I am so glad that Tom Scott featured you a few years back. You're both entertaining and informative; I really dig your presentation style. Be well! Oh, and DarwinsChihuahua's suggestion of a collab with Technology Connections? Could be cool!
Seriously, I wouldn't have known about their museum without Tom Scott because I live in the UK and have been listening to the Evan Doorbell recordings which are on www.evan-doorbell.com/
Really cool to see people are maintaining this old tech in a museum. This is exactly the kind of stuff that is in danger of going dark as times goes on.
Well...i'm completely lost. Yet.....fascinated. My father worked for AT&T for 30+ years in Connecticut and i actually remember him talking about a lot of these processes. Nice work! 👍👍
What u need is an adjustable line build out box that has 88 mH load coils capacitors and resistors to simulate the line. We used them at Bell Labs to recreate troubles in the switch lab. The load coils were typically used on 24 and gauge pairs. NL or non loaded cable has a horrible frequency response so the load coils were always on loops usually over a few miles. See if u can get a load coil can the kind usually mounted on outside plant poles and cannibalize some 88 mH load coils. Make your own simulator. BTW, that’s why railroad open wire comm lines back in the day used 13 and 19 gauge hard drawn copper or copperweld on open wire glass insulators to minimize losses. They used larger gauge wire that had two properties that didn’t require load coils. Larger gauge (sans load coils) was good for RR telegraph and dispatch phone shout down and ring down lines.
I was thinking along similar lines. For the phones that are "too close" to run those tests - add a long run of wire - I was thinking 24 guage, e.g. spool of such wire pair - and twisted pair on loop, most of what might otherwise be excessive inductance would mostly cancel out - but enough inductance, capacitance, and resistance would remain to make it work well for testing. But yes, better yet, some type of switch box or the like where you could change these simulated "line" conditions - add/drop length, resistance, capacitance, inductance in the loop+phone test set. Maybe even an option to vary some other (e.g. resistive) leakage between the pair (like and old pair with some moisture/water penetration, shorts or intermittent/partial shorts on the line, etc.).
@@ConnectionsMuseum Read this about line build outs. Good tutorial. www.anixter.com/content/dam/Suppliers/Superior%20Essex/White%20Papers/WP-Cable-Loading.pdf
@@ConnectionsMuseum BTW, u gotta watch this AT&T archive video about Common Battery Central Office, the last was retired in 1978. . When I was young (in 1950's) our home fone didn't have a dial. Only big cities had dial phones. Operator, "Number please" ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-7qLU_urEYVE.html
You can make a build-out box. A 26 gauge twisted pair subscriber loop has about 83 nF of capacitance per mile. 26H88 88 mH powdered iron core loading coils are placed every 6000 feet. A loop may be simulated with lumped components with inductors in series and capacitors in parallel between the inductors. What is going on is that the inductance raises the impedance of the loop, reducing attenuation, but causing a cut-off around 3,400 Hz. Too short a loop will have too low impedance and be flagged by automated testing. Here is a good short non technical reference to give some background: www.gordostuff.com/2011/07/loading-coils-more-on-local-loop.html Some types of transmission cables are continuously loaded by wrapping conductors with permalloy tape rather than having lumped inductance at intervals. Also recommended is looking at the problem of line length and the desire to have a universal subscriber set which works regardless of loop length. The BSTJ, April 1951, pp 239-270, has a great article on the development of the model 500 telephone. This is the best place to find it: worldradiohistory.com/Archive-Bell-System-Technical-Journal/50s/Bell-1951b.o.pdf
In our 5XB office we always had 1st trial cards busied out to the recorder, but then we were dealing with 5 DT markers and 10 completing markers carrying live traffic, 17K subscribers. We murdered enough trees as it was! As a trivia note we saved all our cards and sold them in December to a recycling firm and that paid for the office Christmas party. My office was much louder than yours though!
It still amazes me the sophistication of relay logic after working as a switchman then moving into computers and electronic switching. Sarah keep up the good work..
