How do text messages travel from one phone carrier to another?

[Beamin]

Say I have Verizon in MD and send it to a att phone in MA. It goes over a data channel in CDMA to my local tower then it ____________________ tower transmits on a voice/data channel to the gsm handset?

...then the tower has an internet connection goes to local isp  somehow connects to sprints network then goes to the tower...

But no because many remote towers were in places that didn't have the internet when texts came out in the 2000's. Could it have sent the texts over a phone line where my local tower literally calls another remote tower over twisted pair and a telco exchange?
Problem with this one is that every tower would have its own phone number and need a huge amount of incoming phone lines and the "handshake" with a dial up connection is way to slow even if it picks up the instant it hears a ring AC signal.

Wasn't it because of this complexity that the original GSM standard used a satellite up link from each tower and down link on every tower therefor not needing local telco's to handle the exchanges? I haven't in the US ever seen any geo stationary antennas or dishes on dedicated cell towers. I do know that your prefix with your carrier is actually located at one of the local telcos, or at least it was in the 2000's just like you land line twisted pair at your house was.

There is a hundred ways to do this but finding reliable info seems to be just generic stuff on google. IS the internet now completely divorced from the phone company like it was back in the day moving along twisted pairs? Who owns the actual fibers? The town who owns the tel poles or the company using them? 

[IanB]

Don't you realize that the Internet has always run over the phone companies' wires? Ever since the 1970's? The Internet IS the phone system, always has been. All that has happened over the years is that the phone companies have upgraded their backbones from copper wires to microwave links to fiber. Over the same period all phone conversations became digitized and sent as digitally compressed audio over the same links.

[Beamin]

Don't you realize that the Internet has always run over the phone companies' wires? Ever since the 1970's? The Internet IS the phone system, always has been. All that has happened over the years is that the phone companies have upgraded their links from copper wires to microwave links to fiber. Over the same period all phone conversations became digitized and sent as digitally compressed audio over the same links.

But in the 90's things started changing and cable companies started making up the back bone. I remember my father designing much of the boards that connected it together.

How did they over come that 52k over twisted pairs speed limit? Or did the telco implement the 52k dial up speeds ( remember your 56k modem never went above 52k?) because they needed to conserve bandwidth over their lines?

[IanB]

The basic copper phone wires only existed between your house and the local telephone exchange. A long time ago, starting in the 60's, the connections between telephone exchanges started being upgraded to higher and higher capacity channels making up the data backbone. Everyone operating a bit of the backbone had an agreement to share each other's data and pass data across the boundaries between one company's network and another. When new companies started adding to the backbone they joined in with the data sharing agreement.

This is partly what network neutrality is all about. The idea is that once the data is on the backbone it is just data and everyone has equal responsibility to share it around and pass it across each other's networks. Everyone shares equally and the costs all balance out in the end.

When one company says "that data is special and we are going to charge extra to carry it", that is when net neutrality goes wrong. Suddenly you get retaliatory pricing, protectionism, and limits on the free flow of data.

[Beamin]

The basic copper phone wires only existed between your house and the local telephone exchange. A long time ago, starting in the 60's, the connections between telephone exchanges started being upgraded to higher and higher capacity channels making up the data backbone. Everyone operating a bit of the backbone had an agreement to share each other's data and pass data across the boundaries between one company's network and another. When new companies started adding to the backbone they joined in with the data sharing agreement.

This is partly what network neutrality is all about. The idea is that once the data is on the backbone it is just data and everyone has equal responsibility to share it around and pass it across each other's networks. Everyone shares equally and the costs all balance out in the end.

When one company says "that data is special and we are going to charge extra to carry it", that is when net neutrality goes wrong. Suddenly you get retaliatory pricing, protectionism, and limits on the free flow of data.

So everything traveled over twisted copper pairs? That must have been terribly slow. Even by the 90's lots of data started moving around even with several thousand dial up users per town they handled that with fiber?

[IanB]

So everything traveled over twisted copper pairs?

Why do you keep introducing twisted copper pairs? I have not once mentioned twisted pairs in any of my replies.

