Dialing Through The Step-by-Step Telephone Switching System
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- เผยแพร่เมื่อ 5 ต.ค. 2024
- Watch a rotary dial telephone call progress through the SXS switching system to telephone number Beechwood 4-5789.
You can see a complete SXS Central Office in operation at this link • Strowger, (SXS), step ...
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As a young kid in the early 80’s, I remember my friend had a setup similar to this in his bedroom. His grandfather was involved with the local telco and procured some old switching equipment as they were transitioning over to the new system. He set it up in his bedroom with 2 handsets and powered by car batteries. It was fascinating to watch, and amazed me to realize that every call I had ever made was routed in this manner. I still find it extremely interesting all these years later. Thanks for the videos.
I like tor read anecdotes because they generally reflect good memories, so thanks for that and thanks for watching.
As a millennial born in 1987 I appreciate stuff like this and Evan Doorbells videos. I'm a network engineer now, but the fact that a worldwide automated network existed without transistors, or digital circuits absolutely fascinates me. If I had a time machine I know I would go back and play with it... and maybe meet my grandfather. Thanks for the perspective on where we've been so we can better understand where were going and where we are now.
It's always rewarding to me when I see such enthusiasm from a young person.That such a massive network of electromechanical relays could be designed, built and function so well was truly amazing. In case you weren't aware, I have much longer, very detailed videos of this equipment. Just search my channel name, Hicken65, on You Tube. Thanks for watching.
There is something insanely gratifying about watching these things work
That's true and it's all free! Thanks for watching.
You're probably gonna think I'm kidding, but ...I was working at an ATT (actually Pacific Tel & Tel) Central Office (Melrose CO, in Hollywood) at the end of the seventies...with mostly "Horizontal Crossbar" (mechanical switching) equipment, and gradually shifting over to ESS (electronic switching). When Gen. Tel. made me an offer, I was delighted (with a couple more dollars/hour, and a CO closer to my Long Beach home), but was kind've appalled in that the office turned out to be something like 95% (old-fashioned) "Step x Step" equipment...which I'd thought had LONG AGO been shipped to Central or South America!!! Also, we used heavier gauge wire on the Main-Frame, which was a pain (also used soldering irons, exclusively)!!
BTW, working on the Step x Step equipment meant PHYSICALLY adjusting the devices, using little metal gauges...like adjusting the points in old automobiles. These switches DID work, but it was like working on ancient "Model T" technology!!
I remember when I worked at our hometown non-Bell Telephone company in the mid-late 70s, which had mostly AE equipment, and several times, I was in various exchanges around the city. You’d hear the step-by-step switch relays humming and clicking away, madly connecting dozens of calls at once. DTMF telephone subscriber sets were still somewhat of a luxury at that time, and probably only about 35% of callers had them. I haven’t heard that clicking sound for many years… until now. Thanks for bring back those great memories of my early telephony days. Very cool!
A symphony of ratchets and snapping armatures. I'm glad it brought back fond memories.Thanks for watching.
Thanks for this! I find electro-mechanical devices fascinating, because all the logic is physical and not digital. I've really been enjoying Technology Connection's series on how old PinBall machines work.
You're welcome. You may be interested in my long, detailed videos on this equipment. Just search on my channel name "Hicken65". Thanks for watching.
Wow amazing it all worked pretty reliably, when I was a kid I used to ride my bike in the telephone company parking lot and they would have the doors open on hot summer days, so once in a while I would peak into see the rows of switching gear and the people who all kept it going. One day they gave me a tour and I was so impressed by all those moving parts, I was in awe of it all....
Thanks. I enjoy receiving nice anecdotes like this. Fond memories are truly a wonderful part of life.
Thanks for a truly excellent video! Clear explanation and clear presentation. The slo-mo was especially good because we just can NOT see what's happening at 10 pulses per second. I will definitely look for your other videos.
I got hooked on phones (not phonics) when I was around 10 years old. Back then Bell Tel owned the equipment and the customer leased it, WE products were not available for purchase. This somewhat slowed my learning process, as I could take apart our home telephone only when my parents weren't home. I managed to get tours of two SXS offices (one 10,000 lines, one 30,000 lines) and one brand new #5 crossbar office, when I was in high school. I've never seen a panel office in person (from what I've read about them, in my humble opinion they were a step in the wrong direction).
In college (1965) I built my own single-digit dial exchange, which went through some design modifications from time to time. None of the parts were actual TELCO parts, they were all various relays that I bought at a military surplus store in Cleveland. I guess I found enough relays that all operated at the same voltage, were sufficiently sensitive, etc. The wiring was unbalanced, but for the short distances involved that was not a problem. I installed phones (non-Bell instruments, which could be legally bought from various mail-order companies) in several rooms of our house, and in two neighbors' houses, so my brother and I could talk to our friends. The "exchange" even had dial-9 access to our home phone line (by then my parents had given up on trying to modify my behavior). And the TELCO access could be restricted on a line-by-line basis, so our friends could NOT use our phone line from their houses.
I have often toyed with the idea of building another similar system, with current parts. Of course it would not be authentic TELCO parts, but it could be made to work pretty inexpensively. The challenge would be finding a stepper relay (I always dreamed of owning a Strowger switch). I might have to duplicate the stepping function using an Arduino as a pulse counter (travesty!). Again, not "authentic" at all, but it would allow for DTMF decoding, as well as dial pulses.
(BTW, lately I have begun collecting military surplus field telephones, which are magneto/LB, not CB.)
Thanks again for the excellent video! This has definitely revived my interest in telephone switching!
I love reading stories like yours. Thanks for sharing. You should consider joining Telephone Collectors International. There are a number of folks in that organization that have working SXS systems. You could enquire on their forum if anyone has equipment they would be willing to sell you. Thanks for watching.
In my early days as a computer technician I had occasion to visit NY and NJ central and long lines offices to service AMARC and ELMOS computer systems. My escort, would, after I expressed interest in the system, give me a tour. The room with the racks of switching equipment, would be busy clacking away. The fellow escorting me would say that after working there they could judge the time of day based on the amount of clatter as folks would call home. If a big new event happened the noise level would also peak. The floors in the facility which housed the lead acid submarine batteries providing the 48 volts that powered the system were impressive to. Those were the days...
Those were the days, indeed. The switching sounds were quite rhythmic and you could always tell when some significant event was occurring as there would be a substantial sudden increase in the clattering. Then it was time to turn on the radio and find out what was happening.
The old exchange system was always a source of fascination and wonder when i was a kid. How the heck did this thing manage to handle millions of calls at the same time, each with their own dedicated connection and no interference from the other calls? Now i know. Well, sort of. This is fantastic. Thank you for sharing your knowledge!!
Well, I'm glad you enjoyed the video and thanks for watching.
