Combined tala updating with imsi attach
This shall initiate the security functions in the new MME.
If the security functions authenticate the UE correctly, the new MME shall send a Context Request (IMSI, complete TAU Request message, MME Address, UE Validated) message to the old MME/S4 SGSN with the UE Validated set.
The e Node B shall include TAI ECGI of the current cell in every S1AP Uplink NAS Transport message it sends.
There are situations where e Node B can contain cells from more than one TA and cell changes that happen on same s Node B are not notified to the MME.
If the Context Request is sent to an old S4 SGSN the old S4 SGSN responds with a Context Response message. If the integrity check of TAU Request message (sent in step 2) failed, then authentication is mandatory.
If GUTI allocation is going to be done and the network supports ciphering, the NAS messages shall be ciphered.
The TAU procedure is initiated by an UE in either ECM-IDLE state or ECM-CONNECTED state.
The decision to perform SGW change during the tracking area update procedure is made by the MME independently from the triggers above.
NOTE: The MME delays the authentication such that the UE first updates its registered PLMN-ID to the new PLMN-ID selected by the RAN during handover.
If the MME has changed the new MME sends a Context Acknowledge (SGW change indication) message to the old MME/old S4 SGSN.
SGW change indication indicates a new SGW has been selected.
If the new MME is configured to allow emergency services for unauthenticated UE the new MME behave as follows: Step 7.
The MME (if the MME has changed then it is the new MME) determines to relocate the SGW.