Date: Wed, 27 Mar 91 02:01:46 CST From: Al L Varney <firstname.lastname@example.org> 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 <email@example.com> firstname.lastname@example.org (Fred R. Goldstein) writes: > In article <email@example.com>, firstname.lastname@example.org > (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 <email@example.com> Subject: Re: It's Heeerrre ... Organization: AT&T Network Systems In article <firstname.lastname@example.org> email@example.com (Dave Levenson) writes: > In article <firstname.lastname@example.org>, email@example.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 <firstname.lastname@example.org> Subject: Re: Questions About New Service Being Installed Organization: AT&T Network Systems Oops! Some corrections: In article <email@example.com> firstname.lastname@example.org (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: email@example.com (Alan Leon Varney) Subject: Re: What's a 1A3B? Organization: AT&T Network Systems In article <firstname.lastname@example.org> email@example.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: firstname.lastname@example.org (Alan L Varney) Subject: Re: What is a 1A ESS Master Scanner? Organization: AT&T Network Systems, Lisle, IL In article <email@example.com> firstname.lastname@example.org (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: email@example.com (Alan L Varney) Subject: 1A ESS Master Scanner Correction Organization: AT&T Network Systems, Lisle, IL In response to an article from firstname.lastname@example.org (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