1. HUAWEI BSC6000 Base Station Subsystem
Signaling Analysis Guide 9 TMSI Reallocation
9 TMSI Reallocation
About This Chapter
The TMSI reallocation takes place in ciphering mode. It is generally related to another procedure,
such as location update or call establishment.
9.1 TMSI Reallocation Procedure
The purpose of the TMSI reallocation procedure is to provide identity confidentiality, that is, to
protect a user against being identified and located by an intruder. Usually, the TMSI reallocation
is performed at least at each change of a location area. It can be initiated at any time by the
network if an RR connection exists between the network and an MS.
9.2 Internal BSC Signaling Procedure of TMSI Reallocation
This topic describes the internal BSC signaling procedure of TMSI reallocation.
9.3 Abnormal TMSI Reallocation Cases
This topic describes the abnormal TMSI reallocation cases.
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2. HUAWEI BSC6000 Base Station Subsystem
9 TMSI Reallocation Signaling Analysis Guide
9.1 TMSI Reallocation Procedure
The purpose of the TMSI reallocation procedure is to provide identity confidentiality, that is, to
protect a user against being identified and located by an intruder. Usually, the TMSI reallocation
is performed at least at each change of a location area. It can be initiated at any time by the
network if an RR connection exists between the network and an MS.
Figure 9-1 shows the TMSI reallocation procedure.
Figure 9-1 TMSI reallocation procedure
MS BTS BSC MSC
TMSI
Reallocation Command(1)
SDCCH
Start T3250
TMSI
Reallocation Complete(2)
SDCCH
StopT3250
The TMSI reallocation procedure is as follows:
l The network initiates the TMSI reallocation procedure by sending a TMSI Reallocation
Command message to the MS and starts timer T3250. The TMSI Reallocation Command
message carries a new combination of TMSI and LAI allocated by the network or an LAI
and the IMSI if the used TMSI is deleted. Usually, the TMSI Reallocation Command
message is sent to the MS using an RR connection in ciphering mode.
l Upon receiving the TMSI Reallocation Command message, the MS stores the LAI in the
SIM. If the received identity is the IMSI of the relevant MS, the MS deletes any TMSI. If
the received identity is a TMSI, the MS stores the TMSI in the SIM. In both cases, the MS
sends a TMSI Reallocation Complete message to the network.
Upon receiving the TMSI Reallocation Complete message, the network stops timer T3250.
If a TMSI is sent to the MS, the network considers the new TMSI as valid. If an IMSI is
sent to the MS, the network considers the old TMSI as deleted.
9.2 Internal BSC Signaling Procedure of TMSI Reallocation
This topic describes the internal BSC signaling procedure of TMSI reallocation.
The network initiates and controls the TMSI reallocation procedure and the BSC does no special
processing.
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3. HUAWEI BSC6000 Base Station Subsystem
Signaling Analysis Guide 9 TMSI Reallocation
9.3 Abnormal TMSI Reallocation Cases
This topic describes the abnormal TMSI reallocation cases.
9.3.1 TMSI Reallocation Caused by RR Connection Failure on the Network Side
This topic describes the fault, probable causes, and handling suggestions.
9.3.2 TMSI Reallocation Caused by T3250 Expiry
This topic describes the fault, probable causes, and handling suggestions.
9.3.1 TMSI Reallocation Caused by RR Connection Failure on the
Network Side
This topic describes the fault, probable causes, and handling suggestions.
Fault
The TMSI is reallocated due to RR connection failure on the network side.
Probable Causes
If the RR connection fails before the TMSI Reallocation Complete message is received, all MM
connections should be released and both the old and the new TMSIs should be considered as
occupied for a certain recovery time.
During this period the network may:
l Use the IMSI for paging if the MS is the called party. Upon response from the MS, the
TMSI reallocation is restarted.
l Consider the new TMSI as valid if the MS is the calling party.
Initiate an identification procedure followed by a new TMSI reallocation if the MS uses the old
TMSI.
Handling Suggestions
No handling is required.
9.3.2 TMSI Reallocation Caused by T3250 Expiry
This topic describes the fault, probable causes, and handling suggestions.
Fault
The network releases the RR connection.
Probable Causes
The TMSI reallocation is supervised by the timer T3250 in the network. At the first expiry of
timer T3250, the network releases the RR connection. In this case, the network aborts the
reallocation procedure, releases all MM connections, and follows the rules for RR connection
failure.
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4. HUAWEI BSC6000 Base Station Subsystem
9 TMSI Reallocation Signaling Analysis Guide
Handling Suggestions
The BSC does no special processing.
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