PSTHRU is jogging a memory... Hum.
I had a look at pmr.txt and was wondering where you found the
Tops-20 stuff? I found SWSKIT V21 BB-H348C-RM_1982, but the stuff
looks like nothing I remember. In particular, pmr.mac looks
suspiciously incomplete but appears to just fork a program called
pts. That executable appears to be built from pts.sno, which is
in SNOBOL, of all things.
We were big fans of SNOBOL, but I don't remember using it except
for reformatting scanned user id sheets during registration for
bulk user creation. Running SNOBOL as a daemon would probably
struck us as being too memory and computationally intensive (it's
an interpreted language).
Is there any interest on actually trying to resurrect this
stuff? NFT and FAL wouldn't need pmr.mac nor pts.sno, but I would
need to reverse engineer the format of the DNCONN configuration
file. DNCONN is a nice idea; you give it a node name and it
builds the appropriate forwarding string for you. What's missing
appears to be other NRT PMR daemons.
The SNOBOL code doesn't appear to forward interrupt messages. I
don't know about DNCONN.
Regarding the node::node2:: ... syntax, I wasn't aware (or had
completely forgotten) that VMS would do this, but I'm not
surprised. One thing that impressed we Tops-20 folks at Columbia
was the degree of integration of DECnet. There are hooks in
Tops-20 to do something equivalent, but they never made it all the
way into the EXEC. There is a vestigial driver in the monitor,
but I don't see any code for it.
I was aware of node::node2:: ... being used for MAIL11 because that has to get transmogrified for SMTP (which runs over DECnet as well as TCP and some other transports). It is handled in roughly the same way as the Unix 'bang' format, meaning node!node1. I forget where the @ goes (or if there is one) for Unix. We standardized on SMTP and would route MAIL11 for any host that wanted it. We also rewrote the mailing client in C so it could run on Unix. I don't remember if that made it over to VMS, but it very well could have.
On 11/28/22 9:21 AM, Paul Koning wrote:
I remember it well. It was indeed used in Phase II, and also in the DEC internal network for Phase III nodes to reach out of area. And later, when "hidden areas" appeared, to reach those.
RSTS has an implementation called PMR; VMS also, called PSTHRU I think. The PyDECnet implementation was reverse engineered from the RSTS version; my Macro-10 is too feeble to read the TOPS-20 version. And yes, it's compatible with the others; I have tested TOPS-20 talking via my implementation. The protocol is really quite simple, you can see the reverse engineered protocol spec in doc/protocols/pmr.txt in the PyDECnet source tree.
Since it just does a simple repeating of incoming traffic it should be quite a simple program and not much of a performance issue. The RSTS version is single threaded (one process per PMR connection). The same goes for the PyDECnet version, though it would not be hard to make it multi-threaded (not much reason to do so, though).
As mentioned in the document, the various implementations seem to differ a little. Support or lack of it for interrupt messages is one detail; connect data is another. An interesting omission is the lack of support (in any version I know of) for returning connect confirm data, which means that it gets in the way of some protocols that rely on that data for version number exchange.
By the way, while the node::node2:: ... syntax appears in a bunch of places, that isn't necessarily PMR. For example, VMS supports that for file access, when the intermediate nodes are VMS; that works simply because of RMS-32 transparent network access. And MAIL11 does the analog of PMR internally; I haven't studied the details.
paul
On Nov 27, 2022, at 6:25 PM, Thomas DeBellis <tommytimesharing@gmail.com> wrote:
Tops-20 NFT, FAL and NRT will do something called Tops-20 NFT, FAL and NRT will do something called Poor Man's Routing (or PMR, for short). The Tops-10 NRT client will also do it. PMR is something I dimly recall from Phase II or III; this was back before 36 bit hosts could do full routing. Here is some background:
On CCnet, we had enough 20's that not all could be connected to each other in a star network. Not even Columbia had enough KMC's to 'star' our 20's; the closest we got was a ring. CMU had even more. When a 20 wasn't next door to whatever system you wanted to get to, you had SET HOST to one that did and then do another SET HOST accordingly. Or maybe you had to do that a few times.
The manual procedure and all the accounts involved was clunky enough that pretty much only systems staff did this. It was out of the question for researchers and paying customers.
So I think some site on CCnet came up with the idea of automating it to a certain extent. It was called "Poor Man's Routing" and the way it worked is that you specified the route to the system in question. Let's say you were on NODEA:: and wanted to go to NODEC:: yet did not have direct connectivity. If both NODEA:: and NODEC:: had connectivity to NODEB::, then the relevant part of the configuration looked something like this:
NODEA:: ↔ NODEB:: ↔ NODEC::
If NODEB:: was a PMR host, then you could do something like SET HOST NODEB::NODEC:: and the parser would convert this to some intermediate string. Instead of opening a connection on DECnet object 23, it would use object 123 and NODEB:: was responsible for taking the rest of the string and getting you to the right place.
It worked well enough if the systems in question weren't excessively loaded (which was invariably never the case) and it saved us when the dates for version 6 slipped. I had been under the impression that some site on CCnet had done this and remember eagerly flushing all of it when we finished the field test.
Much to my surprise an acquaintance of mine at Marlboro (Larry Campbell) formalized this with a separate module called DNCONN.MAC. I put this into a conditional assembly in part to save some address space (only to get blown out of the water by some vestigial code that had never been hit).
Does anybody remember PMR? Did it exist for the other systems which supported DECnet? Just curious whether I should turn this on for anyone.
PS: So much for my silly subject line of the day...