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endc call flow

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The endc call flow describes the sequence of signaling messages exchanged between different network entities to establish, maintain, and terminate an endc connection. Here's a simplified technical explanation of the endc call flow:

  1. Initial Connection to LTE (e.g., LTE eNodeB)
    • The UE (User Equipment) starts by connecting to the LTE network, typically using the 4G eNodeB.
  2. Establishing 4G Core Network Connection
    • The UE performs the usual procedures to establish an EPS (Evolved Packet System) session with the EPC (Evolved Packet Core) network.
  3. Handover to 5G (NR)
    • When the UE decides to utilize 5G capabilities, it initiates a procedure called "Redirection" or "Handover" to 5G. This process involves the UE connecting to both the LTE eNodeB (for LTE) and the gNB (for NR).
  4. Dual Connectivity Setup
    • After successfully connecting to the gNB and maintaining the connection with the LTE eNodeB, the dual connectivity is established.
    • The gNB and eNodeB coordinate to ensure data can be transmitted to and from the UE over both the LTE and NR links.
  5. Data Transfer & Control
    • With dual connectivity set up, data can now be transferred simultaneously over both the LTE and 5G networks, depending on the specific needs and network conditions.
    • Control signaling, such as handover commands or resource allocation messages, can also be exchanged between the gNB and eNodeB as required.
  6. End of 5G Session or Handover Back to LTE
    • Depending on network conditions, service requirements, or other factors, the UE might end its 5G session or hand back to LTE.
    • This process involves signaling between the gNB, eNodeB, and the UE to release resources, terminate the 5G connection, and ensure a seamless transition back to LTE-only mode if needed.
  7. LTE Release & Cleanup
    • Once the 5G session is terminated or the UE is handed back to LTE, the resources allocated for 5G (like dedicated radio bearers, QoS parameters, etc.) are released.
    • The UE reverts to a single LTE connection, and any temporary configurations related to the endc setup are cleaned up.

The endc call flow is about enabling seamless dual connectivity between LTE and 5G NR networks. It ensures that UE devices can leverage the benefits of 5G while maintaining backward compatibility and continuity of service with existing LTE networks. The above steps provide a high-level overview, and the actual signaling and procedures involve more detailed interactions between various network entities, including the UE, gNB, eNodeB, and core network elements.