Date: Wed, 27 Mar 91 02:01:46 CST
From: Al L Varney <varney@ihlpf.att.com>
Subject: Re: Questions About New Service Being Installed
Organization: AT&T Network Systems

Well, this will be brief, since it's from memory; I've rearranged the
previous discussion order somewhat.  If you really MUST have more
info., read the back issues of the Bell System Technical Journals.  At
least one issue was devoted to each switch.

First, the obligatory note:  ESS(tm) is a trademark of AT&T and
5ESS(tm) is a registered trademark of AT&T.  The proper names are:
 1 ESS Switch     1A ESS Switch    4 ESS Switch   5ESS Switch
but I will use the obvious abbreviations below.

In article <telecom11.243.8@eecs.nwu.edu> goldstein@delni.enet.dec.com
(Fred R. Goldstein) writes:

> In article <telecom11.240.4@eecs.nwu.edu>, rees@pisa.citi.umich.edu
> (Jim Rees) writes...

>> The 1ESS has relays in it, not to do the actual switching,
>> but to switch ringing voltage and the like on to the loop.  It makes a
>> lot of noise, although nothing like a panel office!

> The 1ESS (and the 1A, which uses a less antiquated processor) uses
> reed relays to do the actual switching.  They're vacuum-sealed, so
> they're quieter than the old ones.  I suspect that the 1 can do Caller
> ID too, though Im not sure.
> The 1 uses an antique CPU with ferrite sheet EPROMs and mag cores.

   The No. 1 ESS Switch indeed uses sealed relays for the switching
fabric, but "reed relays" ???  Nope.  The actual T/R path is through
magnetic-latching relays, surrounded with some metal and a coil.
Pulse the coil one way, the contacts close and REMEMBER to stay
closed.  Pulse the other way, the contacts open and REMEMBER to stay
that way.  No current is used to maintain either position.  They are
the size of a Christmas tree bulb and make little noise.  The
traffic-dependent noise you hear is the "wire-spring" relays that
exist in the remainder of the switch, primarily in the Trunk/Junctor
circuits.

   The 1E "CPU" consists of about 10 feet of circuits in a standard
seven foot high "bay", arranged across from it's "mate" CPU.  The CPUs
run in lock- step, comparing results of every instruction.  The memory
is separate; for programs high office data, "EPROM" memory is formed
from ferrite spots stuck to 6X12(?) inch sheets of aluminum.  Typical
office might have 40 feet of such memory, duplicated.  Temporary
(writable) memory is usually mag cores (32K by 23 bits + 1 parity per
two foot bay).  Program memory words are 37 bits wide, with an added 8
bits for Hamming-code parity (I believe automatic single-bit error
correction is in the hardware).  Architecture could be called "early
RISC, messy" -- most instructions are one cycle or 5.5 microseconds.
Capacity is roughly 35K lines.
 
>> What's the difference between a 1 and a 1A (is it just the processor?
>> Does 1A run Unix?)

> The 1A goes to semiconductor memory.

   No. 1A ESS Switches use the same switching fabric as 1E.  The circa
1973 processor is two CPUs in a six-foot wide frame, running in
lock-step.  Program and temporary memory are on separate busses, but
look identical.  Most modern version of memory puts 14 256K-by-14-bit
units in a three-foot bay -- max of two bays per office allows at most
four Mwords (12 Mbytes).  Instruction set vaguely resembles an
orthoganal version of 1E, with a typical instruction (24 or 48 bits
wide) taking .7 milliseconds.  Many shift/rotate/mask/insert options
could be used, without added time, due to a complete 48-bit "barrel"
shifter.  For comparison, "clock speed" is 20 MHz; even though memory
bus is 20 feet long, 700 nanoseconds can do a 48-bit read or 24-bit
write.  An overlapping dual-parity scheme is used on each memory word.
Disk backup is used, with about 10 Mwords available.  Original disk
drives used 26(?) inch platters, with 100 fixed heads on each side,
thus no seek overhead.  Existing switches handle 90K lines.  No fans
in either 1E or 1A equipment, just ambient cooling.

