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File Transfer Protocol - FTP

The original information service was called FTP, which stands for File Transfer Protocol. This is probably the world's least friendly information service. It operates really at the level of machine-machine communication, and is used by more modern client programs just as that way of getting something from a server. However, it is still used by people as a sort of lowest common denominator means of access to a file on a remote computer. In the table 2.1, we show a printout of a real ftp session.

Internet FTP is interactive or synchronous, which means that you formulate your commands as you type at the terminal. FTP maintains Control Connection between the client and server, and sends commands over this in ASCII or ordinary text!

When data is going to move, the client and server open a Data Connection. The Data connection can keep going whilst the user issues further commands.

There are three categories of FTP Commands on the control channel:

Access Control
User, Passwd, Account, CWD, CDUP, QUIT

Transfer Parameters
Type, Structure, Mode

File Service Commands
Retrieve, Store, Append, etc

Basically, the user is asked to type a set of commands to access a file on a remote computer that may well resemble those she might type on accessing a file on her local computer. The additional information required includes: the name of the remote computer; account information for permission to access to the remote computer; and differences in the way files are kept remotely and locally. None of these things is very friendly to the non-computer user!

A common technique for sharing information freely using FTP is to provide an anonymous account which people can use to access public files on an FTP server. When challenged to login, the user gives the name ``anonymous'', and when asked for a password, they simply reply with their email address (or name, or sometimes, just the word ``guest'').

Table 2.1:  Example of Anonymous FTP

The two most useful things in FTP are the ability to get a listing of files in a directory on a remote server, and the ability to retrieve multiple files by wildcard matching of file names. The least useful things about FTP are that you have to know something about the name of the file you are seeking, and where it is, and also that there is no connection between that name and what is necessarily in the file.

next up previous contents
Next: Electronic Mail and Up: Information - Are Previous: Telnet

Jon Crowcroft
Wed May 10 11:46:29 BST 1995