AT&T Tech Channel - 2011-07-25
See more from the AT&T Archives at http://techchannel.att.com/archives The purpose of this film was to show employees, back in 1951, how calls were automatically switched through an SxS office. This film gives a general appreciation of the importance, complexity, and cost of switching equipment in an average 1950s telephone office. The path of a call is illustrated as it runs through a demonstration unit. "Careful adherance to Bell System maintenance practices" is stressed. While this is only part I, Part II eventually showed the equipment in various types of use, and Part II showed the internal circuit operations. Switchers today are digital and look drastically different. These systems at this time were still not even transistorized, so this film shows a system that's not only years back in time, but many generations back in terms of technology. Producer: Audio Productions, Inc. Footage courtesy of AT&T Archives and History Center, Warren, NJ
Despite having thousands of parts, there’s a beautiful simplicity to the concepts and physical directness of the system. It’s fascinating to see the creativity that goes into mechanical logic systems.
It mirrors the difference between a steam locomotive and a diesel-electric.
I worked for South Central Bell in the downtown Nashville, TN central office 50+ years ago. We had four exchanges of step-by-step in that office: 242, 254, 255, and 256. 244 was a crossbar switch, and 259 was Nashville’s first ESS. I started as a frame man. Our MDF carried all six of those exchanges. Twelve feet tall and half a city block long. That means a jumper wire connecting the terminal on the horizontal or number side of the frame to the assigned terminal on the vertical or outside cable side could be over 200 feet long. There was such a jumper for each one of the 60,000 numbers in our CO. If you figure the average length as half of the max, that meant there was around 1200 miles of jumper wire on that frame, or enough to run a single two-wire jumper from Chicago to Houston.
Good stuff, your Main Distributing Frame, what did you have on the Vertical side for protection, gas or carbon arrestors? Were they Cook or Reliable? Did you have an IDF as well ?
@DC10 Fomin since the frame was the same vintage as the step switches, they were protected by carbons. Don’t know that I ever noticed the manufacturer. I would have assumed Western Electric like all the switch gear. There was an IDF on the second floor
@Norman Morgan Amazing to catch you on the air, I used to work for GTE AUTOMATIC ELECTRIC and did a lot of C.O. engineering, watching these videos brings back many memories, thank you for your comment, best regards.
From 1962 thru 1965 I was a dial central office repairman in the U.S. Army, both stateside and in Korea. Our telephone exchanges utilized this type of equipment and it was referred to as Stroeger stepping switches. When I got out of the Army I applied for a job with New England Telephone (their name at the time) and when I told the personnel guy what I was experienced with he chuckled and said he didn't think there was any of that equipment around any more. I declined his union job as a floor sweeper.
The name's Strowger. Almon Strowger. ;)
"Do you expect me to talk?"
"No, Mr Strowger! I expect you to dial!" :D
Fun Fact: The first step-by-step switch and indeed the very first automatic telephone exchange was invented by Almon Strowger.
Almon Strowger was an undertaker by trade. He became convinced that the manual telephone exchange operator, who was the daughter of the only other undertaker in town, was deliberately directing all calls for "the undertaker" to her father's practice instead of dividing them equally between the two as was standard practice at the time.
Strowger decided that he needed to invent a way for telephone customers to dial the number themselves and used cut out pieces of paper to represent the electrical contacts so that he could work out how the equipment should work.
If I remember correctly, Strowger was granted a patent for his automatic telephone exchange in 1929.
Strowger's exchange required two extra wires from the exchange to each telephone to carry the dialling signals, but some clever lateral thinking allowed for using the same two wires for nearly all signalling as well as for speech.
That was actually fun to read. Thank you.
The very 1st strowger automatic exchange in the world was installed here in LA porte Indiana in the 1890s we have some of the original equipment at our museum...
@a1wireless1964 If that's so, then I must have been wrong about the date of the patent. But the earlier the patent, the cooler it seems. :)
@Melkior Wiseman It is indeed cool and it indeed is from the 1890s!