Before fiber optics there were all sorts of ways to get high capacity data links for both analog and digital. For example, they could use coaxial cables and multiplex the signals so they could get many channels over one wire. Think about analog TV. One coaxial cable from the antenna to the TV set could carry many TV channels at once, and each of those TV channels needed much more bandwidth than a phone audio channel. They could presumably get 100's of phone conversations multiplexed into one cable.

To go longer distances between cities they could use point to point microwave links. You might have noticed tall buildings and towers with microwave dishes fixed to the side of them and pointing sideways. These were part of the growing data backbone.

Over time analog data became digitized and compressed, and then they could squeeze even more down the same channels. Today the whole communications infrastructure is digital and phone conversations are just a small part of the total data carried. But when it started out most of the data was either phone data or private data where companies leased dedicated data channels between their offices. What began as the phone network grew into the internet.

[amyk]

To answer the question in your title succinctly: the same way voice calls do.

[vk6zgo]

The basic copper phone wires only existed between your house and the local telephone exchange. A long time ago, starting in the 60's, the connections between telephone exchanges started being upgraded to higher and higher capacity channels making up the data backbone. Everyone operating a bit of the backbone had an agreement to share each other's data and pass data across the boundaries between one company's network and another. When new companies started adding to the backbone they joined in with the data sharing agreement.

This is partly what network neutrality is all about. The idea is that once the data is on the backbone it is just data and everyone has equal responsibility to share it around and pass it across each other's networks. Everyone shares equally and the costs all balance out in the end.

When one company says "that data is special and we are going to charge extra to carry it", that is when net neutrality goes wrong. Suddenly you get retaliatory pricing, protectionism, and limits on the free flow of data.

So everything traveled over twisted copper pairs? That must have been terribly slow. Even by the 90's lots of data started moving around even with several thousand dial up users per town they handled that with fiber?

No,you didn't read the answer properly.

Most of the connections were via wideband systems like microwave, coax, &, even earlier than most people realise, optic fibre.
These systems were "wideband" in the senses of both occupied RF spectrum & analog bandwidth of the signals sent through them.

Using sophisticated modulation methods, what we should really call the "virtual bandwidth" is increased radically, so the underlying systems can carry much more information than their designed capacity would be if they were using analog signals.

All of the cell phone towers were connected  to these wideband carriers all the time (no dialling up necessary).

When they had data (your text or phone call), for a particular company, that company would know which tower was closest to you, & switch the data,to go there.
Even though the connections were via the PTSD supplier, they looked to the company using them, as if they were a dedicated network especially for them.
Real phone companies (as distinct from the "resellers" common these days) have been doing stuff like this for 50 years or more, first with analog signals (things like Networked TV programmes, &  data for Banks, etc.), so it wasn't a great leap to do it for cellphones.

[Beamin]

The basic copper phone wires only existed between your house and the local telephone exchange. A long time ago, starting in the 60's, the connections between telephone exchanges started being upgraded to higher and higher capacity channels making up the data backbone. Everyone operating a bit of the backbone had an agreement to share each other's data and pass data across the boundaries between one company's network and another. When new companies started adding to the backbone they joined in with the data sharing agreement.

This is partly what network neutrality is all about. The idea is that once the data is on the backbone it is just data and everyone has equal responsibility to share it around and pass it across each other's networks. Everyone shares equally and the costs all balance out in the end.

When one company says "that data is special and we are going to charge extra to carry it", that is when net neutrality goes wrong. Suddenly you get retaliatory pricing, protectionism, and limits on the free flow of data.

So everything traveled over twisted copper pairs? That must have been terribly slow. Even by the 90's lots of data started moving around even with several thousand dial up users per town they handled that with fiber?

No,you didn't read the answer properly.

Most of the connections were via wideband systems like microwave, coax, &, even earlier than most people realise, optic fibre.
These systems were "wideband" in the senses of both occupied RF spectrum & analog bandwidth of the signals sent through them.

Using sophisticated modulation methods, what we should really call the "virtual bandwidth" is increased radically, so the underlying systems can carry much more information than their designed capacity would be if they were using analog signals.

All of the cell phone towers were connected  to these wideband carriers all the time (no dialling up necessary).