Sarah, at 13:00, are you talking about a REN test? I know there are still few places that use "half-ringers" inside the NID, I ran into them every so often in my time in older neighborhoods doing DSL, and would have to bypass them, then when I worked doing VoIP, we would occasionally find them hidden in what is now customer premise wiring, and was told "it's an old thing they used to use for line testing" but if this is what it is, I've never seen the opposite end of this! Cool!
I love the sound of the equipment in the background throughout the video. We had 1AESS's early in my career, but they're long gone, and even our 4ESS was recently retired. It's a thing of beauty, with amazing wire work on the backplanes, the likes of which will never happen again. Makes me wonder what it would have been like to have hired in 40 or so years earlier....
2:05 Having just watched your video explaining the timers, my first guess as to the cause of different timers expiring would be that while the printer was still busy printing the first card, the work timer expired before being able to print the second card.
After that video he did about the jukebox, I knew that the Connections Museum would be an awesome video topic. The selection accumulator in the jukebox reminds me of how the panel switch commutators work.
I would love an episode to dissect the logic which initiates the punching and dropping of a card; I have no knowledge of the 5XB but would be a fascinating discovery to find (my guess) that no "traditional" CPU and code was used but rather hard wired logic paths that trigger the end-game; the punch solenoids and location on the template.. Awesome channel BTW
Automatic issues reports. This is so awesome. 2022 going into 2023 and a big majority of telecommunication services companies don't even have basic log analysis systems or worse, don't even care about errors in them.
Re: The continuity error checking, that's actually pretty darn awesome. As soon as you started describing it the nuance of capacitance in the loop became obvious. Ya never think about that until you're deep inside the machine, so to speak. It makes me wonder -- given natural capacitance of long electrical lines, does that mean calls inside the museum actually sound "better" than they would in reality, given the very short loops?
When the museum is open again, I really hope you can get to visit and experience it yourself. There's something truly magical about hearing the signals moving around you in three dimensions. The room has a heartbeat from the timing switches. Speaking of, hey Sarah, would you consider letting me record a few minutes of room audio while the place is empty?
@@MichaelWallace-oq3wd Oh yes, I'm on NPSTN myself so I know all too well how VoIP can ruin a wonderful soundscape. Being the only one on a line certainly is the best experience, which is kind of a shame -- you'd think VoIP systems would manage things better, but the packet nature of the internet doesn't really help that. Strictly inside the office though, from a 302 on the panel to a pay phone on the #1 Crossbar, that has to sound like something special when coming through that particular phone + switch combination in such close quarters... barring the actual sounds of the switching equipment, of course.
You know its strange...I don't ever really listen to the call audio at the museum. I guess its different being inside a switchroom, but the audio on the phone itself never sounded as interesting as the machines themselves. That, and its too loud to really hear the call audio clearly anyway. We do have a payphone that is very quiet, and you can go in there and listen to the sounds. The audio quality in the museum has a lot more depth to it, and is a lot more nuanced. Many of Evan's recordings sound very compressed in comparison. I'm not sure if that is due to the recording equipment, or the quality of long telephone loops. Maybe both.
I love these systems. Even though I worked SxS local, intertoll class 4 w/ SxS cama, I still would like to know how crossbar 1 and 5 works. Thank you for this video. It enables me to remember my bell system switching days which really was pleasant in the 70's. I gotta see this if I ever get to Seattle from Joplin Mo.
Such an interesting video! Would be interesting to see what happens if you are able to run the continuity test with a whole spool of cable between the phone and the switch. 😉 keep the great videos coming!
@@ConnectionsMuseum Awesome channel you have, so good to see the preservation of history! I was curious if *maybe* adding a resistor or some type of resistance would work the same as adding additional copper between the switch & the phone in the CO.
