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NR-RRC Connection Reestablishment (with UE Information)

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In 5G (New Radio or NR), NR-RRC (Radio Resource Control) Connection Reestablishment is a procedure used to reestablish a connection between the User Equipment (UE) and the network after an interruption or loss of the radio link. This process is essential for maintaining continuous communication in scenarios where the existing RRC connection is compromised. Let's delve into the technical aspects of NR-RRC Connection Reestablishment, including UE information:

  1. Triggering the Reestablishment:RRC Connection Reestablishment is triggered when the current RRC connection between the UE and the network is lost or becomes unstable due to reasons like radio link failure or other network-related issues.
  2. RRC Connection Release:Before initiating reestablishment, the UE releases the existing RRC connection, freeing up resources and preparing for the establishment of a new connection.
  3. Measurement and Gap Configuration:The UE may perform measurements to assess the radio environment and determine the most suitable cell for reconnection. Measurement gaps might be configured to ensure accurate measurements without disrupting ongoing communication.
  4. Failure Cause and RRC Parameters:The UE includes a failure cause indicating the reason for reestablishment and relevant RRC parameters, which are essential for the network to process the reestablishment request.
  5. Random Access Procedure:The UE initiates a random access procedure to request RRC connection reestablishment. This involves contention resolution and sending a Random Access Preamble.
  6. Preamble Transmission and Contention Resolution:The UE selects a random access preamble, transmits it over the Random Access Channel (RACH), and resolves any contention if multiple UEs select the same preamble.
  7. Random Access Response:The network responds with a Random Access Response, providing crucial information like the Timing Advance (TA) and RRC Configuration. This helps the UE in synchronizing and configuring its radio parameters.
  8. RRC Connection Reestablishment Request:The UE sends an RRC Connection Reestablishment Request, including the failure cause, the previously used RRC context, and other relevant information to the network.
  9. Network Processing:The network processes the reestablishment request, verifying the failure cause, evaluating the UE's previous context, and determining the appropriate action for reconnection.
  10. RRC Connection Reestablishment Complete:The network sends an RRC Connection Reestablishment Complete message to the UE, confirming the successful reestablishment and providing any additional configuration parameters.
  11. UE Processing:The UE processes the RRC Connection Reestablishment Complete message, updates its radio configuration, and acknowledges the successful reestablishment.
  12. Continuation of Communication:Following successful reestablishment, communication resumes between the UE and the network using the newly established RRC connection.

In summary, NR-RRC Connection Reestablishment is a critical procedure to restore communication between the UE and the network after a disruption. The reestablishment involves a series of signaling messages and procedures, enabling a seamless transition back to a stable RRC connection.