The principle of sending short messages by mobile phone. Why does iphone4s turn off cellular data to send SMS as usual? Is the sending principle of SMS irrelevant to GSM?

SMS is sent through voice signaling channel. As long as your mobile phone is on, there is a signaling channel when there is a signal, and you can send a message at any time. The SDCCH mentioned above is a dedicated signaling channel. When you have nothing to do, send a message and leave. SACCH is an associated signaling channel, that is, when you make a phone call or surf the Internet, the channel you are using is called a business channel, but you still need a signaling channel, but you won't be given a signaling channel specially, but the signaling will be sent to you in the business channel (your mobile phone can't monitor two channels at the same time). This channel is called an associated signaling channel.

Therefore, when texting, it has nothing to do with the data. You can text when it is closed.

Short messages are sent by GSM. Use GPRS or EDGE to surf the internet. As far as your mobile phone is concerned, there is only one communication module, and whether it is a short message call or surfing the Internet, it is sent from your mobile phone antenna through this communication module.

Why not all through the internet? First of all, the Internet generally uses TCP/IP, which has a great feature. Deeply loved by users. Even this network cable or this channel, you can use it, and I can also use it. In this case, the quality of service cannot be guaranteed. In wireless, this quality of service cannot be guaranteed, because the wireless channel itself is unstable. Generally speaking, people hope that the time delay will not be too big, so they can't use the Internet.

In addition, when surfing the Internet, your mobile phone actually takes up four time slots at a time (of course, it is used with others), and when calling and sending text messages, you only need 1 time slot. Your mobile phone is busy for a long time, which will consume more power. . . Especially for smart phones nowadays, I usually turn off data.

Third, if everyone uses the internet, if you turn off the data, you can't be contacted by phone or text message, which is definitely not acceptable. . .

In addition, the problem of adding MMS is added. MMS is indeed sent and received through the data network. But generally, MMS can be sent and received normally even if the data is turned off. This should be done by the terminal chip itself. In the same way, avoid someone sending you MMS. Just because you turned off the data, you never got it. . .