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sa call flow

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The Standalone (SA) call flow in a 5G network involves the establishment of a connection between a mobile device (User Equipment - UE) and the 5G core network. Below is a detailed technical explanation of the SA call flow in 5G:

1. UE Attachment and Registration:

  1. Initial Access:
    • The UE initiates the connection by performing initial access. This involves synchronization with the 5G cell and random access procedures.
  2. Random Access Procedure:
    • The UE sends a Random Access Preamble to the gNB (5G New Radio NodeB) to request resources for transmission.
  3. RRC Connection Establishment:
    • The gNB responds with a Random Access Response, and subsequent messages are exchanged to establish the Radio Resource Control (RRC) connection between the UE and gNB.
  4. Security Setup:
    • Security procedures are performed to establish a secure communication link between the UE and the gNB, including key exchange and authentication.
  5. UE Registration:
    • The UE registers with the 5G core network (5GC) by sending a Registration Request to the gNB, which is then forwarded to the Access and Mobility Management Function (AMF) in the 5GC.
  6. Authentication and Key Agreement (AKA):
    • The AMF performs authentication and key agreement procedures with the UE to ensure secure communication.

2. Session Establishment:

  1. PDU Session Establishment Request:
    • The UE sends a PDU Session Establishment Request to the AMF, indicating its request to establish a data session.
  2. SM Context Establishment:
    • The AMF establishes a Session Management (SM) context for the UE, storing information related to the data session.
  3. N2 Interface Establishment:
    • The AMF communicates with the Session Management Function (SMF) to establish the N2 interface towards the gNB.
  4. N2 Tunnel Establishment:
    • The SMF interacts with the gNB to establish the N2 tunnel for user data transfer.
  5. PDU Session Establishment Accept:
    • The AMF responds to the UE with a PDU Session Establishment Accept message, confirming the establishment of the data session.

3. Data Transfer:

  1. Data Transmission:
    • With the PDU session established, the UE can now transmit user data via the gNB and the established N2 tunnel.
  2. User Plane Establishment:
    • The gNB ensures the establishment of the user plane, allowing for the seamless transfer of data between the UE and the 5GC.

4. Session Release:

  1. UE Request for Release:
    • The UE may request the release of the PDU session when it is no longer needed.
  2. Session Release Procedure:
    • The AMF triggers the session release procedure, informing the SMF and the gNB to release the resources associated with the PDU session.
  3. Session Release Confirmation:
    • Confirmation messages are exchanged to confirm the release of the session.

Conclusion:

The Standalone (SA) call flow in 5G involves multiple steps, including initial access, security setup, registration, session establishment, data transfer, and session release. Each step ensures the secure and efficient communication between the UE and the 5G core network, providing high-speed and low-latency connectivity.