LTE TRACKING AREA UPDATE PROCEDURE

Tracking Area Update-LTE

The network knows the location of a UE that is roaming within a network. This makes it possible for the mobile subscriber to receive a call wherever it is. To keep the network up to date with the subscriber’s location, the UE performs location updating.

Tracking Area Update

The location of a UE in LTE_IDLE mode is maintained on a Tracking Area (TA) List level. In LTE there is only one common Intra-LTE TA concept defined both for the RAN and for the CN. When a UE in LTE_IDLE mode moves into a cell that belongs to a TA different from the one(s) it is currently registered with, it performs a TA Update. The cell tracking area is broadcast in System Information.

Traffic Case Tracking Area Update

1. The UE performs cell re-selection (typically based on system information received in the previous cell).

2. The UE reads the System Information, broadcast in the selected cell.

4. If the TA that the cell belongs is not the TA that the UE is registered in, the RRC Connection is established, with the NAS message “Tracking Area Update (TAU) Request”.

5. The Tracking Area Update (TAU) Request message is provided to the MME in the “Initial UE Message”.

6. Conditional step:

If the integrity protection check fails the MME performs authentication and activates the NAS security functions using the Authentication and NAS Security Activation procedure.

7. The MME sends the NAS message “Tracking Area Update (TAU) Accept” to the UE, using the DL NAS Signalling Transfer procedure.

8. If the GUTI has been re-allocated, the NAS message “Tracking Area Update (TAU) Complete” is transferred to the MME, using the UL NAS Signalling Transfer procedure

9. Since the MME did not establish any bearers or user plane connection the MME releases the radio connection (andRAN resources) by the MME-initiated Connection Release.