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From: [e-mail] (Frank da Cruz)
Subject: Case Study #03: Autodownload
Date: 9 Jan 2000 15:32:17 GMT
Organization: Columbia University
Message-ID: <85a9m1$nhl$[e-mail]>
To: [e-mail]


Today we're showcasing C-Kermit's "autodownload" feature.  Kermit 95
and MS-DOS Kermit have this feature too.  If you use Kermit as a terminal
emulator (or in C-Kermit's case, to make terminal connections) AND for
file transfer, autodownload makes file transfer ridiculously easy.

First, recall the contortions needed when you don't have this feature: you
have to tell Kermit on the host to send (or receive), then "escape back" to
your terminal emulator, tell it to receive (or send), wait for the transfer
to complete, and then tell your terminal emulator to resume terminal
emulation.  Four steps, not counting the waiting.  With autodownload,
there's just one step.

To illustrate, let's say you have a Linux PC on your desk, and you use
C-Kermit 7.0 there to place a call (or make a Telnet connection) to a VMS
host, which also has C-Kermit.  You log in, read your mail, etc, and then
when you want to send (download) a file, say "oofa.txt", from VMS to Linux,
you just tell VMS C-Kermit to send it; assuming VMS C-Kermit is installed
correctly, you simply type:

  kermit -s oofa.txt

at the DCL prompt.  Ditto if this were UNIX instead of VMS, except in
UNIX it's the "shell prompt".  Ditto for AOS/VS, except there it's the "CLI
prompt", and so on.  (Of course you could also start C-Kermit and type
"send oofa.txt" at the C-Kermit> prompt, and then exit when done, but who
needs the extra steps?)

Now, after a second or two (or more -- we'll discuss the delay below),
Kermit on the host sends its first file-transfer packet, and C-Kermit on
your desktop PC recognizes it and instantly switches from terminal mode to
file-transfer mode, in which it puts up a running progress display, in most
cases complete with thermometer and other info.  When the transfer is
complete, C-Kermit automatically goes back to its terminal screen.

That's it; that's autodownload.  Try it!  Notice that, after making the
initial connection, you never had to interact directly with your desktop
Kermit again.  Even when (eventually) you log out from the host, your
desktop Kermit pops back to its prompt automatically when the connection
closes.  Thus, you control everything from within the terminal screen by the
commands that you give to the host.  All that confusing "escaping back" and
"reconnecting" is no longer needed.

What about uploading?  It works exactly the same way, except in this case
you have to tell the host Kermit to GET a file, rather than to SEND one.
Suppose you have just saved a web page from your Web browser on your PC
(as, say, "oofa.html") and you want to upload it to the host.  Just give the
following command at the DCL (shell, CLI, ...) prompt on your host:

  kermit -g oofa.html

(Or equivalently, start C-Kermit on the host, tell it to "get oofa.html",
and then exit when done.)

When your desktop Kermit sees the first packet, it automatically pops back
to file-transfer mode and awaits further instructions from the host Kermit,
which then sends the name of the file it wants; your desktop Kermit sends
the file and then returns to the terminal screen automatically when done.

Now let's talk about the delay.  If it takes a little while for the transfer
to start, it's because (a) the host Kermit is processing its initialization
file; (b) it has its DELAY parameter set to some annoying number of seconds,
like 5 or 10 or 20; or (c) both.  The DELAY parameter is there for the
benefit of terminal emulators that don't have the autodownload feature.  It
gives the user time to manually put the emulator into the appropriate
file-transfer mode.  But we don't need a delay if we are autodownloading.
The way to get rid of it is to include:

  set delay 0

in the host Kermit's initialization or customization file, or to include
the equivalent "-D 0" command-line option:

  kermit -D 0 -g oofa.html

Now let's consider the host Kermit's initialization file.  The standard
C-Kermit initialization file is rather big -- it defines all sorts of macros
and services that you won't need in this situation.  However, it also
"chains" to your customization file, where you might well have set some
performance-enhancing parameters to override Kermit's (former) conservative
default settings.

But C-Kermit 7.0, unlike its predecessors, uses fast settings by default
because computers and connections are much faster and more reliable now
than they were when the Kermit protocol was first designed.  So C-Kermit on
the host doesn't need to execute its initialization file -- or your
customization file -- at all, unless you are actually making a connection
FROM the host to somewhere else.

There are two ways to start host Kermit without executing its initialization
file.  First, you can change the name of the standard initialization file so
C-Kermit won't find it automatically (and then explicitly execute it any
time you actually need it), and second you can give the -Y (uppercase)
command-line option, which tells C-Kermit to skip its initialization file:

  kermit -YD 0 -g oofa.html

If the host is VMS, you have to enclose uppercase command-line items in
doublequotes:

  kermit "-YD" 0 -g oofa.html

Since the -Y option does not take an argument, it can be "bundled" before
the -D option.  But it need not be; the following is OK too:

  kermit -Y -D 0 -g oofa.html

Finally, if the remote host is UNIX, you might consider using G-Kermit there
instead of C-Kermit:

  http://www.columbia.edu/kermit/gkermit.html

It's perfect for use with a Kermit autodownload-capable terminal emulator on
your desktop -- in fact, that's what it's designed for.  G-Kermit is small,
its delay is 1 second, and it has no initialization file to slow it down:

  gkermit -s oofa.txt
  gkermit -r oofa.html

In most cases, G-Kermit goes just as fast as C-Kermit.

Still reading?  OK...  Are there any situations where autodownload is a
BAD thing?  Indeed there are.  First, consider a multihop connection in
which both your desktop computer and the intermediate one are capable of
autodownloads.  When the remote(st) Kermit sends its first packet, BOTH
Kermits see it at the same time, both automatically enter file-transfer
mode, and both reply to it.  This can't work.  C-Kermit 7.0 solves this
problem by filtering out "autodetected" packets and not passing them down
the line, but earlier versions don't do this.

A second scenario in which autodownload is inappropriate is when you are
using your terminal emulator to look at a C-Kermit packet log on the host.
(Try it some time :-)

In such situations, you can disable autodownload in C-Kermit with the
command:

  SET TERMINAL AUTODOWNLOAD OFF

You would also do this on a multihop connection when you want the
intermediate C-Kermit to be the transparent one, and autodownloads to go
through it to your desktop.  There is, by the way, a (new) C-Kermit
command-line option that tells it to be 100% transparent, intended for
exactly this situation: "C-Kermit in the Middle":

  kermit -0

(that's hyphen followed by digit 0).  This sets TERMINAL AUTODOWNLOAD OFF,
disables the escape character, APC, and everything else.

Still there?  Perhaps you're wondering if autodownload works with external
protocols like Zmodem?  In a word, yes.  If you have a Zmodem program that
works with C-Kermit as an external protocol, then C-Kermit will indeed start
it up automatically when you initiate a Zmodem download from the host.
AutoUPloads, however, are not possible with Zmodem.  External protocols are
described in detail in the manual, "Using C-Kermit", Chapter 14.

- Frank