My father started at Chesapeake Bell after WWII as a lineman, then as a central office repairman. He took care of this equipment. I am MaBell baby. they used to let me into the central office after I looked up to a camera over the door. I have experienced an entire room of these operating. It was almost musical. I know more than you.
To some people, the sounds in a SXS office were just cacophonous noise. I always found it to be a pleasant rhythmic chatter. Thanks for watching.
I am a att facility tech with 43years service. I came along after all this was history but remember a couple offices that were still step offices and it was very noisy compared to the new 5e offices. I never really understood how all of it worked. I do remember some customers calling in repair complaints that their phone sounded funny(the 5e had a much different dial tone). Great video!
Glad you liked it. Thanks for watching.
This brought bank memories when i was growing up. The phone company where I lived sponsored an explorer group that was learning about communications. We got to visit the CO where all the switch equipment was and boy was there a lot of noise! Was a large city so a lot of banks of equipment. They had just started installing the then new electronic switching equipment and it was interesting to see the difference in what was required with the new equipment. Still using the same principle of pulse switching at that time, but done with transistors etc. instead of the relays. I still have some of the relays and things they gave us for leaning. during one meeting one of the instructors was laughing that they had spent most of the day trying to figure which of 100's of green wires on the new equipment was giving them an issue.
I don't think it would be worthwhile having a group of young people visit a CO these days. I can't imagine any of them would even bother to lift their eyes away from their smart phones. Nothing to see here. Move along.
I just gotta say Iove the telephone number references. Beachwood 4-5789 and Pennsylvania 6-5000. The Marvellettes and Glenn Miller. Bravo!
There were some other songs with exchange name telephone numbers, such as "Bigelow 6-200", "Lonesome 7-7203" and "Echo Valley 2-6809", but the two I used are my favourites. Thanks for watching.
The real Pennsylvania 6-5000 would have been at a panel office not a step by step office.
@@netking66 Is 736-5000 a rural number? Would've thought it could've been direct dial by 1944.
@@That_AMC_Guy ???? Suppose there could be other 736-5000 numbers in USA, but they are not as well known as the one for New York's Pennsylvania Hotel.
Note to "DARK APPERITION": Your comment "so, is there an 'A' relay for every trunk lines on each level of the selector? or just 1 that unlatches after a free trunk line has been selected? otherwise, that would be a whooole Lotta relays!" was received in my email, but for some reason did not show up in You Tube. So, to answer your question, yes, every selector that can be reached from a trunk on a bank assembly has its own A relay, along with a minimum of four other relays (B, C, D and E).In a SXS office there certainly is a whole lotta relays.
I also remember the wooden ladders with wheels that traversed the bank of switches in the central office and climbed up one. Dad was there. He was involved in building repertory huts that boosted the signal strength. As an engineer I understand 48 volts is not good for transmission. I used to have a 48 volt battery Dad got at the phone company. I also own a 1951 model phone with the wall box and the rotary dial phone separate. Later he got a second class radio license from Georgia Tech and helped install one of the first air-to-ground stations to allow calls from an aircraft. He was a crew chief on a C46 and flew the aluminum highway from Burma to Shanghai. Then to Nagasaki after the bomb and retrieved some wooden crates from a stone structure that was the police station . They were license plates. I have made inquires to his friends at that time and confirmed the story. Do you know how I can find if there is a value of the plate? I know from a person that the number on the plate defines the main street address and the secondary street and the house number. Thanks Q
Well your father certainly had a diverse and interesting career and its good that you have these fond memories. Sorry, I can't be of any help on the license plate.
Spent many happy hours doing bank and wiper routines, replacing wiper cords, replacing broken wipers, lubricating switches with dag oil, adjusting relays, tracing calls forwards and backwards, clearing alarms.. Those were the days.
Me too. The fond memories linger still. Thanks for watching.
Thank you for the detailed information. I saw the mechanical switching mechanism in the National Museum of Scotland and was curious how it worked.
Fortunately, there are a number of museums around the world that are able to demonstrate SXS apparatus. If your curiosity yearns for more detail, you'll find it in my much longer videos. Just search my channel name, Hicken65. Thanks for watching.
Absolutely fascinating and very well-presented. Step-by-step. Thank you.
Glad you liked it and thanks for watching.
I grew up with one of those black dial phones. The sound quality was
incredible.
My sister and I would sometimes play a practical joke on our mom. When
mom was in another room, one of us would dial our own number, and before
the last digit finished clicking, we would put the handset back in the
cradle, then run and hide. A second or two later, the phone would ring,
and mom would answer it to hear nothing on the other end. Somehow doing
this would have our phone call itself.
I remember dial-the-weather, dial-a-joke, and other such services.
Sigh. Technology has taken all the fun away.
The old systems had meany quirks and weaknesses that could be (and were) exploited by those who wanted to "play " the system. It was fun while it lasted. Thanks for watching.
I learned how to do this at our house (a SXS office), and also at both grandparents' houses (one was SXS, the other was panel). However, dialing one's own number always returned a busy signal, presumably because when the connector finally got to one's own number, the sleeve was already grounded. Therefore I suspect that if you could ring your phone by dialing your own complete number, you were *not* in a SXS office. In each of the three offices that I "gamed," there was a four-digit number to get "call-back." I remember 1197 in one office, and 4197 in another office; I don't recall the third office (maybe it duplicated one of the others).
Four digit codes were provided to enable a 2-party subscriber to call the other party on their same line. These were known as revertive calls. The calling subscriber would dial the 4-digit code and hang up. Both the calling and called subscribers phones would ring. When the the ringing stopped, it meant that the called subscriber had answered and the calling subscriber would pick up the receiver and a conversation could begin. Instructions on how to place these types of calls were provided in the front of the telephone directory.
@@Hicken65 Ah, yes, I had forgotten the term "revertive ringing." Indeed our house and grandparents' house next door were on the same party line. (My mother hated this because *her* mother listened in on her calls.) IIRC we were 337R and 337J. In the early 50s we got 500 sets and new phone numbers, published as 2+5 digits. However we soon learned that we could dial just the last five digits (3-xxxx) for calls within that CO (a small SXS office).
@@gregm.857 Most small towns retained short dialing capability after the introduction of 7 character telephone numbers. This was made possible by the introduction of digit absorbing first selectors.
Sound in slow motion is aaamaaaaaaaazing!!!! Rotate all the wipers!
At the time I was making these videos, I too was delighted when I first heard the slow motion sound effects. Thanks for watching.
It seemed quite simple yet complex and probably explains why we got accidently disconnected sometimes or got a wrong number even if you dialled correctly. And on rare occasions a crossed line, I remember one years ago you could hear these switches really loud and this raspy super loud ring noise and then another person on the line., What would cause that, this was in the early 90's on an Australian phone exchange or CO as you call them.
