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Reply To: P-TMSI & TLLI


Quoted definitions:

Temporary Logical Link Identity
• Used on the GPRS air interface (RLC/MAC) to address the mobile.
• Allocated by the MS based on P-TMSI (local or foreign TLLI) or directly (random TLLI).
• Auxiliary TLLI is allocated by the SGSN but this is no longer required from R99 onwards.
• Part of the TLLI codespace is reserved for G-RNTI.
• Used by LLC in SGSN to uniquely identify the MS.
• TLLI along with NSAPI is used by SGSN to identify the PDP context to which a packet belongs.

Packet Temporary Mobile Subscriber Identity
• Variants exist based on the type of CN: P-TMSI-GSM-MAP, P-TMSI-and-RAI-GSM-MAP. Here we refer to P-TMSI-GSM-MAP when we say P-TMSI.
• Used instead of IMSI to implement subscriber confidentiality in the PS domain.
• Allocated by SGSN which maps it to the IMSI.
• Extensively used by GMM.
• Generally reallocated when Routing Area changes. Has local context within a RA, outside which it has to be combined with RAI.
• Used by RRC for CN originated paging. If it exists, preferred over IMSI for packet paging.
• A P-TMSI signature exists to enable GMM establish the context of a mobile.