Heroin Bob and the Maple City Four.. Freeman Gosden and Charles Coralle, Amos & Andy! got their start on WRAF, the radio station in 1920s. Also the home of Jiffy-Pop! Popcorn
Where I live this Step exchange was fully dismanteled in the early 1990s when all of the exchanges went to digital equipment. Not only was this mechanical stuff noisy, but it housed a lot of space. Our local phone company got rid of dozens of buildings around the city as they no longer needed so much space. It is amazing how this matrix of wires, magnets, springs, and mechanics eventually connected phones together.
This equipment WAS reliable. Far more important reasons for replacing it to reduce the number of employees included far lower power requirements, faster processing of calls, and making available features such as caller ID, call forwarding, all waiting, number portability, and many, many other features that we take for granted today. Yes, I also worked in Central offices or many years, on these switches, and also through most all of the later ESS switches, both analog and digital.
This system was in use in rural Maine through the 1970's. Very noisy, but fascinating to be in a room with dozens of these devices running simultaneously. I believe this was the first system to be put into wide use after operator-assisted calling ended.
Wow, I never realized there was so much MECHANICAL engineering involved with the early phone system. That's some fine engineering there! I'm an electronics guy myself, but I have much respect for the Mechanical people.
Tapping out a number was a useful skill when a phone had a dial lock. You had to get it just right or you’d get a wrong number. The lazy way was to only learn to dial zero (10 taps) and ask the operator to connect you because “something is wrong” with your dial.
that and the fact an old pay phone was simply a Ground start trunk with a mechanical coin switch on the dial.. if you could momentarily ground the ring lead and then hookswitch the number you could call for free every time :)
Today, an entire building full of those switches can fit into a small electronic box the size of a loaf of bread. Amazing progress.
That said, there's definitely something to admire about the old mechanical system.
Oh today it can for into a box even smaller then just one slice of bread ;) it's crazy how powerful stuff has become
bigloudnoise can’t something like a modern flagship smartphone do it, given the right connections?
So many jobs gone. Ah the progress.
Abu Baker - so much wasted time saved.... oh yes, the progress
And then you have... so many jobs created from the progress... oh... the progress...
@John Da yeah just forget about the millions more it's created you boomer.
Man, mechanical switching....That is a trip. Just astounding the number of tiny parts involved.
Yeah, so how did VoIP replace this?
Smaller, cheaper, and faster.
These systems were large, power hungry, and not very smart. It only supported simple telephone calls, and had no common control or advanced routing of any kind. A VoIP system requires a small box connected to the internet, which can do orders of magnitude more. The only thing a VoIP box can't do is ring a big bell or work when the power is out. While the older systems were fun to watch and listen to, they are completely obsolete and most people don't care.
It would be nice, however, to still get a voice signal that doesn't sound like 2 bits in 8khz or less that only sometimes get through.
No joke. The fact that such reliability over scale was achieved is just mind-blowing.
@User 2C47 Weirdly, land lines are becoming more of an inconvenience these days because of analog compression being so damn lossy compared to digital. It can absolutely butcher the sound quality. Most land lines, at least in the US, are moving over to VoIP because it's not only cheaper, but sounds better in the end.
Tons of Pittsburgh Switchgear? baby!
When I was a kid, my dad was a CO manager for C&P. I would go to work with him sometimes in the summer, and often he would hand me a bottle of solvent and a pack of long, wood-handled q-tips and send me into the stacks to clean contacts on these switches. I thought it was great fun! That was a loud place to work though. Imagine an entire building with thousands of these switches all clattering all day long...
I was involved in the change out of much of this electromechanical equipment during the 80's and 90's. It was amazing to see one line of digital equipment replace an entire room full of equipment. Put a good many people out of a job in the process.
Was the old equipment "confiscated" by the phone companies(after removal)? I'm really interested in getting my hands on one of these old selectors or even an old operator manual.
Patrick yeah it would be super cool to have one of those selectors. There's probably a bunch of those in a old warehouse somewhere.
