Abbreviation for Packet-Temporary Mobile Subscriber Identity
General Information:
The P-TMSI is introduced as temporary identifier of a GPRS subscriber for
GPRS-mobility management. The mobile station will use the P-TMSI for identification
purposes
towards the SGSN. Please note the close relationship between P-TMSI and
TLLI (Temporary Logical Link Identity).
Detailed Information:
The P-TMSI serves the same purpose as the TMSI (Temporary Mobile Subscriber
Identity) which is subscriber confidentiality.
Opposed to the TMSI which is allocated by the VLR (Visitor Location Register),
the P-TMSI can only be allocated by the SGSN.
And there is another difference of TMSI and P-TMSI: While the P-TMSI
can be allocated in deciphered mode the TMSI will only be allocated in
ciphered
mode.
To avoid ambiguities between the two parameters the P-TMSI always has
the two most significant bits set to '11'bin. Consequently, the VLR will
only
use TMSI
values with the two most significant bits set to '00'bin, '01'bin or
'10'bin (see figure).
Each P-TMSI is unique only in the routing area in which it was allocated.
Outside this routing area the P-TMSI plus the RAI (Routing Area Identification)
will
be used to uniquely identify a mobile station.