How do text messages travel from one phone carrier to another? - Page 1
Forum section: electronics / general

author: Beamin
author_rank: Super Contributor
timestamp: December 01, 2018, 11:47:42 pm
content: 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?

author: IanB
author_rank: Super Contributor
timestamp: December 01, 2018, 11:54:30 pm
content: 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.

author: Beamin
author_rank: Super Contributor
timestamp: December 02, 2018, 12:00:00 am
content: Quote from: IanB on December 01, 2018, 11:54:30 pmBut 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?

author: IanB
author_rank: Super Contributor
timestamp: December 02, 2018, 12:07:31 am
content: 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.

author: Beamin
author_rank: Super Contributor
timestamp: December 02, 2018, 12:33:02 am
content: Quote from: IanB on December 02, 2018, 12:07:31 amSo 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?

author: IanB
author_rank: Super Contributor
timestamp: December 02, 2018, 01:44:24 am
content: Quote from: Beamin on December 02, 2018, 12:33:02 amWhy 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.

author: amyk
author_rank: Super Contributor
timestamp: December 02, 2018, 02:46:49 am
content: To answer the question in your title succinctly: the same way voice calls do.

author: vk6zgo
author_rank: Super Contributor
timestamp: December 02, 2018, 03:05:09 am
content: Quote from: Beamin on December 02, 2018, 12:33:02 amNo,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 carriersall 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.

author: Beamin
author_rank: Super Contributor
timestamp: December 02, 2018, 03:21:17 pm
content: Quote from: vk6zgo on December 02, 2018, 03:05:09 am

author: Beamin
author_rank: Super Contributor
timestamp: December 02, 2018, 03:37:55 pm
content: Quote from: vk6zgo on December 02, 2018, 03:05:09 amSo 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.

author: newbrain
author_rank: Super Contributor
timestamp: December 02, 2018, 04:41:50 pm
content: Quote from: Beamin on December 01, 2018, 11:47:42 pmWhat? 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.

author: dmills
author_rank: Super Contributor
timestamp: December 03, 2018, 08:16:57 am
content: 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.

author: Beamin
author_rank: Super Contributor
timestamp: December 04, 2018, 08:49:18 am
content: Quote from: dmills on December 03, 2018, 08:16:57 amI 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.

author: amyk
author_rank: Super Contributor
timestamp: December 05, 2018, 01:04:55 am
content: They wouldn't be able to charge you subscriber fees if it was truly decentralised.

author: tggzzz
author_rank: Super Contributor
timestamp: December 05, 2018, 09:19:51 am
content: Quote from: Beamin on December 04, 2018, 08:49:18 amSigh. 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.

author: dmills
author_rank: Super Contributor
timestamp: December 05, 2018, 10:10:30 am
content: 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.

author: Beamin
author_rank: Super Contributor
timestamp: December 07, 2018, 02:47:42 pm
content: 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.

author: madires
author_rank: Super Contributor
timestamp: December 07, 2018, 03:11:57 pm
content: Please seehttps://en.wikipedia.org/wiki/T-carrierfor the old workhorse of the US telecommunications industry.

author: tggzzz
author_rank: Super Contributor
timestamp: December 07, 2018, 03:24:03 pm
content: Quote from: Beamin on December 07, 2018, 02:47:42 pmThere 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.

author: IanB
author_rank: Super Contributor
timestamp: December 07, 2018, 04:19:51 pm
content: Quote from: Beamin on December 07, 2018, 02:47:42 pmThis 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.

author: Beamin
author_rank: Super Contributor
timestamp: January 07, 2019, 10:04:52 am
content: Quote from: IanB on December 07, 2018, 04:19:51 pmIs 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.

author: Jeroen3
author_rank: Super Contributor
timestamp: January 07, 2019, 11:01:46 am
content: 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.QuoteYou 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

author: madires
author_rank: Super Contributor
timestamp: January 07, 2019, 03:09:57 pm
content: Quote from: Beamin on January 07, 2019, 10:04:52 amPOTS 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.

author: tooki
author_rank: Super Contributor
timestamp: January 07, 2019, 03:14:28 pm
content: Quote from: Beamin on January 07, 2019, 10:04:52 am53Kbps 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 amIt’s 300-3400Hz, more or less:https://en.wikipedia.org/wiki/Voice_frequency100-10KHz would sound almost as good as CD, for voice calls.Quote from: Beamin on January 07, 2019, 10:04:52 amIt’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 bornAnd 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 amWell, for the longest time, cellphones hadlessdata 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 carriershavebeen doing this, allowing calls made within their networks, when using a supported handset on both ends, to have better sound quality. But supportbetweencarriers has been slow to roll out. Seehttps://en.wikipedia.org/wiki/Wideband_audioQuote from: Beamin on January 07, 2019, 10:04:52 amWhat the hell do you mean?!?

