Hi Experts.
I’m adding Scenarios for Tracking Area Update required in LTE by UE if required add in same.
Any other scenario add here?
Usually TAU doesn’t happen when TAC changes, we have TA list of 16 TACs, when TAList gets changed then only TAU happens.
TAU will be triggered only if TAC received is not in TA list, irrespective of scenario.
Good point. Do you mean TAI list defined in MME given to UE during attach accept message?
UE mm will be maintaining TA list and TAC will be received in sib1 if I am not wrong.
So UE will check whether TAC is there in the list if not TAU request will be triggered to MME.
Yes it’s in sib1 as well.
But I think you need to get TAI list consist of multiple TAC in attach accept.
Any Core Expert to confirm for TAI list there in MME end?
How it is given to UE?
Any rule for TAI how many TAC it consists of?
Yes could be.
I think in Attach accept and TAU accept, MME provides TAList to UE.
Also there is no fix numbers of TAC in 1 TA list.
Can be from 1 to max number supported by MME design like in my case 16 but TAList is dynamic in our netwrk.
If it finds UEs do frequent TAU then that TAC gets dynamically added in the TAlist to avoid frequent TAU.
Ok 
good point dynamic TA.
Dear Experts.
Is there any periodic Tracking Update Timer configured at eNB/gNB end, like T3412 which is configured at CORE end?
Periodic TAU timer runs at UE and Core.
RAN side there is no periodic TAU timer available.
Ok thanks!
And is this value transmitted in NAs message to UE?
Yes, during Attach/TAU UE gets this info.
Most commonly used value 54 mins.
Yes. In case of LTE it is 54 min.
Where can I get this value in case of 5G?
In which message will I find this value?
In Registration Accept, t3512 is the new timer.
That’s mean paging is done on TAL, not TAC??
One more scenario to add here I think would be:
Before the DDS switch, the device will send a TAU request with active flag 0 (zero).
