What is the principle of receiving text messages during travel?

The mobile phone will send out information regularly, and the surrounding base stations (BTS) will accept this information and update the location. The base station closer to you is your service base station. When you travel from one city to another, not only your base station has changed, but also the MSC (Mobile Switching Center) in your area has changed and moved to another city. At this time, the mobile phone sends a message, the base station receives and sends a base station controller BSC, and then visits the MSC, which will retrieve your information according to the HLR (Home Location Register) of your registered place. If you find that it is a user in another city, send a text message to welcome to XX city. Of course, this short message is done through SMS (Short Message Service Center).

If you change MSC, you will roam across provinces.