The second category is temporarily stored data related to the network. Such as location area identification code (LAI), mobile user temporary identification code (TMSI), public telephone network code prohibited from access, etc.

SIM card is called "user identification card". It is actually a smart card containing large-scale integrated circuits, which is used to register important data and information of users. The most important function of SIM card is authentication and encryption. When a user moves to a new area to make or receive a call, the switch must authenticate the user to determine whether it is a legal user.