[TUHS] Known Specimens of Pre-5ESS UNIX Telephone Switching Software?

Kevin Bowling kevin.bowling at kev009.com
Fri Oct 6 00:19:03 AEST 2023

On Tue, Oct 3, 2023 at 11:52 PM Kevin Bowling <kevin.bowling at kev009.com> wrote:
> On Tue, Sep 26, 2023 at 7:46 PM Heinz Lycklama <heinz at osta.com> wrote:
> >
> > To answer Jon's following question (2 minutes later):
> > ________________________________
> > Oh yeah, and I think that this is why Heinz wrote MERT,
> > but he should know more than me about it.
> > ________________________________
> > Yes, my Dept. in MH was involved in the early days of digital switching
> > and the need for real-time response was certainly recognized.
> > But MERT was not developed with a specific telephony project in mind.
> > I was mostly involved in software in support of current projects
> > being done in the Dept. We started the MERT project at the
> > time that DEC announced their PDP-11/45 mini-computer in
> > the early 1970's because it supported 3 separate address
> > spaces - system, supervisor, and user. This enabled us to
> > run operating system environments with different user
> > application program needs, specifically real-time under
> > control of one supervisor and time-sharing applications
> > in another supervisor, to start with. Hence its name -
> > Multi-Environment Real Time (MERT). Once we had MERT up
> > and running on the PDP-11/45 and PDP-11/70 computers, some
> > projects in other Bell Labs locations involved in telephony projects
> > started building their projects on the MERT system. The
> > DMERT system was developed later on by projects at yet
> > another Bell Labs location.
> I don't have access to IEEE but there is a paper on MERT
> https://ieeexplore.ieee.org/document/6770410.  The 3B20D and DMERT are
> also cronicaled in the BSTJ, I have hard copies of that but it should
> be on IEEE.
> There is a lot of detail on the 3B20D and 3B21D in the 254 BSPs as
> well as some coverage of UNIX RTR
> https://www.telecomarchive.com/plant-all.html.
> There is more coverage of the 3B20 elsewhere, for instance
> https://dl.acm.org/doi/pdf/10.1145/1500412.1500418.  Wing N. Toy, one
> of the hardware engineers, published some nice books that tangentially
> touch on these designs but contain a lot of great microcoding
> knowledge.

I was reviewing this book
https://archive.org/details/computerhardware0000toyw and it is one of
the best computer architecture books I've seen.  Somehow in 400 pages
the authors manage to cover logic, language implementation,
compilation, instruction set design, various aspects of operating
systems design, and fault tolerance citing timeless pedagogical
hardware (PDP11, VAX, S/370, System/38, iAPX-432, WE32000) and
software (VMS, UNIX, DMERT).  Readers of this list will enjoy it!

> Regards,
> Kevin
> > Heinz
> >
> > On 9/25/2023 6:37 PM, Jon Steinhart wrote:
> >
> > segaloco via TUHS writes:
> >
> > Hello, my studies lately bring me to the question: Are there any extant
> > examples of telephone switching software, built on UNIX, from the various
> > parts of the Bell System prior to the introduction of the 5ESS and 3B20D?
> > My focus veers earlier as some 5ESS/3B20D/DMERT technology is still in
> > active use, that sleeping dragon can lie.
> >
> > What's gotten me curious is reading about 1ESS in a BSTJ volume I
> > picked up, noting the particulars on how previous concerns of manual and
> > electro-mechanical systems were abstracted into software.  Even without
> > surviving examples, were previous systems such as the 1ESS central
> > control ever ported to or considered for porting to UNIX, or was the
> > hardware interface to the telco lines too specific to consider a future
> > swap-out with, say, a PDP11 running arbitrary software?  Columbus's SCCS
> > (switching, not source code) also comes to mind, although all I know that
> > survives of that is the CB-UNIX 2.3 manual descriptions of bits and pieces.
> >
> > By the way, it's funny, I have UNIX to thank for my current experiments
> > with telephones and other signalling stuff, what with making me study the
> > Bell System more generally.  It's starting to come full circle in that I
> > want to take a crack at reading dialing, at least pulse, into some sort
> > of software abstraction on a SBC that can, among other things, provide a
> > switching service on top of a UNIX-like kernel.  I don't know what I'd do
> > with such a thing other than assign work conference call rooms their own
> > phone numbers to dial with a telephone on a serial line...but if I can even
> > get that far I'd call it a success.  One less dependency on the mobile...
> >
> > - Matt G.
> >
> > Heinz might know something about this.  If I remember correctly, one of the
> > projects in his group was SS1, an all-digital exchange.  I have some vague
> > memory of him and Carl poring over some gigantic switch statement looking
> > for a bug - the long distance code wasn't sending the ST pulse and as a
> > result all of the key pulse senders at the Berkeley Heights telephone
> > exchange were taken off line and needed a technician to go in and manually
> > reset them.  They were not amused.  Fortunately, they and BTL were both
> > children of Ma Bell.
> >
> > If my memory serves me correctly, the system had a pair of PDP-11/10s that
> > ran Hal Alles's digital filter code, a PDP11/70 behind the whole thing,
> > Harry Breece's active replacement circuitry for the hybrid transformers,
> > and some huge insanely fast wire-wrapped boards designed by John Sheets
> > that did TDM switching.
> >
> > Jon
> >
> >

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