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5g call flow nsa

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The 5G Non-Standalone (NSA) architecture allows operators to introduce 5G services using the existing 4G infrastructure, primarily the Evolved Packet Core (EPC).

Here's a technical explanation of the 5G NSA call flow:

1. Initial Registration:

  1. UE (User Equipment) Attach: The UE, which is 5G-capable but not yet registered, attaches to the 4G network using LTE.
  2. Attach Request: The UE sends an Attach Request to the eNodeB (eNB) as it would in a traditional LTE attach procedure.
  3. Core Network Selection: The MME (Mobility Management Entity) in the EPC identifies that the UE is 5G-capable and determines that it should use the 5G network for data traffic while still maintaining control plane connectivity via LTE.

2. 5G NR (New Radio) Registration:

  1. RRC Connection Establishment: After the initial LTE attach, the UE establishes an RRC (Radio Resource Control) connection with the eNB.
  2. Dual Connectivity: The MME sets up Dual Connectivity, where the UE is connected to both the 4G eNB and the 5G gNB (Next-Generation NodeB).
  3. RAN Connection: The eNB establishes a connection to the 5G gNB. This connection allows the UE to access 5G NR services while maintaining its LTE connection.

3. Data Transfer:

  1. Data Session Establishment: When the UE initiates a data session that requires 5G NR capabilities, the gNB takes over the data path. This could be for services like high-speed data, low latency, etc.
  2. Data Path: The data traffic from the UE is then routed through the 5G gNB to the 5G Core Network (5GC) while still maintaining control plane connectivity with the MME in the EPC.

4. Mobility:

  1. Handover: If the UE moves to an area where 5G coverage is better, the control plane signaling remains with the LTE MME, but the data path is transferred to a new gNB in the 5G network. This allows seamless mobility without interrupting ongoing sessions.

5. Call Termination:

  1. Detach Procedure: When the UE detaches from the network (e.g., end of session or powering off), it sends a Detach Request. The MME in the EPC releases resources related to the 5G NSA connection while maintaining the LTE connection for control purposes.