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5g nr call flow

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The 5G NR (New Radio) call flow involves several steps and messages exchanged between the User Equipment (UE), the Radio Access Network (RAN), and the Core Network (CN). Here's a technical overview of the 5G NR call flow:

  1. UE Attach Procedure:
    • The UE initiates the attach procedure by sending an initial registration message (RRC Connection Request) to the gNB (gNodeB), which is the access point in 5G NR.
    • The gNB responds with an RRC Connection Setup message, assigning Radio Resources to the UE.
    • The UE then sends an RRC Connection Complete message, indicating successful connection setup.
  2. Registration and Authentication:
    • The UE performs a registration procedure by sending a Registration Request to the gNB.
    • The gNB forwards the registration request to the Access and Mobility Management Function (AMF) in the Core Network (CN).
    • The AMF initiates authentication and authorization procedures, verifying the UE's identity and capabilities.
  3. Security Setup:
    • Once authentication is successful, the AMF and UE negotiate security keys and algorithms for encryption and integrity protection using the Non-Access Stratum (NAS) security procedures.
  4. PDUSession Establishment:
    • The UE initiates a PDU (Packet Data Unit) session establishment by sending a request to the gNB.
    • The gNB communicates with the Session Management Function (SMF) in the CN to establish a PDU session.
  5. Bearer Setup:
    • The SMF and gNB coordinate to establish the necessary bearers for data transfer, configuring Quality of Service (QoS) parameters.
  6. Initial Context Setup:
    • The gNB and the AMF set up the initial context for the UE, defining the parameters and configurations required for data transfer.
  7. Data Transfer:
    • With the initial context established, the UE can now send and receive user data through the gNB.
  8. Handover (Optional):
    • In a mobile environment, handover may occur as the UE moves across different gNB coverage areas. The handover procedure involves the source gNB, target gNB, and the AMF to ensure a seamless transfer of the UE's connection.
  9. UE Detach Procedure:
    • When the UE wants to disconnect from the network, it sends a Detach Request to the gNB, which then releases the radio resources and notifies the AMF.
  10. PDU Session Release:
  • The SMF releases the PDU session upon receiving a release request from either the UE or the network.

These steps provide a high-level overview of the 5G NR call flow. The actual sequence may vary based on specific deployment scenarios, network configurations, and mobility events. Each of these steps involves the exchange of various signaling messages between the UE, gNB, and the Core Network elements.