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5g nsa call flow

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Non-Standalone (NSA) is a deployment option for 5G (fifth-generation) networks that relies on the existing 4G LTE (Long-Term Evolution) infrastructure for certain functions. The 5G NSA deployment allows for an easier and faster rollout of 5G services while leveraging the established 4G network. The call flow in a 5G NSA network involves several key steps, including the registration of the user equipment (UE) and the establishment of a data connection. Below is a technical explanation of the 5G NSA call flow:

  1. Initial Access:
    • The UE initiates the connection by performing initial access procedures. These include cell search, synchronization, and random access.
    • The UE scans and detects 5G NR (New Radio) cells and selects a suitable cell for connection.
  2. PLMN Selection and Registration:
    • The UE selects a Public Land Mobile Network (PLMN) and registers with the 4G E-UTRAN (Evolved Universal Terrestrial Radio Access Network).
    • The registration includes the exchange of relevant information such as the UE's identity and capabilities.
  3. Attach Procedure:
    • The UE initiates the attach procedure to register with the 4G network and obtain a Temporary Mobile Subscriber Identity (TMSI) and an IP address.
  4. Establishment of 4G Data Connection:
    • The UE establishes a data connection with the 4G E-UTRAN. This involves the establishment of a Radio Bearer for data transfer.
  5. Service Request for 5G NR:
    • The UE sends a Service Request to the 4G core network (EPC - Evolved Packet Core) indicating its desire to use 5G services.
    • The 4G core network, upon receiving the Service Request, recognizes that the UE is requesting 5G connectivity.
  6. NG-RAN Node Selection:
    • The EPC selects a 5G NR cell, and the handover preparation begins. The 4G E-UTRAN informs the 5G NG-RAN (Next-Generation Radio Access Network) about the impending handover.
  7. RRC Connection Reconfiguration:
    • The NG-RAN configures the Radio Resource Control (RRC) connection for 5G NR. This involves the establishment of a new radio bearer for 5G data transfer.
  8. Data Forwarding over 5G NR:
    • The data transfer switches from the 4G E-UTRAN to the 5G NR cell. The UE is now connected to both the 4G and 5G networks simultaneously.
  9. Dual Connectivity:
    • The UE maintains a connection with both the 4G and 5G networks. This configuration is known as Dual Connectivity, where the 4G and 5G connections coexist.
  10. Data Handover:
    • The data traffic is gradually shifted from the 4G connection to the 5G connection. This process ensures a smooth handover without service disruption.
  11. LTE-to-NR Handover Complete:
    • The handover is complete when the UE is fully transitioned to the 5G NR cell. The UE is now solely connected to the 5G network for data transfer.

This sequence of steps outlines the technical flow for a 5G NSA call, highlighting the collaboration between the 4G and 5G networks to enable seamless connectivity for the user equipment. Keep in mind that the specifics of the call flow may vary based on the network architecture and vendor implementations.