File transfers via Annex terminal controller

[Stephen G. Simpson]

Earlier I posted a query in comp.sys.sun about Zmodem file transfers via
an Annex terminal controller.  The problem was that, when I would try to
use the Zmodem protocol to transfer files over a PC-modem dial-in
connection via an Annex to a Sun 3, the Sun session would go into the
background and I would get an Annex command prompt.

Several netters responded, and with their help and that of our system
administrator, and some experimentation on my own, I solved the problem.
So, I am posting now to share what I have learned.

The Annex terminal controller provides three ways for a dial-in user to
send an "attention" signal.  When Annex sees such a signal, it puts the
current session into the background and gives the user an Annex command
prompt.  This permits the user to run several sessions on the same or
different computers simultaneously.

The three types of attention signal are: break, long break, and a special
"attn" character which the user can define using an stty command from the
Annex prompt.  All of these can be disabled or enabled by the user.  The
Annex installer can also set defaults for these parameters.

On many Annex installations, break and long break are recognized but the
"attn" character is undefined.  Apparently these are the factory defaults.
However, some error-correcting modems don't like to transmit breaks
properly.  For this reason, some installations define the "attn" character
to be Ctrl-A, Ctrl-, or something else.  (This allows the user to
transmit an attention signal to Annex even if his modem won't send a
break.)

On our particular installation here, the dial-in default setting for attn
is Ctrl- (this choice was made whoever installed our Annex).  This
interferes with Zmodem because apparently Zmodem uses Ctrl- to do some
useful work.  On some other installations, the attn character is Ctrl-A,
and this interferes with Kermit for the same reason.

I found two ways to solve the problem.  One way is to disable the attn
character.  The Annex command to do this is

Annex: stty attn none

This is fine for me because, fortunately, my modem is able to send a break
properly, so I don't need a special attn character.

The other way is to instruct Zmodem to "escape" or "quote" all control
codes.  This is done using the -e switch when invoking Zmodem.

Thanks to Robert Claeson of ERBE in Sweden, Reid Simpson of Xylogic,
and Dan Ehrlich of Penn State.