[HECnet] More NRT

[Thomas DeBellis]

Paul,

Thanks for the doc; I'll be giving it a careful look through. Where 
might I pick up a copy of DNTERM?

It is a true statement that the Tops-20 NRT server is little more than a 
character stream.  Like I said, it's very close to Telnet without the 
IAC's and option negotiations.  For my future purposes (handling a 
security concern with the Tops-20 FAL architecture), it is perfect.

I remembered some more about CTERM; it appears to implement a concept 
called break masks.  Under Tops-20, if you are doing something that 
needs to handle characters specially, one alternative is to turn off 
echo, swallow a character and then determine what to do.  This was used 
in some Tops-10 video based 'SYSTAT'ing programs that I am aware of.

However, this means you're doing a context switch on every blessed 
character.  And so are 90 other people, which is Bad. It's way too much 
overhead.  A break mask means that you can have the monitor swallow and 
echo characters and determine when to return control to the user 
program.  This was worked on enough so that TEXTI% actually had 
something called an 'EMACS' mode, specifically to support this.

I don't recall whether this was pushed out to the front end; hard to 
say.  The VT100 really handed it to the front end.

There were some early attempts towards break masks in some Telnet 
options; host controlled local echoing and some such.  I don't remember 
the RFC, but it is quite old.

I don't remember whether LAT will handle a break mask; if it could, then 
that's great--the LAT host worries about gobbling characters and when to 
send a packet to the host.  That's far more efficient.


I modified SETHOST to have an additional entry point to force 4.2 
behavior; meaning using two separate forks for input and output instead 
of handing the whole thing off to the monitor with MTOPR%.  This was so 
I could use SYSDPY to see the actual scheduler tests that the forks were 
waiting for; that's not as easy when the whole thing is in the monitor.

So RSX and VMS accept the connection and both the client (me) and the 
remote wind up waiting.  As soon as I type a character, I get thrown 
off, so I would imagine that there is some additional negotiations to be 
done.  I'm hesitant to try this on RSTS as somebody is going to need to 
restart the NRT server.

NRT is pretty simple; on connection, it reads a configuration message, 
but only looks at the first byte to see what the remote system is.  
That's enough for it to blat about it not being to either Tops-10 or 
Tops-20.  The other stuff is completely ignored; I don't see evidence of 
any configuration being sent. I guess those other bytes are what I 
should be looking at. Maybe they'll be in your doc?

What was interesting was the multi-forking behavior versus handing 
everything off to the monitor.  I remember this code back in the 1980's 
and we thought it was the greatest thing ever.  We modified our EXEC to 
do the call itself and not even bother forking SETHOST.

The multi-fork code performance is incredible; stuff blinks right on to 
the screen.  The monitor-only code is far slower. I'm at a loss to 
explain that and wonder if it has anything to do with KLH10's NI 
implementation.

> ------------------------------------------------------------------------
> On 5/5/20 5:06 PM, Paul Koning wrote:
>
> I was pretty sure I had done a short writeup a while ago.  Just found it.  It was done in 2000, as part of an effort on my part to improve "dnterm", the Linux remote terminal client.  I'm fairly sure I created it by reverse engineering the source code of the RSTS client.  Take it with some grains of salt, but I'm fairly sure it was sufficiently accurate to allow dnterm to talk all four protocols.
>
> BTW, Linux uses TOPS-20 mode, I think.  That's basically a raw character (character at a time) transport.  RSTS has a choice of line mode or character mode.  RSX and VMS, as Johnny explained, try to offload the entire terminal driver semantics onto the other end, which makes the client a nice challenge on a system like RSTS that is entirely different.
>
> 	paul
>> ------------------------------------------------------------------------
>> On May 5, 2020, at 4:08 PM, Thomas DeBellis <tommytimesharing at gmail.com> wrote:
>>
>> Johnny,
>>
>> Thanks for the screen shots!  It figures RSX gets it right with everybody...  One wonders whether the group didn't have sufficient 'weight' to throw around to get others groups to see their point of view, as it were.  At a certain point, there appears to have been a significant amount of NIH going on, particularly after the VMS/BLISS corporate direction/mandates came down.
>>
>> So RRS and HOST are different NRT client applications, then?  Can you comment on the protocols spoken?  Or would you have source available?
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