[Simh] VAX DZ terminal controller unit?

[Gary Lee Phillips]

On Thu, May 19, 2011 at 12:03 PM, Jason Stevens <neozeed at gmail.com> wrote:
> I'd try the 'modem' setup for the DZ ... I recall something similar
> with Unix/32v
>
> set dz lines=16
> att dz -m 2311
>

Well, that sounded promising, but as far as I can tell, it made no
difference at all.

After a telnet session to the DZ port 8501, no matter how it
terminates, the unit remains locked up for several minutes and cannot
connect to the VAX emulation again. Eventually a security error is
reported to the OPA0 terminal, saying that no input could be obtained
from TTA0 and the connection has timed out. Then it is possible once
again to connect through port 8501 for another session.

Sessions work fine while they are connected. The issue is
disconnecting and being able to reconnect. There appears to be some
failure in handshake between the DZ emulation and the VAX driver, such
that the closed telnet session, even if a hangup was sent, remains
active (virtual DSR asserted, maybe?) for some length of time. This
would be OK if the DZ emulation itself rotated through the available
lines, sending the next connect request to line 2, and the next to
line 3, and so forth, but it doesn't do that. As far as it is
concerned, line 0 is now clear and the next SYNC results in a new
connection to line 0. But the VAX driver isn't accepting that
connection, or so it seems.

The timeout seems to vary, anywhere from five minutes to fifteen or
more. In one case the line was still tied up after sitting unused
overnight.

Just to clarify, as there seems to be some confusion, I want to use
the DZ emulation to allow terminal sessions that originate on the same
host box that runs the SIMH software to connect to the emulated VAX.
This is not possible if the emulation and the host share the same NIC,
but it can be done by going through the DZ, which provides a
host-based port number. I am not trying to connect an actual VT
terminal, and I don't see that the DZ emulation is really intended to
do that. As for LAT, I found it cumbersome to use even when I had a
real VAX and a real terminal server. It doesn't seem appropriate to
this particular situation at all.

--Gary