TMSI
Temporary Mobile Subscriber Identity

In order to ensure subscriber identity confidentiality the VLR (Visitor Location Register) and SGSN (Serving GPRS Support Node) may allocate TMSI (Temporary Mobile Subscriber Identities) to visiting mobile subscribers. The VLR and SGSN must be capable of correlating an allocated TMSI with the IMSI (International Mobile Subscriber Identity) of the MS (Mobile Station) to which it is allocated. A MS may be allocated two TMSI, one for services provided through the VLR, and the other known as the P-TMSI (Packet TMSI) for services provided through the SGSN.