Section: 4.7.6 P-TMSI reallocation procedure 4.7.6.0 General
Content: A temporary mobile station identity for GPRS services, the Packet-TMSI (P-TMSI), is used for identification within the radio interface signalling procedures. The structure of the P-TMSI is specified in 3GPP TS 23.003[ Numbering, addressing and identification ]  [10]. The P-TMSI has significance only within a routing area. Outside the routing area the P-TMSI has to be combined with the routing area identification (RAI) to provide for an unambiguous identity. The purpose of the P-TMSI reallocation procedure is to provide identity confidentiality, i.e. to protect a user against being identified and located by an intruder (see 3GPP TS 43.020[ Security related network functions ]  [13], 3GPP TS 23.060[ General Packet Radio Service (GPRS); Service description; Stage 2 ]  [74] and 3GPP TS 33.102[ 3G security; Security architecture ]  [5a]). Usually, P-TMSI reallocation is performed at least at each change of a routing area (Such choices are left to the network operator). The reallocation of a P-TMSI is performed by the unique procedure defined in subclause 4.7.6. This procedure can only be initiated by the network in state GMM-REGISTERED. P-TMSI can also be implicitly reallocated in the attach or routing area updating procedures (see subclauses .1 and 4.7.5). The implicit reallocation of a P-TMSI is described in the corresponding subclauses. NOTE: Normally, the P-TMSI reallocation will take place in conjunction with another GMM procedure, e.g. at routing area updating (see 3GPP TS 29.002[ Mobile Application Part (MAP) specification ]  [37]).