I was (lightly) into phreaking in the 80/90's. I'm old. I think you'd be surprised by how much clarity you've brought to the blind hacking my friends and I used to do. Apple, inc. started with the Blue Box. You are laying bare the origins of desktop computing. Much respect...
Sarah, you absolutely nail these videos. Your passion is evident and you have a way to make these very complex pieces of equipment seem almost approachable. I hope one day I can make my way to Washington if only to see your museum.
I appreciate and respect the high quality of information you all provide from this channel. I wanted to understand analog telephony as a career IT person some months ago and have been very happy with the learning, especially from my fellow lgbt siblings. Thank you.
Always great to see things from an American angle. Would have loved to see the relay sets operating when you tested the outgoing trunk. At 8 minutes into the video you pulled a plug from the test socket using the cord. In the UK you would have been reprimanded for this sloppy behaviour. Keep up the good work and behave with your trunks! Mark, Manchester UK.
Thanks :) Here, you *must* pull the plug by the cord, and the cords are woven in double and triple layers-made to be yanked on. The screw that attaches the red plastic sleeve to the plug is hot, and if you pull it while the voltmeter is on and you’re touching ground (earth) you’ll get a shock. When I do reach for the red sleeve on the plug, I try to only use the back part of it, to avoid that screw. Here’s a video of the relays operating :) twitter.com/museumofcomm/status/1551969229741559808
@@ConnectionsMuseum Wow! We would never allow that to happen. Anyway still great to see your "Central Office" in the UK known as "Telephone Exchange" keep up the great work, Mark.
pretty sure I took the wrong bus to get here. or maybe I fell asleep and just ended up in the part of town I've never seen before. ;) I have so so many questions!
My dad was a Michigan Bell lineman from 1965-1996. I grew up around this stuff but was never interested in it until the last few years. Excellent videos!
Excellent video. We had a SxS Cama system that had a test frame that was somewhat similar at southwestern bell in Eldon Missouri, I was a switchman there who worked both Cama and toll circuits for the lake area there and it was fantastic work. This really brings back memories. Would you do a video on revertive pulsing in relation to panel switch etc?
Regarding "barging" into the calls, when the police/etc wanted to listen in on a call, is this the frame that would occur on? or would it be closer to the subscriber?
Weird question, Sarah. And pardon me if you have addressed this in another video I haven't seen. When I was a kid, my dad worked at a few different COs. They had a very distinct and cool scent to them. I always loved to visit and hang around. His clothes would even smell like the CO when he got home. Does your CO have that scent? Thanks for the videos!!!
I only have a boring and very small ip PBX at work. My test line is actualy a virtual extension set to put the caller on hold forever. I know the PBX and phone work if i hear the on hold music.
There are circuits called MF Receivers (MFRs) that are basically a series of band-pass filters that only allow certain audio frequencies to pass through. The tones are detected by tubes after they pass through the filters. When a tube detects a tone, it conducts, and allows current through to operate relays that correspond to the detected tones. A special gating circuit locks out the detectors until it hears the KP tone. This prevents talk-off and false registrations from spurious tones that may appear on the line. You can see these circuits in our video about MF signaling.
Panel had the 'IART' Incoming Automatic Routine Test frame. It would test outgoing trunks from an office during the night(lite traffic). Panel also had the OGT OutGoing Trunk test frame. Things became more interesting with the advent of MF Multi-Frequency...
Is it possible to use a trunk circuit between two different central offices to "extend" a subscriber line from one office to another? For example, a rural subscriber wants a line with a dial tone and phone number from a nearby city.
Kawaii and and I informative, I remember when I was very little I would "help" mom at her cleaning job and the guys would show me and let me help them with the phone system at Bell Atlantic here in WV when she would clean the local exchange buildings, it's what got me into networking and ultimately IT.
Interesting I had a surplus WE "wire chiefs test set" Beautiful thing in a wood cabinet but never knew how to use it only knew that it was used for testing subscriber and trunk lines. As you mentioned the voltmeter function of your OGTT was my test set a similar simplified form?
Almost certainly similar. Testing of conductors was pretty standardized. If a switch man suspected trouble with the wire conductors themselves, he would refer it out to a wire chief who used their test desk (or set) to investigate further.
The BSP refers to something called "soak current" at the end of the test (where the tick tock sound is). What is soak current and how does this apply to the test?
The reasons for this are a little complex. Soak current is defined as the amount of current that fully "saturates" the relay windings. It is designed to test that a relay will release within a prescribed period of time after the windings have had a chance to fully energize and the magnetic structure of the relay is fully engaged. This is in contrast to "operate" current, which is merely the amount of current that causes the armature to move into the operated position. Operate current is less than soak current. The other reason is that the test line that we're using here must "synchronize" with automatic trunk test frames (not discussed in this video). These are test frames that progress through each trunk, call the test line, and monitor the results of each test before advancing to the next trunk. In order for this to work, the test line and test frame must be in sync, and they rely on specific signals to do that. One of those signals is the application of "soak" current at the correct time.
