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File
Transfer Protocol
FTP stands
for File Transfer Protocol. Simply
put, it is a means of communication
over the network specifically designed
for moving files between computers
on the network. Of primary use to
most of us is transferring files to/from
our desktop/laptop personal computers
and the unix workstations (saga, epic,
elaine, etc), but it can also be used
to communicate with machines at companies
like Netscape to download software,
or any PCs or other machines running
FTP servers.
FTP, the File Transfer
Protocol, documented in RFC
959, is one of oldest Internet
protocols still in widespread use.
FTP is implemented using the TCP
Protocol.
As shown in the following
diagram, FTP uses separate command
and data connections. The Protocol
Interpreter (PI) implements the FTP
protocol itself, while the Data Transfer
Process (DTP) actually performs data
transfer. The FTP protocol and the
data transfer use entirely separate
TCP sessions.
-------------
|/---------\|
|| User || --------
||Interface|<--->| User |
|\----^----/| --------
---------- | | |
|/------\| FTP Commands |/----V----\|
||Server|<---------------->| User ||
|| PI || FTP Replies || PI ||
|\--^---/| |\----^----/|
| | | | | |
-------- |/--V---\| Data |/----V----\| --------
| File |<--->|Server|<---------------->| User |<--->| File |
|System| || DTP || Connection || DTP || |System|
-------- |\------/| |\---------/| --------
---------- -------------
Server-FTP USER-FTP
NOTES: 1. The data connection may be used in either direction.
2. The data connection need not exist all of the time.
FTP servers listen on
port 21. Data connections are initiated
by the server from its port 20, to
a port on the client identified in
a PORT command.
For a discussion of running FTP through
firewalls, see RFC
1579.
FTP Applications:
Recommended Programs:
| Mac: |
Fetch |
Nice
graphical interface that supports
drag-and-drop |
| PC: |
WS-FTP |
Pretty good
graphical interface once you
get used to it. |
|
|
built-in |
Windows 95 built-in
support for ftp, command-line
oriented. |
| Unix: |
ftp |
Standard unix
command-line ftp program, virtually
identical to the PC built-in. |
|
|
ncftp |
Slightly more
feature-packed version, also
command line oriented. |
Obtaining the Programs:
Fetch can be obtained over AppleShare.
Go to the Chooser and select AppleShare.
Select the Stanford zone and the machine
called Site-Licensed. Log in with
your leland/SuNet username and password.
Choose Site-Licensed in the window
that appears by dou ble-clicking on
it (do NOT check the check-box!) and
the Site-Licensed machine will appear
on the desktop just like any other
folder. Find the Fetch program on
Site-Licensed and copy it to your
local machine (just drag it like any
other file).
Both Fetch and WS-FTP
(along with other networking software)
can also be copied from a CD-ROM which
can be obtained from the RCCs.
Fetch and WS-FTP (along
with other networking software) can
also be found on the web at http://www-leland.stanford.edu/dept/itss/macstanford
(/dept/pcstanford for PC users).
PC built-in FTP is installed
by default with Windows95 Unix ftp
and ncftp programs are installed on
the leland systems.
FTP Servers of Interest:
- ftp.stanford.edu - contains
a lot of software available free
to Stanford users
- leland machines (saga/epic/elaine/tree/cardinal/amy/etc)
- to get to your account
- ftp.netscape.com - the netscape
ftp server (ftp is built-in to PCs
and Unix boxes but web access is
not! (well, let's not consider lynx))
Using FTP to Download
(transfer from another machine to
yours):
- Connect to the server (and
login). Servers with restricted
access require a username and a
password (including ftp.stanford.edu
and the leland machines). Other
servers (such as ftp.netscape.com)
support "anonymous login"
where the standard is to use the
username "anonymous" and
your full email address as your
password.
- Find the file(s)/folder(s)
you want to download. Navigating
the folder hierarchy is just like
it is on Macs, PCs, etc. Double-click
a folder to open it. (Command-line
FTP programs are more like navigating
in dos/unix; use the "cd"
command).
- Choose the appropriate download
mode! There are two transfer
modes in FTP. The first is called
either "ascii" or "text",
and the other is called "binary"
or "image". The reason
for the two modes is that different
machines represent End-Of-Line char
acters in different ways. "text"
mode automatically corrects for
these differences so that the text
you download appears correct on
your machine, so for text files
you should use text mode (otherwise,
you may find, for example, that
all your text appears on one line
after it is downloaded). But if
you use text mode on a non-text
file, it will corrupt the file!
It will try to interpret non-text
data as text and therefore change
the file. And for something non-text
like a graphic or a microsoft word
document (which contains formatting),
you will find very unpleasant results
if you use text mode! In short,
if it isn't text, use binary
mode (which leaves the file
untouched). (Note: PostScript files
(.ps extensions) are text files,
not binary)
- Begin the transfer and get
the file (make sure you know where
the file is being put on your local
machine)!
Using FTP to Upload
(transfer from your machine to another):
- Connect to the server (and
login). Servers with restricted
access require a username and a
password (including ftp.stanford.edu
and the leland machines). Other
servers (such as ftp.netscape.com)
support "anonymous login"
where the standard is to use the
username "anonymous" and
your full email address as your
password.
- If you're using Fetch, choose
to "Put" files/folders,
and you will be prompted to specify
the files.
- Find the file(s)/folder(s)
you want to upload on your computer.
Navigating the folder hierarchy
is just like it is on Macs, PCs,
etc. Double-click a folder to open
it. (Command-line FTP programs are
more like navigating in dos/unix;
use the "cd" command).
Be careful what you upload! Unix
is not especially partial to filenames
with spaces and odd characters.
- Choose the appropriate
upload mode! See the notes on
download for details. Note that
Fetch chooses different names for
the file types when uploading. "Raw
Data" is the same as binary/image.
"Text" is text.
- Begin the transfer!
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