Hello Experts.
In which case does DU send “cell barred” to CU in the initial F1 setup message?
I think there is no such case. DU hosts lower layer function of a gNB, while “cell barred” is higher layer state.
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The DU (Data Unit) sends “cell barred” to CU (Control Unit) in the initial F1 setup message in the following cases:
- The cell is not configured for 5G NR.
- The cell is in a state where it cannot accept new UEs, such as during a handover or a cell outage.
- The UE does not meet the access requirements for the cell, such as not having the correct subscription or not being authorized to access the network.
- The DU is unable to establish a radio connection with the UE.
In all of these cases, the DU will send a “cell barred” message to the CU to prevent the UE from being able to connect to the cell.
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F1 setup is a non-UE-associated common procedure. If you mean UE context setup procedure, I don’t think “cell barred” should be sent even if the cases you list occur.
You are right. The F1 setup is a non-UE-associated common procedure, so the DU should not send “cell barred” to the CU in the initial F1 setup message, even if the cases I listed occur.
The cases I listed are situations where the DU would not be able to establish a radio connection with the UE, and therefore would not be able to send the UE a RRC connection establishment request. In these cases, the DU would simply send a RRC Connection Release message to the UE to terminate the connection.
The “cell barred” message is only sent in the UE context setup procedure, when the DU is able to establish a radio connection with the UE but the UE does not meet the access requirements for the cell. In this case, the DU would send the “cell barred” message to the CU to prevent the UE from being able to connect to the cell.
Even in UE context setup procedure, I think “cell barred” is a higher layer concept. It can be sent from CU to DU, not DU to CU.
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