author: tggzzz
author_rank: Super Contributor
timestamp: January 07, 2019, 03:38:56 pm
content: Quote from: tooki on January 07, 2019, 03:14:28 pmI did. The quality was highly variable. Sometimes the best course was to "hang up and try again".QuotePrecisely, although that isn't limited to one carrier and one manufacturer.Quote from: Beamin on January 07, 2019, 10:04:52 amThe 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 pmQuite.

author: tooki
author_rank: Super Contributor
timestamp: January 07, 2019, 04:01:02 pm
content: Quote from: tggzzz on January 07, 2019, 03:38:56 pmWell, that happens even today!Quote from: tggzzz on January 07, 2019, 03:38:56 pmWho said it was?!? I said “Bellera” to pin down the time, I didn’t mean exclusively “under the Bell system”.Quote from: tggzzz on January 07, 2019, 03:38:56 pmWeknowthey can’t. They’re why hold music sounds so terrible, those codecs are hardcore optimized for voice, and on non-voice they absolutely fall flat and degrade into pure compression artifacts.

author: madires
author_rank: Super Contributor
timestamp: January 07, 2019, 04:04:26 pm
content: Quote from: tooki on January 07, 2019, 03:14:28 pmThere's G.722 with 7kHz for a higher audio quality. Most marketing departments call it "HD voice".

author: coppice
author_rank: Super Contributor
timestamp: January 07, 2019, 04:04:48 pm
content: Quote from: tooki on January 07, 2019, 03:14:28 pm300-3400Hz is NOT enough. Clear speech requires about 7kHz bandwidth. Without the energy between about 5kHz and 7kHz you cannot distinguish between unvoiced sounds, so something like F S F S F S sounds like the same character repeating. Its the 3kHz bandwidth limit that has people spelling out things as "foxtrot uniform charlie kilo, this call is bloody awful". The old analogue local lines were not filtered down to 3kHz, but seldom achieved much more. Long distance analogue calls were always limited to about 3kHz. The PSTN has never compressed the hell out of anything. The A-law and u-law codecs used for the digital telephone network apply just about the lightest possible compression there is - they just reduce 13 bit samples to 8 bits in a pseudo-logarithmic manner. Digital cellular started with heavy compression, to keep the bit rate viable, but sounded a lot better than most analogue cellular calls, which were mostly pretty horrible.Quote from: tooki on January 07, 2019, 03:14:28 pmMost countries only achieved a fully digital telephone network in the late 90s, so unless you are quite young you've probably heard some local calls which were analogue from end to end. They were not too bad, but in the 60s and 70s when most long distance calls were analogue end to end the quality was highly variable, and could be bloody awful. The shift to a digital backbone was the best thing that ever happened to the PSTN.

author: tooki
author_rank: Super Contributor
timestamp: January 07, 2019, 04:14:27 pm
content: Quote from: madires on January 07, 2019, 04:04:26 pmI know — I already linked to info about that in the post you’re quoting.Quote from: coppice on January 07, 2019, 04:04:48 pmI don’t think it was quite that bad. (I mean, a bad circuit could be, but a good one was good enough.)Quote from: coppice on January 07, 2019, 04:04:48 pmYeah, that’s true, local calls (or at least within the same local exchange) probably were analog.And yes, no doubt analog long distance was terrible!

author: newbrain
author_rank: Super Contributor
timestamp: January 07, 2019, 04:27:55 pm
content: Quote from: tooki on January 07, 2019, 03:14:28 pmOld analog lines were, in my personal experience, ranging from horrible to bad.When the land line was finally switched to a digital exchange (the last mile was still analog, and still is) quality went up quite a bit.The only compression done on POTS on digital trunks was A-law or u-law (depending on your country), which causes very little loss in quality.One of the initial phases in a mobile phone call is codec negotiation, where the phones and the network agree on which transcoder to use for compressing voice.In some lucky case AMR-WB can be selected, but there also cases where the selected codec is worse than POTS quality.For GSM and 3G, both circuit calls, it is possible that compressed voice is directly exchanged between the user terminals, with obvious advantages, instead of being:1. compressed in one mobile2. expanded in the network - where depends on 2G/3G and network architecture3. transported as A/u-law samples4. re-compressed before being sent to the other mobile5. re-expanded in the mobileSearch for "transcoder free operation", but all the planets must be correctly aligned for that to work.Quote from: tggzzz on January 07, 2019, 03:38:56 pmExactly, so much that DTMF tones needs to be transported out of band. As above, they might or might not be transformed back to samples in the network.