When they had data (your text or phone call), for a particular company, that company would know which tower was closest to you, & switch the data,to go there.
Even though the connections were via the PTSD supplier, they looked to the company using them, as if they were a dedicated network especially for them.
Real phone companies (as distinct from the "resellers" common these days) have been doing stuff like this for 50 years or more, first with analog signals (things like Networked TV programmes, &  data for Banks, etc.), so it wasn't a great leap to do it for cellphones.

[Beamin]

The basic copper phone wires only existed between your house and the local telephone exchange. A long time ago, starting in the 60's, the connections between telephone exchanges started being upgraded to higher and higher capacity channels making up the data backbone. Everyone operating a bit of the backbone had an agreement to share each other's data and pass data across the boundaries between one company's network and another. When new companies started adding to the backbone they joined in with the data sharing agreement.

This is partly what network neutrality is all about. The idea is that once the data is on the backbone it is just data and everyone has equal responsibility to share it around and pass it across each other's networks. Everyone shares equally and the costs all balance out in the end.

When one company says "that data is special and we are going to charge extra to carry it", that is when net neutrality goes wrong. Suddenly you get retaliatory pricing, protectionism, and limits on the free flow of data.

So everything traveled over twisted copper pairs? That must have been terribly slow. Even by the 90's lots of data started moving around even with several thousand dial up users per town they handled that with fiber?

No,you didn't read the answer properly.

Most of the connections were via wideband systems like microwave, coax, &, even earlier than most people realise, optic fibre.
These systems were "wideband" in the senses of both occupied RF spectrum & analog bandwidth of the signals sent through them.

Using sophisticated modulation methods, what we should really call the "virtual bandwidth" is increased radically, so the underlying systems can carry much more information than their designed capacity would be if they were using analog signals.

All of the cell phone towers were connected  to these wideband carriers all the time (no dialling up necessary).

When they had data (your text or phone call), for a particular company, that company would know which tower was closest to you, & switch the data,to go there.
Even though the connections were via the PTSD supplier, they looked to the company using them, as if they were a dedicated network especially for them.
Real phone companies (as distinct from the "resellers" common these days) have been doing stuff like this for 50 years or more, first with analog signals (things like Networked TV programmes, &  data for Banks, etc.), so it wasn't a great leap to do it for cellphones.

So I think that was the answer to my question: a wideband system over coax. I knew about the ATT long lines microwave back haul with those huge red and white wave guide horns, I have actually climbed one of them until I felt too close to the RF plus I'm not a fan of heights so didn't go up to the top. The view was incredible and also to know where you are looking you could shoot a laser with the help of friends holding mirrors on the next tower and the next... that you could reach the opposite corner of the country.  I wonder how accurate that would have to be if you used 6" mirrors.


So it was a wideband system, this worked with analog? The only way I could see that would be to treat your cable like the air in an antenna system and make up channels and modulate signal with RF that never gets radiated out into the air. I know cable TV worked like that. How did radio stations get live from the studio to the tower? TV stations had small microwave dishes, and this was how that weird talking head prank worked in the 80's they just over powered the real transmitter. But radio stations studios don't have those.

What was the name of the cable system? Is longlines just for back up now? Seems like a huge waste of infrastructure to not repurpose a cross country site to site links.

Back to text messages: the tower dials into this wide band system? At that point what form is the text message in? I couldn't even speculate. I know modern systems would have the tower just connect to the internet on site and send it anyway they want. But I don't see a lot of rural cell towers being upgraded with fiber from comcast Verizon etc. In the 90's how would you send a digital text over an analog system, use modems?

Fun fact: Many T-Mobile towers have the circuit breakers located outside the base of the tower, have no fence around, and you just open the box and shut it off, then wait for a white van to pull up and turn it back on. Maybe its like the lights and they want you to turn off the cell phone tower when you are not using it. I wonder how many dropped calls that created. A huge lever with no one around to see you pull it down. Stupid, most sites you are on camera as soon as you approach the fence.

[newbrain]

Wasn't it because of this complexity that the original GSM standard used a satellite up link from each tower and down link on every tower therefor not needing local telco's to handle the exchanges?

What? Not that I ever heard of.

Satellites links might be used, but are in general a last resort as they bring in a lot of problems...
GPS, though, can be and is often used a frequency reference.

