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5gc call flow

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The 5G Core (5GC) call flow describes the sequence of signaling messages exchanged between different entities in the 5G Core Network during the setup, establishment, and release of a communication session (call) between a User Equipment (UE) and another user or service. The call flow involves interactions between the UE, the Access and Mobility Management Function (AMF), the Session Management Function (SMF), the User Plane Function (UPF), and potentially other network elements. Below is a simplified technical overview of the 5G Core call flow:

1. Initial Registration and Attach:

  • UE to AMF:
    • The UE initiates registration by sending a Registration Request to the AMF.
  • AMF:
    • The AMF authenticates and authorizes the UE.
    • It establishes a connection with the UE and assigns temporary identifiers.

2. Session Establishment:

  • UE to AMF:
    • The UE requests a new session by sending a Service Request to the AMF.
  • AMF:
    • The AMF selects a suitable SMF for the session.

3. SMF and UPF Selection:

  • AMF to SMF:
    • The AMF sends a Session Management Request to the selected SMF.
  • SMF:
    • The SMF selects a UPF for the session and establishes the connection.

4. PDU Session Establishment:

  • SMF to UPF:
    • The SMF requests the UPF to establish a Packet Data Unit (PDU) session.
  • UPF:
    • The UPF establishes the PDU session and allocates resources.

5. UE Authentication and Ciphering:

  • AMF to UE:
    • The AMF triggers an authentication procedure with the UE.
    • Upon successful authentication, the AMF provides security parameters, and ciphering is activated.

6. Initial Context Setup:

  • AMF to SMF:
    • The AMF sends an Initial Context Setup Request to the SMF.
  • SMF:
    • The SMF creates the initial context and informs the UPF about the QoS requirements.

7. Data Transfer:

  • UE to UPF:
    • The UE sends user data through the established PDU session.
  • UPF:
    • The UPF forwards the user data to its destination.

8. Handover (Optional):

  • AMF to AMF (in case of handover):
    • If the UE moves to a new cell, a handover may occur, and the source AMF communicates with the target AMF to ensure a seamless transition.

9. PDU Session Modification (Optional):

  • SMF to UPF:
    • The SMF may modify the PDU session (e.g., change QoS parameters) based on network conditions or user requirements.

10. PDU Session Release:

  • SMF to UPF:
    • The SMF sends a request to release the PDU session.
  • UPF:
    • The UPF releases the allocated resources for the session.

11. Session Termination:

  • UE to AMF:
    • The UE sends a Service Request to terminate the session.
  • AMF:
    • The AMF releases resources, updates the UE status, and sends a Session Release Command to the SMF.

12. Session Release and UE Detach:

  • SMF to UPF:
    • The SMF sends a request to release the PDU session.
  • UPF:
    • The UPF releases the resources.
  • AMF:
    • The AMF sends a Detach Request to the UE.

Notes:

  • The 5G Core call flow is orchestrated by various signaling protocols, including NGAP (Next-Generation Application Part), N1 (control plane) and N2 (user plane) interfaces, and others.
  • The flow can be influenced by factors like network conditions, mobility events, and user requests.
  • This is a simplified overview, and actual call flows may involve additional steps for specific services, scenarios, or network configurations.

The 5G Core call flow involves a series of interactions between network elements to establish, manage, and release communication sessions, reflecting the advanced capabilities and flexibility of the 5G architecture.