In a SXS CO, lots of things could go wrong .Misaligned wipers, broken sleeve wipers, dirty contacts, frayed wires, solder splashes on the distributing frame, etc. Outside the CO, wet and crossed wires and inductance problems were often a problem.
I can remember when we dialed long distance direct after you dialed the last number you would hear like a thousand clicks as it made its way down through the network until it rang it was so cool but in a lot of ways you kind of miss that kids today have no idea
Yes, in the good old days all the signalling was performed on the voice transmission path, so there was lots to hear.
Thanks again for another great video! I'm wondering what you can tell us about digit absorption in an SXS office. I remember dialing phones within the C.O. and it was obvious by the sounds I heard that my call was not extended beyond the first selector until I got to the fourth digit. It was later explained to me that the first selector absorbed the first three digits, if they matched the C.O.s NXX. Only the last four digits progressed through the switches to the destination. Thanks!
Digit absorption is explained in my video "The selector In The Step-By-Step Telephone Switching System Part 2". Just search my channel name, Hicken65, on You Tube. Thanks for watching.
My dad knows this stuff. Extremely methodical video though. Why did we need so many repeated slow mo examples?
It allows the viewer to relate each digit dialed to the vertical steps taken by the each switch since in slow motion, each vertical step can easily be followed.
Also, repetition enhances comprehension and memory. After seeing it several times, at a speed you can follow, you will probably retain it for a long time.
Lots of crossed lines in rotary exchanges in those days.We still had a rotary exchange in our town Roodepoort South Africa in 1996.
In North America, the last Step-by-step switch in the Public Switched Telephone Network was located in Nantes, Quebec, Canada. It was decommissioned in June, 2002.
My Mother would call her sister at times at work. She lived in Zionsville Ind and worked at a bank in town. After telling the Operator the name of the town I distinctly remember her saying " Uptown 33164."
People really liked exchange names. There was a great deal of public opposition when the telephone companies announced they were going to be replaced with all numbers.
Thank you. You answered my question about what zionsville office was called. its 769 now.
Just try to imagine working in a room full of huge rows of these things clicking, even though it was automatic somebody probably had to be there to fix it if something went wrong.
Large offices always had techs on site performing preventative maintenance routines and fixing any trouble conditions that arose.
my dad worked at AT&T (Western Bell at the time and then Bellsouth) for almost 40 years. I remember going to work with him and seeing *HEARING* the deafening roar of thousands of these things running at once. what a great memory.
Whay I want to know is why this guy is calling the Marvellettes at Beachwood 5 - 4789? Which came first, this tech video or the rock hit Mo Town song?
I appreciate how thorough you were with your explanations and clear visuals. But I'm still having trouble understanding one element of the system: line finding. What exactly is happening, electrically, that allows these switches to automatically find an idle trunk to the next switch?
Does the electrical energy of a trunk that is in use power the magnet which generates rotation until it finds a denergized trunk?
Yes, you are correct. An "in use" trunk grounds its sleeve lead back to the selector bank terminal. This ground operates the E relay in the selector, which in turn operates the rotary magnet. Details can be found in my long video entitled "The Selector in The Step-By-Step Telephone Switching System Part 1", which you can find by searching that title or my channel name "Hicken65" on TH-cam. Thanks for watching.
That was an amazing lesson on how mechanical analog telephone switching works. I always knew the first three numbers were looking for a central office but didnt know how the last 4 numbers actually made the connection. Thank you :) Question though.. If you were dialing outside of your LATA would the switch automatically transfer you to that LATA or is that why (I'm only 29 so bear with me!) "in state" long distance required you to dial 1 before the 7 digit number to tell the switch an inter lata call was about to made?
Well, I'm not really familiar with the complexities of LATA arrangements in the U.S. as I live in Canada. Here, every call I make to a North American number is 10 digits. If the number is long distance, I still must dial "1" first. If I don't, I get a recording telling me I must dial "1". The "1" routes me to a switch that is capable of recording the call details necessary for billing the call. If your call is within your state and is within your area code, but is inter LATA, I presume the 1 is still required to route your call to the inter LATA carrier. But its beyond my realm of knowledge. Here's how things worked in the golden days of Step-by-step switching.
Let’s describe a typical (not all were set up this way) telephone company situation using a step-by-step switching system before the breakup of the Bell System. Subscribers received a monthly telephone bill, which was a fixed, flat rate amount for all “local” seven digit calls and an additional variable amount for all “long distance” calls. The local calls could include just the central office switch in which the subscriber’s line was located or other switches in the same city or in nearby cities or towns (this was called extended area service). The long distance calls would be billed based on the distance of the destination and the length of time of the call. As such, a means of recording the call details was necessary. In the 1940’s and earlier, all such calls required the subscriber to dial the operator, which generally meant dialling the numeral “0”. The operator would enter the call details on a ticket, which was then sent to the accounting department. In the 1950’s, Direct Distance Dialling (DDD) was introduced, which allowed subscribers to dial their own long distance calls. This was combined with the introduction of area codes, which gave every subscriber a unique 10-digit telephone number. As well, a hierarchial network of toll switching central offices were established to route the calls. These were equipped with Automatic Message Accounting (AMA) equipment, which recorded all the necessary call details to bill the call without operator intervention. In order to make a DDD call, the subscriber had to dial an access code, such as “1”, before the telephone number. This would cause the step-by-step equipment to select a long distance access trunk to its toll center to handle the routing and billing functions. If the call was to a number within the same area code, the subscriber dialed the access code and seven digits. If the call was to a different area code, the subscriber dialed the access code and ten digits. The access code was taken up by the step-by-step switch and only the actual telephone number was pulsed out to the toll center.
Wow, my home town used to have a Central Office like that, I remember all that noise coming out of the room when my mother sent me to pay the service. Was small town and locally we only diled the last 3 digits of the phone number, our was 574
The switchover to standard 7-character telephone numbers began in the late 1940's. Telephone directories began to list 7-character (typically 2-letter, 5-numeral) numbers. However, for many years the switch design could still generally accommodate the "shortcut" dialing that the local townsfolk were accustomed to. Thanks for watching.
Hicken65 yes, to make national long distance we have to provide the operator the 7 digits of the phone number, if was international to USA we had to provide also the area code, by that time we shared the area code 809 with other caribbean islands, our range of digits was from 809-521-XXXX to 809-599-XXXX and 809-681-XXXX to 809-689-XXXX, bigest cities applyed 7 digits dialing, smaller towns some 4 last digits of the phone number and some others the last 3 digits like my town. My town was introduce the DDD in 1986.
