Why UE sends RRC Connection Request followed by EUTRA triggered RRC Connection Release?

Question

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).

Answer 1

In 3GPP Release 10, RRC specs has introducted "extendedWaitTime-r10" IE within the "RRC connection Release" message. EnodeB uses this IE to ask UEs, not to send RRC connection request till the duration assigned to "extendedWaitTime-r10" . It ranges from 1 to 1800 seconds.
I am not sure which software version you are using in both the sides UE as well as eNodeB. However, MME' NAS layer has provision in detach request (network to UE side).
In the network to UE direction:
Bits
3 2 1
0 0 1 re-attach required
0 1 0 re-attach not required
0 1 1 IMSI detach
1 1 0 reserved
1 1 1 reserved
By using "re-attach not required" cause, MME can ask to UE not try re-attach to the network.

Comments

Can you let me know the specific 3Bit IE which is sent by MME inside detach request