Were these switches often referred to as ‘decade switches’? I’m a middle aged electrician with many years of prem cabling, and early in my career I worked with an old Bell technician who taught me a tremendous amount about switch rooms, MDFs, terminating and such. I’m 50 now and still use that knowledge daily. Anyway I recall him talking about decade switches
@AbandonedCranium , probably sold to a 3rd world country.
I worked on one of these type of telephone exchanges in the Australian Navy in the 1980's, all I can remember now is they are called 'group selectors' and line finders. Quite good to work on, mostly cleaning contacts and adjusting the mechanics.. There were exactly like this one.. I think from memory it was called a "10-100 exchange".. thanks for the vid..
I'd often wondered how the older rotary system worked. That's quite fascinating! (Even for someone born in 1990. 😉)
Stumbled onto these vids and it brought back memories of my father who worked for NJ Bell in switching offices just like this one! I had parts of them as toys! The noise in those buildings was deafening, I've never heard anything like it. They broke down often as he was called in many a times in the middle of the night of course they paid well. Plus, as a kid I thought all the tools we used around the house with NJ Bell on it was normal, I think I used up my last roll of electric tape about a year ago and my Dad retired in 1985 after 40yrs. Great stuff!
+rob condit My father and grandfather worked the AT&T > Bell Atlantic > NyNex what not in NY. I grew up surrounded by the logos on various things. I now work in telecom and have my grandfathers Bell System (38-Y-3991A) stencil at my desk, which has the same shapes I use in Visio to draw call flow diagrams for Cisco apps. The evolution of this technology is so cool.
Just watched the video again and its amazing the engineering that took place to make it all happen, sure didn't understand it as a kid!
When referring to Japanese, Chinese, and Korean, the modern term is East Asian. For Burmese, it's Southeast Asian. For Indian, South Asian. For Asian Russian, North Asian.
My dad worked for our local phone company. He would get called out on trouble which was almost always one of these switches getting stuck when the person hung up (like around the 2:00 mark). He taught me how to find the stuck switch and flick it back into place, and he'd collect his OT for fixing the trouble lol!
sportster1988 In the Miami wire center you could tell what time it was by the noise from the switches especially if you were on third shift. ANd listening to that damn trouble gong ringing all night long. One night I couldn't turn it off and I looked and every bay had a trouble lamp. Lightning had struck a 1212 cable outside and blown all the protectors out to ground and every line finder was operated. The only thing I could do was pull all the heat coils once I figured out what cable was hit.
Remember Calling Party Hold? We'd call a crappy restaurant and leave the phone of the hook so they couldn't get take out orders until the testdesk had someone put a toothpick on the calling party.
This is really cool to see. I have listened to pretty much all of Evan Doorbell audio files he hosts on his website but had no clue what the actual vintage SxS equipment looked like.
Don't laugh, these switches were very reliable but they needed people to maintain them. I worked under the old Bell System, back in the day when employees took a lot of pride in their work. It was a very strict workplace but we were proud to say I work for "MaBell".
+Bri G. EMP Proof !
+Bri G. I love learning about analog... It seems so complicated compared to our new age digital solutions. I can completely see where someone would have huge pride in maintaining these systems. Very technical, precise and methodical skill set required to keep machines like these running. Calibration is mission critical, both then and now.
everything is interchangeable, modular, oh and soon-to-be refuse. Is Salvage still a real word in the dictionary, or was that excised with the digital age?
The PBX at my office in 1982 was a step-by-step PBX and the PBX operator connected incoming calls at a cord board. My keyset phone was rotary which made using services that required Touch Tone to be impossible. So I bought a telephone set microphone from Radio Shack that had Touch Tone buttons surrounding the microphone. When making calls, I dialed 9 on the rotary dial to get a second dial tone from the central office and then dialed the number on the Touch Tone pad surrounding the microphone.
My first job, at GTE. Working in a step by step central office from 1968 to '68. This was a real trip down memory lane. Knew those switches well, and all the parts and maintenance routines.
Absolutely awesome to see and learn the mechanics behind these old switch banks.