I just remembered another way to drop a card in a #5 crossbar office but I don't know what the trouble indication would be on the card. My guess is it may be related to the continuity test. Place a call to another line within the office where the called line is a ground start line and happens to be off hook but not ground started yet. The way I did this was to go where there were 2 coin first payphones (ground start lines) and take one off hook but not deposit any coins, then make a normal call to that payphone from the other one. Just after dialing the last digit on the calling payphone, the called payphone (which would not have battery because it was ground start with no coin deposited yet) I would hear the battery turn on just for a split second and then turn off. On the calling payphone, I would hear the typical sound of a card drop (2 second pause followed by reorder). On payphones, C/O personnel would tend to just disable them at the test board rather than challenge the customer so I never got to find out what kind of card was dropped.
I really enjoy the videos that Sara has made, especially the ones related to troubleshooting and explaining how certain components work. Sara, your knowledge of this equipment is amazing. Is it all from working in the museum, or did you once work for AT&T? I’m a lifelong fan of telco equipment. As a Teen, I had a neighbor who worked for AT&T Long Lines. He was a good mentor and explained a lot to me. He also brought home a lot of “surplus” parts, switches, test lamps, relays headsets etc. Later in life I woofed as a consulting engineer for several local phone companies and for AT&T so I spent a lot of time around switching equipment, but never got into the detail the way you do. I hope to get out to visit the museum soon.
Once humans are allowed to see each other again I've simply got to get myself over to the left coast to come visit and see/hear/smell all this beautiful equipment in person. I see on your site that there's one in Denver, too? I'll have to plan a trip some time and check that one out. (I doubt the Denver one has any internet celebrities like you, though. ◡̈ ) Meanwhile, though, your videos are amazing! Thank you!
Hi Sarah very nice work getting the cards working! I do a lot of DS1 work and we still use some AT&T DS1s. Do you guys have any older DS1 T1 equipment at the Connection Museum? I really enjoy your videos even though I don't understand all of it. I enjoy how the equipment was made back then. I would have love to worked for the phone company back then in the CO. Anyways have a great day ! Don in Chicago
In the 80's dialing 1-800 COCA COLA would drop a card at my local 5XB tried it 5 or so times one weekend before giving up, telco called Monday said 10 digits max after the 1 or the call won't go through.
I'd love to get one of the cards! Wouldn't it be easier/cheaper to mail them in an envelope rather than a shipping tube though? Or would that give too little protection?
Awesome video with very informative explanations. :) I can recall when using a 16 digit keypad on #5 crossbar, dialing A, B, C, or D at the dialtone did not break the dialtone or got me reorder as if I had pressed * or # at the dialtone. I also think that dialing A,B,C, or D on an office code didn't drop a card either. The way I did it was dialing A, B, C, or D as the last digit of a phone number. I don't know how an originating register handles that, is there an A, B, C, or D designation in the 2 out of 5 format? No route (as was explained by the person at the C/O who butted in on my line after dropping cards with 0+ringback number) from your explanation is actually "no translation". Makes sense the way you describe it. I suppose that kind of trouble card is not very common since all possible combinations of dialing are supposed to be accounted for but Dial Administration didn't think of the possibility that anyone would call a test number through 0+ dialing. Another interesting way I could drop a card is dialing the Automatic Number Announcement (ANA) and squeezing in another digit except 1. So, for example, in my area at the time the ANA code was 760 and I would dial 7608 but dial the 8 really fast after the 0 before the marker could handle the call. Like this: 7....6....08 The marker would make it's usual click-clunk sound but the line would lose battery for about 2 seconds. I asked the C/O person why the line lost battery and his reply was "because it's crossing points". I don't know what that means. He also explained that the marker would automatically put in 1111 after the 760 and that's why 7...6....01 would not drop a card. I wonder how the marker is programmed to translate 3 digit codes into 7 digits, or does the O/R do that? I'd love to hear a demonstration of the sound on the line of the card being dropped. From what I remember, after dialing the last digit (or mutilating it), there was a faint click, about a second later another faint tick sound (probably 2nd trial), followed by reorder. I also remember that the line was locked during the time the card was being dropped and I had to wait until reorder before I could hang up again to get another dialtone. When the office was unmanned on weekends, I assumed they turned off the trouble recorder because the whole process sounded like it was sped up and only took about 1 second instead of a full 2 seconds.
