5G Data Inactivity Timer expired - message flow

Hi All,
For 5G, if data inactivity timer expired, then what message flow is there for connected ps call?
Does sgnb send rrc connection release or some different message?
I.e. sgnb release required?

For SA RRC release.
For NSA sgnb release.

It depend upon the configuration.

If Inactivity time expires for data in NR, SgNB send “SgNB Activity Notification to MeNB”.
After this its up to MeNB, it can send by “SgNB release request” to SgNB or it can keep SgNB configured.
In second case it will only release SgNB if RRC Release happened in LTE.
2nd case (to not release SgNB even after data inactivity timer expiry), have advantage that it reduces signalling in air interface (RRC) as well as in backhaul (to change bearers).

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Ok, for 2nd case any other parameters configured to avoid release?

2nd point talk about SgNB release at the time when LTE RRC is released.
If LTE is going to release, then it is not possible to retain NR.
SgNB has to be released.

Hello Experts.

From 5G Bullets i understood:

If dataInactivityTimer at gNB expires and it send RRCRelease message while UE in poor coverage, then UE may fail to receive the message, and stay in RRC Connected while gNB release all resources. For such cases, it’s useful UE to have an Inactivity Timer to allow it to release itself to RRC Idle.
So dataInactivityTimer value should be larger than gNB Inactivity Timer, this way the normal release mechanism will always be attempted first (gNB monitors periods of inactivity and releases UE to RRC Idle or RRC inactive).
Now, if dataInactivityTimer expires, the UE will release itself to RRC Idle and inform NAS layer that an RRC Release has occurred - and the cause “RRC Connection Failure”. Then this will trigger the NAS to initiate Registration procedure to Core.

dataInactivityTimer (MAC-CellGroupConfig): 1, 2, 3, 5, 7, 10, 15, 20, 40, 50, 60, 80, 100, 120, 150 180 seconds

But now my query: I am guessing this trigger by NAS layer is only when there’s some uplink data to be sent. But I would expect a service request and not a registration request.

Any help?

Thank you @Nitin. Quite resonable information.

In Hauwei RAN there is a 3rd option where Sgnb does not need to inform MeNB about the inactivity of the NR leg and will initiate SCG release by itself once SCG inactivity timer expires. This is done by sending “SCG release Required” message to the MeNB.