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

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Beamin:

--- Quote from: IanB on December 07, 2018, 04:19:51 pm ---
--- Quote from: Beamin on December 07, 2018, 02:47:42 pm ---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?
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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.

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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.


--- Quote --- 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.
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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:

--- Quote from: Beamin on January 07, 2019, 10:04:52 am ---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.

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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:

--- Quote from: Beamin on January 07, 2019, 10:04:52 am ---Is this somehow related to why a 56k modem never could go above 52k, the phone company would limit the data...
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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. ”


--- Quote from: Beamin on January 07, 2019, 10:04:52 am ---... 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.
--- End quote ---
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.


--- Quote from: Beamin on January 07, 2019, 10:04:52 am ---Facetime someone then call them and you will realize how bad phone lines sound.
--- End quote ---
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.


--- Quote from: Beamin on January 07, 2019, 10:04:52 am ---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?

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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


--- Quote from: Beamin on January 07, 2019, 10:04:52 am ---Kind of a strange thought that faster signals would be higher pitched, but not really because it's not a steady sine/square wave.

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What the hell do you mean?!?

tggzzz:

--- Quote from: tooki on January 07, 2019, 03:14:28 pm ---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

--- End quote ---

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


--- Quote ---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.

--- End quote ---

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


--- Quote from: Beamin on January 07, 2019, 10:04:52 am ---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?

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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.


--- Quote from: tooki on January 07, 2019, 03:14:28 pm ---
--- Quote from: Beamin on January 07, 2019, 10:04:52 am ---Kind of a strange thought that faster signals would be higher pitched, but not really because it's not a steady sine/square wave.

--- End quote ---
What the hell do you mean?!?

--- End quote ---

Quite.

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