How RRC Inactive to RRC idle transition happen in NR SA?

Hi Experts,
Does anyone knows how RRC Inactive to RRC idle transition happen in NR SA?

RRC inactive mode is more or less same as idle mode with the exception that UE will store the RRC context for some time.
After some timer expiry, UE will just delete that context and move to RRC idle mode.

Yes, this I know.

Which timer? There is no timer given to UE in SuspendConfig except T380, which is used for periodic RNA update.

3GPP has given below statement.
In response to a request to resume the RRC connection, the network may resume the suspended RRC connection and send UE to RRC_CONNECTED, or reject the request to resume and send UE to RRC_INACTIVE (with a wait timer), or directly re-suspend the RRC connection and send UE to RRC_INACTIVE, or directly release the RRC connection and send UE to RRC_IDLE, or instruct the UE to initiate NAS level recovery (in this case the network sends an RRC setup message).

image

Oops, I am wrong.

But there is no clear information on how /what criteria is used to change UE state from Inactive to Idle.

Looks like there is no time based transition as of now.

Shouldn’t there be an RRC connection release to go to idle mode from inactive state?

If UE is in inactive, RRC release cannot be given to it.
3GPP said that, RRC Inactive to RRC Idle transition happen via RRC Connected.

In response to a request to resume the RRC connection, the network may resume the suspended RRC connection and send UE to RRC_CONNECTED, or reject the request to resume and send UE to RRC_INACTIVE (with a wait timer), or directly re-suspend the RRC connection and send UE to RRC_INACTIVE, or directly release the RRC connection and send UE to RRC_IDLE, or instruct the UE to initiate NAS level recovery (in this case the network sends an RRC setup message).

But depend on what criteria does this happen?
No where mentioned…

Hi Experts,
What is reason for UE to move for NR RRC inactive state?
I mean, is there any timer in gNB getting expired or some other cause?
I am not able to find it reason for same.

It’s like cell-fach state in umts, reduce UE power consumption when transition between Idle & Connected frequently.
Huawei has timers parameters.

Ok, so it’s timer controlled like inactivity timer we have in LTE?

Yes. One procedure related to RRC inactive state is RNA update.

RRC connection release given to UE with suspend config IE.
Now with any paging notification UE move to RRC connected by RRC resume request or RRC resume request.
Why gNB send RRC connection release with suspend config IE?
Is there is some logic behind this?
As per our discussion it’s due to timer which you mentioned it’s there in Huawei.

Suspend is for RRC inactive UE support.

Yes but it’s due to timer expiry gnb send rrc connection release.
Is it correct?
May I know name of timer and recommended value?
Not able to find it for Ericsson and Nokia.
If we stop data to UE then also UE move to RRC inactive.

PHY, MAC, RLC, PDCP resource are released, RRC is kept.
gNB remember UE context.

gNB considers UE as inactive:

  • UE is signalling-only, no DRB for more tha 60 s.
  • After UE setup a DRB, UE don’t transmit or receive data for a timer (UeInactivityTimer)
  • UE support this state

This timer can be set by Huawei parameter (UeInactivityTimer), default 20s.

Thanks understood :+1:
So basically UE move to RRC idle after 1500 s may be some other timer as well there.

1500 s is fixed now.

Below parameters for nokia

Inactivity handling (NSA mode)

nsaInactivityTimer =10 s

Inactivity handling (SA mode)

drbInactivityTimerSA=10 s
srbInactivityTimerSA=60 S
inactivityTimerSA=10 S