   UNIX (also tm) grew up about the same time as 1A, but really !!!
You don't switch 300K calls per hour on a non-MMU machine with UNIX.
The OS is really a task dispenser with routines voluntarily giving up
control every two or three milliseconds (sort of like Multi-Finder,
no?).  Much polling and processing takes place on a timed interrupt
level, forced every five milliseconds.  No other interrupts occur
normally.

>> What I'd like to know is what are 2 and 3ESS? 

> The 2BESS is a "suburban" office, built in the '70s to early '80s,
> using (I think) reed relays like a 1A.  It is basically a scaled down
> version of the 1A, with a different processor.

   No. 2 ESS existed in 1968, so it's really scaled down from 1E.
Every- thing was redesigned from the ground up, so there is
essentially no shared circuitry with 1E.  The processor was "strange".
A 22 bit instruction word with one "long" 21 bit instruction or two
10-bit instructions; the remaining bit was = 1 only on words where
transfers of control were expected to arrive.  A bit-twiddlers toy.
10K lines??  (The processor was also used to drive the "Automatic
Intercept System" [AIS], the one that says "The number you have
reached, nyen-nyen-one-pause-six-six-six-six has been changed.  The
new ...".  This was my first project with AT&T.)

   No. 2B ESS Switch was just a re-worked version of the No. 3 ESS
processor with mico-code interpreting the original 2E instructions
(but faster than the original hardware).  I believe it gave a 50%+
increase in capacity.

> The 3ESS is a very small analog office, of which very few were built
> (ca. 1980).

   Don't know numbers, but there were quite a few in more "rural"
areas.  The "3A" processor -- no relation to the "3B" line -- was
small and fast.  I believe this was the first to use mico-code;
1E/1A/4E/2E don't.  Don't know much else, except a whole office could
fit in a semi-trailer (with MDF!) for emergency use.  Several were
tested on the trailer, shipped and then slid into place with attached
air pallets.

>> And what kind of hardware does a 4ESS have (I've never seen one)?

> As someone else noted, the 4ESS is a different beast, a big digital
> toll switch.

   Well, actually a Tandem switch, but BIG anyway.  Same processor as
1A, with a totally digital switch.  These are rated at 100K Trunks,
600K+ calls/hour.

  There was also (past tense, I believe) the No. 101 ESS switch, an
early PBX.  This used a processor from another project, with a unique
PAM fabric (pulse amplitude modulation).  Essentially, every
line/trunk had an appearance on a single wire, with a different
combination connected at an 8KHz rate.  This allowed noise-less
switching and many connections to a single line/trunk without loading
problems.  This same fabric was used in AIS, to allow many people to
listen to "six" at the same time.  "Six" was a single trunk connected
to a repeating .5 second recording.  Adjusting the volume on those
trunks was boring!!

Oh, oh, another long article.  Maybe I'll do 5ESS later, Pat.  In
closing, I've had the pleasure of programming all of these switches
except the No. 3 ESS switch.  They all had something worth learning as
far as designing to a particular goal.  In most cases, the capacity of
the switch drove the design.


Al Varney, AT&T, Lisle, IL

Date: Thu, 19 Sep 91 12:12:53 CDT
From: Al L Varney <varney@ihlpf.att.com>
Subject: Re: It's Heeerrre ...
Organization: AT&T Network Systems

In article <telecom11.752.6@eecs.nwu.edu> dave@westmark.westmark.com
(Dave Levenson) writes:

> In article <telecom11.743.5@eecs.nwu.edu>, john@zygot.ati.com (John
> Higdon) writes:

>> Although I have not observed it lately, my 1ESS used to do a peculiar
>> thing with forwarding. Forwarding would sometimes take several minutes
>> to actually take effect, even though I had received the confirmation
>> tones. Sometimes when I cleared forwarding, it really was not cleared
>>  -- again after hearing the two tones. Most bizzare were the times I
>> would clear forwarding and it would actually clear, but then
>> re-establish itself later to some previously forwarded-to number.

