M900/M1800 Base Station Subsystem Signaling Analysis Manual Contents

Issue 02 (2007-06-30) Huawei Technologies Proprietary i

Contents

8 TMSI Reallocation Procedure..................................................................................................8-1 8.1 Overview of TMSI Reallocation Procedure ..................................................................................................8-2 8.2 TMSI Reallocation Procedure .......................................................................................................................8-2 8.3 Signaling Procedure in the BSC....................................................................................................................8-3 8.4 Abnormal Cases and Troubleshooting...........................................................................................................8-3

8.4.1 Network Side .......................................................................................................................................8-3 8.4.2 Expiry of Timer T3250 ........................................................................................................................8-3

Figures M900/M1800 Base Station Subsystem

Signaling Analysis Manual

ii Huawei Technologies Proprietary Issue 02 (2007-06-30)

Figures

Figure 8-1 TMSI reallocation procedure ............................................................................................................8-2

M900/M1800 Base Station Subsystem Signaling Analysis Manual 8 TMSI Reallocation Procedure

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8 TMSI Reallocation Procedure

About This Chapter

The following table lists the contents of this chapter.

Section Describes

8.1 Overview of TMSI Reallocation Procedure

An overview of the TMSI reallocation procedure.

8.2 TMSI Reallocation Procedure The TMSI reallocation procedure.

8.3 Signaling Procedure in the BSC The internal processing procedure of the BSC.

8.4 Abnormal Cases and Troubleshooting

The abnormal cases when the TMSI reallocation procedure fails and how to troubleshoot them.

8 TMSI Reallocation Procedure M900/M1800 Base Station Subsystem

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8.1 Overview of TMSI Reallocation Procedure The TMSI reallocation takes place in conjunction with another procedure, such as at location updating or at call setup. It is performed in ciphered mode.

The purpose of the TMSI reallocation is to provide identity confidentiality for an MS, such as, to protect the MS against being identified or located by an intruder. If the identity confidentiality service is applied for an IMSI, a TMSI is used for the identification within the radio interface signaling procedures.

Usually the TMSI reallocation is performed at least at each change of a location area. The network can initiate the TMSI reallocation at any time if an RR connection exists between the network and an MS.

For the TMSI reallocation procedure, refer to the GSM protocol 24008.

8.2 TMSI Reallocation Procedure Figure 8-1 TMSI reallocation procedure

MS MSCBSCBTS

TMSI Reallocation Command(1)

TMSI Reallocation Complete(2)

Start T3250

Stop T3250

SDCCH

SDCCH

The network initiates the TMSI reallocation procedure by sending a TMSI Reallocation Command message to the MS and starts the timer T3250. The TMSI Reallocation Command message contains a new combination of TMSI and LAI allocated by the network or a combination of a LAI and the IMSI if the used TMSI is deleted. Usually the TMSI Reallocation Command message is sent to the MS through an RR connection in ciphered mode. :

Upon receipt of 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 the previous two cases, the MS sends a TMSI Reallocation Complete message to the network.

Upon receipt of the TMSI Reallocation Complete message, the network stops the timer T3250. If a TMSI was sent to the MS, the network considers the new TMSI as valid. If an IMSI was sent to the MS, the network considers the old TMSI as deleted.

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8.3 Signaling Procedure in the BSC The TMSI reallocation is initiated and controlled by the network and has no special processing on the BSC side.

8.4 Abnormal Cases and Troubleshooting 8.4.1 Network Side

Case Description RR connection fails.

Probable Causes If the RR connection is lost 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 can:

Use the IMSI for paging if the MS is the called party. Upon response from the MS, the TMSI reallocation is restarted.

Consider the new TMSI as valid if the MS is used as calling party. Use the identification procedure followed by a new TMSI reallocation if the MS uses the

old TMSI.

Troubleshooting No special processing is needed by the BSC.

8.4.2 Expiry of Timer T3250

Case Description The network releases the RR connection.

Probable Causes In the network, the timer T3250 detects the TMSI reallocation procedure. When the timer T3250 expires for the first time, the network releases the RR connection. In this case, the network shall abort the reallocation procedure and release all MM connections. You need to follow the rules described for RR connection failure.

Troubleshooting No special processing is required by the BSC.