Is a temporary identity issued to a GPRS enabled mobile device to track its location within in a GSM or a UMTS network, and is unique within a given Routing Area (RA). The location update procedure allows a mobile device to inform the cellular network, whenever it moves from one location area to the next.
The P-TMSI is used by the GPRS network to page the specified mobile device. When a subscriber is paged in an attempt to deliver a call or SMS and the subscriber does not reply to that page then the subscriber is marked as absent in both the MSC/VLR and the Home Location Register (HLR) (Mobile not reachable flag MNRF is set). The next time the mobile performs a location update, the HLR is updated and the mobile not reachable flag is cleared. The P-TMSI is comprised of 32bits and is associated with the TLLI (Temporary Logical Link Identifier).