How does network behave when UE sends TAU to a new/different MME ?

Question

There are couple of procedures are defined which consist of NAS as well as RRC signalling messages exchange.
Some of the NAS message sends to an UE through RRC Connection Reconfiguration message as piggybacked and some as DL Info transfer.

I want to know, Is there any procedure exists in lte when an UE receives RRC Connection Reconfiguration along with NAS message and responds back to network with NAS message first and then Reconfiguration Complete to eNodeB.

Usually, I saw UE sends RRC Connection Reconfiguration Complete message first then NAS response message.

Answer 1

On behalf of Bart:

I believe there is no such scenario as indicated in the question.

Before TAU can happen with MME the UE needs to have S1 with it. So...
There is UE attached to MME -old, because of any reasons it performs the HO to MME-new. When this is done it's done. Then as a separate scenario/operation IF the TAU triggers are matched UE will perform TAU.

In my opinion it's hard to call it something different than just TAU, especially a TAU with new MME.