Introduction to Internet Resources and Services

Spring '99
#43405 (Tue)
#43400 (Thu)

Class Notes: File Transfer Protocol (FTP)

Introduction to FTP

• The File Transfer Protocol (FTP) is an application protocol.

• It is used to download files from and upload files to an FTP server.
  • Download - retrieve file, from server to client.

  • Upload - transmit file, from client to server.

• Authentication is by a username and password.

• Ftp often is used to access your account on a Unix server.

Anonymous FTP

• Some FTP servers provide public access through anonymous FTP.

• Login with username anonymous; give your email address as password.

• Access is granted to a limited slice of the system.

• Widely (but not universally) supported convention is to place public files in /pub area.

• Typical uses:
  • Retrieve software, e.g. ftp://ftp.netscape.com/pub/communicator/

  • Publish information, e.g. ftp://ftp.isi.edu/in-notes/

FTP Clients

• Both web browsers and dedicated clients may be used for FTP.

• Browser typically limited to anon FTP.

• Dedicated client offers control of transfer type.

• Dedicated client can do FTP upload.

• Dedicated client can transfer multiple files.

  Common FTP Commands
  command	action
  dir	directory listing
  cd	change directory
  cdup	same as "cd .."
  pwd	print working (display current) directory
  ascii	do transfers as "text" file
  binary	do transfers as "binary" file
  get	retrieve single file
  mget	retrieve multiple files, with wildcards (*)
  quit	quit

Text and Binary Files

• In the days when FTP was designed, different computers used varying text file formats and character sets.

• While most of the differences have disappeared, some persist today.

• Unix and MS-DOS systems use different line termination methods for text files.

          Unix:   Hello World!<NL>
          MS-DOS: Hello World!<CR><NL>
  
  	    <NL> = newline (ASCII code 10, CTRL/J)
  	    <CR> = carriage return (ASCII code 13, CTRL/M)
  

• FTP transfers are performed erither in ascii or binary mode. It is important to use the right one.

$Id: notes_ftp.html,v 4.3 1999/03/04 08:32:54 chip Exp $