I have scenario where in I have to gracefully shutdown/disconnect all UE's in connected state at RRC and go for reboot of the complete system. Here are the steps that I have followed -
1. Find all UE's in RRC which are in connected state
2. Send UE Context Release Request to MME for the UE with Cause as Misc_Cause_O_M_Intervention.
3. Once we receive UE Context Release Command from MME, Start UE Release procedure at eNodeb.
4. When we send RRC Connection Release Use Cause as "other"
5. Send UE Context Release Complete to MME.
6. Repeat Above steps for all UE's.
7. Go for reboot.
Here in this scenario, after sending RRC Connection Release to UE, it is immediately trying to connect to eNodeb with message RRC Connection Request with establishmentCause as "HighPriorityAccess" and MME is releasing the UE again.
I wanted to know why UE is trying to connect again.
FYI: UE was just in connected state and it was doing any data transfer (Both in Uplink and Downlink).