19 Nov
2021
19 Nov
'21
7:06 p.m.
All,
This discussion has been quite interesting! Back in the 1982, I did programming for a
large RSX11M/DECnet based system that input commodity trading data from around eight
different commodity exchanges (CBOT, COMEX, Mercantile, etc.) as well as commodity news
service and distributed it to over 200 VT100s located all over the U.S.
The host system was an 11/44 connected to the development 11/44 via DMCs and
they shared a DT07 bus with box. In the DT07 was a couple DZ11s for data input
from the exchanges and a DV11 with 16 synchronous serial ports that were connected
to twelve remotely located 11/23s running RSX11S & DECnet.
The 11/23s were downloaded RSX11S via their DUV11s and the re-entrant RSX tasks
received DECnet task to task data packets about trades and then displayed individualized
data to ~20 VT100s on DZV11s and DLV11-Js.
A DUP11 on one of the 11/44s also did RJE jobs to an IBM mainframe. A watch-dog
timer ran between the 11/44s so that a semi-hot fail over could occur and the DT07 would
move the I/O to the development system if the primary had hardware issues.
Later I had an 11/24 that connected into this network via the CPUs 2nd DL11 port that
was often used for a TU58. I don?t remember exactly what it connected to on the 11/44
side. All the network connections were 9600 baud point to point lease lines from
AT&T.
If anyone out there has a DECnet distribution for RSX11S, I?d love to get a copy
to experiment with today.
Best,
Mark
On Nov 19, 2021, at 10:50 AM, Johnny Billquist <bqt
at softjar.se> wrote:
Well, I meant this in the context of a DUP11, but sure, it's also true with DMC.
But basically, in RSX, DECnet is just a component of something called the communications
executive, or CEX. CEX provides its own environment in which multiple processes run, and
provide services.
CEX then provides an interface to its drivers from RSX, which means that any RSX program
can make use of the services and protocols that CEX have, without have DECnet in the
picture.
So for example, CEX provides communication lines, which are packet based. If that is over
asynch lines it utlizes DDCMP over async serial. Any application in RSX can make use of
this. If you instead have a synch line, like a DUP11, or DMC, that is another interface
inside CEX. From the outside it makes no difference if it is a DUP or a DMC. Bottom side
is synch serial, using DDCMP. With DMC this is all done in the hardware. With a DUP11, CEX
is doing the DDCMP layer in software.
For the user program this is all invisible. You just communicate over the DUP11, and it
will be doing DDCMP.
If you actually want to use the DUP11 *whithout* DDCMP, then you'd go for the DUP11
device driver instead of accessing it through CEX.
And talking to a device using CEX in RSX means you talk to the "direct line
access" interface, or DLX. That is just one interface, independent of what underlying
hardware you are going to access. In the DLX, you start by opening the link, and for that
you use the name, which is the same as the line name you see for DECnet. But you are in
fact then just talking at the line level, using whatever protocol layer is used for that
line. DDCMP, for example.
Anything using DDCMP is always in packets. Don't matter how the hardware looks.
DLX is also used to access ethernet, by the way. And that is how I coexist with DECnet in
RSX, since ethernet can allow multiple channels on the same hardware.
I hope this makes sense. Else I can try to explain it more.
Johnny