Hi NR experts,
If a UE enters the RRC Inactive state, what are the required states for the resume procedure?
Check this out: RRC Modes in 5G
What do you mean by “to resume, what all states are required?”
For the UE to resume from RRC Inactive state, it requires either paging from the network or uplink data present in the UE buffer to trigger the resume procedure.
I mean, can the UE resume ongoing data when transitioning from RRC Inactive to RRC Connected?
Or does it follow conditions that lead to RRC Inactive to Idle transition?
Very well mentioned!
Yes, that is the purpose of the RRC Inactive state – to enable faster data resumption.
Let’s say a user is downloading or uploading data in NR Connected mode.
After some time of inactivity, the user transitions to the RRC Inactive state.
Now, if the user resumes the download, will the file be downloaded from the beginning or continue from where it stopped?
In the scenario you described, the file download should have been completed in the RRC Connected state before the UE transitions to the Inactive state, unless a Radio Link Failure (RLF) occurs midway.
If an RLF is triggered, the UE would either perform a reestablishment to move back to the Connected state or transition to the Idle state if the reestablishment fails.
Correct!
If it’s a video file, the user can pause it while in the RRC Connected mode. After the inactivity timer expires, the UE transitions to the RRC Inactive state. Once the user resumes the video, the UE reactivates the RRC Connected state through an RRC Resume procedure.
Do you know how many inactivity timers need to be configured in an SA gNB? Are there two separate inactivity timers—one for transitioning to the RRC Inactive state and another for the Idle state?
There are separate inactivity timers for different scenarios in an SA gNB:
- SRB/DRB Inactivity Timer: This controls the release of signaling and data radio bearers when there is no activity for a specified duration.
- Idle Mode Inactivity Timer: Determines when the UE transitions from RRC Connected to RRC Idle due to inactivity.
- Inactive Mode Inactivity Timer: Manages the transition from RRC Inactive to RRC Idle if the UE remains inactive for too long without resuming the connection.
These timers help optimize network resource usage while ensuring fast reconnection when needed.
If the main flag for RRC Inactive is enabled in the gNB, is it mandatory for the gNB to transition the UE to the RRC Inactive state?
In that case, the RRC Release message should include the Suspend Config IE to inform the UE about the transition.
If the UE supports the RRC Inactive state and the feature is enabled, then yes, the gNB must transition the UE to the RRC Inactive state, and the RRC Release message should include the Suspend Config IE.
Hi @Ali_Khalaf , I noticed that you mentioned if the UE in RRC Inactive mode moves to a new gNB, it will send an RRC Resume Request.
However, I believe that if the target gNB is within the same RNA, the UE will remain in RRC Inactive. Could you please check and confirm?
For the RRC Resume Request, different causes are sent by the UE. Is there any case where Mobility Update is included? Also, can the UE send an RRC Resume Request to the same gNB for MO (Mobile Originated) data?
If the target gNB is within the same RNA, the UE remains in RRC Inactive mode.
However, if the target gNB is outside the RNA, the UE transitions from RRC Inactive to Connected mode, sending an RRC Resume Request to the target gNB to reestablish its connection.
Okay, what is the cause indicated in the RRC Resume Request?
Is it RNA Update?
Yes, one of the reasons for the RRC Resume Request is RNA Update.
Is this understanding correct? Can you confirm, please? 
Yes, if the UE moves to a gNB within the same RNA area, the gNB will send an RRC Release again after receiving the RRC Resume Request from the UE.
The same applies to periodic RNA Updates as well.
Need to check whether, during a Periodic RNA Update, the RRC Resume Request procedure will be fully completed to transition the UE back to Connected state, or if the gNB will send an RRC Release again with Suspend Config to return the UE to Inactive state.
When the UE is in RRC Inactive mode and moves to a new gNB within the same RNA, it sends an RRC Resume Request to the new gNB. The new gNB updates the UE’s information, and after completing the update, it sends an RRC Release message back to the UE, keeping it in RRC Inactive mode.
For a Periodic RNA Update, even if the UE has not moved, it follows the same procedure sending an RRC Resume Request to confirm its location in the RNA. The gNB processes the request and then sends an RRC Release message, keeping the UE in RRC Inactive mode.