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5g nr nsa call flow

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Non-Standalone (NSA) 5G NR (New Radio) refers to the deployment option where 5G is introduced alongside existing 4G LTE infrastructure. In NSA mode, the control plane is handled by the 4G LTE network, while the user plane can leverage both 4G and 5G resources. The call flow involves several steps, including initial access, registration, and data transfer. Below is a simplified technical explanation of the 5G NR NSA call flow:

  1. UE (User Equipment) Attachment to 4G LTE Network:
    • The UE initiates the connection by attaching to the 4G LTE network using the LTE RRC (Radio Resource Control) connection setup procedure.
  2. Initial Registration with 4G Core Network:
    • The UE performs initial registration with the 4G EPC (Evolved Packet Core) network, obtaining an EPS (Evolved Packet System) bearer.
  3. RRC Connection Establishment with 4G LTE eNB (eNodeB):
    • The UE establishes an RRC connection with the 4G LTE eNB.
  4. NR (New Radio) Cell Selection and Registration:
    • The UE performs cell selection and registration with the 5G NR cell. This involves scanning and selecting a suitable 5G NR cell and registering with it.
  5. Dual Connectivity Setup (EN-DC):
    • The 4G LTE eNB and the 5G NR gNB (Next-Generation NodeB) coordinate to establish dual connectivity, allowing the UE to simultaneously connect to both 4G and 5G networks.
  6. Bearer Setup for 5G NR:
    • The 5G NR gNB initiates the setup of a 5G NR bearer for the user. This involves signaling to the 4G LTE eNB to establish a dual connectivity bearer for the 5G NR part.
  7. Data Transfer:
    • The data transfer can now occur using both 4G and 5G resources. The control plane signaling is handled by the 4G LTE network, while the user plane traffic can be offloaded to the 5G NR network for better performance.
  8. Handover (Optional):
    • If the UE moves out of the coverage area of the 4G LTE cell or if the 5G NR network offers better signal quality, a handover may occur. The handover process involves transferring the connection seamlessly from one cell to another.

It's important to note that this is a high-level overview, and the actual implementation details can vary based on network configurations and vendor-specific implementations. Additionally, 5G NR NSA deployments are part of the transition to full standalone (SA) 5G networks, where both the control and user planes are handled by the 5G core network.