I worked for Telecom Australia as a communications technician when the exchanges had step-by-step equipment, like the others who posted here we had pride in our skills and workmanship.
Eventually step-by-step was replaced by the Ericsson "crossbar" system which had central control units albeit comprised of electro-mechanical relays - a foretaste of the future's all-electronic systems.
We used to joke about the "telephone exchanges of the future" which would have a staff of 2 manning them - a man and a dog (the dog to guard the building and the man to feed the dog). I used to think "Naaah it'll never happen".
I left Telecom ages ago but I notice the modern exchange buildings in my area seem to be unmanned and visited by maintenance crews.
I actually have this unit in my workshop at home, Cool Stuff indeed, makes you appreciate the evolution and engineering of the PSTN, i feel honoured to have been given this piece of hardware as a gift from Telstra Staff, due to the mere fact that i showed high interest when attending the telecommunications museum in melbourne. i still can't believe i own this hardware....... unbeleivable but cool
I worked on this starting in 79, also Strowger rotary exchanges from the 30s. In early 80s we switched to NC400 crossbar but nobody understood them so they were quickly changed to solid state. I still have fond memories of maintaining step by step and even oiling the tone generator.
Absolutely amazing. I wasn't expecting this kind of electromechanical complexity. I thought I'd see a bunch of valves (emulating transistors) or something like that.
I did my apprenticeship in various exchanges in the early 80's, and got to work on Strowger (what you call SxS), crossbar (which were huge lumps of metal bars with springy needles), the updated crossbar (which was huge arrays of reed switches doing exactly the same thing as crossbar), System-Y, and System-X (which was the first all solid-state equipment, and was insanely static sensitive)
What's not mentioned on this video is the current consumption of those Strowger systems!! From what I remember, Leeds exchange in England drew something like 200 megawatts during busy hours, and the system had battery backups (huge lead-acid batteries) in the basement that would keep the exchange running at that current usage for up to 30mins until the diesel generators span up. Also, the heat from all those actuator coils in the electromagnets made it stifling in the summer.
Those battery rooms were disgusting places too, with the stink of the acid, and as an apprentice guess who had to check the electrolyte levels regularly :)
Ah, nostalgia...
actually, I was there when they went from strowger to the first common control reed switches. While strowgers take a lot of current to move the shaft, that is just momentary. and goes to zero with no traffic. The early computer controlled switches used a LOT of power to run the multiple computers and memories, and a significant current to hold up the reed relays of the network for the duration of the call, as well as the loop current to customers, which remained the same. The consumption of old and new switches was comparable, clearly displayed on the 50v rectifier output current meter. Even now, the digital multiplexor technology uses lots of power for the computers and the network, which consumes power even with no traffic.
Yes, that seems to be often missed: older systems had a VERY low idle current (effectively just the leakage on open wire lines). Progress eh?
5ess had a room full of lead acid batteries to run the 48volts for the switch. Working on 20 year old memories though.
man comments like this just adds to the video by blowing my mind. its crazy the kind of terrible ass workplaces existed that i could never think of existing haha.
My father spent 20 years working for Ma Bell, and part of that experience included these kind of switchers. When I was young, he described to me how they worked. But, until this video, I'd never seen them in action. Pretty nifty.
Even today with our "digital miracles" This and the original automatic transmissions still freaking amaze me!
Yes......The Strowger switches and their ancillary equipment were fascinating. The engineers were geniuses, and had a remedy ready for any design flaw imaginable......
Worked on these, as well as Planel Swt, #1 Crossbar, #5 Crossbar, ESS in my 47 year career. AT&T was a family back then, not like today.
& all the old school management that cared about u retired in 1990 @ the call center in Bell of Pennsylvania, Pittsburgh.
I love seeing your old archive footage the work that was done was incredible.
When I was growing up, my neighbor worked for AT&T Long Lines. He used to give me old telephone parts including switches that I wired up to make a small phone system of my own.
Later as an adult engineer, I did work for SNET and New England Tel. There was a lot of SXS central offices in operation well into the early 80’s. I did a lot of work converting offices from mechanical switches to ESS.