Many 5XB offices had ATA in later years. Automatic Trouble Analysis sent the trouble indications to a centralized location where they were read by a PDP/11 running analysis software. When the office was staffed during regular business hours, they probably disabled ATA and captured trouble records locally. We have both the trouble recorder and the ATA/MDT (Maintenance Data Transmitter) setup, but the ATA bits still don't work. A future project. Regarding '1111' being added for some things, it depends on whether or not the office had pretranslators. Without pretranslators, the marker will only get called in after the 7th digit is dialed (or the 8th, if you count a +1 or a +0 at the beginning). So you couldn't just dial 411, you'd have to dial 411-1111. If the office was outfitted with pretranslators, the OR would call in the pretranslator after the third digit. The pretranslator did a lookup on the 3 digits, and told the OR when to call in the marker. The pretranslator could give the OR a variety of instructions for how to handle any three digit code. In many cases, markers could also prepend or postpend an arbitrary set of digits to any number, so the call could be routed correctly. This was useful when dealing with step offices.
@@ConnectionsMuseum , where I worked, Livonia, MI was an early adopter of ATA. It was only run in parallel with the Trouble Recorder long enough to get the bugs out of ATA. Other areas may have operated differently. Regarding pretranslators, an interesting trouble condition happened if there was a 10 digit detailed billed call (with local AMA), and the pretranslator called for a 7 digit marker start. 7 digits was the default in those days, if the pretranslator failed. OR didn't care. CM didn't care. OS didn't care. The transverter cared and dropped the cards. It knew there needed to be 10 digits. I used to tell people that pretranslator issues could cause AMA issues ,and they thought I was crazy. They felt there was no connection between the two frames. Indeed there was no direct connection. The pretranslator was long gone by the time the OS called the transverter, but the damage was already done.
@@bobbymac7835 Huh! Yeah I can see how that would work. If the TV expects 10 digits, and it only gets 7 because the pretranslator defaulted to 7, that would make it cranky! Our PTR is also setup for 7 digits marker start by default. We don't have the transverter wired up yet, but that should happen sometime this year, hopefully. They never wired it at the museum because our trunks are flat rate/1MR, not arranged for AMA. We're doing the modifications to convert them soon.
I see there was no stuck coin or coin return failure on that first card...(S2 10). BTW, keep up the good videos! I enjoy the technical side of pre ess central offices.
It amazes me how the engineers came up with an analog card system for troubleshooting and how well it works. I don't suppose there are any crossbar system still in operation are there?
I assume there are still some running in the world somewhere. But there *is* a #5 crossbar in the museum, a few feet away from where they're working, behind the card puncher.
i think the high traffic punching may be a result of . 1. just as soon as you hang up a call comes through. 2. the so called "ringing off the hook" no sooner than you get the phone on the hook it rings again and the recorder did not have time to reset. in order to validate the test couldnt you put a resistor in series with the phone to emulate a mile of wire?
I have not looked at the circuit, but it probably fails the continuity test on purpose in this scenario as it it cannot determine the difference between a line that is shorted out and a line that is actually just short. Modern ring testing circuits would probably also give a fault code in that scenario as they would assume there is no way a phone is actually just 20ft away, so therefore it must be a problem.
Question: What happens if 2 trouble indications come in at the same time to the trouble recorder? In my own experimentation with this with 2 phone lines (from memory), one line will reach the trouble recorder, the other will skip it and will sound the same as if the trouble recorder was turned off. I don't think there are provisions for prioritizing trouble reports and there is no "queue".
