# Enabling TMSI Reallocation

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Descriptions

The TMSI (Temporary Mobile Subscriber Identity) reallocation function periodically assigns a new TMSI to a mobile subscriber. The purpose of this function is to prevent an intruder from identifying a mobile subscriber by listening to the signaling on the radio path. To increase confidentiality, the TMSI is reallocated at particular moments in time.

TMSI reallocation is performed in the following way:

•The mobile subscriber sends the TMSI together with the location area identity (LAI) to the VLR when accessing the network, e.g. during a location update.

•The VLR allocates a new TMSI to the mobile subscriber and sends it in a coded form (ciphering) to the mobile subscriber.

•The mobile subscriber stores the new TMSI and sends an acknowledgment to the MSC/VLR to release the old TMSI in the subscriber database and within the TMSI/IMSI correlation table.

To enable TMSI Reallocation, VLR parameters need to be configured on NSS side.

Implementation

| Enable TMSI Reallocation

1.Go to EMS >Configuration >NSS >VLR.

2.Click the button at the upper right corner.

1.On the System tab, configure the relevant parameters given in the following table.

2.Click the button to update parameters to application servers.

Sub-parameter | Description (Click highlight SAVE after change) | Recommended Value
TMSI Allocation | TMSI allocation control flag: •Disable: TMSI allocation is forbidden for all system subscribers. •Allocation: To allocate the exclusive TMSI to the same subscriber every time a call management service is requested. •Reallocation: To allocate a new TMSI every time a call management service is requested. | Reallocation

See Also

• Enable Ciphering

• Enable VLR Purge

• Enabling Equipment Identity Register

• Manage VLR Subscribers

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