It’s technically known as a 184 plug but nobody calls it that. Ring is strapped to sleeve, so any ground on the ring conductor of the jack will be routed thru the plug back to the sleeve conductor of the jack, which marks the trunk as busy. www.telecomarchive.com/cc/pdf/plugs/plugs,%20184%20185%20186,%201,%201979-04-30.pdf
@@ConnectionsMuseum So basically it's just a switch that's normally open. Plugging one into a jack creates continuity between the two leads. The equipment isn't looking for anything special, it's just looking to see that a potential (or, ground, lack thereof) applied on one wire doesn't return on another. That makes me wonder, when a trunk is *actually* busy, I assume something similar happens, just within the switching machinery itself? I believe from one of your videos about the panel switch you mentioned that the equipment tests the sleeve lead when trunk-hunting for ground. So when a trunk is in use by a call, one of the frames that's participating in the call is grounding the sleeve lead? (I'm assuming that leaves T and R for, lack of a better term, "incoming" and "outgoing", one lead for the calling party to talk on, one lead for the called party to talk on)
@@teknikal_domain Yep. Ground on sleeve indicates "busy". Doesn't matter how it gets there. Either the machine puts it there to mark a path as busy, or a human puts it there by inserting a plug and closing a ground from the ring of the jack to the sleeve of the jack via the shorted plug. That same sleeve lead exits the jack and is carried to the trunk appearance on the crossbar network. If the marker tests that point on the network, it will see ground there, and will know that it can't try to make a service connection through that trunk.
@@ConnectionsMuseum I have this weird fascination with communications protocols and how machines exchange information. It's honestly baffling the amount of things that the telephone network did with "ground," "battery," and "no continuity," and "polarity reversal" as the main communication choices. I also just realized the XB markers must have some brain-melting number of wires, if they have to be able to test any potential crosspoint on the switching fabric. I imagine they're not fun machines to troubleshoot if it's more than just a bad relay.
One of my favorite things about this channel is Sarah's little interpretive dances.
I was (lightly) into phreaking in the 80/90's. I'm old. I think you'd be surprised by how much clarity you've brought to the blind hacking my friends and I used to do. Apple, inc. started with the Blue Box. You are laying bare the origins of desktop computing. Much respect...
Sarah, you absolutely nail these videos. Your passion is evident and you have a way to make these very complex pieces of equipment seem almost approachable.
I hope one day I can make my way to Washington if only to see your museum.
I'm so pleased, and thankful that you continue to share your awesome knowledge in a manner that's easy to understand. Thanks to the whole staff.
Thanks for the walk-through! No worries on simpler videos… I will watch them all!
I appreciate and respect the high quality of information you all provide from this channel. I wanted to understand analog telephony as a career IT person some months ago and have been very happy with the learning, especially from my fellow lgbt siblings. Thank you.
Always great to see things from an American angle. Would have loved to see the relay sets operating when you tested the outgoing trunk. At 8 minutes into the video you pulled a plug from the test socket using the cord. In the UK you would have been reprimanded for this sloppy behaviour. Keep up the good work and behave with your trunks! Mark, Manchester UK.
Thanks :) Here, you *must* pull the plug by the cord, and the cords are woven in double and triple layers-made to be yanked on. The screw that attaches the red plastic sleeve to the plug is hot, and if you pull it while the voltmeter is on and you’re touching ground (earth) you’ll get a shock. When I do reach for the red sleeve on the plug, I try to only use the back part of it, to avoid that screw.
Here’s a video of the relays operating :)
twitter.com/museumofcomm/status/1551969229741559808
@@ConnectionsMuseum Wow! We would never allow that to happen. Anyway still great to see your "Central Office" in the UK known as "Telephone Exchange" keep up the great work, Mark.
The sleeve screws were "live" on GPO sleeves in 1980 in my Strowger in Manchester East and Ardwick.
pretty sure I took the wrong bus to get here. or maybe I fell asleep and just ended up in the part of town I've never seen before. ;) I have so so many questions!
I'm an old phone guy and have worked on this equipment.
My dad was a Michigan Bell lineman from 1965-1996. I grew up around this stuff but was never interested in it until the last few years. Excellent videos!
These are always fascinating!! Thanks for the detailed walkthrough :)
Excellent video. We had a SxS Cama system that had a test frame that was somewhat similar at southwestern bell in Eldon Missouri, I was a switchman there who worked both Cama and toll circuits for the lake area there and it was fantastic work. This really brings back memories. Would you do a video on revertive pulsing in relation to panel switch etc?
I love the sound the panel makes.
Regarding "barging" into the calls, when the police/etc wanted to listen in on a call, is this the frame that would occur on? or would it be closer to the subscriber?
Thanks Sarah
“Oh, and here’s how to do phone phreaking from inside the CO. Except don’t do that. But you could if you want to.”
Weird question, Sarah. And pardon me if you have addressed this in another video I haven't seen. When I was a kid, my dad worked at a few different COs. They had a very distinct and cool scent to them. I always loved to visit and hang around. His clothes would even smell like the CO when he got home. Does your CO have that scent? Thanks for the videos!!!