@@Hicken65 Thanks for a really excellent video. I was going to ask whether you had covered "digit absorbing" first selectors. I can understand how you could wire one to ignore a specific first digit. (e.g. if the selector steps up to the 6th level, it just resets and drops back down to initial resting position.) But how would you configure a selector to ignore several initial digits, if they were all different numbers of pulses? If you wired the selector to drop back down and "absorb" e.g. 3, 4, 5, and 6, then it seems to me that the fifth digit could not be any of those numbers. That means the 5th digit could be only six of ten possible numbers, limiting that exchange to 600 lines. Is that right? Or was there some other means of "absorbing" multiple digits?
@@gregm.857 Yes, digit absorbing is covered in my video "The Selector In The Step-By-Step Telephone Switching System Part 2". Just search my channel name, Hicken65 on You Tube. Thanks for watching.
So, to summarize, when you call, say, number 2356, that's what happens. When you take the phone off the hook, a free line finder connects you to 1st selector, which waits for you to dial first number. When you dial two, the shaft moves up to two levels, and then rotates around the dial until it connects to a contact that leads to a free 2nd selector, connects to it and waits for you to dial second number. When you dial 3, the 2nd selector shaft moves up three levels, and once again rotates until it connects to a free connector. Which then waits till you dial number 5, moves up five levels, and stops waiting for the last number. When you dial the last number, it rotates the shaft 6 steps, and it connects to the contact which goes to a phone somewhere which has number 2356 registered to it? And when you're done talking and hang up, all the selectors drop their shafts back down below first level.
By the way, what's the difference between selector and connector? Is it only that selectors are connected to other selectors or connectors, and connectors are connected only to receiving phones? Or is there some kind of difference in their construction? In addition, since there are many numbers registered on a single connector (10 x 10 if I understand correctly), are there several connectors with same numbers registered to them? Because if, say, we dial the number 2356, than means that number 2357 is just one contact away, and while we're talking nobody would be able to call any other of 99 numbers registered to that connector, unless there's another one for redundancy?
All in all, that sounds like such a simple, obvious solution, but look how much it changed the world! Simply amazing!
Well done! You have captured the essence of what happens. There are some differences between selectors and connectors. Selectors automatically rotate to find an idle trunk, while connectors rotate based on the last digit pulsed because they have to connect to a particular terminal. Connectors have more work to do than selectors, such as test for a busy line, provide ringing current to an idle line, trip the ring on answer, provide talk battery to both parties and supervise the connected call. Typically, about ten connectors handled the same set of 100 telephone numbers. For details on the connector, see my video "The Connector In The Step-By-Step Telephone Switching System", which can be found by searching my channel name, Hicken65, on You Tube.
@@Hicken65 Thank you, I will watch the other videos! I now have half a mind to try and build my own tiny demonstration switching station from the ground up. I mean, the details are many and the design is ingenious, but on its basic level, it is quite simple! Might be a nice project to do in my spare time.
@@s.s.85 Try to convince the other half of your mind. It's always great to get another switcher hobbyist on board. Good luck with your endeavors.
I remember when I was a kid, you could dial your own phone number, hang up quickly, and your own phone would Ring!!!
In the days of electromechanical switching, some systems would allow this to occur, but only if you were on a party line. If you were a single party subscriber and served by a SxS switch like the one in the video, you would simply be disconnected as soon as you hung up and your phone would not ring.
A lot of this could be simplified by only explaining the selector and turn search once.
My folks had a phone exactly like that one. Don't drop that beast on your foot! One problem w/rotary dials was accidently slipping a finger out of the hole before rotating all the way to the stop.
The model 302's with the zinc alloy housings weigh about 3 kilograms.
Thank you for such a perfect video!
Well, I'm glad you enjoyed it and thanks for watching.
Love your videos.
I wonder if anybody picked up on the phone number used in the film. The Marvelettes had a hit song in 1962 called Beechwood 4-5789. Was probably never issued so people would not harass the owner.
Well, anyone who watched the video all the way through would have picked up on it, since at the end there is a 30 second clip of the song, and photo of the Marvelettes and the 45 RPM record. Since the song was written in 1962, the 7-digit telephone number 234-5789 would already have been in use across many area codes and for these subscribers annoyance calls were likely a problem.
Glenn Miller had a piece called "Pennsylvania 6-5000", another number seen in the video. th-cam.com/video/m_muFwwTSMs/w-d-xo.html
There's another famous number from show biz on the vintage instrument that appears at the beginning: PE 6-5000. Or "Pennsylvania six five oh oh oh" as performed by the Glen Miller Orchestra big band in 1940.
What happened when someone dialed 0 for the operator? I assume ten pulses were transmitted to the switching system which connected the caller to an operator. But did all the selectors operate to connect the call?
I have a doubt, those were 7 digits, so.... 999.999 switchers to redirect all those 99 finals? also, what happened when one dials its own number?
My demonstration unit was designed to demonstrate how a call progressed through a SXS switching system. When a call is established through it, all 7 switches are tied up for the entire duration of the call. So the demo unit can only have one established call at any given time. In a very large central office, each established intraoffice call would also tie up 7 switches, but there were many thousands of these switches. Each telephone line did not have its own dedicated switch or set of switches.To make efficient use of the switches, there was a great deal of shared access to them. For example, line finders were arranged in groups of up to 20 that had shared access by 200 lines and connectors were arranged in groups of up to 10 that shared access to the same 100 telephone numbers. Between the line finders and connectors were the selectors that shared access trunks paths between the ranks (1sts, 2nds, 3rds, 4ths and 5ths).Typically, SXS systems were provided with sufficient switches such that 7% to 10% of the telephone lines could be in use simultaneously. Each office was engineered to meet specific service criteria regulated by the government. A large office serving 50,000 lines would have around 25,000 switches. If you call your own number you get busy tone.
Thanks for explaining all this in such detail (including your newer videos that walk us through the selector, etc.). And it seems to me like the banks _should_ be considered part of the switch, because that's how any ordinary switch is considered: all contacts in the switching operation are parts of that switch. But I still don't understand some things:
How do you connect a subscriber line to their number assignment in this system?
1. I get how the connector handles the last 2 digits; that's straightforward. But then how do you go from there? In other words:
2. Let's say your last 4 digits are -2947, like my home phone number here in Orem, Utah. All right then, you have your connector that handles the 4 and the 7 in the obvious way. But then how do you hook that connector to any or all of the 10 hunt positions on the 9th bank row of a selector immediately before it? And how can any one of those 10 positions lead to that same connector at any given time?
3. And then how do you make sure that last selector is connected to the 2nd row of hunt positions on a selector just before that?