> ... A NJ Bell employee explained it thusly: There are two processors,
> one running the switch, and the other reading all the inputs, and
> not writing to memory or producing any outputs.  The idea was that
> the second processor was a hot standby, and capable of taking over
> control of the switch if the active one 'failed'.

A good start at describing the system; in fact, the standby is
processing inputs and COMPARING it's output to the active processor.
 
> When you turned on (or off) forwarding, you made an entry in the
> 'recent change store' memory of the active processor.  The active
> processor would update its RCS and would always scan it before looking
> in the translation store for call processing instructions.  At regular
> intervals, the RCS was written into translation store, which was
> shared by both processors.  RCS was then cleared, and made ready for
> new 'recent change' data.  Administrative changes (such as subscriber
> number and class-of-service changes) were also written into RCS first,
> and into translations later.
  
In No. 1 ESS(tm), the translation store was an early form of EEPROM,
implemented with aluminum cards and ferrite spots on the cards.
The cards could only be written by manually inserting them into
a "card writer".  This was done at 1-to-7 day intervals.  RCS held
all the changes until then.  But call forwarding changes so often
that it is never written to the translation store.
 
> When a processor switch occurred, the newly-active processor was able
> to access the shared translations store, but not the other processor's
> RCS.  So some recent changes were lost, until the mate processor was
> restored to service, or until its RCS could be dumped into
> translations.
  
Not even close.  Both processors have access to all memory.  The RCS
and other writable-memory areas are duplicated, and both copies are
updated by the active processor (but the standby monitors the written
data and addresses).  No single fault in processor, bus or memory
systems or any changeover results in the loss of any data.

The known problem windows involve only the infrequent (yearly?)
installation of new system software, where one processor/memory system
is loaded with new data.  During the update, RCS is mapped from one
memory system to the other; again, no loss.  But a failure of the RCS
update (takes less than 1 minute) could result in recovery with a mix
of old and new data, so the recovery software removes RCS and other
data when a memory/processor failure occurs during that part of an
update.  Recovery software knows when an update is in progress.

Manual procedures are used to recover the RCS in such a rare case.
Administrative systems have records that are tagged from the last time
a "card write" occurred; these are re-applied.  And the call
forwarding information is typically transmitted to an off-line system
for re-application just before the update.

> This was supposed to have been fixed with the introduction of the
> 1A-ESS switch, where RCS and translations are both disk resident, and
> both shared.

RCS for call forwarding is still non-disk data, but there are very
frequent 'snapshots' made automatically to disk.  Neither system has
any "non-shared" memory, nor any memory even labeled as belonging to a
specific processor.

"The grass is always greener on the other side of the fence."
                or, for systems,
"Either (1) the current system is garbage, and the new will be great,
 or     (2) the current system is garbage, and the old was better."


Al Varney, AT&T Network Systems, Lisle, IL

Date: Sun, 31 Mar 91 20:20:05 CST
From: Al L Varney <varney@ihlpf.att.com>
Subject: Re: Questions About New Service Being Installed
Organization: AT&T Network Systems

Oops!  Some corrections:

In article <telecom11.246.5@eecs.nwu.edu> varney@ihlpf.att.com (Al
"Oops" Varney) writes:

> [In other articles, Fred R. Goldstein and Jim Rees write:]
 
Fred> The 1ESS has relays in it, not to do the actual switching,
Fred> but to switch ringing voltage and the like on to the loop.  It makes a
Fred> lot of noise, although nothing like a panel office!

  This is correct, in the sense that the "switches" are not "relays".
 
