Section: 2 Identification of mobile subscribers 2.1 General
Content: A unique International Mobile Subscription Identity (IMSI) shall be allocated to each mobile subscriber in the GSM/UMTS/EPS system. NOTE: This IMSI is the concept referred to by ITU-T as "International Mobile Subscription Identity". In order to support the subscriber identity confidentiality service the VLRs, SGSNs and MME may allocate Temporary Mobile Subscriber Identities (TMSI) to visiting mobile subscribers. The VLR,SGSN and MME must be capable of correlating an allocated TMSI with the IMSI of the MS to which it is allocated. An MS may be allocated three TMSIs, one for services provided through the MSC, one for services provided through the SGSN (P-TMSI for short) and one for the services provided via the MME (M-TMSI part GUTI for short). For addressing on resources used for GPRS, a Temporary Logical Link Identity (TLLI) is used. The TLLI to use is built by the MS either on the basis of the P-TMSI (local or foreign TLLI), or directly (random TLLI). In order to speed up the search for subscriber data in the VLR a supplementary Local Mobile Station Identity (LMSI) is defined. The LMSI may be allocated by the VLR at location updating and is sent to the HLR together with the IMSI. The HLR makes no use of it but includes it together with the IMSI in all messages sent to the VLR concerning that MS.