4. What parts of the system are connected to the back ends of the wipers?
Haha, wow, okay, thanks, Mr. Hicken, for going to all that effort for me! Oh yeah, those terminal strips in the distributing frames are those bars that you press the wires into, that have the little contacts in there that slice through the insulation as you press the wires into place, right? I remember when my parents' scrapbook store in Spanish Fork, here in Utah, converted from a key system into a small AT&T Partner PBX, and then doubled it as Lucent took over the Partner brand. It was interesting to watch the installers there the first time around, as they adapted the multicore cables from those pink sub-unit boxes (I don't remember the technical term for those) over to the PBX and to the phones by putting adapter plugs on them, and using the few existing distributing frames in the building (two main sets: one in the boiler room with the Partner system, and one on the opposite end of that basement).
And so are you saying that if you drew me a diagram of this semisimplified setup that you described for me, it would look like this?
1. 10 phone lines in a group, all of which are connected to different parts of the same linefinder through the distributing frame
2. Customer on one of them picks up the handset.
3. That linefinder on a rack at the starting end of the office with 19 more of them goes up some to some gang of 3 rows of contacts, and then maybe twists.
4. Then the first-selector that it connected to is on a shelf with 9 more of them (or 2 shelves with 5 and 5, etc.), and this shelf is drawn as part of a rack with 9 other shelves that also have 10 selectors.
5. This block of racks of shelves is just past the linefinders at the start of the office because these selectors are all designated as firsts (and because the first digit is only allowed to be a 2 here, these selectors may even have normal-posts with their digits 1, and 3-0 snipped off on the left but not the right).
6. The relays on this selector connect that caller to dial tone.
7. The customer dials the 2.
8. That selector goes up to the 2nd gang of 2 rows of contacts and then maybe twists.
9. The next block of racks here represents the racks of 10X10 2nd- or 5th-selectors. As such, all digits are allowed so they have no digit absorption.
10. The customer dials the 9.
11. A selector somewhere in this second 10X10 block starts climbing to the 9th row of contacts, and then may twist.
But because there are 10 different positions we can use on this second set of selectors, the set of connectors whose customer's number is -2947 must be on the 9th of 10 shelves of 10 connectors each. So the next parts of the diagram are:
12. 1 block of 10X10 connectors
13. One of the 10 connectors that are only on the 9th set can be used to ring the phone of our called party, so the block is divided into 10 distinct sections, and the 9th row or column is highlighted or darkened.
14. The customer dials the 4.
15. One of the connectors from row 9 climbs to the 4th row of contacts and waits.
16. The customer finally dials the 7.
17. That connector then twists over to the 7th contact.
18. The relay that handles the ringing closes and rings the -2947 phone!
19. The called party picks up and answers, and both talk!
20. Both customers hang up, and the switches reset.
So for every digit between the first selector and the connector, you have to specify that those selectors and the connector only be reached from that number's set from the racks of shelves. Correct?
And then this raises a question of what should be an elephant in the room: You said that there are 10 phones to each linefinder, right? Then what happens if more than one phone on that finder try to make a call at the same time?
And from linefinder through connector, where do the other ends of the wipers connect straight to?
Thanks for your replies already! And thanks for the video link. I'll go watch that. Opes, yeah, I did mean 4 instead of 7! I've corrected myself up there. So I was right that the middle digits have to be pulled only from the corresponding racks or shelves, because that's the only way to assign those parts of the phone number, right?
Oh yeah, hehe, I should have guessed that a quick-connect concept would more likely come from somewhat of modernization based on a long amount of experience with something less convenient.
SO then what happens if like PE 6-6000 to BE 5-5789 while a call is already going on? Does it just use a completely different system?
My demonstration unit was designed to demonstrate how a call progressed through a SXS switching system. When a call is established through it, all 7 switches are tied up for the entire duration of the call. So the demo unit can only have one established call at any given time. In a very large central office, each established intraoffice call would also tie up 7 switches, but there were many thousands of these switches. Each telephone line did not have its own dedicated switch or set of switches.To make efficient use of the switches, there was a great deal of shared access to them. For example, line finders were arranged in groups of up to 20 that had shared access by 200 lines and connectors were arranged in groups of up to 10 that shared access to the same 100 telephone numbers. Between the line finders and connectors were the selectors that shared access trunks paths between the ranks (1sts, 2nds, 3rds, 4ths and 5ths).Typically, SXS systems were provided with sufficient switches such that 7% to 10% of the telephone lines could be in use simultaneously. Each office was engineered to meet specific service criteria regulated by the government.
Hi. This is such a great presentation. I wonder how the dial, ringing and busy feedback tones were generated. Were transistor oscillators available back then? One per subscriber line or shared? Thanks.
The SXS central office equipment for ringing and tone generation was shared by all subscribers. In the heyday of SXS switching, it was performed by heavy-duty machines driven by electric motors. These machines consisted of such items as stators, rotors, cams, brushes, worm gears, etc. The outputs were wired to the SXS switches, which controlled their connection to subscriber lines.These devices continually evolved as time went by and eventually became solid state electronic devices. Thanks for watching.
How does it know it's an idle trunk and how does it choose that trunk?
You will notice that there are two sets of wipers on the selector shaft. The bottom set of wipers are the tip and ring transmission path wipers. The upper set are the "sleeve" or control lead wipers. It is this upper set that determines when an idle trunk is found. The wipers sweep across the ten sleeve terminals on the level of the bank assembly associated with the dialed digit. They sweep from left to right (i.e. from terminal 1 through to terminal 0). Each terminal is the sleeve lead of the trunk path to the succeeding selector or connector. If that succeeding circuit is in use, its sleeve terminal will be grounded. If it is idle, there will be no electrical potential on its sleeve terminal. As the selector begins rotary hunting, the sleeve wiper detects whether or not there is ground potential on the sleeve terminal. If there is, the succeeding circuit is in use and so the selector rotary steps one more position. The first sleeve terminal reached in which there is no ground potential will cause the selector to stop rotary hunting, because the succeeding circuit on this terminal is idle. You will notice that on my demo unit, the selectors always rotary hunt to the last, or tenth terminal before they find an idle trunk. This is because my demo unit only has one working trunk on any of the levels dialed and I have connected that trunk to the tenth terminal position. I did this because this is after all a demonstration unit and so I wanted to enhance the demonstration by maximizing the amount of rotary motion of the wipers. To create this affect, I wired a permanent ground potential to sleeve terminals 1 through 9 on each of the dialed levels, which simulated a "busy" trunk condition. If you are keenly interested, I have provided very long, detailed videos on the line finder, selector and connector. Just search my channel name, hicken65, on You Tube. Thanks for watching.
@@Hicken65 Very fascinating. I guess it makes sense. I have a question tho. I understand how the selector modules work, but how does it actually route the call to the desired telephone?
The last switch in the train is the connector, which processes the tens and units digits of the station number. The telephone sets are connected to the bank terminals of the connectors. The particular tens and units digits dialed will cause the connector switch wipers to come to rest on the particular terminals of the called telephone. The video shows this starting at the 10:00 minute mark.