It sure does. Central offices all have the same unique smell :)
I only have a boring and very small ip PBX at work. My test line is actualy a virtual extension set to put the caller on hold forever. I know the PBX and phone work if i hear the on hold music.
One question I have is my perception is the 1XB is a relay machine, but how does it process/translate MF into work?
There are circuits called MF Receivers (MFRs) that are basically a series of band-pass filters that only allow certain audio frequencies to pass through. The tones are detected by tubes after they pass through the filters. When a tube detects a tone, it conducts, and allows current through to operate relays that correspond to the detected tones.
A special gating circuit locks out the detectors until it hears the KP tone. This prevents talk-off and false registrations from spurious tones that may appear on the line. You can see these circuits in our video about MF signaling.
Panel had the 'IART' Incoming Automatic Routine Test frame. It would test outgoing trunks from an office during the night(lite traffic). Panel also had the OGT OutGoing Trunk test frame. Things became more interesting with the advent of MF Multi-Frequency...
Long time no see, keep up the great work
Thanks for another great video.
Why did I suddenly get 'All Trunks Busy' tone one night at 12:00 AM? Only intermittent dial tone since.
Sarah you got this wow thats alot of CONTROLS and such😯🤯
Is it possible to use a trunk circuit between two different central offices to "extend" a subscriber line from one office to another? For example, a rural subscriber wants a line with a dial tone and phone number from a nearby city.
Yep, it’s called Foreign Exchange service, and it was offered by many telcos.
Kawaii and and I informative, I remember when I was very little I would "help" mom at her cleaning job and the guys would show me and let me help them with the phone system at Bell Atlantic here in WV when she would clean the local exchange buildings, it's what got me into networking and ultimately IT.
Interesting I had a surplus WE "wire chiefs test set" Beautiful thing in a wood cabinet but never knew how to use it only knew that it was used for testing subscriber and trunk lines. As you mentioned the voltmeter function of your OGTT was my test set a similar simplified form?
Almost certainly similar. Testing of conductors was pretty standardized. If a switch man suspected trouble with the wire conductors themselves, he would refer it out to a wire chief who used their test desk (or set) to investigate further.
Subbed. Marc sent me.
Very cool i stumbled on this channel by accident but i love it
Keep em coming!
Hello, I have a qustion...
Why telepony system using the circuit by 600 ohm? Do you have any video of transformer history about 600 or 900 ohm??
Did I miss tonight's video Sarah?
The BSP refers to something called "soak current" at the end of the test (where the tick tock sound is). What is soak current and how does this apply to the test?
The reasons for this are a little complex. Soak current is defined as the amount of current that fully "saturates" the relay windings. It is designed to test that a relay will release within a prescribed period of time after the windings have had a chance to fully energize and the magnetic structure of the relay is fully engaged. This is in contrast to "operate" current, which is merely the amount of current that causes the armature to move into the operated position. Operate current is less than soak current.
The other reason is that the test line that we're using here must "synchronize" with automatic trunk test frames (not discussed in this video). These are test frames that progress through each trunk, call the test line, and monitor the results of each test before advancing to the next trunk. In order for this to work, the test line and test frame must be in sync, and they rely on specific signals to do that. One of those signals is the application of "soak" current at the correct time.
What's inside a busy plug? What's inside a deny plug?
It’s technically known as a 184 plug but nobody calls it that. Ring is strapped to sleeve, so any ground on the ring conductor of the jack will be routed thru the plug back to the sleeve conductor of the jack, which marks the trunk as busy.
www.telecomarchive.com/cc/pdf/plugs/plugs,%20184%20185%20186,%201,%201979-04-30.pdf
@@ConnectionsMuseum So basically it's just a switch that's normally open. Plugging one into a jack creates continuity between the two leads. The equipment isn't looking for anything special, it's just looking to see that a potential (or, ground, lack thereof) applied on one wire doesn't return on another.
That makes me wonder, when a trunk is *actually* busy, I assume something similar happens, just within the switching machinery itself? I believe from one of your videos about the panel switch you mentioned that the equipment tests the sleeve lead when trunk-hunting for ground. So when a trunk is in use by a call, one of the frames that's participating in the call is grounding the sleeve lead? (I'm assuming that leaves T and R for, lack of a better term, "incoming" and "outgoing", one lead for the calling party to talk on, one lead for the called party to talk on)
@@teknikal_domain Yep. Ground on sleeve indicates "busy". Doesn't matter how it gets there. Either the machine puts it there to mark a path as busy, or a human puts it there by inserting a plug and closing a ground from the ring of the jack to the sleeve of the jack via the shorted plug.
That same sleeve lead exits the jack and is carried to the trunk appearance on the crossbar network. If the marker tests that point on the network, it will see ground there, and will know that it can't try to make a service connection through that trunk.
@@ConnectionsMuseum I have this weird fascination with communications protocols and how machines exchange information. It's honestly baffling the amount of things that the telephone network did with "ground," "battery," and "no continuity," and "polarity reversal" as the main communication choices.
I also just realized the XB markers must have some brain-melting number of wires, if they have to be able to test any potential crosspoint on the switching fabric. I imagine they're not fun machines to troubleshoot if it's more than just a bad relay.