Phone Land Lines

[zbang]

Doing some back of the envelope math (check this, I may have dropped a decimal)
48v / 30ma = 1600 ohms (total loop resistance)
The "average" telephone set is 200 ohm, so the wire must be less than 1400 ohm for the loop or 700 ohm to figure the distance and keep the current.
19g copper is 8.2 ohm/1k ft so (700 / 8.2) gives about 85k ft or about 16 miles for the loop.
24g copper is more like 26.2 ohm/1k and that sucks the length in by call it a third, so 5-ish miles.
(Is it going to perform well? really depends on the set and how much current that really needs)

Lots of older cable plant was 19g, or larger if open-wire on insulators. OTOH, telco's really don't like loops longer than maybe 30-35k ft and would rather install remotes (like the "SLC 96") if there are clusters of subscribers.

(I used to live and breath this stuff, but that was over 30 years ago.)

 

[electrofelon]

Yeah your 5 mile figure is about what I saw as typical....I don't think larger gauge is that common?? I think/assume stretching that range out with higher voltage and/or thicker cable is not real popular approach for long runs in rural areas because they would, as you say, prefer a pair gain device to reduce costs and infrastructure. But that device is going to need power...

 

[GoldDigger]

We had that when I was very young. I don't really know details as I was maybe 6 or 7 years old when we moved from that place. I do remember the being able to listen in on other conversations thing. Also remember my mother talking to friends and apparently you only could talk for so long before the system gave you some warning and eventually disconnected the call so that it would free up the line again for others? May even been an operator that told them to end the call? I remember mom always saying "I'll call you back" then hung up and pretty much immediately called back and continued their gossip session.

What you were probably doing was either

1. Talking over the dial tone, which would get relatively weaker as more joined in, and would time out just as it would if you left your phone off-hook on a conventional line. The 48V battery would be temporarily disconnected, preventing the microphone and speaker from working.
2. The first person on the circuit dialing at least one digit to cause the dial tone to be removed. It had to be the first person with pulse dialing, since otherwise the two or more phones in parallel would prevent the DC from being interrupted. Eventually the pulse register would time out and drop dial tone, as above. If touch-tone dialing was supported any phone could break dial tone at any time before it timed out.

 

[GoldDigger]

Yeah your 5 mile figure is about what I saw as typical....I don't think larger gauge is that common?? I think/assume stretching that range out with higher voltage and/or thicker cable is not real popular approach for long runs in rural areas because they would, as you say, prefer a pair gain device to reduce costs and infrastructure. But that device is going to need power...

Which could often be powered by the 48 volt line voltage.

 

[garbo]

In CA AT&T has applied to the CAPUC to be allowed to do away with land lines (twisted pair/ copper) for voice service. It is getting strong opposition from people without smart phones (older people?) and people in the rural areas prone to power outages or cell tower failures. Before I got fiber installed to my house I was used to measuring 48VDC on the copper wires to my land phone. Now with fiber the land line is plugged into the fiber modem. If I unplug the LL to the modem, I loose the dial tone on the land phone. So in a power outage, I loose power to the modem and also the land phone. Has anyone else discovered this and maybe has a simple solution? So it appears that once the fiber was installed, the 48VDC was shut off (by AT&T) on the LL and now it is generated (fake signal) by the modem when the land phone is used. Has anyone else discovered this?
I could always hook up an inverter to power the modem in an outage as a worst case scenario.
This was also posted in Campfire Chat before I read Rogers comment.

Had a hard wired copper Ma Bell line in my house for over thirty years and seldom lost service. Yesterday we lost our Comcast TV, WIFI & phone for over 5 hours.Two months ago they sent out a message saying there would be working on upgrading cable lines and we lost every thing for four hours. I seldom use the so called Comcast land line being my cell phone works great.

 

[zbang]

Basic problem there is that the POTS infrastructure was designed by Ma Bell for virtually zero downtime, something like 99.9999% ("five 9's")availability. The cable TV and following fiber infrastructure dropped two or three 9's off that because "Who cares if they loose the TV for a few hours", it also wasn't regulated as a Common Carrier (that's a different hairball).