author: Lord of nothing
author_rank: Super Contributor
timestamp: January 07, 2019, 05:07:18 pm
content: Quotewhat ever that is.Normally you have "HD Voice" who is mention before. The work perfect.There are some good Explanation Video from CCC and Defcon who explain how a 2G,... Network work include how the Voice Codeq work.

author: tooki
author_rank: Super Contributor
timestamp: January 08, 2019, 12:20:18 am
content: FaceTime is like Skype, except with better audio/video quality!It’s too bad there’s no indication of whether a given phone call is using HD voice or not — I have a hunch we don’t notice when it’s working, but of course we do notice when we have a bad connection.

author: Lord of nothing
author_rank: Super Contributor
timestamp: January 08, 2019, 11:03:50 am
content: Some have, do, show:https://www.google.com/search?q=hdvoice+icon&num=100&client=firefox-b&source=lnms&tbm=isch

author: johnh
author_rank: Regular Contributor
timestamp: January 09, 2019, 06:47:09 am
content: With VoLTE over 4G Codec choice is negotiated between devices. Either a handset or Media GatewayThe network might strip/remove some codec choices by manipulating the SDP, in the INVITE and response in 200OKThe media gateway can used to perform trans-coding, this a last choice because of the performance penalty of trans-coding.

author: Zbig
author_rank: Frequent Contributor
timestamp: January 09, 2019, 12:01:28 pm
content: As this thread has already diverted to codec quality, bandwidth and compression, I remember how surprised I was back in the day upon learning at school about the concept of "comfort noise". Apparently, in digital communications devices, there was an audible background noise artificially injected locally by the user's terminal equipment (telephone). Turns out people would get confused when, in the periods of both talking parties going silent, the line would go totally silent as well. They were so used to the poor quality of analogue telephony and its inherent background noise that they would associate the noise with the connection ongoing. In order to save time and/or bandwidth, the equipment was gating the audio signal (passing it through only once its level has exceeded some arbitrary threshold) and inserting the locally-generated artificial static during the pauses. I remember how outraged my teenage geek self was at the idea or "ruining" the clear, digital signal path deliberately so it could sound as bad as POTS. If memory serves, 2G cellphones, DECT phones were all doing that, among others. I'm not sure I'm not imagining this now but I think I even saw an option to disable or enable the comfort noise in a VOIP gateway device.Fast forward some twenty years, I have both VoLTE and VoWiFi available with my telco and on my phone. While the improvement in quality is apparent and very welcome, I have more than once found myself going like "Hello? You still there?" when the person I was talking to went silent for a while. It was then when it dawned on me that I can no longer hear any "comfort noise" during the pauses in our conversation.That's why I now wonder: is the comfort noise feature now being omitted on purpose? Have they arrived at the conclusion that the new generations don't need it anymore as they don't remember/weren't born in the era of analogue telephony and it's time to abandon the idea? Or is it the negligence/incompetence on the device manufacturer's part? Are the codecs/standards specific in the topic of whether to use comfort noise or not?

author: madires
author_rank: Super Contributor
timestamp: January 09, 2019, 03:12:49 pm
content: Usually VoIP phones have some configuration switches for comfort noise. And there's RFC 3389 (https://tools.ietf.org/html/rfc3389) to help managing the comfort noise feature.

author: coppice
author_rank: Super Contributor
timestamp: January 09, 2019, 04:12:58 pm
content: Quote from: Zbig on January 09, 2019, 12:01:28 pmRubbish. Comfort noise has nothing to do with poor quality lines. Its about silence suppression, and the effect it has on the background mush you normally hear from the far end room in a high quality call. If you are only trying to carry speech, you can stop transmission and save bandwidth, when there is nobody talking. However, the background noise from the room stops along with the voice, and that's confusing. It seems like the call has dropped. A proper comfort noise system estimates the volume and spectral character of the background noise in the room, and sends those parameter to the far end at infrequent intervals. The receiving end then synthesises background noise of a similar character to play to the recipient. Done well, you barely notice the silence suppression cutting in and out, and you can save maybe 30% of the total bits transmitted.

author: Zbig
author_rank: Frequent Contributor
timestamp: January 09, 2019, 07:35:48 pm
content: Quote from: coppice on January 09, 2019, 04:12:58 pmSorry, you lost me there. You were saying...?

author: MadScientist
author_rank: Frequent Contributor
timestamp: June 30, 2021, 03:27:18 pm
content: Having worked briefly in this area. The whole telco billing system is more complex then the switching system.