One thing we learned was that the electronic equipment needed air conditioning. Before that, telephone central office buildings were not air conditioned. This drove up power requirements and required new electrical services and larger emergency generators.
Of the 200 or so Central offices in Connecticut, I probably did well over 100 of these conversions.
The most common ESS was the Western Electric #5ESS They produced thousands of them in the 1980’s. At each site, a temporary building addition would be built, the new ESS installed and wired. When it was operational, the old SXS or crossbar switches removed and the new ESS was slid into the old building while in operation. The cables were then shortened, by “half-taps” (splices) and the temporary building removed.
An enormous amount of work and cost.
Bill Moran where have all those switches gone? It would be super cool to get some of those to do something with.
A few found their way into experimenter’s shelves, but the vast majority were scrapped to recover the metals they contained. I remember truckloads of them being hauled off for scrapping.
any tips on what to brush up on getting into CO work?
Digital switching also used this logic.
I saw a similar thing at a museum in Georgia.
It was comprised tall, cylindrical switches.
I was training in the US Army's Signal Corps.
You can't do this anymore, but when I was a kid I was inspired by this episode of Gilligan's Island where a phone cable got washed ashore by a storm. Their dialing mechanism didn't work correctly.
So I experimented by tapping the reciever to simulate the pulsing that the dial normally makes. I called my Grandma; It WORKED!
It should have worked for the Professor too.
Beautiful devices, fascinating to watch them in action. The technicians must have been highly skilled to maintain them in perfect working order.
Seeing slo-mo done in the fifties really has its own vibe. Love it
I worked for the phone company in 1970 when this was still in use. The #5 cross-bar (touchtone) was just being tested and put into service, in Los Angeles. and the switchroom was very noisy, with about 20-30 'walls' of these switchers, the film here just shows part of one wall, or rack as they were called. New guys in the switchroom got a year or two of cleaning and adjusting these things.
I took a rotary telephone apart when I was probably 7 or 8 years old. It's amazing how many steps there were to this system. Hundreds of contacts and springs... Almost like a washing machine timer if I remember right. It's so cool to know that those contacts inside the phone, pulsed a signal in real time to these switches. Makes a lot more sense. An in old timer told me he could hear the switch box at the end of his street chattering all day long lol
Beautiful, I really enjoyed this video, thanks for posting it. Another example of a great accomplishment which happened mostly behind the scenes and which most people never gave a thought to.
I remember doing banks and wipers on Se50 and type 2000 switches back in the early 70s in Telecom Australia. You had a tool that was shipped in a curve to wipe and clean the switches. This brought back many memories.
This is absolutely astounding. As a kid, I used to like pulse dialing not with the rotary dial, but with the off hook switch. To dial a 7, I’d just press the off hook button quickly 7 times. I don’t know why I did this, it was slow and error prone. I was weird. But I remember very well using these systems. It was really crappy in terms of audio quality, but it worked when it needed to. It was not uncommon calling my friends on a line with excessive background noise I’d tell them, “this line sucks I’ll call you back on another one”.
This system still amazed me. It looks like a high maintenance and troublesome system but it worked. You can even call the mainland with it (I was born and raised in Hawaii so making calls to the mainland was really neat and expensive). With the advent of Lucents amazing 5ESS digital switches and DTMF, that made pulse dialing irrelevant pretty quickly.
Pulse dialing lasted a long time in other places. I believe some of the former Soviet countries still have it. Although the last time I personally used one was 12 years ago.
Right now I'm literally sitting in the same room that these or a variant would have been in many years ago. They updated to DMS100 in the 70's ish which is in another room in this building, and it's been running since with zero downtime. It's neat to see this old tech, and how things changed. POTS (and rest of telecommunications really) and everything that goes into making it work is something often taken for granted.
What's in the room, now?
@Flayed Man a desk, a laptop, a printer. basically an office, probably
For our younger viewers, POTS = Plain Old Telephone Service.