AFAIK 19g was being installed into the 1950s at least (often in lead-sheathed cables), then 22g and 24g took over.

Re using loop current to power a "repeater" device-
I don't think that was ever done since a current of more than maybe 20ma was considered "off hook" (ready for dialing/talking), and as noted there is considerable resistance/voltage drop. 'course, go back far enough and telephone sets had their own "local" batteries but I think those went out in most areas by the 1910's (?).

BTW the "PairGain(tm)" device was specifically for extending T-1 lines, AFAIK the only method available before the 80s for a single loop/line was a higher loop voltage; there may be another method I'm not aware of.

The folks at Bell Labs who designed a lot of this stuff were really ingenious and quite smart.

 

[GoldDigger]

You have to be careful here. The battery backup often kept only phone service working to provide access to emergency services. That was only POTS. Backup for Ethernet and TV was not provided.

This is where your confusion over the term VOIP comes in. As I stated above, most people do not have VOIP phones.

This is why I strongly recommend your own UPS if you want to use your computers and other internet connected devices during an outage. Cable companies give you nothing that they don't have to.

-Hal

"Get a Storm-Ready device with a Battery Backup and keep your home online through network and power outages with cellular data at no additional charge."
So it does not power the cable connection at all (no TV), but does not need it for either phone or broadband. It gives you service even if the outside cable plant is compromised.

 

[ggunn]

Basic problem there is that the POTS infrastructure was designed by Ma Bell for virtually zero downtime, something like 99.9999% ("five 9's")availability).

I apologize for the nit picking, but 99.9999% is six nines.

It always comes down to the question of how many nines you would like to buy.

 

[LarryFine]

I apologize for the nit picking, but 99.9999% is six nines.

That's funny. I was going to point out that the .9999 was only four nines.

 

[zbang]

Yep, six 9's (99.9999); one of my fingers is out of commission right now and my typing is terrible. five 9s comes out to something like 6 minutes of outage a year, six 9's is more like 30 seconds.

(Four nines is 99.99. I don't think the cable companies even hit three.)

 

[tortuga]

There is a old building I work on that now has some form of commercial Coax as the main internet and VOIP phones (no fiber yet) and a old 'T carrier' type modem connected to what appears to be a standard incoming phone line.
the T modem needs 4 or more pairs (found out the hard way when I put it back). The management originally got rid of it and switched to all VOIP phones but apparently there is a requirement to have a landline in the elevator that works during outages, and since the VOIP phone system failed that test the 'landline' came back, same thing with the fire alarm panel. I am not sure what the PUC regulations are but I think those old T[1-3] lines do have a guaranteed level of up time with alot of .9's.

 

[gadfly56]

We had that when I was very young. I don't really know details as I was maybe 6 or 7 years old when we moved from that place. I do remember the being able to listen in on other conversations thing. Also remember my mother talking to friends and apparently you only could talk for so long before the system gave you some warning and eventually disconnected the call so that it would free up the line again for others? May even been an operator that told them to end the call? I remember mom always saying "I'll call you back" then hung up and pretty much immediately called back and continued their gossip session.

Back in the 60's I'd heard stories of people not being able to call the local first aid squad because someone wouldn't get off the party line.

 

[electrofelon]

Phone stuff is really interesting to me for several reasons.

1. Despite it being old technology now, it is kinda cool all the stuff they figured out with multiplexing, extending distances, etc.

2 I'm also really fascinated how the phone companies seemed to completely drop the ball on broadband. Sure Verizon does FiOS in places, but very select places geographically. There was/is DSL and ISDN , but it's like they hardly ever put any effort into that and it was only in select places. They have the poles and the easements and all that, but they hardly did anything. Just strange.

3. I'm super curious why many phone companies haven't gone bankrupt. Their customer base has got to be a fraction of what it was.