Let's see that again in slow motion!!!!
Ooohkaaay
How does it know a trunk is idle ??
When the switch rotates horizontally, the upper set of wipers brush across the sleeve terminals of the trunks. When a trunk is in use, its sleeve terminal has ground potential on it. When a trunk is idle, there is no ground potential on its sleeve terminal. The lack of ground potential prevents a relay from operating in the selector which in turn halts further rotation of the wipers. A much more detailed explanation of the operation of the selector can be found in my long video " The Selector In The Step-By-Step Telephone Switching System". Just search my channel name, Hicken65, on You Tube.
@@Hicken65 Thank you
How many potential phone lines could be connected with this unit?
My SXS demonstration unit has not been designed to replicate a small, expandable SXS central office, but instead is set up to merely demonstrate how a call progressed through such an office. In its existing configuration, my demonstration SXS unit can only have two telephone sets connected because it only has two line circuits (i.e. two line relays and two cutoff relays). Also, the unit can only have one telephone call in progress at any given time. This is because the unit only has one set of seven Strowger switches (i.e one line finder; one 1st selector; one 2nd selector; one 3rd selector; one 4th selector; one 5th selector and one connector). Each of the seven switch types can only serve one call at a time and are dedicated to that call for its entire duration. I could expand the unit to serve 100 telephones by adding 98 more line circuits, but it would still only be capable of having one call in progress at any given time. To increase simultaneous call capacity would necessitate adding more sets of the Strowger switches, along with their bank assemblies and some additional preference circuitry.
@@Hicken65 my late father worked at AT&T for almost 40 years. I remember going to work with him one day and the noise of the switching office was just deafening! the amount of calls going in and out of that room was insane... This was in the early 80's.
@@enkrypt3d There was always a crescendo of clatter as the busy hour drew near. Thanks for watching.
Why are there two levels to the rotary switch? Wouldn't each side of the selector blade connect two wires to connect? What does the other bank do?
Also was position 10 usually the first free line and they'd fill up 10, 9, 8, etc until position 1 was occupied then the call would report no available circuit?
Ah...
I have seen switches with three banks and what looks like 5/6 wires. What would those extra lines be for?
Gotcha. How does the line finder know how many steps up to go before sweeping across to find an open line? How does it isolate the first found open line between the two voice banks, does it just use the sleeve to find ground?
Thank you for your replies. I also found this: pbxbook.com/other/trunks.html
Hold and choose
Hold and choose
Where do u get the step by step things that move i don’t know what u call them
In general, they are called Step-By-Step switches. There are three main types of these switches, namely, line finders, selectors and connectors.The vast majority of these switches went to the scrapyards when they were decommissioned by the telephone companies, mostly in the 1980's and 1990's. A few were saved and made their way into telecommunications museums and the hands of collectors like myself. They rarely come up for sale.
@@Hicken65 what are the parts of the three types and is it required for a telephone system
@@ryanbelknap814 The parts are all identified and explained in my long videos on these three switch types. Just search my channel name, Hicken65 on You Tube. A telephone switching system has all three types of these switches.
It was easy to tap phones connected to these exchanges….tap 10 times to dial 0 and 1 tap for 1 and so on.
Yes, so you could still call repair service if your dial was broken.
What is the difference between step by step and common control system?
Step-by-Step (SXS) is called a direct control system. Setting up a call is under direct control of the caller's dial and builds up one step at a time as each digit is dialed. Each switch used in setting up a call is retained in use for the entire duration of that call. In a common control system, there are a number of devices that are only used to set up a call. Once the call has been set up, these devices are released and become available for setting up another call. So a central office would only need a few of these devices because their per call holding time would be very short. For example, In a Bell System large (30,000 lines) No. 5 Crossbar office, there would typically be 4 Dial Tone Markers available to all callers to set up dial tone connections. The per call holding time of these Markers was one-quarter of a second. The dialed digits would be received and stored in a register device. After receiving all the digits the register would request a Completing Marker to set up the connection to a trunk. There would be about 8 Completing Markers and their per call holding times ranged from one-third to one-half second, depending on the type of call. So a small group of devices controlled the setting up of calls, and access to these devices was shared in common by all callers.
អគុណបងthank👍👏
You're welcome and thanks for watching.
I noticed that the linefinder has three switch banks for the tip, ring, and sleeve while the selector switches have only two (I assume for the tip and ring). I was just wondering how the sleeve gets cut through the selector switches to the connector switch.
Each line finder bank handles the tip, ring and sleeve terminals for 200 lines. Each line finder bank assembly has 3 tiers.The bottom bank tier contains the transmission path (tip and ring) terminals for lines numbered 00 to 99. The middle tier contains the tip and ring terminals for lines numbered 100 to 199. The top tier contains the sleeve terminals for all 200 lines (00 to199). Each tier has 10 levels of terminals. On each level, there is an upper set of 10 terminals and a lower set of 10 terminals separated by an insulator. So on the bottom and middle tiers, each level has the tip and ring terminals for 10 lines, with the ring terminals appearing on the upper side of the level and the tip terminals appearing on the lower side of the level. On the top bank tier, each level has the sleeve terminals for 20 lines, with the sleeve terminals for 10 lines in the 100 to 199 range appearing on the upper side of the levels and the sleeve terminals for 10 lines in the 00 to 99 range appearing on the lower side of the levels. To handle the connectivity through the line finder switch to the first selector, there is a ring wiper and a tip wiper for the bottom bank tier, a ring wiper and a tip wiper for the middle bank tier and for the top bank tier there is a sleeve wiper for the upper side sleeve terminals and a sleeve wiper for the lower side sleeve terminals.
Each selector bank handles the tip, ring and sleeve terminals for 100 trunks. Each selector bank assembly has 2 tiers. The bottom bank tier contains the tip and ring terminals for all 100 trunks numbered 00 to 99. The top bank tier contains the sleeve terminals for all 100 trunks. Each tier has 10 levels of terminals. On the bottom bank tier, on each level there is an upper set of 10 terminals and a lower set of 10 terminals separated by an insulator. So on the bottom bank tier, each level has the tip and ring terminals for 10 trunks, with the ring terminals appearing on the upper side of the level and the tip terminals appearing on the lower side of the level. On the top bank tier, each level has the sleeve terminals for 10 trunks. Since only 100 sleeve terminals are required, there is no need for an upper and lower side separated by an insulator (although many selector banks assemblies are equipped this way in order to accommodate a fourth control terminal used for special applications). The selector has a ring wiper and a tip wiper for the bottom bank tier two sleeve wipers for the upper bank tier which are just bridged together electrically since there is only one sleeve wire. The tip, ring and sleeve wires from the line finder pass through the first selector, through the wiper cord and wipers and connect to the terminals of the selected trunk. This 3-wire connecting path is repeated through each selector rank and finally to the connector switch. If you need more detail, be sure to look at my very long videos on this subject. I have a detailed video for each of the three switch types, linefinders, selectors and connectors. Just search my channel name, Hicken65 on You tube. Thanks for watching.