Jim> The 1ESS (and the 1A, which uses a less antiquated processor) uses
Jim> reed relays to do the actual switching.  They're vacuum-sealed, so
Jim> they're quieter than the old ones.  I suspect that the 1 can do Caller
Jim> ID too, though Im not sure.
 
>   The No. 1 ESS Switch indeed uses sealed relays for the switching

      But I meant to say "reed switch" here ^^^^^^

> fabric, but "reed relays" ???  Nope.  The actual T/R path is through
> magnetic-latching relays, surrounded with some metal and a coil.
                    ^^^^^^
        ...and here          

> Pulse the coil one way, the contacts close and REMEMBER to stay
> closed.  Pulse the other way, the contacts open and REMEMBER to stay
> that way.  No current is used to maintain either position.

  I E-mailed a better explanation to Jim, but in summary, the reason I
disagreed about the term "reed relay" was because of the word "relay";
but then I used it myself (Ooof)!  They are "switches" because they do
not actually switch a current based on another current or pulse.  They
are switched "dry" (sans current); the contacts can't be cleaned and
will stick or weld shut if switched "wet" frequently.  Therefore,
external relays to trunks and lines must be used to remove battery/
ground before setting up a path through the network.  A matrix of
switch crosspoints is arranged so that closing a tip/ring crosspoint
in a matrix automatically opens all the other pairs in the same X row
and Y column.  When a path is "released", it's X and Y matrix points
are marked idle, but the crosspoints remain closed until some other
action selects another crosspoint in the same X row or Y column.

Further errata:

> Instruction set vaguely resembles an orthoganal version of 1E, with
   No "Freudian" jokes, please... it's ^^^^^^^^^^ "orthogonal".

> a typical instruction (24 or 48 bits wide) taking .7 milliseconds.
                         let's try "microseconds", eh? ^^^^^^^^^^^^

>Al Varney, AT&T, Lisle, IL

  You really ought to read the stuff before you publish, dum-dum.

 Al

Date: Wed, 01 Jun 1994 11:39:29 +0600
From: varney@uscbu.ih.att.com (Alan Leon Varney)
Subject: Re: What's a 1A3B?
Organization: AT&T Network Systems

In article <telecom14.252.8@eecs.nwu.edu> stans@panix.com (Stan Schwartz) 
writes:

> Here in downstate NYNEXland if an exchange has not been "taken over"
> by a pager or cellular company, you can dial the NNX and 9901 to find
> out what kind of switch is in that C/O.  For example, dialing
> (516)694-9901 will tell you that you have reached the Farmingdale 5ESS
> test number, serving the following prefixes ... (you get the idea).

> When dialing (516) 352-9901, however, I am told that I have reached
> the Floral Park 1A3B, the only one of it's kind in Nassau County.  Now
> I have heard of 5ESS's and DMS-100's, but what is a 1A3B, and why is
> it such a distinction to have one?

   It's no distinction, except in areas quickly going to digital COs.
The "1A3B" is really a 1A ESS(tm) switch with an Attached Processor
System (APS) controlled by a 3B20 Duplex(tm) processor.  The 3B20D
supplies the switch with backup disk storage, and possibily other
services such as SS7.

   There are several hundred such analog COs deployed across the USA.


Al Varney

Date: Sat, 12 Dec 92 13:33:44 CST
From: varney@ihlpl.att.com (Alan L Varney)
Subject: Re: What is a 1A ESS Master Scanner?
Organization: AT&T Network Systems, Lisle, IL

In article <telecom12.898.6@eecs.nwu.edu> bote@access.digex.com (John
Boteler) writes:

> When our ring plant decided not to ring the phones every so often, the
> switch guru for our ESS#1A said "We rebuilt the master scanner and we
> haven't found a lick of trouble since."

> Would someone who actually has working knowledge please describe a
> master scanner? Is it software or hardware? If it's hardware, how do
> you effectively "rebuild" it without disrupting service?

