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TMSI Number

Temporary mobile station identities (TMSIs) are allocated within a VLR for enhancing the system security. A TMSI corresponds to an IMSI uniquely within a VLR.
The structure of TMSI can be codetermined by the carrier and the equipment provider.
The principles for TMSI allocation are as follows:


  • A TMSI is composed of four bytes, which can be eight hexadecimals.
  • The 32 bits of a TMSI cannot be all ones, because an all-one TMSI in a SIM card indicates an invalid TMSI.
A typical example of TMSI is 60340039.