[HECnet] DAP

[Paul Koning]

> On Dec 9, 2019, at 5:00 PM, Thomas DeBellis <tommytimesharing at gmail.com> wrote:
> 
> I would be surprised if there needed to be any updates to DAP to support Phase V as Phase V doesn't change the programming API in a significant enough way (if at all) as to require corresponding changes to DAP.
> 
> As long as it can make a connection and check connection status, Etc., it seems happy enough.   It doesn't talk to the management layer at all, as far as I can tell.
> 
> There is some Phase II era code, which was put in to allow a kind of "poor man's" routing.  Now I would guess that it would only be useful for a non-adjacent node to talk to a DN200.

Poor man's routing applies in two places.  In Phase II, to allow you to talk to a non-neighbor node (without benefit of "intercept" support).  And later on, to allow Phase III nodes to talk out of area and Phase IV nodes to talk to "hidden area" nodes.  These two were I think internal to DEC, because the internal DECnet was too large for the architecture.

There seem to be two approaches to poor-man's routing: VMS did it in DAP without any extra protocol machinery, simply because of the fact that VMS RMS lets you specify file names that start with a node name.  So a request for STAR::FRODO::foo.txt is handled by STAR doing "transparent network access" to file FRODO::foo.txt.  

In other applications, poor man's routing would be handled by noticing more than one node name in the destination specification, which would tell it to connect to the PMR (PSTHRU) object instead of the usual object.  I've been trying to reverse engineer that; unfortunately I don't seem to have any RSTS applications that call this.  Strange, because I'm fairly sure we had a "set host" client that did.

Fairly recently I saw the TOPS-10 (or -20?) PMR, but my MACRO-10 skills are terribly rusty.

	paul