I used to be a Coca-Cola delivery man and went into a lot of non-public spaces in the 90's. Some of my favorites were the old Bell South buildings, they were built to be bomb-proof in the 1950's and were just fortresses.
Some of the freight elevators were larger than my first apartment. There would often times be a single rack of equipment in a room the size of a basketball court or larger. Amazing to see how quickly technology progressed.
I love old technologies. Magnificent. Great video.
Great video. Those leads to the terminals got quite a workout. Wonder how long they would last? Amazing how such complex mechanical devices been totally supplanted by solid state electronics made possible by the invention of the transistor at Western Electric's sister co, Bell Labs.
OMG, does this video bring back memories. I was hired in '78 to install SXS in Eureka, CA. While the rest of the state was removing SXS and replacing it with quiet ESS switches. We ran lots and lots of cable, wire wrapped and soldered at the main frame and between the switches was another array of specialized wiring to connect the switches. In the 80s we were able to convert the SXS switch to dial tone by adding a small box to the rear of the switch. Those were the days, before divestiture.
judy i can't grasp how this worked. does that mean each selector had only 9 levels to go up? So how many connections on each level? it could be more than 9 right?
And how were selectors set up? Was there a row for the 1 digit, then a row for the 2 digit and so on?? or could a second or third selector serve for any number?
When you said "dial tone " could be added with addition of a converter to the selector, I think you meant " touch tone " could be added. The dial office already had dial tone.
Why were they installing SXS in 1978?
@Tech Howden there's a SXS you can actually dial into it right now and hear it in operation. Its really cool
I freaking love this! Love love love electromechanical switching. I have old traffic light control boxes made by Crouse-Hinds That advance the traffic signals in virtually the same way.
Older stuff like this is actually easier to understand and greatly fascinates me
For the time, that was some impressive technology.
When I was a kid we went to the open house of UTS and toured their building. The engineer who explained these said the nickname for them was "bang and click".
Fun fact: I forget the year or the Philadelphia suburb, but at this particular office these devices went silent for 15 minutes once a week, like clockwork, unplanned. It took a few weeks to realize the problem: none; people focused their attention to the "Amos and Andy" radio show, when it was over normal use returned.
Worked for At&T about 5 or so years ago. They told me that there were certain phone numbers that could not be transferred to other carriers because they were actually hard wired into the system. While it was probably different from this, as this all would have been touch-tone, by now, I can at least kind of understand now why this was the case (99% of all numbers could be transferred, I never actually personally had to deal with this issue, it was just something that came up during training.)
Worked on WECO 701 PBX’s as a PacBell PBX repairman in Silicon Valley mid to late 70’s. They were being replaced by Northern Telecom and AT& T Dimension EAPBX’s. I liked the Stromberg Carlson XY Switch better though. Faster to trace a call and easier to maintain and switch plates were universal. I still have one in my shop.
The folks that put these films on YouTube are the luckiest folks on the planet. I absolutely love this! Wow! I'm duly and truly impressed!!
René Núñez - 2019-12-05
When I hired on to AT&T (Southwestern Bell at the time) my central office had just been converted from Xbar to 1ESS. When I retired from same central office over 36 years later it was DMS and we were testing interoffice fiber for 100 gbs circuits. I trained my entire career to keep up with technology. It was both challenging and rewarding.
Ay Bee - 2021-06-08
And when did it dawn on you that it was always about mass surveillance?
DC10 Fomin - 2022-06-13
I left Lucent in 2003 we had the 5ESS, funny you mention the DMS, that was a Nortel switch, used to be called the big Brown machine, nice to see comments like yours, brings back good memories, I started in the telecom business in 1970 at GTE Automatic Electric Co, used to engineer step by step central offices, I am now 73, best regards to you!
P - 2023-04-08
@Ay Bee He's right. Nothing whatsoever to do with communicating across town or across the country, for interstate business, convenience, or friendship. What a massive genius...
Pibble - 2023-04-13
I have similar experience starting with manual patch cords, analog multiplexing and finally digital fiber. Very fun and amazing!