Establishment and Maintenance of the RRC connection in LTE

Establishment and Maintenance of the RRC connection in LTE

In Long-Term Evolution (LTE), the Radio Resource Control (RRC) connection plays a crucial role in establishing and maintaining the communication link between the User Equipment (UE) and the Evolved NodeB (eNB). The process involves several steps:

  1. RRC Connection Establishment:
    • Random Access Procedure: The UE initiates communication with the network by performing a random access procedure. It sends a random access preamble to the eNB.
    • Contention Resolution: In case of contention (multiple UEs attempting to access the network simultaneously), the eNB resolves the contention and allocates resources to the UE.
    • Random Access Response: The eNB responds with a random access response, providing the UE with initial downlink timing and assignment of resources.
  2. RRC Connection Setup:
    • RRC Connection Request: The UE sends an RRC connection request to the eNB, indicating its desire to establish a connection.
    • Security Setup: If security is not already established, the eNB and UE perform security procedures, including key agreement.
    • RRC Connection Setup: The eNB acknowledges the connection request and initiates the RRC connection setup.
  3. RRC Connection Reconfiguration:
    • UE Capability Exchange: The UE and eNB exchange information about their capabilities.
    • Radio Resource Configuration: The eNB configures the radio resources for the UE based on its capabilities and network conditions.
    • RRC Connection Reconfiguration: The eNB sends an RRC connection reconfiguration message to the UE, instructing it to apply the new configuration.
  4. RRC Connection Release:
    • UE Request: The UE may request the release of the RRC connection, indicating that it no longer needs to be connected.
    • UE Inactivity: If the UE is inactive for a specified period, the network may release the RRC connection to conserve resources.
  5. RRC Connection Maintenance:
    • Keep-Alive Signals: Periodic signals are exchanged between the UE and the network to maintain the connection.
    • Mobility Management: The network monitors the UE’s mobility and adjusts the connection parameters as needed, such as handovers between cells.
  6. Handovers:
    • Inter-eNB Handover: In the case of mobility, the UE may move from one eNB’s coverage area to another. The network initiates a handover process to maintain the connection seamlessly.

Throughout the RRC connection lifecycle, various signaling messages are exchanged between the UE and the eNB to ensure proper communication. The establishment and maintenance of the RRC connection are critical for providing seamless and efficient connectivity in LTE networks.

The establishment and maintenance of the RRC connection includes: 

  • Allocation of temporary identifiers between UE and E-UTRAN.
  • Configuration of signaling radio bearer(s) for RRC connection.
  • Low priority SRB and high priority SRB.
  • Security functions including key management.
  • Establishment, configuration, maintenance and release of point to point Radio Bearers

The Mobility management functions includes: 

  • UE measurement reporting and control of the reporting for inter-cell and inter-RAT mobility.
  • Handover.
  • UE cell selection and reselection and control of cell selection and reselection.
  • Context transfer at handover.
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