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NR-RRC Connection Reestablishment Reject

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In 5G New Radio (NR), the NR-RRC Connection Reestablishment Reject is a message sent by the network's base station (gNB or gNodeB) to a user equipment (UE) when it rejects the UE's attempt to reestablish an RRC (Radio Resource Control) connection. RRC connection reestablishment is a procedure initiated by the UE when it has lost its previous connection or context with the network and needs to reestablish communication. The NR-RRC Connection Reestablishment Reject message indicates that the reestablishment request has been rejected and may include specific reasons for the rejection. Here's a technical explanation of the NR-RRC Connection Reestablishment Reject message:

RRC Connection Reestablishment:

  • The RRC connection reestablishment procedure is initiated by the UE when it has lost synchronization with the network or has encountered a radio link failure, and it needs to recover its connection.
  • This procedure is essential for maintaining continuous communication between the UE and the network, especially in scenarios involving mobility or temporary signal loss.

UE Request and Reestablishment Request Message:

  • The UE initiates the RRC connection reestablishment procedure by sending an NR-RRC Connection Reestablishment Request message to the gNB.
  • This message includes information about the UE's identity, the previous RRC context, and the reason for the reestablishment.

Rejection Scenarios:

  • The NR-RRC Connection Reestablishment Reject message is sent by the gNB in response to the UE's reestablishment request when the network cannot accept or support the reestablishment for specific reasons.

Common scenarios leading to rejection include:

  • UE not found: The network may not have the UE's previous context or may not recognize the UE based on the provided identity.
  • Resource constraints: The gNB may be unable to allocate the necessary resources (e.g., frequency bands or time slots) to accommodate the UE's reestablishment request.
  • Security issues: If the UE's identity or security credentials are not valid or if there are authentication failures, the network may reject the reestablishment.

Message Content:

The NR-RRC Connection Reestablishment Reject message typically includes the following information:

  • A rejection cause code or cause value: This code indicates the specific reason for the rejection. Common cause codes are defined in the 3GPP specifications.
  • Optionally, additional information or parameters related to the rejection cause.

UE Response:

  • Upon receiving the NR-RRC Connection Reestablishment Reject message, the UE processes the message and takes appropriate actions based on the rejection cause.
  • The UE may attempt to address the issue and initiate a new reestablishment request if necessary.

Error Handling:

  • Error handling and recovery mechanisms may be triggered at both the UE and network sides to resolve issues leading to the rejection.
  • The network may provide guidance or recommendations to the UE on how to proceed.

Log and Monitoring:

  • The rejection and the associated cause code are often logged for network management and troubleshooting purposes.
  • Network operators and administrators can use this information to diagnose and resolve issues in the network.

In summary, the NR-RRC Connection Reestablishment Reject message is used in 5G NR networks to indicate the rejection of a UE's request to reestablish an RRC connection. The rejection can occur for various reasons, including resource constraints, invalid configurations, or security concerns. The message provides specific cause information to help diagnose and address the issue, allowing for efficient network management and communication.