The GSM network is not really complicated (at least wrt 3, 4 and 5G).
The towers do not call each other directly, there's a hierarchy of exchanges.
Some are controlling the radio base stations, that are mostly "dumb".
Some aggregate the traffic from many of these controllers and maybe also act as gateways towards other phone networks.
Some keep the administrative data and permission of each subscriber.
Some are dedicated to know where the mobiles are, and the mobiles make sure to tell the network periodically.

There may be a mix of functions, and in general, nowadays, there is a split from the controlling logic and signalling plane and the actual user data/voice plane.

When you send a text (or initiate a call, not much difference there) the whereabouts of the recipient are looked up.
In their supposed area paging happens: a broadcast message asking "Are you here?", in case the mobile answer "Yes, here I am" the call (or SMS data forwarding) can go on.
The SMS are stored for some time if the recipient is not available.
For a call, a circuit connection* is set up (for GSM and 3G networks) and the digitalized, compressed, voice is passed between the mobiles, that have in the meantime agreed on the compression format to use.
If you move from one cell to another, this circuit connection is seamlessly handed over to the new tower.

If you text/phone someone on another operator, your operator will just ask for a connection to their operator, that shall take care of the finding and delivering of the message/voice.

4G networks and onwards do no set up a circuit, and the packetized voice is treated as (high priority) data (VoLTE).
Most 4G networks, though, still fall back to 3G for voice calls.

How the links between all these nodes are physically realized is for the most part immaterial, as long as bandwidth, latencies and error rates are well defined and within the limits: copper cable, fibre, point to point radio or even satellites are only ways to move bits from one place to another.

The public Internet and the phone networks are logically separated, though they might share the same physical links, and of course many protocols (IP for one).

*Circuit connection: disregarding how it actually is implemented, it's "as if" a dedicated physical wire had been connected between the two end points.

All of the above is a bit oversimplified, but not too far from truth.

[dmills]

Search term "SS7 signalling" the CCC made a big thing of it at congress a few years back and the videos on the lectures are available on line.

It is old, stretched way past what it was meant to do (It dates from the landline era), horrifically insecure, and complicated but it works.   

Regards, Dan.

[Beamin]

Search term "SS7 signalling" the CCC made a big thing of it at congress a few years back and the videos on the lectures are available on line.

It is old, stretched way past what it was meant to do (It dates from the landline era), horrifically insecure, and complicated but it works.   

Regards, Dan.

I don't think anyone really knows the answer to this question. I'm trying to think of it as if you could follow the electrons or photons for fiber where does the signal physically go, if you had to stop the signal with a pair or wire cutters what wires would you need to cut. For example if you were in England with two cell phones with roaming capabilities but with American exchanges and you send a text to the phone next to you, that text probably went all the way to America and back, to send a message a few feet away the signal probably traveled 10,000+ miles. If the borg was making a telephone system, the phones would know they could use their Bluetooth to send the data using the least amount of energy and time, the borg seeks perfection over anything else. Seriously if we used the fictional borg from star trek as an example think how much more efficient things would be when the average soldier could make decisions of a four star general in the same time it takes to pull or not pull a trigger. The efficiency alone could defeat all other armies.

[amyk]

They wouldn't be able to charge you subscriber fees if it was truly decentralised.

[tggzzz]

Search term "SS7 signalling" the CCC made a big thing of it at congress a few years back and the videos on the lectures are available on line.

It is old, stretched way past what it was meant to do (It dates from the landline era), horrifically insecure, and complicated but it works.   

Regards, Dan.

I don't think anyone really knows the answer to this question.

Sigh. Of course they know.

SS7 signalling is used to send messages between various computers in the telecoms system.

To understand what is in the messages, read any textbook on GSM, or search for terms such as BSC and MSC in the context of GSM.

ISTR that to setup a GSM voice call, up to 45 messages are sent, so be prepared to have a learning curve.

There's no point in people here trying poorly duplicate information that is well explained in many other places.

Your other questions and hypotheses are not even wrong.

[dmills]

As I said, old, complicated, very 'Telecom' and baroque as hell, but SS7 works.
There is no magic, it is just Engineering, all the way down, and is actually rather well documented.

Regards, Dan.