> I am most curious.

   If you are MOST curious (i.e., willing to spend money), you should
know that almost all the hardware (and some software, tools, testing
details, etc.) associated with 1/1A ESS(tm) switches is described at a
high level in two special issues of the Bell Labs Technical Journal
(BSTJ), one on the 1 ESS switch, and a later one that describes the 1A
Processor (used in both 1A ESS and 4ESS(tm) switches).

   "No. 1 Electronic Switching System", BSTJ, Vol. 43 No. 5,
          September 1964, Parts 1 & 2.
   "The 1A Processor", BSTJ, Vol. 43 No. 5, February 1977.

   I'm told the AT&T Customer Information Center maintains copies of
the BSTJ "special" issues, so even if your library doesn't have it --
it's still available.  For even more money, you could order AT&T
Practice 231-030-010, "Scanners - Description and Theory, No. 1 and
No. 1A ESS", which describes a "middle" level of detail on scanners in
these systems (51 pages, including fold-outs!).

   For those who are somewhat less curious, ...

   The master scanner was one of the original frames of equipment
designed for No. 1 ESS, and is one of the few to have never been
upgraded in later years.  Essentially, these frames (each switch must
have one, but many have more) serve as input devices for arbitrary DC
signals in the system.  Lines and trunks have scanners dedicated to
those functions, so master scanners are used for detecting other
things.  For example, detection of blown fuses, power failures,
diagnostic results, open doors (if they are alarmed), low power in the
battery plant, low paper in a printer, someone pressing a key on a
control panel, etc.

   Each master scanner contains some duplicated control circuits and a
64-row by 16-point matrix of current detectors.  Each detector is
called a "ferrod" (a ferrite rod with some wire threaded through and
around it).  These operate essentially like old "core" memory units,
in that read-out is controlled by pulsing X and Y leads, with the
selected row responding because the coincident-current exceeds some
minimum.  But unlike core memory, the 0 or 1 response is determined by
the amount of current flow in the "control" winding of the ferrod.

   For master scanners, a ferrod has about 35 ohms resistance and will
respond with a 0 if more than 3.9 ma in flowing.  Less than 1.8 ma
will yield a 1.  In between those values, the readout is not
predictable.

   One of the units monitored by a master scanner is the ringing and
tone plant.  Among other things, the beginning of various ringing
current phases is detected.  If this is not reliable, ringing will be
unreliable.

   Failure of a ferrod and it's windings is rare, but it can happen.
Since it's just a transformer + some wire, it's pretty durable.
Because the ferrod matrix is not duplicated, a failure requires some
non-obvious steps to remove the ferrod with minimum interference.
Some folks might call this "rebuilding", since it's not the simple
matter of circuit board removal used with electronic parts.

Date: Mon,  4 Jan 93 16:23:18 CST
From: varney@ihlpl.att.com (Alan L Varney)
Subject: 1A ESS Master Scanner Correction
Organization: AT&T Network Systems, Lisle, IL

In response to an article from bote@access.digex.com (John Boteler), I
wrote:

> If you are MOST curious (i.e., willing to spend money), you
> should know that almost all the hardware (and some software, tools,
> testing details, etc.) associated with 1/1A ESS(tm) switches is
> described at a high level in two special issues of the Bell Labs
> Technical Journal (BSTJ), one on the 1 ESS switch, and a later one that
> describes the 1A Processor (used in both 1A ESS and 4ESS(tm) switches).

> "No. 1 Electronic Switching System", BSTJ, Vol. 43 No. 5,
>        September 1964, Parts 1 & 2.
> "The 1A Processor", BSTJ, Vol. 43 No. 5, February 1977.

   Terry Kennedy has (rightly) questioned the Volume numbers ... the
second reference should be:

    "The 1A Processor", BSTJ, Vol. 56 No. 2, February 1977.


Al Varney -- just MY mistake