showing both local and remote directories simultaneously
Allows you to transfer many files in a single FTP session
Permits drag-and-drop file transfer
Simplifies deleting directories and files on remote and local computers
Familiar Windows Explorer style appearance for both local and remote computers
Allows you to set up scheduled file transfers at future times for automatic file transmission
Gracefully recovers from interrupted file transfers, continuing from the point where the transfer was interrupted. Automatically reconnects to sites that disconnect you when your connection exceeds the maximum connect time. Secure connection..

ASCII v. Binary File Types:

FTP has two modes of transfer: ASCII text and Binary.

• ASCII text:
  Text that contains symbols typed from the keyboard that does not contain any nonprintable, binary codes.
   Usually have .txt, .htm, or .html file extensions.
• Binary:
   A two-digit numbering system consisting of zero and one. Keyboard characters are formed from binary numbers; there are several binary numbers that have no corresponding printable or readable character.
  Binary file extensions include .exe, .zip, .jpg, .gif, .doc, .xls, and many more

ASCII mode
A file transfer setting in which all data being transferred consist of printable characters. Thus, no special treatment of the transferred data is needed to preserve nonprintable characters.
Binary mode
A file transfer setting in which all of the characters, whether they can be displayed or not, are preserved during the file transfer process. Graphics files, word-processed documents, and spreadsheets are examples of files that must be transferred in binary mode.