[Beamin]

So I read up on the SS7 pretty interesting stuff. I guess my question is more basic, is there a dedicated line set up between exchanges that's like a dial up or terminal connection that is always connected that would have sent the data? Kind of like how a BBS system worked but it would be on a dedicated physical line between exchange offices that could relay all the messages together. The reason I kept saying "twisted pair" is because I was thinking in terms of how you would actually build this or if you hopped a ride on the messages where would the signal physically travel. It would make a really interesting video if you could watch someone send a text then show the route your electrons and photons are traveling and all the complexity and equipment that is required to send your "LOL" or "BRB" text to a friend hundreds of miles away in less then a second. Also interesting would be how much $ in equipment is used to send that text or hours spent installing it and the lines.

[madires]

Please see https://en.wikipedia.org/wiki/T-carrier for the old workhorse of the US telecommunications industry.

[tggzzz]

I guess my question is more basic, is there a dedicated line set up between exchanges that's like a dial up or terminal connection that is always connected that would have sent the data?

There are many many lines between exchanges, usually fibre optic since the early/mid 80s.

Dedicated? Yes, repeat no - depending on the level at which you are considering them.

By analogy, consider a  VPN. Is that dedicated or not?

Ditto, consider subsea fibre links.

[IanB]

I guess my question is more basic, is there a dedicated line set up between exchanges that's like a dial up or terminal connection that is always connected that would have sent the data?

This is kind of a strange question. Ever since the phone system has existed,since over 100 years ago, the phone company has installed and maintained dedicated wires between exchanges and between cities to carry voice and data messages around the country. From the phone company's point of view there is nothing strange or unusual about lines being always connected. All the phone company's wires are always connected all the time--it is their business to install and maintain these wires.

When you make a dial up connection the phone company decides where your connection needs to go and it than allocates a channel over its installed network of dedicated, always-on connections to carry your call. When you make a phone call you are basically renting some time on that permanent, always on network that the phone company maintains.

[Beamin]

I guess my question is more basic, is there a dedicated line set up between exchanges that's like a dial up or terminal connection that is always connected that would have sent the data?

This is kind of a strange question. Ever since the phone system has existed,since over 100 years ago, the phone company has installed and maintained dedicated wires between exchanges and between cities to carry voice and data messages around the country. From the phone company's point of view there is nothing strange or unusual about lines being always connected. All the phone company's wires are always connected all the time--it is their business to install and maintain these wires.

When you make a dial up connection the phone company decides where your connection needs to go and it than allocates a channel over its installed network of dedicated, always-on connections to carry your call. When you make a phone call you are basically renting some time on that permanent, always on network that the phone company maintains.

Is this somehow related to why a 56k modem never could go above 52k, the phone company would limit the data, or is a voice line that has a frequency range from 100hz to 10k hz (Can't remember exactly what the range is but it's low, hence why phone calls sound so shitty and why I have terrible time hearing people. Facetime someone then call them and you will realize how bad phone lines sound. I was really hoping with the advent of cell phones and everything being data we would get CD player sound quality with our phones. I would pay extra for that) the limiting factor in how much data you can send? Kind of a strange thought that faster signals would be higher pitched, but not really because it's not a steady sine/square wave.

[Jeroen3]

It's not my age of tech, but the 52k "limit" sound like overhead and checksum that limit the effective data over the physical medium of 56k.

I was really hoping with the advent of cell phones and everything being data we would get CD player sound quality with our phones. I would pay extra for that) the limiting factor in how much data you can send? Kind of a strange thought that faster signals would be higher pitched, but not really because it's not a steady sine/square wave.

You do, 3G calls are significantly better, 4G calls are like they are next to you. Especially when in the car. But you'd need 4G everywhere. Also, calling over with WiFi (VoWiFi) is a thing now with some providers and phones.

Signals are only higher pitched when they are played back faster. That's not how digital signalling works.
Please view this: Xiph.org Digital Show & Tell

[madires]

Is this somehow related to why a 56k modem never could go above 52k, the phone company would limit the data, or is a voice line that has a frequency range from 100hz to 10k hz (Can't remember exactly what the range is but it's low, hence why phone calls sound so shitty and why I have terrible time hearing people.