@@Hicken65 Thanks, Lenny. I had a misconception about where the TRS terminals are actually located on the bank assemblies. Your explanation cleared that up for me. I do plan on watching your longer videos about the switch types soon. I worked on #5 crossbar back in the day but never did get to work on SXS, so this is kind of new for me but very interesting.
@@birdman4967 Aah, it's always nice to hear from former CO techs. I found XB to be much more challenging to troubleshoot than SXS, but SXS is more interesting to watch.
I have an old Stromberg Carlson dial phone I’d like to fix and get it working. Dial is stiff and returns slow. Advice? Are there schematics I could follow?
I'm not personally familiar with SC phones. However, if you go to the Telephone Collectors International website (just Google that name), and click on TCI Library. A search box appears in the upper right side of the screen. Enter Stromberg and a long list of SC data items will appear. These include all the wiring diagrams for most of the SC sets. There is also a 1949 brochure (T-106) in there that explodes the dial, lists all its major parts and has lubrication instructions.I would take the dial apart and clean it with compressed air and electronic contact cleaner, then lubricate. If that doesn't work, you may have to search Internet suppliers of Antique Phone parts.
In an actual CO wouldn’t the selectors be distributed around the building based upon each digit instead of being in the same frame? I’m trying g to work out in my head how the selectors are wired together in an actual scenario so that calls make it over the actual subscriber line running out of the CO to the customer.
Yes they would.
Hicken65 thank you! I’ve been watching these videos and they all have the selectors in the same frame which is misleading. I can now imagine an exchange CO where the 3rd digit might be a floor of the CO each handling the 1000 selectors required to decode the 4th through 6th digit with the last selector handling the last digit.
Now I’m trying to picture how the last selector then is wired with the other 10 final selectors to determine if the line is engaged or not to prevent subsequent calls from patching the calls together improperly.
To see an actual in service sxs central office, search for "Weedsport SXS" on You Tube.This is a 23 minute video of the SXS office serving Weedsport, NY in 1990. For a detailed video of how the final selectror or connector works, see my video "The Connector In The Step-By-Step Telephone Switching System" on my Hicken65 You Tube channel.
while the last nr has been dialed and the call is connected, can the selectors be used for another call in the mean time (it doesn't look like) ?
The seven switches (1 line finder, 5 selectors and 1 connector) used on this call would remain tied up and dedicated to this call for its entire duration. This is necessary since the physical voice transmission path from the calling to called telephones passes through all of these switches. A large central office has over 20,000 of these switches, sufficient to handle the expected number of calls in the busiest hour of telephone traffic.
@@Hicken65 I already expected this to be the case. Thanks for confirming this !
@@Hicken65 I remember the every so often bad quality phone call when I was a kid in the 80s. It helped to hang up and call again. Probably worn out contacts on the selectors eh
@@maicod You're welcome.
@@maicod Well, that's one of many possibilities.
Hey. I got one more request. I am making a pation project for my ELA course. Would you mind sending me the video you use in your introduction. I'll watermark your name into the video with my editor, it would just be important to me. Thanks.
What would the switches do if you talk that phone off the hook. And don't dial out and just leave the. Phone off the hook for a long time?
Well, this became problematic, because a customer was needlessly tying up a line finder and first selector. Timing circuits were introduced so that after a fixed interval, the first selector and line finder were forcibly released and the line prevented from reinitiating a dial tone request without hanging up first.
@@Hicken65 Just wondering what switch sounds the off hook warning tone.
When Receiver Off Hook (ROH) tone was used, it was generated by an ROH tone generator that fed through an ROH tone connecting relay circuit and then through to the tip and ring leads of the first selector, back through the line finder and out to the off-hook telephone set.
How hard is it to set up a very small version of a step by step system that would allow calls from any phone to any other in the system? Also what parts would I need? The system would be about 50 lines.
EDIT: I would want at least 3 calls to be able to go at once.
Well, you'd need 50 line circuits, one for each line. For one simultaneous call through the system, you'd need one line finder, one first selector and one connector. Add a set of these three switches to equal the number of simultaneous calls you want. So if you want 10 simultaneous calls, you need 10 line finders, 10 first selectors and 10 connectors. You need one line finder bank for each line finder. You need one selector bank for each first selector. You need one connector bank for each connector. You need a 48 Volt dc power supply, a ringing generator, a dial tone generator and an interrupter for the ringing and for busy tone. You need mounting framework for all the equipment, a jack spring assembly for each switch to plug into and terminal strips for the bank wiring. For a system with more than one simultaneous call, you would have to dedicate sets of line circuits to each line finder. For example, if you had 10 line finders, you would assign 5 lines to each line finder. Only one of the 5 lines could be in use on an originating call at any given time. To get around this and give all 50 lines access to all 10 line finders, you would have to add a Group And Alarm Relay Circuit to the system.
@@Hicken65 Since that sounds like it would need a lot of equipment, is there a way that I can set up one of those systems, but without having as many lines and line finders? Like having 1 call at a time and potentially less lines, It really doesn't have to be very complex because I am doing it as a hobby however I do want it to be able to be used as an actual system.
@@KJ7BZC You need one line circuit for each line. For one simultaneous call through the system, you'd need one line finder, one first selector and one connector. You need one line finder bank, one selector bank and one connector bank. You need a 48 Volt dc power supply, a ringing generator, a dial tone generator and an interrupter for the ringing and for busy tone. You need mounting framework for all the equipment, a jack spring assembly for each switch to plug into and terminal strips for the bank wiring. You would be able to originate a call from any telephone set, dial through to any other telephone set and have it ring, get answered and have a conversation.Step offices used repeaters to refresh the dial pulses being sent to distant central offices. You won't need any of those.
@@Hicken65 Thanks, any ideas where I can obtain the switches and equipment, or does it just show up randomly?
@@KJ7BZC Well, you could join the Telephone Collectors International organization. They are online, so you can just Google Telephone Collectors International. They have a forum. You can explain what you're trying to do and ask if anyone has parts for sale.,
So in a town with say 1000 subscribers, how many of each unit would be in the exchange?