4 finally, why is that old obsolete phone stuff almost never gets removed

 

[Fred B]

2 I'm also really fascinated how the phone companies seemed to completely drop the ball on broadband. Sure Verizon does FiOS in places, but very select places geographically. There was/is DSL and ISDN , but it's like they hardly ever put any effort into that and it was only in select places. They have the poles and the easements and all that, but they hardly did anything. Just strange.

My contact with them, as I wanted it, was that they can't "legally" come into an area that has cable broad band already, such as Spectrum Cable. Seems to me someone had been putting money into someones pockets, to make that restriction. Or it's simply collusion between these companies. Artificially restricting competition and keeping prices excessively high. Paying for 100Mps and lucky to get high teens, low 20's. and their reply when complaining to them is that "they show" everything is working fine, but no one ever comes to actually test site. They don't have to, there is no compitition for a viable option. Dial up? that's a laugh. Satalite? Even worse, and more expensive an lower speed with less reliability.

Second thing that comes up is a statement that there is not enough potential demand to warrant the cost to build the system. And the "free" money given out by the goverment to expand high speed internet can't be used in areas that have cable broadband. So, no incentive to build.

 

[kwired]

What you were probably doing was either

1. Talking over the dial tone, which would get relatively weaker as more joined in, and would time out just as it would if you left your phone off-hook on a conventional line. The 48V battery would be temporarily disconnected, preventing the microphone and speaker from working.
2. The first person on the circuit dialing at least one digit to cause the dial tone to be removed. It had to be the first person with pulse dialing, since otherwise the two or more phones in parallel would prevent the DC from being interrupted. Eventually the pulse register would time out and drop dial tone, as above. If touch-tone dialing was supported any phone could break dial tone at any time before it timed out.

But that wouldn't have let my mother say "I'll call you back" if the connection was dropped without warning, something had to prompt her to do that. This likely about 1973 to 1975, we moved from that place in 75, I was a second grader when we moved so I'd say I was 5-7 years old during the times I did observe (and actually remember this) and I do remember her doing that a lot when she was gabbing on the phone. I also do remember picking up the receiver and hearing an already ongoing conversation.

 

[grich]

But that wouldn't have let my mother say "I'll call you back" if the connection was dropped without warning, something had to prompt her to do that. This likely about 1973 to 1975, we moved from that place in 75, I was a second grader when we moved so I'd say I was 5-7 years old during the times I did observe (and actually remember this) and I do remember her doing that a lot when she was gabbing on the phone. I also do remember picking up the receiver and hearing an already ongoing conversation.

In the small Missouri town we lived in back in the 80's, the telco switch was a step-by-step with a limited number of line finders to connect calls with. There was a 5-minute time limit on local calls...you would get a warning beep one minute before the call would be dropped. There were also a few 2-party circuits in town, all eliminated when the new Northern Telecom DMS-10 switch was installed almost 40 years ago. Touch-tone dialing...woo-hoo! The local co-op telco decommissioned that switch a year or two ago, along with all their copper wire plant, replaced with fiber.

 

[ggunn]

How I nearly got kicked out of college:

Back when dinosaurs walked the earth, when I was in college the first time, the university I was attending (LSU) had its own telephone exchange and every dorm room had a phone. It was set up so that to call around within the system you only had to dial the last four digits of the number. A quirk in the system made it so that if two phones on the system called a third and the third phone was off the hook, callers on the first two phones could talk to each other over the busy signal. Being bored college students during finals, we played around with this and called it the "Spook Line".

Another thing - the antiquated phone system was easily overloaded, to the point that if enough phones were on the Spook Line with the first three of the four digits the same, if you tried to call anyone with those three leading numbers, you were on it before you could dial a fourth number, and so forth. The night it went viral, if you picked up your phone, you were on it.

Of course, with hundreds of people on the Spook Line at the same time it was like being in a crowded room, so our dorm was full of guys yelling at the top of their lungs trying to be heard. This went on until late at night; I had gotten bored with it and I just wanted to sleep, so I had an idea. I had a turntable and a small guitar amp in my room. I plugged the turntable into the amp and got some wire and alligator clips, which I used to connect the amp's speaker output to the wires in the microphone part of the handset. I put a stack of albums on the turntable and started them playing. The signal from my phone was so much stronger than anyone else's that no one could hear anything else, so guys around me quit yelling into their phones. and I could finally get some sleep, or so I thought.

