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| How do text messages travel from one phone carrier to another? |
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| newbrain:
--- Quote from: Beamin on December 01, 2018, 11:47:42 pm ---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? --- End quote --- 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:
--- Quote from: dmills on December 03, 2018, 08:16:57 am ---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. --- End quote --- 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:
--- Quote from: Beamin on December 04, 2018, 08:49:18 am --- --- Quote from: dmills on December 03, 2018, 08:16:57 am ---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. --- End quote --- I don't think anyone really knows the answer to this question. --- End quote --- 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. |
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