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5g endc call flow

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5G EN-DC (Evolved-Universal Terrestrial Radio Access-New Radio Dual Connectivity) refers to the simultaneous use of LTE (4G) and 5G NR (New Radio) radio access technologies by a user equipment (UE). This enables a smoother migration from 4G to 5G by allowing a device to maintain simultaneous connections to both 4G and 5G networks. Here's a technical breakdown of the EN-DC call flow:

1. Initialization:

  1. UE Capability Reporting: The UE starts by informing the 4G eNB (eNodeB) about its dual-connectivity capabilities. This could be done using the UE capability message.
  2. Configuration in the Core Network (CN): The 4G core network (EPC) is aware of the 5G network slices and capabilities. It knows which services can be offloaded to 5G.

2. Connection Setup:

  1. Initial Connection: The UE establishes an initial connection with the 4G eNB. This is similar to any standard LTE connection setup.
  2. Secondary Connection: After the initial setup, the UE establishes a secondary connection with the 5G gNB (gNodeB). This is usually initiated by the 4G eNB when it detects a need for 5G resources, like higher data rates or reduced latency.

3. Data Transfer:

  1. Primary Path (LTE): Most of the control signaling and some user data traffic use the LTE path. This is because the 4G network is mature and has extensive coverage.
  2. Secondary Path (5G): High-bandwidth data services or applications requiring low latency can be offloaded to the 5G network. The UE sends specific traffic like this through the 5G gNB.

4. Mobility and Handover:

  1. Idle State: The UE can be in idle mode, connected to the 4G network.
  2. Active State: When specific requirements arise, the 4G eNB decides to move the UE's data sessions to the 5G gNB. This can be done using Xn interface signaling between the 4G eNB and the 5G gNB.
  3. Data Path Switch: After successful handover signaling, the data path is switched to the 5G network while maintaining the 4G connection for other services. This ensures uninterrupted services during the transition.

5. Session Termination:

  1. Session Release: When the UE no longer requires 5G resources or is moving out of the 5G coverage area, the session can be terminated.
  2. Deactivation: The 4G eNB initiates the termination process by deactivating the 5G connection, ensuring that all data paths revert to 4G seamlessly.

Key Components:

  • 4G eNB: LTE base station responsible for the LTE radio interface and connectivity.
  • 5G gNB: The new 5G base station that provides the NR radio interface.
  • EPC (Evolved Packet Core): Core network responsible for managing user sessions, mobility, and connectivity.
  • Xn Interface: Interface between 4G eNB and 5G gNB for signaling and data transfer during EN-DC.