NSA UE Behavior After Inactive Timer Expiry

5G NR
, ,
1

Dear all,

When the NSA UE inactive timer expires in 5G (e.g., after 10 seconds), the gNB notifies the eNB to release the PSCell, and the UE transitions to RRC_CONNECTED mode in 4G. I have a few questions regarding the subsequent behavior:

  1. Will the eNB send a B1 measurement control message again to this UE?
  2. Does the UE retain the previous B1 event information and continue searching for a 5G cell and reporting it? If so, wouldn’t this cause a ping-pong state transition?
  3. Does the UE remain solely in the 4G connected state without monitoring 5G? In such a scenario, if there is incoming large data, will the eNB instruct the UE to measure and reconnect to 5G?

Looking forward to your insights.

2
  1. Will the eNB send a B1 measurement control message again to this UE?
  • Yes, the eNB can send a B1 measurement control message again to the UE. This is typically done to ensure that the UE continues to monitor and report the presence of 5G cells, which helps in deciding when to re-establish the 5G connection.
  1. Does the UE retain the previous B1 event information and continue searching for a 5G cell and reporting it? If so, wouldn’t this cause a ping-pong state transition?
  • The UE does retain the previous B1 event information and continues to search for and report 5G cells. However, to avoid frequent ping-pong transitions between 4G and 5G, the network employs hysteresis and time-to-trigger mechanisms. These mechanisms help stabilize the connection by preventing immediate re-selection to 5G unless the conditions are consistently met over a period of time.
  1. Does the UE remain solely in the 4G connected state without monitoring 5G? In such a scenario, if there is incoming large data, will the eNB instruct the UE to measure and reconnect to 5G?
  • The UE does not remain solely in the 4G connected state without monitoring 5G. It continues to monitor 5G cells as per the measurement configuration provided by the eNB. If there is incoming large data, the eNB can instruct the UE to measure and reconnect to 5G to take advantage of the higher data rates and capacity offered by the 5G network.