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

[Kevin Bowling]

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.

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
>
>