Well a rough estimate would be 80 linefinders, 80 1st selectors, 70 5th selectors, 80 connectors. There typically wouldn't be any 2nd, 3rd or 4th selectors. This is based on 5 groups of 16 line finders and 10 groups of 8 connectors. Digit absorbing 1st selectors would trunk off the thousands digit to one rank of 70 5ths, which would complete the connection to the 10 connector groups.This assumes operator, long distance and service codes could all be trunked off the 1sts. There would be an additional rank of service code selectors to handle service codes and long distance, maybe 10 to 20 selectors.l
@@Hicken65 Thanks, amazing system, still not 100% certain of how it all works ;)
@@dave-j-k I have four very long detailed videos on the line finder, the selector and the connector. If you have a few hours to spare, they should satisfy your curiosity on how everything works. Just search on my You Tube channel name, Hicken65.
@@Hicken65 Thanks. Where did customer billing come into the system?
@@dave-j-k I'm assuming you're referring to the billing for long distance calls. Prior to Direct Distance Dialing (DDD) by the subscriber, long distance calls went through a switchboard operator, who filled out a ticket with the call details. These tickets were sent to the telco accounting department for processing. With the advent of DDD, the toll centre in which the long distance access trunk terminated handled the billing details using adjunct equipment called Centralized Automatic Message Accounting (CAMA). The CAMA equipment produced reels of perforated paper tapes which contained all the pertinent call details (calling number, called number, time of call, length of call, etc.). These were then shipped off to accounting. Initially, the CAMA equipment called in a switchboard operator to ask the calling subscriber for their telephone number, which was then keyed into the CAMA equipment. This process was called Operator Number Identification (ONI). Later, adjunct equipment was placed into each central office which automatically identified the calling number and sent it over the long distance trunk to the CAMA equipment. This process was called Automatic Number Identification (ANI).
This is pretty much ladder logic huh?
Well, it was generally known as "up and around".
How did they ever trace a call through these, that would seem to be impossible.
Well, in a large central office (CO)serving 50,000 lines there would be about 23,000 switches, so it might seem to be a daunting task. It really wasn’t all that difficult, but it was time consuming. There was an orderly arrangement to the equipment layout and a CO technician would know the layout just a stocking person knows where items are located in the many aisles and shelves in a supermarket. Each rank (1sts, 2nds, 3rds, 4ths, and 5ths) of selectors were grouped into their own bays of 160 selectors per bay. These bays were numbered, with the 1xx series for the 1st selectors, the 2xx series for the 2nd selectors, and so on. The trunking patterns between selector ranks were identified on designation cards hung on the bays. The connectors were typically arranged into groups of 10, each group serving a particular set of 100 telephone numbers. In this video, for example, the connector group serving the BEechwood4-5789 telephone number would serve the BE4-5700 to 5799 numbers and would be designated as the
BE4-57XX connector group. Again, the CO technician would be able to quickly find the location of any given connector group in the CO. If the police asked for a trace to see who was calling BE4-5789, the CO technician would quickly locate the connector group and scan the 10 connectors to find the particular one with its wipers resting on terminal 89. The technician would immediately bridge a ground to the sleeve lead of this terminal, which would keep the switch train held up even if the calling party hung up the phone. The designation card would identify the 5th selector bay and shelves
that had access to that connector. The technician would locate that bay and scan the shelves of 5th selectors to find the one with its wipers on
level 7 and on the particular trunk terminal leading to the connector used on the call. The designation card would identify the bay and shelves of all the 4th selectors that could access this particular 5th selector and the backwards hunt would continue through to the 1st selector. The tag on the 1st selector would identify the particular linefinder group and linefinder to which it was attached. The technician would check which terminal the linefinder wipers were resting on, thereby identifying the caller’s linefinder group and terminal. A check with the records department would identify the name and address of the customer assigned to that line.
It wasn’t difficult to trace calls forward. Tracing them backwards was a bit more involved.
It was difficult and time consuming, and had to be done in person at the central office. Cliff Stoll talks about this in 'the Cuckoo's Egg' where the German police had to track down a cyber- spy on a rotary dial network (true story). Nova did a documentary on it called "The KGB, the computer, and me". It's on TH-cam.
Where can I find parts to build one of these for myself?
Well, that's a daunting task. All of this equipment that remains is in the hands of collectors or telecom museums. Sometimes bits and pieces show up on EBay. You're best bet is to join the Telephone Collectors International (www.telephonecollectors.org) group email list and ask if anyone has equipment for sale.
@@Hicken65Thanks for the reply! I've been looking for Strowger switches and stuff on Ebay and there hasn't been much to see. Thank you for a fascinating video.
Let's see that again in slow motion! :)
Oohkaaay, aaand thaaaanks foooor waaaatchiiing. :)
@@Hicken65 Love your videos!! Would you happen to know where I can look at a network topology / wiring scheme of a large Step-By-Step telephone switching system? I'm having trouble understanding what happens if a switch cannot find an available next step / how the network scales up to prevent this from happening 🤔
@@ICareBecauseYouDo I don't know of any SXS office specification records that survived the trash bin. I can tell you that the telephone traffic on every level of every rank of selectors was measured and forecasted for future years.Traffic engineers would apply the forecasted traffic to capacity tables that defined the relationship between traffic load, quantity of servers and amount of call blockage. Blockage was kept to a low level in the busy hour, ranging from .5% to 2% between selector ranks, with a limit of 4% blockage from end to end. For example, if level 5 of the first selectors was destined for a rank of second selectors, and the desired blockage was 1%, a traffic engineer would determine from the 1% blockage capacity table exactly how many second selectors were required to handle the forecasted load on level 5. This exercise was repeated for all levels of all ranks of selectors. Trunking patterns got complicated when more than 10 trunks were required on any given level. Selectors were divided into sets called subgroups with each subgroup accessing its own set of trunks to the next rank of selectors. A subgroup of trunks ranged in size from 11 to 45 trunks in patterns called "graded multiple", the details of which I cannot begin to describe in a comments reply. When a call was blocked, the selector rotary stepped to the 11th rotary position, which generally caused fast busy tone (120 interruptions per minute) to be returned to the caller.
@@ICareBecauseYouDo If you can source a British book called' Atkinson. Telephony Vol II' from the UK, that goes into great detail about this topic. We called it 'Grading'. All the principles are identical.
@@gharwood1356 Thank you for the tip, sir!
i saw this in a museum
A number of telecom museums around the world have working SXS demonstration units. I hope you were able to try it out. Thanks for watching.
Oh man that dial tone was horrible! This was way before the days of DTMF!
There was quite a variety of dial tones in use prior to the precise dial tone that was standardized for DTMF. Some of them did sound a bit "rough".
Pennsylvania 6-5000! 🎶
Beechwood 4-5789 the Carpenters
The first release of this song was by the Motown group the Marvelettes in 1962. The Carpenters version first appeared on their album "Made in America" in 1981 and they released it as a single in 1982. Other artists include Ian and the Zodiacs (1963), Harpers Bizarre (1976) and Dionne Bromfield (2009).
96
Well thanks for being the 96th commenter.
be cool and send me a comment.