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5g call flow

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The 5G (fifth generation) call flow involves a series of steps and signaling procedures to establish a communication session between two devices. Here's a detailed technical explanation of the 5G call flow:

  1. UE (User Equipment) Attachment:
    • The UE initiates the process by attaching to the 5G network. It sends an Attach Request to the gNB (Next-Generation NodeB) over the air interface.
  2. gNB Registration:
    • The gNB receives the Attach Request and communicates with the AMF (Access and Mobility Management Function) to register the UE to the network.
  3. Access Authentication and Key Agreement (AKA):
    • The AMF initiates the authentication process with the UE. The authentication is based on the 5G AKA protocol, involving the generation of key material for securing the communication.
  4. Security Mode Command:
    • The AMF sends a Security Mode Command to the UE, instructing it to establish a secure connection. This involves the establishment of encryption algorithms and keys.
  5. N1 (NAS) Registration:
    • The UE performs NAS (Non-Access Stratum) registration with the AMF, exchanging necessary information for network access.
  6. PDU Session Establishment:
    • The AMF triggers the establishment of a PDU (Packet Data Unit) session, defining the parameters for data communication. This involves the allocation of a QoS (Quality of Service) profile.
  7. SM (Session Management) Context Setup:
    • The AMF sets up the SM context for managing the session. It communicates with the UPF (User Plane Function) to establish the necessary data forwarding paths.
  8. gNB Configuration Update:
    • The AMF sends a configuration update to the gNB, instructing it to configure the radio resources for the data session.
  9. RRC (Radio Resource Control) Connection Establishment:
    • The gNB initiates the RRC connection setup with the UE to establish the radio resources for the data session.
  10. Data Transfer:
    • Once the radio resources are established, data transfer can occur between the UE and the gNB through the established PDU session.
  11. Handover (Optional):
    • If the UE moves to an area served by a different gNB, a handover process may occur. This involves transferring the active session from one gNB to another while maintaining continuity of service.
  12. PDU Session Release:
    • When the data session is complete, the AMF releases the PDU session and informs the gNB to release the associated resources.
  13. UE Detach:
    • The UE sends a Detach Request when it wants to detach from the 5G network. The network acknowledges the request, and the UE is successfully detached.