4 ms·

The SMS contains only the human facing phone number (also known as MSISDN) but the BTS deals (usually, I don't know, maybe they are smarter now) with IMSI numbe

The SMS contains only the human facing phone number (also known as MSISDN) but the BTS deals (usually, I don't know, maybe they are smarter now) with IMSI numbers which are unique identifiers of SIM cards. The base station doesn't know or care about phone numbers. (Kinda like L2 and L3 in networking - MAC vs IP addresses.)

JAlexoid 8y ago
I'm pretty sure that BTC work with MSINs, primarily.
- pilsetnieks 8y ago
  Yes, that's quite possible, I'm not that familiar of that side of things and might be thinking of the wrong number. Anyway, the point is that they don't use the same numbers you and I have in our phonebooks.
dfox 8y ago
Another issue apart from addressing is that all the SMS related logic resides in the SMSC and rest of the network sees the traffic as opaque payload. The article glosses over how the resulting message structure is actually sent over the radio interface and the SS7 network. In all it involves establishing (somewhat TCP-like) connection between your phone and SMSC across the signalling paths. The fact that this process is somewhat involved and consumes significant amount of radio resources is probably at least partially the reason why SMSes aren't particularly cheap. On the other hand on native LTE sending or receiving SMS could in theory consist of two UDP packets, but I'm not sure how widely is this deployed.
- voltagex_ 8y ago
  SMS over LTE is RCS [1], isn't it? I'd be happy to use it but my carrier/phone manufacturer have decided to limit the RCS apps I can use. 1: https://en.wikipedia.org/wiki/Rich_Communication_Services https://en.wikipedia.org/wiki/Rich_Communication_Services
- fyfy18 8y ago
  I thought SMS was built on top of the existing GSM signalling protocols, and so is effectively free to carriers. The bandwidth costs of a few hundred byte message are nothing compared to streaming a video or a phone call. The only reason why carriers charge for SMS is because they can.
- bestham 8y ago
  An SMS is sent in the GSM SACCH (Slow Associated Control Channel), that channel is normally used for timing information (how far away the handset is from the cell tower and the power control of the handset). Since SMS is not a real time application, they are virtually free. The phone will wait until it is possible to send. This and congestion on the SMSC is why SMSes sent on New Years eve often are delayed.

JAlexoid 8y ago

I'm pretty sure that BTC work with MSINs, primarily.

pilsetnieks 8y ago
Yes, that's quite possible, I'm not that familiar of that side of things and might be thinking of the wrong number. Anyway, the point is that they don't use the same numbers you and I have in our phonebooks.

dfox 8y ago

Another issue apart from addressing is that all the SMS related logic resides in the SMSC and rest of the network sees the traffic as opaque payload. The article glosses over how the resulting message structure is actually sent over the radio interface and the SS7 network. In all it involves establishing (somewhat TCP-like) connection between your phone and SMSC across the signalling paths. The fact that this process is somewhat involved and consumes significant amount of radio resources is probably at least partially the reason why SMSes aren't particularly cheap. On the other hand on native LTE sending or receiving SMS could in theory consist of two UDP packets, but I'm not sure how widely is this deployed.

voltagex_ 8y ago
SMS over LTE is RCS [1], isn't it? I'd be happy to use it but my carrier/phone manufacturer have decided to limit the RCS apps I can use. 1: https://en.wikipedia.org/wiki/Rich_Communication_Services https://en.wikipedia.org/wiki/Rich_Communication_Services
fyfy18 8y ago
I thought SMS was built on top of the existing GSM signalling protocols, and so is effectively free to carriers. The bandwidth costs of a few hundred byte message are nothing compared to streaming a video or a phone call. The only reason why carriers charge for SMS is because they can.
bestham 8y ago
An SMS is sent in the GSM SACCH (Slow Associated Control Channel), that channel is normally used for timing information (how far away the handset is from the cell tower and the power control of the handset). Since SMS is not a real time application, they are virtually free. The phone will wait until it is possible to send. This and congestion on the SMSC is why SMSes sent on New Years eve often are delayed.