Markers have a timer that will time how long they will sit in the queue and wait for the recorder to become available. It's between 3-5 seconds, usually. If its longer than that, it won't wait. There is no priority system for trouble records but there is a queue. It's just that you don't want to hold up equipment for an unreasonable length of time just to drop a trouble card. So if it waits for long enough, it'll just give up and move on with the next call.
This seems like literal ticket spam for the tech to deal with. Is this accurate to the time period and would the admins just throw the tickets away unless they actually got complaints?
All of these situations would naturally happen, with the exception of the MKR not releasing the OR. Holding a MKR relay operated or non-operated will definitely cause cards to drop, but is not realistic. Bad dials, wet cables switch hook jiggling, etc., would cause the DPOR to register bad 2/5 code and pass that to the MKR. Bad MFIR reed relays or circuitry would do the same thing. A broken MKR cross connection or employee work error opening a new route would cause the no RR error. CON errors were 1TR only in light traffic, and were bypassed as nuisance cards. MKR = Completing Marker. OR = Originating Register. DPOR = Dial Pulse Originating Register. MFIR = Multifrequency Incoming Register. RR = Route Relay. CON = Continuity. 1TR = First Trial. These are recollections from the 1970(s).
@@PositionLight one looks at a bunch of cards. If they are from the same line equipment, then it points toward the customer. If the same OR, same digit, then it points toward the OR. And so on....With originating mutilated digits, sometimes it was not possible to determine why it happened. A certain number of them always happened, especially with rotary dial equipment. They just could not be replicated.
So what if back in 5XB days, you made a circuit that would just randomly flash the line, so it would just waste punch cards at the C.O. and make a bunch of repair tickets. Is there any protection from that? Or would they come and beat you because you used a non telco approved appliance on the phone line.
I mean, look. If you're watching this video, then you are (like me) interested in telephone switching. So clearly, you would (like me) think of a thousand ways to break this machine and/or annoy the people who worked on it. It's natural We do that sort of thing. But out of the hundreds of millions of people who used these systems every day...most of them didn't really care too much about how their phone calls worked, or how they could mess with the machines. The vast majority of people just don't care that much, and even if they do, they're distracted by other things like being late to work, or their crying baby, or going out to a movie with a friend. Most callers in 1960 wouldn't take the time to figure out that there was a thing called a card punch, and that specific actions could make the call sound a little bit different, and when it sounded different, it also punched holes in a card somewhere in a big room across town. Some people figured this out, of course. That's why we're here, having this conversation. But most didn't. And even if they did, the fun of annoying someone would probably wear off a little over time. It's fun for the first hour, but after a few days, it would get pretty dull. To answer your question, yes. A machine made to dial random numbers at random intervals would drop cards and annoy the techs. They would see that all the cards came from the wrong line, and send someone out to your house.
@@ConnectionsMuseum Wow, truly inspiring haha, was it Sarah who wrote this? I don’t think it was æstrid, but I could be wrong. Sometimes I wish I grew up during the time period when the telephone network was interesting. I mean don’t get me wrong, there’s still some interesting things to scan and play around with, but nothing a like 5XB or SxS or even 1AESS. Anyways, thanks for replying, it means a lot :)
Have you ever thot of connecting a voip fxs ata adapter to your phone system in the museum as a incoming trunk and a fxo ata adapter as an outgoing trunk so that people from outside of the museum can see how the old phone systems worked and how you can connect extremely old equipment with modern day equipment
Haha, 11 or more pulses in quick succession, yeah, huh? Because once you get to 10, it's like, "OK, that's a 0." But then wait... suddenly... "What's this one more pulse about?! What the hell number is that on the dial?!"
I discovered these videos just a few days ago. This is how Telephones are supposed to work.. In later centers ... and when telephones became "Digital" ... ALL security between users became a "THING of the PAST"
Great video! A cheaper way to mail the cards would be to mail it in a "large envelope" as postage would only be $1.00 instead of having to pay package rates for a tube.
