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  • #51793

    please can you tell me about the diffrence between P-TMSI and the 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.


    ok, so we can say that the PTMSI is the MS id used for SGSN authentication, while TLLI is the data id, used to route the packets from SGSN to the MS.

    Maybe it’s too simplified ?

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