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5g sa call flow

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The 5G Standalone (SA) call flow is a complex sequence of procedures and messages exchanged between various network entities to establish a connection between a 5G user equipment (UE) and the 5G core network. Below is a high-level technical explanation of the 5G SA call flow:

  1. Initial Access and Registration:
    • Random Access Procedure: The UE performs the Random Access Procedure to gain initial access to the 5G network. The UE sends a Random Access Preamble to the gNB (5G New Radio Node B).
    • Random Access Response: The gNB responds with a Random Access Response message, which contains the Timing Advance (TA) value and other necessary information for the UE to adjust its transmission timing.
  2. Authentication and Security:
    • Authentication Procedure: Once the initial access is successful, the UE initiates the authentication procedure. The UE sends an Authentication Request to the Access and Mobility Management Function (AMF) in the 5G core network.
    • Authentication Response: The AMF sends an Authentication Challenge to the UE, which responds with an Authentication Response containing proof of its identity.
    • Security Mode Command/Complete: After successful authentication, the AMF instructs the UE to establish security parameters using the Security Mode Command. The UE responds with the Security Mode Complete message.
  3. Registration:
    • Registration Request: The UE sends a Registration Request message to the AMF, indicating its desire to register with the network.
    • Registration Accept/Reject: Based on the Registration Request, the AMF decides whether to accept or reject the UE's registration. If accepted, the AMF sends a Registration Accept message to the UE.
  4. Session Establishment:
    • PDU Session Establishment Request: The UE sends a PDU Session Establishment Request message to the AMF, requesting the establishment of a data session.
    • PDU Session Establishment Accept/Reject: The AMF processes the request and sends a PDU Session Establishment Accept or Reject message to the UE.
  5. Data Transfer:
    • Data Path Establishment: Once the session is established, the UE can initiate data transfer by sending data packets through the established data path. The gNB ensures that the data packets are routed correctly within the 5G network.
  6. Quality of Service (QoS) Establishment:
    • QoS Flow Setup: The AMF, in coordination with other network entities, sets up the required QoS flows based on the UE's requirements and network conditions. This ensures that the data packets are handled with the appropriate priority and resources.
  7. Handover (Optional):
    • In scenarios where the UE moves from one gNB to another, the network initiates a handover procedure to ensure seamless connectivity. The handover involves signaling between the source gNB, target gNB, and the AMF to transfer the UE's context and data sessions.
  8. Session Release:
    • When the UE no longer requires the session or moves out of the network coverage area, it initiates a session release procedure. The AMF releases the resources associated with the UE's session, ensuring efficient utilization of network resources.