Why did SMS become so popular

Background: This is how sending SMS works

The oldest form of text messaging in mobile communications is SMS. It also works across providers.
Photo: teltarif.de It is well known that you can not only make calls with a cell phone. SMS messages - this abbreviation stands for Short Message Service - are still very popular with many users. And not just on New Year's Eve. The SMS is actually a waste product of the mobile phone standard, which has long developed into an everyday means of communication. With the advent of the OTT (Over The Top) Messenger - the best-known example is WhatsApp - the amount of SMS messages sent has fallen sharply.

The oldest form of text messaging in mobile communications is SMS. It also works across providers.
Photo: teltarif.de Today, SMS are often used for authentication, for example for a login or bank transfer with SMS-TAN or another action where you want to be sure that the right user is meant and authorized.

But as natural as the SMS was or still is, the process in the cellular network is just as complex so that an SMS comes from the sender to the recipient.

From cell phone to base station

An SMS sent by the mobile phone initially takes the same route as a telephone call. An SMS is sent to the SMS center of your own network operator via the network elements known from telephony, such as the transmission mast and base station controller (BSC). The SMS center of your own network operator is also responsible for the customer when he is abroad. The bottom line is that the route via the foreign networks to the SMS center is longer. The SMS center is something like an exchange for the SMS. It requests information from the HLR as to where exactly the SMS should be sent and then forwards it to the Mobile Switching Center, which is currently serving the recipient.

From this exchange, the mobile phone you are looking for is then called out via several transmission masts, the so-called LAC area. This procedure is explained in more detail in the background article on cell phone calls. As with an incoming call, the customer's cell phone is called within the LAC area. The cell phone reports back, authenticates itself and receives the SMS. If the customer cannot be reached, the SMS center saves the SMS. Since the Home Location Register (HLR) has noted that an SMS has not yet been delivered, the SMS center is notified as soon as the customer is available on the network again. The delivery will then be attempted again.

Billing: differences between prepaid and postpaid

In the case of prepaid cards, the invoice information is created when the SMS is sent. The switching center in the HLR determines that the customer is telephoning on a prepaid basis. The credit account is then checked in the corresponding billing system and it is calculated how much the call or the SMS will cost. This is quite easy with a text message because it is a closed message. Thus, the exchange or the SMS center only needs the information "may be sent" or not. For contract customers, an entry is made in the billing system stating that and where the SMS was sent. This entry is then read out in the invoice run.

If the customer has an SMS flat rate, the resulting data records are discarded.

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