POTS is about 3kHz. So everything using POTS lines is limited to 3kHz. A POTS modem (including 56k) performs a handshaking with the other side to determine which maximum transfer rate is feasible for that specific call. Several modem protocols have error correction and data compression features. On top of that any additional protocols, like PPP, will add more overhead and reduce the net data rate.

[tooki]

Is this somehow related to why a 56k modem never could go above 52k, the phone company would limit the data...

53Kbps was a typical maximum payload with overhead. But it’s not an artificial limit by the phone company, as you imply — why would the phone company hamstring a product they spent so much money to install? (56Kbps modems only worked by having the phone company install modems in its local offices, at great expense. Without that, 33.6Kbps was the limit). Wiki says the US government required a cap: “In the United States, government regulation limits the maximum power output, resulting in a maximum data rate of 53.3 kbit/s. ”

... or is a voice line that has a frequency range from 100hz to 10k hz (Can't remember exactly what the range is but it's low, hence why phone calls sound so shitty and why I have terrible time hearing people.

It’s 300-3400Hz, more or less: https://en.wikipedia.org/wiki/Voice_frequency

100-10KHz would sound almost as good as CD, for voice calls.

Facetime someone then call them and you will realize how bad phone lines sound.

It’s no secret that FaceTime sounds awesome. I have found it to exceed every other Internet calling system in quality and reliability. (My personal record is a FaceTime video call over 11 hours, without any significant glitching.) Nothing else has come close, in my experience. It’s been something like 8 years since Apple introduced FaceTime, and IMHO it still stings that Apple’s plans to make FaceTime an open standard were scuttled by some patent troll, who not only stopped them from making it an open standard, but even required them to re-engineer it under the hood into something less efficient.

My love for FaceTime aside, one thing telecom veterans have been saying for a long time is that modern phone lines suck. The 300-3400Hz is actually enough — if it’s done well. And in the olden days of genuine analog lines, it was done well. But we switched to digital trunk lines long ago, and those compress the hell out of the audio. And then with cellphones, we moved to even more severe digital compression (not to mention having to handle lost data).

I doubt if I have actually ever heard a call made on a true analog phone line from end-to-end. Digital trunk lines were the standard by the time I was born

And then to add insult to injury, phones also got worse. The old handsets of the Bell era had nice, big, well-made speakers and microphones in them. The quality of phones post-deregulation plummeted quickly.

I was really hoping with the advent of cell phones and everything being data we would get CD player sound quality with our phones. I would pay extra for that) the limiting factor in how much data you can send?

Well, for the longest time, cellphones had less data to work with than land lines! It’s really only in the 3G era that we meaningfully increased the mobile data rate.

Anyway, the real issue is standards: two cellphones making a call do not create a high-speed point-to-point data link, nor are they just shooting packets at each other (like FaceTime). They’re running a call via the voice network, which has strict standards that are essentially inviolable. So without upgrading the entire voice network infrastructure, you can’t just easily upgrade the voice quality.

Nonetheless, a few carriers have been doing this, allowing calls made within their networks, when using a supported handset on both ends, to have better sound quality. But support between carriers has been slow to roll out. See https://en.wikipedia.org/wiki/Wideband_audio

Kind of a strange thought that faster signals would be higher pitched, but not really because it's not a steady sine/square wave.

What the hell do you mean?!?

[tggzzz]

I doubt if I have actually ever heard a call made on a true analog phone line from end-to-end. Digital trunk lines were the standard by the time I was born

I did. The quality was highly variable. Sometimes the best course was to "hang up and try again".

And then to add insult to injury, phones also got worse. The old handsets of the Bell era had nice, big, well-made speakers and microphones in them. The quality of phones post-deregulation plummeted quickly.

Precisely, although that isn't limited to one carrier and one manufacturer.

I was really hoping with the advent of cell phones and everything being data we would get CD player sound quality with our phones. I would pay extra for that) the limiting factor in how much data you can send?

The GSM codecs greatly reduce the data rate by encoding the signal, just as mp3 etc does. The difference is the GSM codecs incorporate a model of the human voice tract, so it would be surprising if they transmitted arbitrary sounds well.

Kind of a strange thought that faster signals would be higher pitched, but not really because it's not a steady sine/square wave.

What the hell do you mean?!?

Quite.