[HECnet] DMC11 in next simh version... looks nice, and question about TOPS-10

[Rob Jarratt]

-----Original Message-----
From: owner-hecnet at Update.UU.SE [mailto:owner-hecnet at Update.UU.SE]
On Behalf Of Jordi Guillaumes i Pons
Sent: 02 January 2013 22:37
To: hecnet at Update.UU.SE
Subject: Re: [HECnet] DMC11 in next simh version... looks nice, and
question
about TOPS-10

Al 02/01/13 23:32, En/na Paul_Koning at Dell.com ha escrit:
Why those two modes?   Real DMCs are symmetrical, I would have
expected a simulation to do that too.
Just to clarify it, I didn't wrote that software :). I don't want to get
anyone's
merits. And, for your question, I also wonder why did the author wrote it
that way. I guess since it is TCP based one of the partners must put
itself in
listen mode and the other one has to do the initial connect, hence the
need
to differentiate between a "primary" or caller and a "secondary" or
listener.
UDP does not have that problem, but of course you can't (easily) tunnel
UDP
using -for instance- ssh.


I am main author of the code, although the original idea came from
Hans-Ulrich (Ulli) H  lscher who has also done most of the testing and
initiated its move into the official SIMH code, and Mark Pizzolato has done
an amazing job getting it into SIMH and closer to the standard of other
devices.

The reason for primary and secondary modes is as Jordi says, because it uses
a TCP connection. I tried to make it symmetrical but it was not very
reliable and had problems when one end was behind an ISP which blocked the
incoming TCP connections. The easiest way was to for one end to connect and
the other to listen. I think some new features have been added to SIMH which
might make this better, but I didn't have those available to me when I first
wrote the code quite some time ago, perhaps a later release could change to
use this.

You can indeed use the simulated DMC11 to tunnel DECnet over the internet
without using the bridge, my router, Multinet or a hardware router (of
course your emulated node has to be a router though). My HECnet node VAX780
(5.8) is running the DMC11 emulation 24x7 on a Raspberry Pi, it is
configured to connect to Ulli's emulation as and when it is available and so
puts his nodes on HECnet when available.

As for speed, Ulli did some tests but I don't recall the results, certainly
faster than the original hardware. There is also a setting that lets you
artificially slow down the speed so that you can get closer to the
experience you would have had with the real hardware.

Please note that we have only tested it significantly on VAX 780 emulations.
I don't know enough about PDP11 and PDP10 to really test there. I have been
struggling particularly with PDP10, trying to get TOPS-10 to use it, but I
really don't know how and my attempt to build a new monitor with DMR11
emulation (almost identical to DMC11) failed at the link stage, but I don't
know why.

Regards

Rob