Why can you make emergency calls like 110 without a SIM card

First, let's understand how a SIM card works. I do MTK, Spreadtrum solutions, answer only for MTK, but other solutions are much the same. There are several pins in the SIM card slot connected to the PCB motherboard. The exact number of pins depends on how the solution is used. Let me list a few must-haves:

SIM_VDD Indicates the voltage output of the SIM card

SIM_I/O Data input and output interface of the SIM card

SIM_CLK Clock of the SIM card

SIM_RST Reset signal of the SIM card

As long as the mobile phone is powered on normally, it is a process of detecting whether there is a SIM card, searching the network and registering. The registration network is based on the priority of the SIM card or the Pr phone cards and then try to register one by one network until all the networks fail to pass or register successfully. This link does not affect the RF function of the mobile phone at all, that is to say, the RF module can work normally and can receive and transmit signals. Apparently, without a card, which means without an account, I can't access the frequency bands I support.

0311fb7499284f9e241ffaa9c9bed654Now that the phone's RF function is working, it's time to get to the phone protocol. If the phone is not registered successfully, it will choose the best network according to the pre-made rules of the phone, but you can only enjoy limited service on this network, you can not use the mobile network resources as usual, only in the emergency state can use reasonably. The RF module normally sends and receives signals, and then the signals are attached to the network and sent. If there is a mobile GSM network in the area, the signals are attached to the GSM and sent. This process is the same as the normal dialing process.

If your RF module is working, but YOU are in an area where you can't find any frequency networks, you still can't dial an emergency number. You cannot find the available communication networks and attachment, that is to say, even if you are in this place have each band mobile phones can search to, if none of the available global communication network coverage at this point, you can't dial the phone, because only the several specific spectrum is used to support mobile communications, for example, some support FM frequencies, some bands support radar and so on. Then it's just satellite talk.

In China, the emergency numbers are all transferred by intelligent manual transfer. Some places can be connected, and some places can not be connected. This is the operator's problem. Of course, if your phone doesn't have an Internet permit, it's probably the phone's fault. What is an access permit? Is the mobile phone opening the battery after the piece of blue paper, without this, no matter how mobile phone cow force, is also a Shanghai machine.

Tip: If the emergency call fails, try the extra area code, such as 010110.

Shopping Cart