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5g nr sa call flow

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The 5G New Radio (NR) Standalone (SA) call flow involves several steps and procedures to establish a connection between the user equipment (UE) and the 5G core network. The SA mode means that the 5G network operates independently of the 4G LTE network, meaning there's no need for an LTE anchor in the core network. Below is a detailed technical explanation of the 5G NR SA call flow:

  1. Initial Access:
    • Random Access Procedure: The UE initiates the random access procedure by sending a Random Access Preamble on the uplink channel. The base station, known as gNodeB in 5G, receives this preamble and responds with a Random Access Response. This response contains a Timing Advance (TA) command to adjust the UE's transmission timing.
  2. Synchronization and Initial Configuration:
    • Synchronization: After the initial access, the UE needs to synchronize with the gNodeB. This involves the UE sending a synchronization signal, and the gNodeB responds with a downlink synchronization signal, ensuring both devices are synchronized in time and frequency.
    • Beamforming and MIMO Configuration: Once synchronized, the gNodeB can start beamforming and MIMO (Multiple Input Multiple Output) configuration to improve the link quality and capacity.
  3. RRC Connection Establishment:
    • RRC Connection Request: The UE sends an RRC (Radio Resource Control) Connection Request to the gNodeB.
    • RRC Connection Setup: The gNodeB responds with an RRC Connection Setup message, which includes the necessary information for the UE to establish an RRC connection.
  4. Registration and Session Establishment:
    • Initial Registration: The UE performs an initial registration procedure with the 5G Core Network (5GC) to establish its presence.
    • Authentication and Security: The 5GC performs authentication and security procedures to ensure the UE's identity and establish secure communication.
    • Session Establishment: After successful authentication, the 5GC establishes a session with the UE, allocating the necessary resources and setting up the necessary parameters for data transfer.
  5. Data Transfer:
    • Data Path Establishment: Once the session is established, the data path is set up, allowing the UE to transfer data packets to/from the 5GC.
    • Data Transfer: The UE can now send/receive user data packets through the established data path, benefiting from the high data rates and low latency provided by 5G NR.
  6. Mobility and Handover:
    • Intra-5G Handover: If the UE moves, it may need to perform a handover procedure to switch to a different gNodeB while maintaining the ongoing session. This involves the UE connecting to a new gNodeB and the 5GC updating the data path accordingly.
    • Inter-RAT Handover: In some scenarios, the UE might need to perform an inter-RAT (Radio Access Technology) handover to switch between 5G NR and other technologies like 4G LTE or Wi-Fi.
  7. Connection Release:
    • Normal Release: When the UE completes its data transfer or decides to disconnect, it sends an RRC Connection Release message to the gNodeB and 5GC to release the resources.
    • Abnormal Release: In case of abnormal situations like radio link failures, the network may initiate connection release procedures to free up resources.

This is a high-level overview of the 5G NR SA call flow, and in practice, each step involves more detailed signaling messages, procedures, and parameters exchanged between the UE, gNodeB, and 5GC.