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

5G NR
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22

In NSA, RRC is at 4G. But 4G not has RRC-inactive state.
Please check these NSA timers are to remove 5G path when user not have 5G traffic?

23

An UE inactivity at gNB is detected if there is no user data sent or received on SCG split bearer from a UE for an operator configurable time.

The gNB sends after the inactivity detection, an SgNB Release Required message to the MeNBs with the cause value ‘User Inactivity’.

24

What makes UE to change state from Inactive to Idle?
So does this mean it is also timer based?

25

There 's no chance UE will do no activity in 1500 seconds.
For sure something will happen in 1500 seconds.
So all UEs will be in connected mode for good in 5G SA Huawei.
I mean in inactive state.

26

I am asking for call flow only.
So once UE spent 1500 s in inactive mode, and that too under same gNB, then UE will be RRC released to RRC idle.
And how do gNB know that UE is satisfy this condition?
While UE perform RNA update under same gNB, right?

27

Yes dear👍

28

gNB knows UE no data sent/received over 1500 s, gNB will release RRC of this UE.
If UE already move to another gNB in same RNA area, when UE transit from inactive to connected, UE send RRC resume request to gNB2, gNB2 will ask gNB1 for UE context, if gNB1 already release UE context, this resume will be released by gNB2.
Inactive state, UE has I-rnti number. This number contain gNB-id. So in RRC resume, UE send with I-rnti. gNB2 can know gNB1 id.

29

gNB1 or gNB2 can send RRC relase if UE has initated periodic RNA update.
Because in case of UL data gNB has to setup RRC connection, right?

30

Rrc at gNB1 is still kept while UE in inactive state.
If UE moved to gNB2 coverage, UE is not established RRC at gNB2, still gNB1.
So gNB1 release RRC.

31

If UE moves to gNB2 it will send rach to gNB2 only …not gNB1.

32

Yes, RACH when UE initiate RRC resume.
If not, no RACH.

33

Still we have periodic TAU update for 54 mins :wink:

34

I’m speaking about apps on mobile.
In max 20 seconds one of that app will send or receive data.

35

Ideally it does, still we consider periodic tau with no activity for 54 mins.
Though to handle such small data app packets, 3gpp is working on Small data transmission in RRC Inactive state.

36

Ok. So summary is:

Once UE is in inactive mode

  1. If IE have UL data to send, it will initiate RRC resume request.

  2. If UE have DL data, RAN paging will happen.

  3. If there is no DL/UL data for UE, it will keep doing periodic RNA update every T380.

  4. If UE spent 1500 s without any DL/UL data, gNB will release UE context and when UE performs next RNA update gNB will send RRC release to UE.

  5. If UE initiate any UL data while RRC inactive and gNB has already released UE context, then gNB will initiate RRC setup in response to RRC resume by UE. This is to setup UE context again.

2 Likes
37

What is diff between rrc resume request and rrc resume request I ?

38

If UE include short I-RNTI is RRC resume if full I-RNTI its resume request 1.

39

++ UE move to inactive state due to timer expiry.

40

Yeah thats clear to me.

If anyone disagrree with this please raise. Because it’s nowhere documented in Standard I guess.
So need to clear it.

41

This 1500 s is vendor specific, right?