Cool, right? The only thing wrong was that it made it very easy for the head of Campus Security and the Dean of Men to trace the signal back to me, so when they used their passkey to open my door they caught me red handed sitting on the floor twiddling the knobs on my guitar amp. The Dean of Men was not amused, but the Head of Campus Security was having trouble keeping a straight face.

At first the Dean said that I was going to be expelled from the University, but I did some fast talking in my meeting with him the next day. One point I raised was that I had actually solved the problem, since when no one could hear anything but the music I was playing, everyone hung up their phones and what was essentially a primitive Denial of Service attack on the phone system was resolved. After giving me my Stern Talking To, he told me that he would grudgingly allow me to register for the next semester on Disciplinary Probation, which I did, and I never again connected a guitar amplifier to the University telephone system.

I did some other stuff there, though, but those are other stories

 

[kwired]

How I nearly got kicked out of college:

Back when dinosaurs walked the earth, when I was in college the first time, the university I was attending (LSU) had its own telephone exchange and every dorm room had a phone. It was set up so that to call around within the system you only had to dial the last four digits of the number. A quirk in the system made it so that if two phones on the system called a third and the third phone was off the hook, callers on the first two phones could talk to each other over the busy signal. Being bored college students during finals, we played around with this and called it the "Spook Line".

Another thing - the antiquated phone system was easily overloaded, to the point that if enough phones were on the Spook Line with the first three of the four digits the same, if you tried to call anyone with those three leading numbers, you were on it before you could dial a fourth number, and so forth. The night it went viral, if you picked up your phone, you were on it.

Of course, with hundreds of people on the Spook Line at the same time it was like being in a crowded room, so our dorm was full of guys yelling at the top of their lungs trying to be heard. This went on until late at night; I had gotten bored with it and I just wanted to sleep, so I had an idea. I had a turntable and a small guitar amp in my room. I plugged the turntable into the amp and got some wire and alligator clips, which I used to connect the amp's speaker output to the wires in the microphone part of the handset. I put a stack of albums on the turntable and started them playing. The signal from my phone was so much stronger than anyone else's that no one could hear anything else, so guys around me quit yelling into their phones. and I could finally get some sleep, or so I thought.

Cool, right? The only thing wrong was that it made it very easy for the head of Campus Security and the Dean of Men to trace the signal back to me, so when they used their passkey to open my door they caught me red handed sitting on the floor twiddling the knobs on my guitar amp. The Dean of Men was not amused, but the Head of Campus Security was having trouble keeping a straight face.

At first the Dean said that I was going to be expelled from the University, but I did some fast talking in my meeting with him the next day. One point I raised was that I had actually solved the problem, since when no one could hear anything but the music I was playing, everyone hung up their phones and what was essentially a primitive Denial of Service attack on the phone system was resolved. After giving me my Stern Talking To, he told me that he would grudgingly allow me to register for the next semester on Disciplinary Probation, which I did, and I never again connected a guitar amplifier to the University telephone system.

I did some other stuff there, though, but those are other stories

That would be treated almost like a terroristic threat if it happened today, you'd not only be expelled but would also go to jail.

 

[cdoublejj]

Putting the equipment at your end will really not help much. From you to the telcon office are MANY "boxes that require power. They are supposed to have batteries, but they don't last very long. Our area lost power during the night. My end was fine, but the "box" down the road shut down. Dear old windows was doing a update when the "box" went down and trashed my operating system big time!! I was on AT&T.

for that i have WAN fail over on the router, i'm going to try that out. you can have to Internets. technically more. in my case coax cable and fiber. but, i could also do say cellular or starlink as a back up. still not perfect and also very pricey.


i don't think they will keep it around. they are trying to decommsion parts 4g cellular service already. then you'll have to a have v lte or some voip version of 4g or something or other.