Kenshin Trading Co., Ltd. Main products: Shanghai Telecom Tianyi 3G series products. Company address: Room 5007, Building 2, No.391-393 Dongdaming Road, Hongkou District, Shanghai. Registered capital of the company: 654.38 million yuan.
Telephone cards generally refer to SIM cards, which are communication tools provided by communication service providers.
SIM card is the key for GSM mobile phone to connect to GSM network. Once the SIM card is removed from the mobile phone, the mobile phone will not be able to enjoy all kinds of services provided by network operators except emergency calls.
SIM card can not only be used as a key, but also provide a lot of convenience for users. Users only need to insert or embed the SIM card into any GSM terminal to realize communication. SIM card also manages a lot of information provided to users, which can be used to store short messages, especially those received when users are away or absent.
Functional embodiment
Specifically, its functions are mainly reflected in the following aspects. The data stored in the SIM card can be divided into four categories: the first category is fixed data.
This kind of data is written by SIM card center before the mobile phone is sold, including international mobile subscriber identification number (IMSI), authentication key (KI), authentication and encryption algorithm, etc. The second category is temporarily stored network data. Such as location area identification code (LAI), mobile subscriber temporary identification code (TMSI) and public telephone network code without access.
The third category is related business codes, such as personal identification number (PIN), unlocking code (PUK), billing rate, etc. The fourth category is the telephone book.
Almost all the user's data are stored in SIM cards, so SIM cards are also called "subscriber data identification cards". SIM cards can be divided into big cards and small cards. Small cards are called "plug-in SIM cards", that is, chips on big cards.