author: duckduck
author_rank: Frequent Contributor
timestamp: June 30, 2021, 03:52:24 pm
content: How do carriers exchange SMS messages? The same way that carriers exchange any other data: at an internet exchange. Since rack space / servers / bandwidth are not free, there are peering agreements between carriers.https://en.wikipedia.org/wiki/Internet_exchange_pointhttps://en.wikipedia.org/wiki/Peering(much more info here)EDIT:OK, maybe not so much. I'm not sure where SS7 data is exchanged between carriers. Apparently they sell access:https://www22.verizon.com/wholesale/solutions/solution/SS7.html

author: MadScientist
author_rank: Frequent Contributor
timestamp: June 30, 2021, 03:53:49 pm
content: What the OP is referring to is mobile backhaul , E1/T1 bundles were the mainstay , now largely superseded by fibre and to some extent microwaveIn Africa sat based backhaul is used in places.

author: MadScientist
author_rank: Frequent Contributor
timestamp: June 30, 2021, 04:02:41 pm
content: SMS messaging did not the internet abs still doesn’t imho.SMS makes use of resources in the gsm signaling protocol

author: esepecesito
author_rank: Regular Contributor
timestamp: June 30, 2021, 04:46:36 pm
content: Wow! So much answers and only a couple rightThe correct one is "SS7" it is a dinosaur, but still newer as R2, which was replaced by SS7.

author: nctnico
author_rank: Super Contributor
timestamp: June 30, 2021, 06:59:58 pm
content: Quote from: Beamin on December 01, 2018, 11:47:42 pmNowadays text messages are probably split off at the cell tower and transmitted over an IP network with gateways between operators. Back in the old days the text messages where included in the signalling channel on T1/E1 links (which could be aggregated in links with more bandwidth channels) from the base stations and then get exchanged between telecom operators. The problem with this system is that it was never designed to handle the amount of text messages that users where sending so companies started making products to split the text messages from the signalling channels and aggregate these on seperate links between operators.

author: RJSV
author_rank: Super Contributor
timestamp: July 02, 2021, 03:21:58 am
content: Yes, as mentioned, using digital trunk lines, a 'Teleco'organization like DSC, in my limited expertise, I think they sell 'giant switches', that essentially use a decimate and re-bundle strategy for handing mass numbers of signal (DS1 type and DS3 type).Say you have the DSC 'switch'; a cross-point having 8192 (that's 8K) by 8192. Each of those DS3 streams is containing 28 DS1 streams, ... something approx like that. Each DS1 being one single channel. (I don't have enough TELECOM expertise to discuss full or half duplex, but at any rate the job of this mass switch is tofor example pull out any DS1 signals that need to go to Rome, then assemble a new DS3 stream, containing all those DS1 streams. Then, that gets sent on down to Rome, in this case.It's probably very complicated, as you could imagine in a world wide network, with demands for speed, forany many clients, each themselves operating on a mass basis (and with 8K by 8K switch stations peppered throughout.So that's my barely-informed guess, as I had some experience at DSC in Texas(Digital Switch Corporation).After re-building one of those larger mass streams, my guess is that 'Trunk Line' often means a high capacity microwave or even optical transmission.Yeah, no twisted pairs: These systems are the big bunnies.

author: RJSV
author_rank: Super Contributor
timestamp: July 02, 2021, 10:51:56 pm
content: Looking at search results, for Digital Multiplex Hierarchy in telephone / texting systems:An intro into PCM (pulse code modulation) you can search / read about:DS0 represents PCM at 64 kbits/sec. (one signal).DS1 can have up to 24 of those DS0,(~ 1.5 mbits/second.),DS3 has 28 DS1, and so that is 672 individual signal channels.I can't supply much info beyond that, but most search engines have lots of description, regarding 'voice data' and regarding 'SMS' and texting in general.

author: esepecesito
author_rank: Regular Contributor
timestamp: July 06, 2021, 02:12:43 pm
content: Quote from: nctnico on June 30, 2021, 06:59:58 pmAnother change that also lead to change (only partly) to IP was the introduction of number portability: the SMS had to be routed based on the number to a different operator. No Telephony switch was prepared for that massive routing task, so, at least were I worked, it was implemented in a FreeBSD box, that would do the rounting, and because many operators had the same system from the same company, the operator to operator link was also IP. But I guess it is not the norm. The normal thing was and I bet still is SS7. You have to have dedicated SS7 links anyway with other operators, big ones, because each call implies may messages back and forth.

author: madires
author_rank: Super Contributor
timestamp: July 06, 2021, 05:11:24 pm
content: High level view on how SMS works in LTE:https://blog.3g4g.co.uk/2012/02/high-level-view-on-how-sms-works-in-lte.htmlTwo Types of SMS in 5G:https://blog.3g4g.co.uk/2020/09/two-types-of-sms-in-5g.html